Alien fish species in the North Aegean Sea: a review of their distributions integrating unpublished fisheries data

doi:10.21203/rs.3.rs-3766127/v1

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Alien fish species in the North Aegean Sea: a review of their distributions integrating unpublished fisheries data

https://doi.org/10.21203/rs.3.rs-3766127/v1

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published 23 May, 2024

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Fisheries-dependent data and information gathered through fisheries-related scientific surveys can significantly contribute to researching the patterns and processes underlying marine biological invasions and their interactions with fisheries. This study presents an overview of the presence of non-indigenous (NIS) fish species in the North Aegean Sea, offering insights into their distributions and impact on fisheries. The findings are based on a comprehensive compilation of commercial fisheries-dependent and scientific survey data collected in Greece from 2016 to 2023, along with an up-to-date systematic review of the international scientific literature. The study resulted in the identification of 37 non-indigenous fish species, including several recorded for the first time in the area. The results suggest that fish NIS invasions in the North Aegean Sea are dynamic: While most species were classified as casual, and the frequencies of occurrence as well as the quantities in commercial fisheries catches of established species are smaller than in the South Aegean Sea, an increasing trend in species introductions, extent of occurrence, and the area of occupancy of several species was identified. The significance of non-indigenous fish species is growing in relevance to commercial fisheries in the study area, especially in the Northeastern Aegean Sea. There, fish NIS catches are increasing, and new species of potential commercial interest have emerged in the last few years.

Lessepsian immigrants

non-indigenous species

biological invasions

geographic range

commercial fisheries

More than 1,000 marine non-indigenous species (NIS) have been recorded to date in the Mediterranean Sea (Zenetos et al. 2022), including hundreds of Lessepsian immigrants. These are Red Sea endemics and species of Indo-Pacific biogeographical origin that have been entering via the Suez Canal since its opening in 1869 (Galil et al. 2017). Several Lessepsian immigrants have expanded their invaded ranges northwards and westwards, leading to a compositional modification of the regional marine flora and fauna known as the "tropicalization" of the Mediterranean Sea (Bianchi and Morri 2003). Fish, being a part of the food web and crucial to humans, are the most studied NIS group in the Mediterranean (Azzurro et al. 2022a). More than a hundred have been introduced via the Suez Canal (Golani et al. 2021), and at least 51 have reached the Greek seas by naturally dispersing along the Levantine coastline (Zenetos et al. 2020).

Marine invasive species are considered one of the principal stressors of marine ecosystems, interacting with other anthropogenic pressures (Katsanevakis et al. 2016; Geraldi et al. 2020; Korpinen et al. 2021), and their control is the target of major policy and legislative efforts of the EU, such as the Marine Strategy Framework Directive (MSFD, European Commission 2008), the EU Regulation on Invasive Alien Species (European Union 2014), and the EU Biodiversity Strategy for 2030 (European Commission 2020). Marine invasive NIS may also have negative impacts on human activities, such as interfering with fishing operations and causing considerable revenue losses in the fisheries sector (Galanidi et al. 2018). On the other hand, several alien species that have established large populations in their invaded ranges are potential fisheries targets (Van Rijn et al. 2020). Indeed, NIS have favorably transformed some local fisheries, a foremost example being fisheries in Israel (Van Rijn et al. 2020), and to a lesser extent in Turkey (Gucu et al. 2010), or Cyprus (Michailidis 2010; Evagelopoulos et al. 2020). At the same time, targeting by fisheries has been proposed as a promising management measure for controlling nuisance populations of alien species (Nuñez et al. 2012; Ulman et al. 2022; Ofir et al. 2023).

Scientific research on marine biological invasions has grown vigorously in the past few decades (Sagarin and Pauchard 2010; Thomaz et al. 2015; Vaz et al. 2017). Species distribution modeling and ecosystem modeling are examples of modern approaches commonly applied to assess the current state or make future predictions regarding marine biological invasions (Corrales et al. 2020). These tools require comprehensive spatially explicit field observations across space and time but are often constrained by a lack of data (Corrales et al. 2017; Michailidis et al. 2019; Saygu et al. 2020), as most of the published information comprises first records of alien species in newly invaded areas, with a few recent exceptions (e.g., Katsanevakis et al. 2020; Azzurro et al. 2022b; Ragkousis et al. 2023). Data collection from commercial fisheries and research surveys at sea, through the implementation of multiannual programs according to the EU Data Collection Framework (DCF), can, by their sampling design, provide comprehensive, georeferenced information on NIS occurrences, complementing data sourced from underwater biodiversity surveys and citizen science initiatives. Additionally, the above-mentioned data are typically characterized by enhanced temporal and spatial scales and are often collected from offshore locations and/or large depths, where fieldwork may be difficult due to constraints of accessibility or cost. Therefore, publishing the insights gained from analyzing those fisheries data can contribute significantly to advancing research in the field of marine biological invasions (Lefkaditou et al. 2010).

Although the largest species richness and population sizes of fish NIS in the Aegean Sea occur in its southernmost part (Zenetos et al. 2020), several species have also been recorded in the colder and less haline North Aegean Sea. However, information on their distributions is fragmentary and largely restricted to first records. The North Aegean Sea has been identified as one of the Mediterranean hotspots characterized by a seawater warming trend over the last four decades (Pisano et al. 2020), and the area has recently experienced intense and long-duration marine heatwaves (Juza et al. 2022). The land masses of Northern Greece make it a "cul-de-sac" that could prevent northwards range expansion of native marine species sensitive to sea temperature rise (Ben Rais Lasram et al. 2010; Libralato et al. 2015), and at the same time, any niches left empty may open "invasion windows" for Lessepsian species (Johnstone 1986; Oliverio and Taviani 2003). This potential gradual restructuring of the biotic communities may affect ecosystem functioning and impact human activities in the area, similar to what is already happening in other parts of the Eastern Mediterranean (Albano et al. 2021; Edelist et al. 2013). The North Aegean is a productive sea within the generally oligotrophic Eastern Mediterranean, with high fisheries catches, particularly for small pelagics (Machias et al. 2007). Therefore, it is imperative that all available information on alien fish species distributions in the area is compiled to accurately assess the current state of play and deliver a baseline study for the evaluation of future changes.

Publications regarding the importance of NIS in commercial fisheries catches are scarce in Greece. Most published data were produced in experimental fishing surveys of diverse methodological approaches that were usually short-term and carried out in geographically restricted areas (e.g., Peristeraki et al. 2006; Corsini-Foka et al. 2015; Peristeraki et al. 2017; Corsini-Foka et al. 2017). Most available information focuses on the South Aegean Sea, where the presence of alien species is conspicuous (Corsini-Foka et al. 2010; Lefkaditou et al. 2010; Zenetos et al. 2020), whereas their presence in fisheries catches in the Northern Aegean Sea is, to our knowledge, largely undocumented. The only Greek fisheries data that are openly available are those kept by the Hellenic Statistical Authority (ELSTAT 2023). However, these data do not include information on NIS, as alien species catches are often reported by the fishermen aggregated with the catches of related native species. Therefore, the DCF offers a unique opportunity to monitor NIS spreading across the Greek seas and collect long-term data regarding their ranges and interactions with fisheries, following a systematic and comprehensive approach. To our knowledge, the only publication presenting a comprehensive review of fisheries-dependent data on the alien species fished in the Greek seas is that by Lefkaditou et al. (2010).

This study is a review of the current state of the occurrences and importance for fisheries of alien fish species in the North Aegean Sea, based on (a) an up-to-date systematic review of the international scientific literature, and (b) a compilation of data collected from the commercial fisheries and research surveys at sea from 2016 to 2023, implementing the Greek multiannual program according to DCF. This study aims to provide new information that may assist current and future research efforts regarding marine biological invasions and their effects in the area. The specific questions that this study focuses on are: (a) What is the current state of fish NIS invasions in the study area? (b) To what extent are alien fish species important to commercial fisheries in the study area today? (c) What do the available data tell us regarding trends in fish NIS geographic range expansion and importance to commercial fisheries in the study area?

Study area

The study area comprised the North Aegean Sea (see Fig. 1) and was spatially divided into four sub-areas based on the Greek multiannual program: Northeastern Aegean Sea (CHIO-MIT), Thermaikos Gulf and adjacent seas (THERM), Thracian Sea (THR-LIM), and Thessaly and Sporades Islands (VOL-SPOR). The North Aegean Sea experiences the influence of a low-temperature and low-salinity (< 29 psu) plume of waters originating from the Black Sea (BSW) flowing through the Dardanelles Strait. This buoyant plume, with a thickness ranging from 20 to 50 meters, moves cyclonically to the southwest upon entering the Aegean Sea and also northwards into the Thracian Sea (Zervakis and Georgopoulos 2002). The area is additionally affected by the discharge of several small rivers, particularly significant in Thermaikos Gulf (Kourafalou and Barbopoulos 2003). The North Aegean Sea has witnessed the formation of substantial continental shelves in Thermaikos Gulf and the Thracian Sea due to the sediment transported by riverine freshwater discharge (Lykousis and Chronis 1989). In contrast, the Northeastern Aegean Sea is influenced by warm and highly saline (> 38.5 psu) waters originating from the Levantine Sea (LW) (Zervakis and Georgopoulos 2002). Commercial fisheries in the North Aegean Sea are characterized by high catches of small pelagic fish predominantly captured by purse seiners. Bottom trawls are employed to target hake, mullets, shrimps, and cephalopods, while multi-gear small-scale coastal fisheries target a variety of pelagic and demersal species (Tsagarakis et al. 2010). In 2022, the total quantity of small- and medium-scale fisheries landings in the North and Northeastern Aegean Sea reached 35,636 tons, constituting 55% of the overall Greek fisheries landings. The highest landings were observed in the Thracian Sea (16,299 tons) and the area of Thermaikos Gulf and adjacent seas (14,121 tons), while landings in the Northeastern Aegean Sea amounted to 3,630 tons (ELSTAT 2023).

Systematic review of the scientific literature

Α systematic review of the international scientific literature was performed using the extension of the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) approach developed for systematic reviews in ecology and evolutionary biology (Moher et al. 2009; Page et al. 2021; O’Dea et al. 2021). The aim of the review was to collect all scientific publications that contained spatial-temporal information on the distributions of fish NIS in the study area. The stepwise approach of PRISMA was applied as follows:

The original review (Online Resource 1, Fig. S1) was carried out in October – November 2022, whereas a review update (Online Resource 1, Fig. S2) was undertaken in May 2023 to collect any additional literature that had been published in 2023. First, a separate search for each fish NIS in the Google Scholar database (https://scholar.google.com) was performed, targeting all the published literature, with “<species name>” and “Aegean Sea” in the title, abstract or keywords, including the whole text. The alien fish species selected to search the literature for, were those included in the Appendix 1 by Zenetos et al. (2022) on non-indigenous species in the Mediterranean Sea. The search resulted in a total of 18,160 publication records (including duplicates, i.e., publications that appeared in multiple searches because they contained information for more than one species). Subsequently, the publications were screened and those that satisfied the criteria set on the information provided in the title and abstract, were selected: publications that contained fish NIS records located within the four subareas of the study area were retained, including records in Turkish territorial waters. This initial selection of potentially relevant literature consisted of a total of 814 publications (including duplicates). Lastly, the final selection of the relevant publications was made based on the information in the whole text. The final database that contained spatial - temporal information on the occurrence of alien fish species in the study area, consisted of a total of 58 unique publications, mainly papers in scientific journals, but also a few articles in conference proceedings and one scientific meeting report. The database was managed with the open-source reference management tool Zotero (https://www.zotero.org). The dates of the search sessions and the publications selected at each step of the review for each NIS are presented in Table S1 of Online Resource 1.

The following information was retrieved: source of information, species, year of observation, subarea, country, location, geographic coordinates, depth, type of observation, substrate, and abundance. The compiled information was tabulated, such as every row in the table contained the data retrieved for a particular NIS record (Online Resource 1, Table S2). A few NIS records in the selected literature were from misidentified species, or species currently synonymized. Accordingly, Champsodon capensis, Champsodon vorax, Pteragogus pelycus, Etrumeus teres, Liza haematocheilus, Pempheris vanicolensis, and Bregmaceros atlanticus were included in the review results with their currently accepted names. Moreover, Plectorynchus gatterinus and Tylosurus crocodilus were excluded from the list because their records were deemed debatable. Moreover, Tetrodon spadiceus is not unanimously considered to occur in the Mediterranean Sea and Sphoeroides pachygaster is regarded by some experts as a not true alien species, nevertheless both species were included in the final review NIS list (the first with the current name: Lagocephalus spadiceus). Detailed notes on literatute review data cleaning are included in Online Resource 1.

Preparation and compilation of field data

The compiled field data were primarily collected from: (a) the monitoring of commercial fisheries operations (2016–2023), and (b) the MEDITS bottom trawl scientific surveys (1996–2022). Records from commercial fisheries monitoring were included with the caveats that the 2016 records in the Fisheries Research Institute (FRI) database were incomplete and data collection in 2023 was still in progress. Additional NIS records based on samples provided by commercial fishermen to FRI staff during 2007–2021 were also incorporated in the dataset. The commercial fisheries monitoring samples of 2016 and 2023 and the samples provided by commercial fishermen were solely used in the compilation of the species inventory and the analysis of the spatial – temporal patterns in the distributions of the alien fish species in the study area.

The compiled field data consisted of species abundance, biomass, and the associated spatial-temporal metadata, i.e., geographical coordinates, subarea, depth, and sampling year. For commercial fisheries samples, information regarding the observation type (on-board or onshore), the fishing gear used, and whether the species were landed or discarded, were also included. Allochthonous fish were recorded in samples caught with the following fishing gear: set gillnets (GNS), trammel nets (GTR), bottom otter trawls (OTB), beach and boat seines (SB-SV), purse seines (PS), set longlines (LLS), and pots/traps (FPO). Additionally, some NIS individuals provided by professional fishermen, were caught with hand lines and pole lines (hand operated, LHP) and in stationary uncovered pound nets (FPN). A total of 7,377 samples were collected across fishing gear, subareas, and years for the period 2017–2022. The sample sizes across subareas and gear were roughly comparable between years, ranging from 990 to 1,326. The sample sizes across years and gear were also comparable between subareas, ranging from 2,039 to 2,375, except for subarea “Thessaly and Sporades Islands” (VOL-SPOR), where the sample size was 892. Lastly, OTB, GNS, and GTR had the largest sample sizes across subareas and years, ranging from 1,535 to 2,116. PS and LLS had smaller sample sizes, i.e., 661 and 678, respectively, while the respective sample sizes for FPO and SB-SV were 259 and 89.

WoRMS (WoRMS Editorial Board 2023) was followed for the taxonomy and nomenclature of the species and FishBase (Froese and Pauly 2023) for the characterization of their habitat. The biogeographic origin and the mode of introduction in the Mediterranean Sea of each species was determined based on Golani et al. (2021), and the scientific literature for species cases not treated therein. The years of first records and NIS establishment status in Greece were sourced in Zenetos et al. (2020), or the scientific literature.

The establishment status of alien fish species in the study area was assessed based on the operational criterion of at least three valid records well separated in space and/or time, or, alternatively, based on strong evidence of local, self-maintaining populations (Zenetos et al. 2010; Golani et al. 2021). These assessments were based on both the compiled field data and the results of the systematic review of the scientific literature. A species was classified as established in the study area if it was assessed as established in at least one subarea.

The term “invasive” alien species does not have unequivocal meaning: it is often used to imply impact, especially in policy or legislation documents. For example, in the European Union Regulation “on the prevention and management of the introduction and spread of invasive alien species”, an invasive non-indigenous species is one whose “introduction or spread has been found to threaten or adversely impact upon biodiversity and related ecosystem services” (European Union 2014). An alternative perspective is that the term “invasiveness” should refer to the species’ potential to rapidly colonize a large area and should not connote negative environmental impact (Falk-Petersen et al. 2006; Ricciardi and Cohen 2007). Furthermore, “invasive” is a species that has “self-sustaining population in the wild, with individuals surviving a significant distance from the original point of introduction”, while a “fully invasive” species has “individuals dispersing, surviving and reproducing at multiple sites across a greater or lesser spectrum of habitats and extent of occurrence” (Blackburn et al. 2011). Nevertheless, the evidence for NIS impacts is often not strong, but based on expert judgement, non-experimental correlations, and modeling instead of experiments or direct observations (Katsanevakis et al. 2014; Galanidi et al. 2018). Accordingly, the dispersal dynamics of the species were assessed without any reference to impacts, while the cases of rapid dispersal at multiple sites in the assessment area were classified as potentially invasive.

Data analysis

The cumulative occurrence records of all alien species from field data and the literature review results were mapped to illustrate the temporal progress of fish invasions in the study area. Three separate maps were produced corresponding to the 2000s, 2010s, and 2020s. For onshore records with no geographic coordinates available the maps depict the port location. Moreover, additional maps of cumulative occurrence records for the entire study period were produced for each NIS with at least ten records. Temporal dynamics was also illustrated by plotting cumulative numbers (%) of NIS with records as a function of time for the period 1999–2023. The record of L. spadiceus by Ananiadis (1952) was omitted from the plots. The cumulative numbers (%) of fish NIS records and of the publications citing alien fish records were also plotted to evaluate the effect on NIS sightings of research effort. Additionally, the cumulative numbers of all fish NIS, those assessed as established and those assessed as casual according to the operational criterion adopted, were plotted in separate graphs.

NIS beta diversity in the study area (variation in NIS composition among subareas), can be the result of species replacement between sites (turnover) and species loss from subarea to subarea (nestedness). The betapart R package (Baselga et al. 2023) was used to compute total beta diversity with the Sørensen index (beta.SOR), as well as the respective turnover (beta.SIM) and nestedness (beta.SNE) components across subareas and between subarea pairs.

Lastly, the frequency of occurrence, the mean and maximum abundance and biomass, as well as the mean and maximum relative abundance and biomass were estimated for every fish NIS. Estimates were performed for each combination of gear, subarea and year with alien fish records. The MEDITS data were summarized for each combination of subarea and year.

All data analyses were carried out in R (R Core Team 2023) and all maps were produced with the ArcGIS Pro software (ESRI 2023).

Species identification verification with DNA barcoding

The taxonomic identification of specimens of Lagocephalus suezensis was corroborated with DNA barcoding due to their similar morphology with small-sized Lagocephalus sceleratus. Genomic DNA was extracted from approximately 25 mg of tissue from two specimens using the NucleoSpin Tissue extraction kit (Macherey-Nagel, Germany) according to the manufacturer’s protocol. A segment of the cytochrome oxidase subunit I (COI) gene (~ 660 bp) was amplified by polymerase chain reaction (PCR) using the primer pair: Forward FishF2: 5′-TGTAAAACGACGGCCAGTCGACTAATCATAAAGAT-3′ and Reverse-FishR2: 5′-CAGGAAACAGCTATGACACTTCAGGGTGACCGAAG-3’ (Ivanova et al., 2007) with M13 tails (M13F: TGTAAAACGACGGCCAGT and M13R: CAGGAAACAGCTATGAC) (Messing 1983). The PCR cycling conditions included an initial denaturation at 94 ^◦C for 2 min, followed by 35 cycles at 94 ^◦C for 30 s, 52 ^◦C for 40 s, 72 ^◦C for 50 s, and a final extension at 72 ^◦C for 10 min. PCR was conducted in 25 µl volumes and the reaction mixtures contained 2 µl of DNA, 2x Buffer (KAPA Biosystems, South Africa), 1.5 mM of MgCl₂ (KAPA Biosystems, South Africa), 200 µМ of each dNTP (Promega, Madison, WI USA), 0.3 µM of each primer, 0.75 U of KAPA Taq DNA polymerase (KAPA Biosystems, South Africa), and molecular grade water. PCR products were sequenced commercially (Macrogen, The Netherlands). Sequences were checked and manually edited using ProSeq 3.0 (Filatov 2002) and were subsequently compared against GenBank database with nucleotide BLAST (blastn, http://blast.ncbi.nlm.nih.gov/Blast.cg).

Fish NIS distributions and establishment status in the study area

The systematic review of the scientific literature resulted in 186 published records of alien fish species in the study area, in both Greece and Turkey (Online Resource 1, Table S2). After data cleaning, the records corresponded to 32 species (Table 1). Eleven of these species were recorded solely in Turkish territorial waters. The compilation of the field data resulted in a dataset of 251 unpublished records, corresponding to 20 fish NIS (Table 1, Fig. 2). Specifically, 224 field records were obtained from commercial fisheries (Table 2), ten from the MEDITS surveys (Table 3), and 17 records corresponded to specimens provided by commercial fishermen and taxonomically verified by FRI staff (Table 4). The combination of all datasets resulted in an inventory of 37 fish NIS with records in the study area, belonging to 20 orders and 26 families (Table 1). The most species-rich family was the Tetraodontidae, with six species.

Table 1

Inventory of fish NIS with records in the North Aegean Sea in the compiled field data (1996–2023) and/or found in the systematic review of the scientific literature. The table presents for each NIS the depth range of records, the numbers of records, its northernmost record in the Aegean Sea, the year of its first record in each subarea, in the study area as a whole and in Greece; an evaluation of its establishment success in each subarea, the study area as a whole and in Greece. First records in Greece were sourced from Zenetos et al. (2020), with exceptions for which the original sources are given below. The establishment success of the species in Greece were sourced from Zenetos et al. (2020), with exceptions for which the assessment was based on the scientific literature and the authors’ judgement. Subareas of the Greek multiannual program: CHIO-MIT = Northeastern Aegean Sea; THERM = Thermaikos Gulf and adjacent seas; THR-LIM = Thracian Sea – Limnos Island; and VOL-SPOR = Thessaly – Sporades Islands; NIS establishment status: e = established; c = casual, unk = unknown. Original sources: (1) Marletta & Lombardo 2020; (2) Kampouris et al. 2020; (3) Kampouris and Batjakas in Crocetta et al. 2021; (4) Zachariou-Mamalinga & Corsini 1992; (5) Ananiadis 1952.
							First records						Establishment success
	NIS	Depth (m) – Field data	Depth (m) – Literature review	Number of records – Field data	Number of records – Literature review	Northernmost records in the Aegean Sea	CHI-MIT	VOL-SPOR	THERM	THR-LIM	Study area	Greece	CHIO-MIT	VOL-SPOR	THERM	THR-LIM	Study area	Greece
	Acanthuriformes
	Siganidae
1	Siganus luridus (Rüppell, 1829)	5–110	0–15	92	53	CHIO-MIT (Ismen et al., 2015)	2009	2018		2021	2009	1964	e	c		c	e	i
2	Siganus rivulatus Forsskål & Niebuhr, 1775	15–27	3–5	6	14	CHIO-MIT (Ragkousis et al., 2023)	2010				2010	1925	e				e	i
	Acropomatiformes
	Champsodontidae
3	Champsodon nudivittis (Ogilby, 1895)	53–315	6–140	61	8	THR-LIM (this study)	2014	2022	2020	2016	2014	2012	e	c	e	e	e	e
	Pempheridae
4	Pempheris rhomboidea Kossmann & Räuber, 1877	10–20	5	3	1	CHIO-MIT (this study)	2004				2004	1983	e				e	e
	Anguilliformes
	Muraenidae
5	Enchelycore anatina (Lowe, 1838)^a		5		1	CHIO-MIT (Şenbahar and Özaydin, 2020)	2019				2019	1987⁽¹⁾	c				c	e
	Beloniformes
	Hemiramphidae
6	Hemiramphus far (Forsskål, 1775)^a		40–70		2	CHIO-MIT (Akyol and Tosunoğlu, 2020)	2009				2009	1943	c				c	e
	Callionymiformes
	Callionymidae
7	Callionymus filamentosus Valenciennes, 1837	75		1		VOL-SPOR (this study)		2016			2016	2003		c			c	e
	Carangaria incertae sedis
	Sphyraenidae
8	Sphyraena chrysotaenia Klunzinger, 1884	75		1		THR-LIM (this study)				2021	2021	1995				c	c	e
	Centrarchiformes
	Terapontidae
9	Terapon theraps Cuvier, 1829		20		1	THERM (Minos et al., 2012)			2008		2008	2008			c		c	c
	Clupeiformes
	Dussumieriidae
10	Etrumeus golanii DiBattista, Randall & Bowen, 2012	16–180	40–63	8	15	CHIO-MIT (Yarmaz et al., 2010)	2009	2019	2018		2009	2003	e	e	c		e	e
	Eupercaria incertae sedis
	Haemulidae
11	Pomadasys stridens (Forsskål, 1775)^a		24		1	CHIO-MIT (Katsanevakis et al., 2020)	2016				2016	2019	c				c	unk
	Labridae
12	Bodianus speciosus (Bowdich, 1825)^a		11		1	CHIO-MIT (Filiz et al., 2019)	2018				2018		c				c	c
13	Pteragogus trispilus Randall, 2013^a		25		1	CHIO-MIT (Yapıcı et al., 2015)	2014				2014	1992	c				c	e
	Lutjanidae
14	Lutjanus argentimaculatus (Forsskål, 1775)^a		8		1	CHIO-MIT (Akyol, 2019)	2018				2018	2019	c				c	c
	Nemipteridae
15	Nemipterus randalli Russell, 1986^a		90		1	CHIO-MIT (Aydin and Akyol, 2017)	2016				2016	2018	c				c	c
	Sparidae
16	Acanthopagrus bifasciatus (Forsskål, 1775)^a		3		1	CHIO-MIT (Şensurat-Genç et al., 2020)	2018				2018		c				c	c
17	Pagrus major (Temminck & Schlegel, 1843)		32–36		1	THERM (Kampouris et al., 2020)			2019		2019	2019⁽²⁾			c		c	c
	Gadiformes
	Bregmacerotidae
18	Bregmaceros nectabanus Whitley, 1941	69–106	30–150	3	3	THERM (this study)	2005	2022	2023		2005	2014	e	c	c		e	e
	Gobiiformes
	Gobiidae
19	Oxyurichthys petersii (Klunzinger, 1871)	48		1		THERM (this study)			2018		2018	2010			c		c	c
	Holocentriformes
	Holocentridae
20	Sargocentron rubrum (Forsskål, 1775)	23		1		CHIO-MIT (this study)	2016				2016	1940	c				c	e
	Mugiliformes
	Mugilidae
21	Planiliza haematocheilus (Temminck & Schlegel, 1845)		8–10		2	THR-LIM (Minos et al., 2010b)	2006			2003	2003	1995	c			c	c	e
	Mulliformes
	Mullidae
22	Upeneus moluccensis (Bleeker, 1855)	128	5–85	1	4	CHIO-MIT (this study)	2015				2015	1947	e				e	e
23	Upeneus pori Ben-Tuvia & Golani, 1989		20–47		2	THERM (Kampouris et al., 2020)	2009		2018		2009	2003	c		c		c	e
	Perciformes
	Scorpaenidae
24	Pterois miles (Bennett, 1828)	7–130	0–36	11	31	THERM (Katsanevakis et al., 2020)	2019	2019	2019		2019	2009	e	c	c		e	e
	Serranidae
25	Cephalopholis taeniops (Valenciennes, 1828)^a		6–13		2	CHIO-MIT (Engin et al., 2016)	2015				2015		c				c	c
26	Paranthias furcifer (Valenciennes, 1828)^a		12		1	CHIO-MIT (Yapici and Sevingel in Ragkousis et al., 2020)	2019				2019		c				c	c
	Salmoniformes
	Salmonidae
27	Oncorhynchus kisutch (Walbaum, 1792)		2–3		1	THR-LIM (Kampouris and Batjakas in Crocetta et al., 2021)				2021	2021	2021⁽³⁾				c	c	c
	Scombriformes
	Scombridae
28	Scomberomorus commerson (Lacepède, 1800)	37		1		THR-LIM (this study)				2008	2008	2008				c	c	e
	Syngnathiformes
	Fistulariidae
29	Fistularia commersonii Rüppell, 1838	12–62	25–60	3	4	THERM (Karachle et al., 2014)	2006		2003		2003	2001	e		c		e	i
30	Fistularia petimba Lacepède, 1803	68	20	1	1	THR-LIM (this study)	2021			2020	2020	2020	c			c	c	c
	Tetraodontiformes
	Monacanthidae
31	Stephanolepis diaspros Fraser-Brunner, 1940	3–110	5 - 18	30	10	THR-LIM (this study)	2008	2016	2021	2019	2008	1943	e	e	e	c	e	e
	Tetraodontiformes
	Tetraodontidae
32	Lagocephalus guentheri Miranda Ribeiro, 1915	9–41	50	3	1	THR-LIM (this study)	2015			2007	2007	1952	c			e	e	e
33	Lagocephalus sceleratus (Gmelin, 1789)	5–95	2–60	20	13	THR-LIM (this study)	2006	2007	2008	2008	2006	2005	e	e	e	e	e	i
34	Lagocephalus suezensis Clark & Gohar, 1953	7	93	1	1	THR-LIM (this study)	2020		2017		2017	2003	c		c		c	e
35	Sphoeroides pachygaster (Müller & Troschel, 1848)	82–141	80–180	3	3	THR-LIM (this study)	2016	2020		1999	1999	1992⁽⁴⁾	c	c		e	e	e
36	Lagocephalus spadiceus (Richardson, 1845)		146		1	CHIO-MIT (Ananiadis, 1952)	1952				1952	1952⁽⁵⁾	c				c	c
37	Torquigener flavimaculosus Hardy & Randall, 1983		93		1	CHIO-MIT (Ragkousis et al., 2023)	2020				2020	2006	c				c	e
^a Species with no records in the study area except along the Asia minor coastline

Table 2

Fish NIS records in the commercial fisheries monitoring samples in the North Aegean Sea during 2017–2022. The information is aggregated by fishing gear, subarea, year and species and includes the number of samples, the frequency of occurrence (F), mean abundance (N) and biomass (W), mean relative abundance (rel. N) and biomass (rel. W), mean CPUE in terms of abundance and biomass per fishing hour, maximum abundance and biomass, maximum relative abundance and biomass and maximum CPUE in terms of abundance and biomass per fishing hour. Gear codes: FPO = pots, GNS = set gillnets, GTR = trammel nets, LLS = set longlines, OTB = bottom otter trawls, PS = purse seines, SB-SV = beach and boat seines. Subareas of the Greek multiannual program: CHIO-MIT = Northeastern Aegean Sea; THERM = Thermaikos Gulf and adjacent seas; THR-LIM = Thracian Sea – Limnos Island; and VOL-SPOR = Thessaly – Sporades Islands.
Gear code	Subarea	Year	Species	Samples	F	Mean N (ind.)	Mean W (g)	Mean rel. N	Mean rel. W	Mean CPUE (ind./h)	Mean CPUE (g/h)	Max N (ind.)	Max W (g)	Max rel. N	Max rel. W	Max CPUE (ind./h)	Max CPUE (g/h)
FPO	THERM	2022	Stephanolepis diaspros	27	3.70%	0.19	46.30	0.23%	0.85%	0.01	2.01	5	1250	6.10%	22.98%	0.22	54.35
FPO	VOL-SPOR	2022	Stephanolepis diaspros	9	11.11%	0.11	10.00	3.70%	1.12%	0.00	0.08	1	90	33.33%	10.11%	0.01	0.76
GNS	CHIO-MIT	2017	Lagocephalus sceleratus	117	1.71%	0.02	0.43	*	*	0.01	0.14	1	30	0.72%	0.79%	0.44	8.89
GNS	CHIO-MIT	2017	Stephanolepis diaspros	117	0.85%	0.01	0.85	*	*	0.00	0.21	1	100	0.41%	0.40%	0.25	25.00
GNS	CHIO-MIT	2018	Siganus luridus	120	0.83%	0.02	3.13	0.03%	0.04%	0.00	0.31	2	375	3.92%	4.63%	0.20	37.50
GNS	CHIO-MIT	2018	Stephanolepis diaspros	120	1.67%	0.02	1.67	0.01%	0.01%	0.01	0.57	1	175	1.12%	0.88%	0.40	58.33
GNS	CHIO-MIT	2019	Pterois miles	124	0.81%	0.01	2.22	0.02%	*	0.00	0.14	1	275	2.86%	0.77%	0.06	17.74
GNS	CHIO-MIT	2019	Siganus luridus	124	2.42%	0.11	12.90	0.26%	0.15%	0.02	2.38	7	800	24.14%	11.64%	1.67	200.00
GNS	CHIO-MIT	2019	Stephanolepis diaspros	124	1.61%	0.02	2.42	0.01%	0.01%	0.01	0.67	2	225	1.12%	1.15%	1.00	45.00
GNS	CHIO-MIT	2020	Pterois miles	121	0.83%	0.01	2.27	0.03%	0.03%	0.00	0.15	1	275	3.45%	3.78%	0.07	18.33
GNS	CHIO-MIT	2020	Siganus luridus	121	0.83%	0.01	1.16	*	0.02%	0.00	0.33	1	140	0.67%	2.18%	0.29	40.00
GNS	CHIO-MIT	2020	Stephanolepis diaspros	121	0.83%	0.01	1.65	*	*	0.00	0.44	1	200	0.40%	1.11%	0.27	53.33
GNS	CHIO-MIT	2021	Fistularia commersonii	119	1.68%	0.02	4.03	0.10%	0.14%	0.00	0.31	1	240	10.00%	12.37%	0.08	18.46
GNS	CHIO-MIT	2021	Lagocephalus sceleratus	119	0.84%	0.01	6.05	0.02%	0.05%	0.00	0.44	1	720	2.86%	5.41%	0.07	52.05
GNS	CHIO-MIT	2021	Pterois miles	119	0.84%	0.01	1.85	*	*	0.00	0.21	1	220	0.26%	0.67%	0.12	25.38
GNS	CHIO-MIT	2021	Siganus luridus	119	2.52%	0.08	9.29	0.06%	0.05%	0.01	1.51	5	730	5.41%	2.33%	0.89	84.23
GNS	CHIO-MIT	2022	Etrumeus golanii	124	3.23%	0.08	10.69	0.14%	0.06%	0.01	0.93	4	475	8.11%	3.04%	0.32	50.00
GNS	CHIO-MIT	2022	Siganus luridus	124	3.23%	0.11	18.99	0.26%	0.16%	0.02	3.51	7	1350	17.50%	7.41%	2.00	264.00
GNS	VOL-SPOR	2018	Stephanolepis diaspros	42	2.38%	0.02	0.12	0.01%	*	0.01	0.06	1	5	0.56%	0.05%	0.50	2.50
GTR	CHIO-MIT	2017	Siganus luridus	77	9.09%	0.42	53.25	0.81%	0.74%	0.03	4.29	9	1080	18.75%	16.67%	0.72	86.40
GTR	CHIO-MIT	2018	Siganus luridus	69	8.70%	0.39	61.96	0.39%	0.42%	0.03	5.02	11	1980	9.73%	12.68%	0.92	165.00
GTR	CHIO-MIT	2019	Pterois miles	70	1.43%	0.01	1.43	0.03%	0.01%	0.00	0.11	1	100	2.00%	0.82%	0.08	7.59
GTR	CHIO-MIT	2019	Siganus luridus	70	15.71%	1.19	177.71	1.33%	0.99%	0.10	14.46	36	5475	22.00%	16.61%	3.13	476.09
GTR	CHIO-MIT	2020	Etrumeus golanii	69	1.45%	0.43	54.86	0.33%	0.25%	0.04	4.99	30	3785	22.56%	16.94%	2.73	344.09
GTR	CHIO-MIT	2020	Pterois miles	69	4.35%	0.07	16.38	0.08%	0.10%	0.01	1.13	2	460	2.70%	3.42%	0.16	36.32
GTR	CHIO-MIT	2020	Siganus luridus	69	14.49%	0.83	115.43	0.88%	0.82%	0.07	10.11	15	2070	10.64%	14.85%	1.22	167.84
GTR	CHIO-MIT	2020	Siganus rivulatus	69	1.45%	0.04	8.12	0.06%	0.06%	0.00	0.74	3	560	4.17%	4.29%	0.27	50.91
GTR	CHIO-MIT	2020	Stephanolepis diaspros	69	1.45%	0.01	1.81	0.03%	0.01%	0.00	0.19	1	125	2.38%	0.92%	0.11	13.16
GTR	CHIO-MIT	2021	Etrumeus golanii	68	2.94%	2.92	188.24	0.43%	0.53%	0.91	57.13	180	11225	16.86%	23.28%	59.87	3741.67
GTR	CHIO-MIT	2021	Pempheris rhomboidea	68	1.47%	0.04	2.21	0.04%	0.01%	0.00	0.18	3	150	2.39%	0.84%	0.24	12.00
GTR	CHIO-MIT	2021	Pterois miles	68	2.94%	0.12	39.41	0.10%	0.23%	0.01	3.58	4	1520	4.21%	9.37%	0.39	147.10
GTR	CHIO-MIT	2021	Siganus luridus	68	16.18%	0.90	120.96	1.14%	0.79%	0.07	8.39	24	3900	24.49%	16.67%	1.26	205.26
GTR	CHIO-MIT	2021	Siganus rivulatus	68	2.94%	0.03	5.22	0.16%	0.08%	0.00	0.45	1	225	9.09%	3.77%	0.09	20.00
GTR	CHIO-MIT	2021	Stephanolepis diaspros	68	1.47%	0.01	2.57	0.03%	0.01%	0.00	0.21	1	175	2.08%	0.89%	0.08	14.00
GTR	CHIO-MIT	2022	Lagocephalus sceleratus	60	1.67%	0.02	16.25	0.09%	0.38%	0.00	1.71	1	975	5.56%	22.81%	0.11	102.63
GTR	CHIO-MIT	2022	Pempheris rhomboidea	60	3.33%	0.05	3.17	0.05%	0.02%	0.00	0.28	2	150	2.08%	0.92%	0.17	13.04
GTR	CHIO-MIT	2022	Pterois miles	60	1.67%	0.02	5.42	0.04%	0.06%	0.00	0.31	1	325	2.38%	3.79%	0.06	18.57
GTR	CHIO-MIT	2022	Siganus luridus	60	16.67%	0.57	73.17	0.57%	0.39%	0.09	10.46	11	1640	9.52%	6.71%	1.50	183.33
GTR	CHIO-MIT	2022	Stephanolepis diaspros	60	1.67%	0.02	1.25	0.02%	0.01%	0.00	0.11	1	75	1.49%	0.61%	0.09	6.82
GTR	THR-LIM	2019	Stephanolepis diaspros	100	1.00%	0.01	0.45	*	*	0.00	0.04	1	45	0.68%	0.23%	0.09	4.09
GTR	VOL-SPOR	2017	Lagocephalus sceleratus	13	7.69%	0.15	6.15	0.04%	0.03%	0.03	1.23	2	80	0.55%	0.38%	0.40	16.00
GTR	VOL-SPOR	2017	Stephanolepis diaspros	13	7.69%	0.08	7.69	1.10%	0.83%	0.00	0.42	1	100	14.29%	10.75%	0.05	5.41
GTR	VOL-SPOR	2019	Stephanolepis diaspros	53	3.77%	0.04	2.26	0.33%	0.17%	0.00	0.14	1	80	11.11%	5.26%	0.06	4.85
GTR	VOL-SPOR	2020	Stephanolepis diaspros	52	9.62%	0.23	25.19	0.53%	0.31%	0.01	1.66	8	656	17.39%	7.78%	0.44	36.44
GTR	VOL-SPOR	2021	Stephanolepis diaspros	57	1.75%	0.07	7.98	0.13%	0.08%	0.00	0.45	4	455	7.27%	4.52%	0.23	25.63
GTR	VOL-SPOR	2022	Stephanolepis diaspros	51	3.92%	0.04	8.82	0.05%	0.13%	0.01	0.88	1	350	2.22%	5.72%	0.25	25.00
LLS	CHIO-MIT	2018	Siganus luridus	56	1.79%	0.02	3.13	0.04%	0.05%	0.01	1.04	1	175	2.04%	2.70%	0.33	58.33
OTB	CHIO-MIT	2020	Bregmaceros nectabanus	41	2.44%	0.10	0.20	0.01%	*	0.04	0.08	4	8	0.45%	0.02%	1.55	3.10
OTB	CHIO-MIT	2020	Champsodon nudivittis	41	2.44%	0.20	1.46	0.02%	*	0.08	0.57	8	60	0.90%	0.13%	3.10	23.23
OTB	CHIO-MIT	2020	Sphoeroides pachygaster	41	2.44%	0.22	175.61	0.01%	0.17%	0.08	63.09	9	7200	0.48%	7.11%	3.23	2586.83
OTB	CHIO-MIT	2021	Champsodon nudivittis	72	9.72%	1.10	10.56	0.03%	*	0.35	3.57	30	300	0.53%	0.26%	8.57	100.00
OTB	CHIO-MIT	2022	Champsodon nudivittis	68	8.82%	4.12	28.44	0.20%	0.04%	1.64	9.91	105	640	8.01%	1.01%	52.50	200.00
OTB	THERM	2018	Oxyurichthys petersii	136	0.74%	0.04	0.11	*	*	0.01	0.03	6	15	0.98%	0.07%	1.80	4.50
OTB	THERM	2020	Champsodon nudivittis	81	2.47%	0.20	2.15	*	*	0.04	0.40	10	150	0.33%	0.11%	1.85	25.00
OTB	THERM	2021	Champsodon nudivittis	136	4.41%	0.35	3.18	0.01%	*	0.07	0.63	10	200	0.56%	0.20%	2.22	36.36
OTB	THERM	2021	Fistularia commersonii	136	0.74%	0.05	0.26	*	*	0.01	0.05	7	35	0.26%	0.05%	1.27	6.36
OTB	THERM	2022	Champsodon nudivittis	130	1.54%	0.10	0.73	*	*	0.02	0.16	7	60	0.65%	0.11%	1.44	14.40
OTB	THR-LIM	2020	Fistularia petimpa	134	0.75%	0.01	0.07	*	*	0.00	0.02	1	10	0.08%	0.01%	0.27	2.73
OTB	THR-LIM	2021	Champsodon nudivittis	169	3.55%	0.27	2.18	0.01%	*	0.06	0.47	14	210	0.74%	0.37%	3.07	45.99
OTB	THR-LIM	2021	Sphoeroides pachygaster	169	0.59%	0.01	1.54	*	*	0.00	0.34	1	260	0.02%	0.18%	0.22	57.78
OTB	THR-LIM	2021	Sphyraena chrysotaenia	169	0.59%	0.01	0.65	*	*	0.00	0.19	1	110	0.06%	0.21%	0.29	31.43
OTB	THR-LIM	2022	Champsodon nudivittis	184	6.52%	0.73	6.25	0.05%	0.01%	0.16	1.36	20	160	1.79%	0.50%	4.29	33.68
OTB	VOL-SPOR	2021	Lagocephalus sceleratus	20	5.00%	0.05	15.00	*	0.02%	0.02	4.74	1	300	0.07%	0.45%	0.32	94.74
OTB	VOL-SPOR	2022	Bregmaceros nectabanus	34	2.94%	0.26	1.32	0.01%	*	0.04	0.22	9	45	0.47%	0.07%	1.50	7.50
OTB	VOL-SPOR	2022	Champsodon nudivittis	34	2.94%	0.26	1.32	0.01%	*	0.04	0.22	9	45	0.47%	0.07%	1.50	7.50
PS	CHIO-MIT	2022	Etrumeus golanii	10	10.00%	0.30	14.00	*	*	0.90	42.00	3	140	*	*	9.00	420.00
PS	THR-LIM	2021	Lagocephalus sceleratus	51	1.96%	0.02	0.10	*	*	0.04	0.18	1	5	*	*	1.88	9.38
PS	VOL-SPOR	2021	Stephanolepis diaspros	17	5.88%	0.12	0.59	0.02%	*	0.35	1.76	2	10	0.28%	0.01%	6.00	30.00
SB-SV	CHIO-MIT	2018	Siganus luridus	25	4.00%	0.12	0.60	*	*	0.10	0.51	3	15	0.16%	0.04%	2.57	12.86
SB-SV	CHIO-MIT	2018	Stephanolepis diaspros	25	8.00%	0.12	9.00	*	0.02%	0.06	4.40	2	175	0.06%	0.39%	0.96	84.00
* values < 0.01%

Table 3

Fish NIS catches in the MEDITS samplings in the North Aegean Sea during 1996–2022. The information is aggregated by fishing gear, subarea, year and species and includes the number of samples, the frequency of occurrence (F), mean abundance (N) and biomass (W), mean relative abundance (rel. N) and biomass (rel. W), mean CPUE in terms of abundance and biomass per fishing hour, maximum abundance and biomass, maximum relative abundance and biomass and maximum CPUE in terms of abundance and biomass per fishing hour. Subareas of the Greek multiannual program: CHIO-MIT = Northeastern Aegean Sea; THERM = Thermaikos Gulf and adjacent seas; THR-LIM = Thracian Sea – Limnos Island; and VOL-SPOR = Thessaly – Sporades Islands
Subarea	Year	Species	Samples	F	Mean N (ind.)	Mean W (g)	Mean rel. N	Mean rel. W	Mean CPUE (ind./h)	Mean CPUE (g/h)	Max N (ind.)	Max W (g)	Max rel. N	Max rel. W	Max CPUE (ind./h)	Max CPUE (g/h)
VOL-SPOR	2020	Sphoeroides pachygaster	1	0.17	0.17	26.67	0.06%	0.10%	0.33	53.33	1	160	0.36%	0.59%	2	320
THR-LIM	2021	Champsodon nudivittis	1	0.04	0.04	0.16	*	*	0.08	0.32	1	4	0.01%	*	2	8
THR-LIM	2022	Champsodon nudivittis	2	0.08	0.16	1.04	0.02%	*	0.32	2.08	3	21	0.54%	0.06%	6	42
CHIO-MIT	2019	Champsodon nudivittis	1	0.07	0.14	0.57	0.01%	*	0.14	0.57	2	8	0.20%	0.02%	2	8
CHIO-MIT	2020	Champsodon nudivittis	1	0.07	0.07	0.36	*	*	0.07	0.36	1	5	0.05%	0.01%	1	5
CHIO-MIT	2021	Champsodon nudivittis	2	0.14	0.64	5.21	0.06%	0.02%	0.64	5.21	8	70	0.89%	0.25%	8	70
CHIO-MIT	2022	Champsodon nudivittis	2	0.14	1.86	17.14	0.08%	0.03%	2.57	21.43	16	180	0.95%	0.26%	20	180
* values < 0.01%

Table 4

Fish NIS caught by commercial fishermen in the North Aegean Sea and taxonomically verified by FRI (2007–2021). The information is presented per sample and includes the number of specimens provided; their total length and weight ranges; whether the specimens were in landings or discards; the gear that was used; the fishing depth; the year the specimens were caught; and the respective Greek multiannual program sub-area and the location were the specimens were caught along with approximate geographical coordinates. Gear codes: FPO = pots, GNS = set gillnets, GTR = trammel nets, LLS = set longlines, OTB = bottom otter trawls, PS = purse seines, SB-SV = beach and boat seines, LHP = handlines and pole-lines, hand-operated, FPN = stationary uncovered pound nets.
	NIS	Number	TL (mm)	Weight (g)	Gear	Landings/discards	Depth (m)	Year	Sub-area	Location	LAT (DD)	LON (DD)
1	Lagocephalus guentheri	1	133	42.4	GNS	Discards	9	2007	THR-LIM	N.E. of Thasos Island	40.754639	24.792971
2	Lagocephalus guentheri	1	117	28.8	GTR	Discards	13	2007	THR-LIM	Paralia Dikellon, Evros	40.840287	25.69331
3	Lagocephalus guentheri	1	210	173.8	LHP	Discards	41	2007	THR-LIM	Paralia Mirtofitou, Kavala	40.749136	24.192577
4	Lagocephalus sceleratus	1	large		FPN	Discards	5	2008	THR-LIM	Nea Iraklitsa, Kavala	40.861288	24.342005
5	Lagocephalus sceleratus	1	539	1758	ΟΤΒ	Discards	64	2008	THR-LIM	W. of Thasos Ιsland	40.626803	24.488863
6	Lagocephalus sceleratus	1	508	2070	PS	Discards	33	2011	THR-LIM	W. of Thasos Ιsland	40.618264	24.519751
7	Lagocephalus sceleratus	2	53–59		SB-SV	Discards	7	2017	THERM	Chrousou Bay, Chalkidiki	39.965744	23.684798
8	Lagocephalus sceleratus	1			GNS	Discards		2017	CHI-MIT	Kalloni Gulf, Lesvos Island	39.129532	26.179845
9	Lagocephalus sceleratus	14	58–127	2.7–23.6	SB-SV	Discards	7	2017	THERM	Chrousou Bay, Chalkidiki	39.965744	23.684798
10	Lagocephalus sceleratus	20	88–140	6.3–30.6	SB-SV	Discards	7	2017	THERM	Chrousou Bay, Chalkidiki	39.965744	23.684798
11	Lagocephalus sceleratus	2	124–125	16.6–21.6	LHP	Discards	10	2020	THR-LIM	Nea Iraklitsa, Kavala	40.861288	24.342005
12	Lagocephalus sceleratus	1	572		ΟΤΒ	Discards	55	2021	THERM	Leptokarya, Pieria	40.063141	22.580622
13	Lagocephalus sceleratus	1	97	4.2	PS	Discards	40	2021	THR-LIM	E. of Thasos Ιsland	40.686603	24.798011
14	Lagocephalus sceleratus	2	120–123	18.8–19.2	LHP	Discards	20	2020	THR-LIM	Nea Peramos, Kavala	40.829946	24.323868
15	Lagocephalus sceleratus	1	63	44.4	GTR	Discards	24	2020	THR-LIM	Eleftheres, Kavala	40.838603	24.330677
16	Lagocephalus suezensis	2	67–87	2.7–3.8	SB-SV	Discards	7	2017	THERM	Chrousou Bay, Chalkidiki	39.965744	23.684798
17	Scomberomorous commerson	1	807	3315	PS	Landings	37	2008	THR-LIM	Paralia Karianis, Kavala	40.721032	23.963593

The field dataset includes first records of four NIS in the study area: Callionymus filamentosus, Oxyurichthys petersii, Sargocentron rubrum, and Sphyraena chrysotaenia. This study also provides georeferenced metadata for the sole, so far, record of Scomberomorus commerson in the North Aegean Sea. Furthermore, the field data also include records that chronologically precede all previous published records of several fish NIS in Greek waters or the study area: the record of Fistularia petimba in the Thracian Sea (THR-LIM) in 2020, chronologically precedes the oldest published record of this species in Greece, off Samos Island in 2021 (Kondylatos and Nikolidakis in Crocetta et al. 2021). Furthermore, the records of Lagocephalus guentheri and L. suezensis chronologically precede their previously published sightings in the study area. Finally, the field data include the until today northernmost records in the Aegean Sea of Bregmaceros nectabanus, Champsodon nudivittis, F. petimba, L. guentheri, L. sceleratus, L. suezensis, Pempheris rhomboidea, S. pachygaster, Stephanolepis diaspros, and Upeneus moluccensis (Table 1).

The two specimens of L. suezensis that were recorded off Chalkidiki in 2017 were caught along with similarly sized juveniles of L. sceleratus (Table 4). The back of these specimens had dark spots of diverse sizes and irregular shape, whilst L. sceleratus juveniles had similarly sized dark spots of more regular shape. Both specimens were verified taxonomically with DNA barcoding and all barcodes resulted in top species matches for L. suezensis above 99.0% identity on GenBank (both samples provided partial barcodes, i.e., ~ 280 bp and 610 bp, Table S3 in Online Resource 1).

Most of the recorded fish NIS are tropical species of Indo-Pacific origin or Red Sea endemics (28); only four have native geographic ranges in the Atlantic Ocean, three species are natively distributed in both the Indo-Pacific and the Atlantic Oceans, and only one has a cosmopolitan distribution (Online Resource 1, Table S4). Moreover, 28 of the species are considered Lessepsian migrants, two are neonative species that were introduced in the Mediterranean via the Gibraltar strait, and seven were introduced via other human-mediated mechanisms (Online Resource 1, Table S4). Most species are reef-associated (18) or demersal (10), whilst the rest are pelagic (8) or benthopelagic species (1) (Online Resource 1, Table S4). Nineteen species were recorded only from depths shallower than 50 m, whereas nine species were collected from depths down to 100 m (Table 1). Eight species had records in deeper waters (< 200 m), however only C. nudivittis was collected over the continental slope (down to 315 m). The most eurybathic species (bathymetric range in the data > 100 m) were Siganus luridus, C. nudivittis, Etrumeus golanii, B. nectabanus, U. moluccensis, Pterois miles, S. diaspros, and S. pachygaster.

The establishment success in Greek waters for 26 species (Table 1) was classified according to Zenetos et al. (2020): most of them (18) have established populations in Greek waters, four are considered invasive and the rest (3) are casual, while the establishment status of Pomadasys stridens was designated as “unknown”. Μost of the remaining species were designated to be casual in Greece (9) and two to be established. Establishment success in the study area was operationally assessed as follows: most species are casual (24) and the rest (13) are established in at least one subarea. The subarea with the most established species was the Northeastern Aegean Sea (CHIO-MIT) (11), whereas the other subareas had similarly low numbers of established species (3–4). Lagocephalus sceleratus was the only species with established populations in all subareas, followed by C. nudivittis and S. diaspros (three subareas each).

Interestingly, the field data provided strong evidence for the occurrence of self-sustaining, reproducing populations of L. sceleratus in the North Aegean Sea in the late 2010s to early 2020s: 42 juveniles (53–140 mm TL) were caught along the coasts of Northern Greece during the period 2017–2021 (Table 4). Most of them (36) were caught off Chalkidiki, in October and November 2017. The rest were caught at several locations in the Gulf of Kavala in 2020 and 2021. Local fishermen also provided large-sized, adult specimens of L. sceleratus (500–700 mm TL) caught in the Gulf of Kavala (four specimens) in 2008 and 2011 and one specimen from Thermaikos Bay in 2021.

Spatio-temporal patterns in the distributions of alien fish species

NIS beta diversity (compositional dissimilarity) across subareas (beta.SOR = 0.68) was to a larger extent due to species turnover (beta.SIM = 0.47) than to nestedness (beta.SNE = 0.22). Pairwise comparisons revealed that the most dissimilar subareas were THERM and THR-LIM (beta.SOR = 0.74), whereas the most similar were THERM and VOL-SPOR (beta.SOR = 0.43). Species loss accounted for the greatest part of the dissimilarity between CHIO-MIT and VOL-SPOR, THERM and THR-LIM (81%, 56% and 55%, respectively), whereas species replacement was responsible for most of the dissimilarity between VOL-SPOR and THERM or THR-LIM (78% and 89%, respectively), and between THERM and THR-LIM (98%). The exact numbers of NIS shared between subareas and the species occurring in only one subarea are depicted in Fig. 3. The number of NIS that were uniquely present in a single subarea was far larger in CHIO-MIT (16) than in THERM and THR-LIM (3 each) or in VOL-SPOR (1).

Cumulative occurrence maps (Figs. 4 and 5) indicate that sightings of NIS were more numerous and widespread in the 2020s (252 records) than in the 2010s (153), while records from the 2000s were comparatively few (27). This trend was observed at the subarea level as well, except for THR-LIM, where sightings in the 2000s and 2010s were similar (8 and 7, respectively) but still fewer than in the 2020s (33). The majority of records were made in CHIO-MIT (316), while the numbers of NIS sightings in the other subareas were comparable (29–49). The apparent pronounced increase in NIS sightings in the 2020s in THERM and THR-LIM is attributable to the rapid range expansion of C. nudivittis that has been occurring since 2020 (Fig. 5).

Research effort regarding fish NIS distributions in the study area, defined as the number of publications selected in the literature review, increased over time since the late 1990s (Fig. 6a). The cumulative number of reported NIS also increased over time at a similar rate. The accumulation of publications and NIS numbers over time is best described by a linear function, with approximately half of the studies published and half of the species recorded by 2015. However, the accumulation of NIS sightings over time is best described by an exponential function, with almost 90% of the sightings made after 2015.

The rate of increase in the cumulative number of NIS differs between subareas (Fig. 6b-d), with a higher rate in CHIO-MIT than in other subareas. NIS numbers have continuously increased in CHIO-MIT since the late 1990s, whereas a significant increase in NIS numbers in the other subareas did not start before 2015. The temporal increase in the numbers of established NIS (Fig. 6c) was much higher in CHIO-MIT than in the other subareas, where most species remained casual.

Fish NIS effects on commercial fisheries

A total of 14 fish NIS were recorded in the commercial fisheries monitoring samples during 2017–2022, which were caught with the following gear: GTR, GNS, OTB, PS, FPO, SB-SV, and LLS (Table 2). The species most frequently caught across gears, subareas and years was S. diaspros (18 combinations), followed by S. luridus (13), C. nudivittis (9), P. miles (7), and L. sceleratus (6). Stephanolepis diaspros and C. nudivittis were recorded in fisheries catches in all four subareas, whereas L. sceleratus was caught in three subareas. Several species were caught in only one subarea, mostly in CHIO-MIT, with the frequently caught S. luridus and P. miles included among them. Stephanolepis diaspros and S. luridus have been consistently present in commercial fisheries catches throughout the study period. On the other hand, P. miles has been constantly recorded since 2019, and C. nudivittis and E. golanii since 2020.

The total number of the caught fish NIS differed between gear, subareas, and years (Table 2): more species were recorded in OTB (8), GTR (7) and GNS (6) than in PS (3), SB-SV (2), FPO (1), and LLS (1) catches. The highest number of species was recorded in CHIO-MIT (11), whereas six species were caught in THR-LIM, and four in both THERM and VOL-SPOR. Moreover, far more alien fish species were recorded in 2022 (8), 2021 (11) and 2020 (9) than in the three preceding years (3 in each year). In most samples with NIS catches, a single alien species was detected, two species were less common, whereas three species were caught once.

Total fish NIS quantity in the samples pooled across subareas and gear generally followed an increasing trend with time, rising from 38 individuals and 4 kg in 2017 to a maximum abundance of 521 individuals in 2022 and a maximum biomass of 30 kg in 2021. Pooled across years and gear, total fish NIS quantity in samples was greater in CHIO-MIT (1,008 individuals and 85 kg) than in the other subareas (46–185 individuals and 2–3 kg). Moreover, the highest total catches were recorded in OTB and GTR samples (671 and 577 individuals and 13 kg and 67 kg, respectively).

All NIS were discarded except for E. golanii and S. chrysotaenia, which were landed, and S. luridus, which was either landed or discarded on a case-by-case basis.

Static nets

Seven fish NIS were recorded in the GTR samples and six in the GNS samples (Table 2). Almost all GNS samples and most GTR samples that included alien fish species were collected in CHIO-MIT. Within CHIO-MIT, allochthonous species catches with GTR were higher off Samos, Ikaria and Psara, and with GTR also off Chios. THERM was the only subarea with no fish NIS recorded in static nets catches. The species most frequently caught in both types of static nets was S. luridus, with frequencies of occurrence that reached 16.67% (GTR) and 3.23% (GNS) in CHIO-MIT in 2022. The greatest quantities of S. luridus in CHIO-MIT were caught with GTR, with a mean biomass that increased from 53.25 g in 2017 to 177.71 g per sample in 2019, whilst its maximum biomass increased from 1,080 g in 2017 to 5,475 g in 2019 per sample. The congeneric Siganus rivulatus was only recorded in GTR, and it was caught less frequently and in smaller quantities than S. luridus. Stephanolepis diaspros was also frequently caught with GTR in VOL-SPOR, where it attained its maximum frequency of occurrence of 9.62% and its maximum biomass in a sample of 656 g in 2020. Etrumeus golanii was solely recorded in static nets catches in CHIO-MIT and recorded for the first time in GTR samples in 2020 and in GNS samples in 2022. Its maximum frequency of occurrence was 2.94% in GTR samples and 3.23% in GNS samples in 2021 and 2020, respectively. Its maximum quantity in a sample of 180 individuals that weighed 11,225 g was recorded in a GTR sample. Pterois miles was also recorded in static nets samples in CHIO-MIT only. Since 2019 it has been increasing its frequency of occurrence and quantity, reaching a maximum frequency of occurrence of 4.35% in 2022 and a maximum quantity of four individuals in a sample, weighing 1,520 g in 2021. The rest of the fish NIS that were caught with static nets, namely Fistullaria commersonii, L. sceleratus and P. rhomboidea, were scarce and in low quantities.

Bottom trawl

A total of eight alien fish species were recorded in OTB samples across the study area (Table 2). They were very scarce and their quantities in the samples were generally very low, except for C. nudivittis, which was the most frequently caught fish NIS with OTB; it was detected for the first time in CHIO-MIT and THERM in 2020 and has been recorded in THR-LIM and VOL-SPOR since 2021. Its frequency of occurrence and catches in CHIO-MIT and THR-LIM increased with time, especially in CHIO-MIT, where in 2022 it occurred in 9,82% of the samples with a maximum of 105 individuals and 640 g per sample. Although S. pachygaster was not frequent in OTB catches, seven individuals weighing a total of 7,200 g that were collected in CHIO-MIT in 2020, represented the highest NIS weight in an OTB sample in the study area. Bregmaceros nectabanus, F. commersonii, F. petimpa, L. sceleratus, O. petersii, and S. chrysotaenia were also recorded in OTB samples, though they were very scarce and in very low quantities. The MEDITS samples contained only two fish NIS, namely C. nudivittis and S. pachygaster; these also occurred scarcely and in low quantities (Table 3).

Purse seine

Very few PS samples contained alien fish species in the study area (Table 2). Etrumeus golanii, L. sceleratus, and S. diaspros were recorded once in CHIO-MIT in 2022 (3 individuals), THR-LIM in 2021 (1) and VOL-SPOR in 2021 (2), respectively.

Other gear

Fish NIS were recorded in very few FPO, SB-SV, and LLS samples (Table 2). The only fish NIS caught with FPO was S. diaspros, which was recorded in one sample in VOL-SPOR in 2022 (1 individual) and one sample in THERM in 2022 (5 individuals). Siganus luridus and S. diaspros occurred in one (3 individuals) and two (1–2) SB-SV samples, respectively. Siganus luridus was also recorded in one LLS sample in CHIO-MIT in 2018 (1 individual).

This study advances our comprehension of fish NIS distributions in the North Aegean Sea by consolidating relevant information from scientific literature and presenting unpublished occurrence records for several species in Greece, including several first records. Most species were categorized as casual, with lower frequencies of occurrence and quantities in commercial fisheries catches compared to the South Aegean Sea. Nevertheless, fish NIS invasions in the study area are dynamic, as evidenced by the increasing trend of species introductions, extent of occurrence, and area of occupancy for several species. The rapid dispersal of C. nudivittis and the significant increase in the areas of occupancy of E. golanii, P. miles, and Siganus spp. in the Northeastern Aegean in the 2020s suggest their potential classification as invasive. Moreover, the significance of fish NIS is growing in commercial fisheries, particularly in the Northeastern Aegean Sea, where fish NIS catches are increasing, and new species of potential commercial interest have emerged in recent years.

Distributions of alien fish species in the study area: current state

The compiled inventory encompasses records of 37 fish NIS. The most recent published list (Zenetos et al. 2020) included 13 alien fish species with records in the North Aegean Sea MSFD assessment area. All these species are included in this study, except Saurida lessepsianus, not found in the literature, and T. crocodilus, excluded due to questionable records. This work updates the list of Zenetos et al. (2020) with the first records in the study area of C. filamentosus, O. petersii, S. rubrum, and S. chrysotaenia. Additionally, a further seven species were not included in Zenetos et al. (2020) because their presence was reported after 2020, while 11 species with records solely in Turkish territorial waters were also incorporated into the inventory. The present study also provides evidence that potentially supports the upgrade of the O. petersii status from casual (Zenetos et al. 2020) to established; there are two previous records of O. petersii in the Aegean Sea, in Gokova Bay in 2005 (Akyol et al. 2006) and in Kastellorizo Island in 2010 (Apostolopoulos and Karachle 2016). This study adds a third record of six individuals caught in Thermaikos Gulf in 2018.

Thirteen species were operationally assessed as established in the study area. The large numbers of sightings (≥ 20) of C. nudivittis, E. golanii, L. sceleratus, P. miles, Siganus spp., and S. diaspros were deemed robust enough evidence for their establishment success in at least a part of the study area. In contrast, the actual establishment status of the species with few known occurrences that were operationally classified either as casual or as established was regarded as uncertain. Small numbers of records for an allochthonous species in an area, often at large distances apart, may suggest an ability for long-range dispersal and the existence of small satellite populations of the species at the periphery of its range (Lockwood et al. 2013). However, small populations of an NIS may persist undetected due to insufficient research effort (false absences), while NIS occurrence data may be sparse because collected information often remains unpublished. An example of the latter case is S. commerson, for which there are two published records in Greek waters, in the North Aegean Sea (this study) and off Rhodes Island (Corsini-Foka and Kalogirou 2008), while it is known to be targeted by fisheries in the Dodecanese islands (Corsini-Foka et al. 2010). Another potential cause for false absences is the occasional taxonomic misidentifications: for example, F. petimba, L. suezensis, S. commerson, and S. chrysotaenia had only 1–2 published records in the study area, but these species closely resemble other taxonomically related species that are more familiar, so it is possible that they have occasionally been misidentified. Nevertheless, small NIS populations may eventually lead to their local extinction instead of their establishment, due to factors such as environmental and demographic stochasticity, Allee effects, or biotic resistance (Lockwood et al. 2013). On the other hand, it is also possible that a small NIS population may persist for years undetected, but eventually give rise to rapid growth and a large-scale invasion (Azzurro et al. 2016).

Champsodon nudivittis is the only fish NIS that has dispersed widely in the study area and is not common in the South Aegean Sea. There are published records of C. nudivittis along the Turkish coasts of the North Aegean Sea since 2014. Nevertheless, field data have revealed a significant expansion in the extent of occurrence and area of occupancy of this species since 2020, suggesting the possibility that it has become invasive. The Champsodontidae are moderately deep-water species, and therefore their invasion of the Mediterranean Sea through the Suez Canal was likely initiated via a larval stage (Stern et al. 2019). The occurrence of C. nudivittis in the deep waters of the Levantine has been viewed as an indication that its thermal niche may be wider than previously thought or that it changed after its introduction in the Mediterranean Sea (Galil et al. 2019). Its wide thermal niche and the dispersal abilities of its larval stage were considered plausible drivers for its range expansion in the study area. Similarly, E. golanii, P. miles, and Siganus spp. dispersal dynamics may also be classified as potentially invasive: They rapidly dispersed at multiple sites and steadily increased their areas of occupancy in CHIO-MIT in the 2020s. Monitoring the progress of dispersal dynamics of their populations would provide valuable information for accurately assessing their status in the area. In comparison, the extent of occurrence and the area of occupancy for the commonly found L. sceleratus and S. diaspros did not exhibit significant changes during the study period.

Failure of an NIS to establish self-sustaining, reproducing populations can be attributed to various causes, such as small propagule size, long distance from optimal donor habitat, low dispersal ability, unsuitable abiotic environment, and biotic resistance (Lockwood et al. 2013). The abiotic environment of the North Aegean Sea is likely a major cause for many unsuccessful fish NIS introductions. Indeed, the North Aegean Sea is under the influence of the low salinity plume (< 29 psu) of Black Sea waters that enter through the Dardanelles Strait (Zervakis and Georgopoulos 2002). Moreover, satellite data have shown that SST levels along the coastline had a mean of 18–19 ^oC in the Thracian Sea and 19–20 ^oC in the Northwestern Aegean Sea, with minimum values ranging from 9 to 13 ^oC (Androulidakis and Krestenitis 2022). Conversely, the Northeastern Aegean Sea is influenced by the highly saline (> 38.5 psu) waters of Levantine Sea origin (Zervakis and Georgopoulos 2002), and coastal waters SST had a mean of 19–20 ^oC and a minimum of 12–15 ^oC (Androulidakis and Krestenitis 2022). In comparison, the respective mean and minimum SST values in the Southeastern Aegean Sea were 20–23 ^oC and 14–17 ^oC (Androulidakis and Krestenitis 2022). Therefore, decreasing seawater temperature and salinity could be a major driver of the observed South to North gradient of diminishing established fish NIS numbers and populations in the Aegean Sea.

The low fish NIS establishment success in the North Aegean Sea could also be driven by basin circulation patterns. It is plausible to assume that the dispersal of Lessepsian immigrants in the Aegean Sea has both reaction-diffusion and directional components (Lockwood et al. 2013): their populations reproduce and disperse northwards along the Asia Minor coasts and the neighboring islands (the reaction-diffusion component), and their propagules (larvae, young and mobile adults) follow the northwards flow of Levantine waters to the Northeastern Aegean Sea (the directional component). Between the Black Sea waters and the Levantine waters emerges a strong, dynamic thermohaline front (Zodiatis and Balopoulos 1993) that affects biological communities and productivity, separating the more productive North Aegean Sea waters from the oligotrophic waters south of the front (Siokou-Frangou et al. 2002; 2009). A transition between different water bodies is a geographical barrier to the dispersal of NIS (Ben Rais Lasram et al. 2008), and the aforementioned oceanographic front may constitute an environmental barrier to the further northward dispersal of thermophilic NIS in the Aegean Sea.

Trends in the expansion of geographic ranges of non-indigenous fish species in the study area and comparison with the South Aegean Sea

The majority of alien fish species in the Greek seas originate from the Erythrean or Indo-Pacific regions, and their numbers have been steadily increasing since their initial recording in 1930 when L. spadiceus was first reported off Samos Island (Ananiadis 1952). The northern limit of the “Lessepsian province”, where Lessepsian immigrants are distributed in the Eastern Mediterranean, was initially designated by Por (1978) at Rhodes Island. However, some Lessepsian fish species were observed in Greek waters north of Rhodes Island as far as the 38th parallel in 1990 (Papaconstantinou 1990). In the early 2010s, warm-water fauna had shifted further northwards in the Aegean Sea, with seven Lessepsian species recorded in the Northeastern and two in the Northwestern Aegean Sea, respectively (Corsini-Foka et al. 2010). By the late 2010s, 13 non-indigenous fish species had been documented in the North Aegean Sea (Zenetos et al. 2020). This study revealed a total of 37 alien fish species reported in the North Aegean Sea, with the majority documented in the Northeastern Aegean Sea. Beta diversity analysis indicated that this specific subarea serves as the primary source for introducing new species to the rest of the study area.

Zenetos et al. (2020) found that during 2012–2017, NIS introductions in the North Aegean Sea and in the Greek Levantine were decreasing, whereas introductions in the South Aegean Sea were assessed as accelerating. However, the results of this study do not support a slowdown in Lessepsian fish species introductions in the North Aegean Sea in the 2010s, although new introductions do seem to approach a plateau in most subareas in the early 2020s. Moreover, this work revealed that fish NIS occurrence records in the study area increased since the late 1990s at an exponential rate, whereas the increases in NIS and publication numbers were linear. The observed accelerating increase in the number of NIS records could be the combined effect of the rapid increase in the geographic ranges of certain NIS in the last few years, especially in the 2020s, and intensified research effort. Notably, it is only recently that studies compiling large numbers of previously unpublished, georeferenced NIS records have appeared in the literature (Katsanevakis et al. 2020; Ragkousis et al. 2023; the present study). Nevertheless, it can be inferred from the results of this and previous studies in the area that the “Lessepsian province” is still shifting northwards in the Aegean Sea, representing a dynamic transitional zone in the seascape across which biotic composition is responding to environmental change (Peters et al. 2006; Yarrow and Marín 2007).

Fish NIS effects on commercial fisheries in the study area

Published information on the effects of fish NIS on commercial fisheries in Greece is scarce. Only one study reviewed the impact of Lessepsian immigrants on fisheries, reporting two species (F. commersonii and S. diaspros) recorded in boat seine catches in the late 2000s (Lefkaditou et al. 2010). The present study provides comprehensive data on the presence of 14 alien fish species in commercial catches between 2017 and 2022, including MEDITS samples collected from the North Aegean Sea. Additionally, the field data include isolated records of L. guentheri, L. sceleratus, and S. commerson from the late 2000s.

Most of the species recorded in commercial fisheries catches occurred infrequently and in low quantities. The Northeastern Aegean Sea stands out as the hotspot area for alien fish catches, where more species and larger quantities were recorded than elsewhere in the study area. Siganus luridus, E. golanii, and S. diaspros were the most frequently occurring species, comprising a maximum of 11.23 kg and 23.8% of the total fish biomass per sample. However, the numbers of fish NIS and the quantities caught have, on average, increased with time; pooled samples in 2021 had 3.7 times the number of species, 12.5 times the abundance, and 6.7 times the biomass of fish NIS compared to 2017.

Higher species numbers and quantities of fish NIS have been recorded in static nets catches in the South Aegean Sea than in the study area: NIS represented 12–60% of the total fish species richness and 7–77% of the total fish biomass in 94 GNS samples collected off Rhodes in 2014–2015 (Corsini-Foka et al. 2017). Moreover, a total of seven fish NIS in 92 commercial boat seine hauls were reported in the South Aegean Sea during the fishing period 2008–2009, with CPUE reaching, in the case of S. rivulatus, a maximum of 3.5 kg per haul (Lefkaditou et al. 2010). In the study area, allochthonous fish were comparatively less important in static nets catches, rarely exceeding one species per haul, while their mean relative abundance and biomass per haul did not surpass 1.33% and 0.99%, respectively. Moreover, on a boat seine survey that collected a total of 94 samples off Rhodes Island, 11 alien fishes were recorded, while alien fish biomass per year ranged from 2.9 to 37.8 kg during 2002–2010 (Corsini-Foka and Kondylatos 2015). Instead, small quantities of S. luridus and S. diaspros were recorded in a few samples in the monitoring of boat seine catches in the study area. Lastly, the number of species recorded in MEDITS and OTB samples in the study area during 2016–2023 (10 species) was similar to those recorded in the South Aegean in MEDITS and other scientific surveys during 1996–2014 (nine species) (Peristeraki et al. 2006; Lefkaditou et al. 2010; Peristeraki et al. 2017), but the only species present in bottom trawl catches in both Aegean Sea subbasins were S. pachygaster, S. diaspros, and U. moluccensis. Bottom trawl catches of fish NIS have been generally small across the Aegean Sea.

The field data revealed that the majority of fish NIS catches in the study area are discarded, except for E. golanii and S. chrysotaenia, while S. luridus is landed or discarded on a case-by-case basis. It appears that the small catches and the absence of market interest result in low commercial value and thus no incentive to land most alien fish species. Lefkaditou et al. (2010) commented that discarding was the fate of the major part of Lessepsian fish caught in Greek waters apart from Siganus spp., whereas Corsini-Foka et al. (2010) reported that Siganus spp., S. chrysotaenia, S. commerson, and E. golanii were commercially exploited in the Dodecanese islands in the early 2010s. More recently, F. commersonii was reported to have minor commercial value in the Southeastern Aegean Sea (Corsini-Foka et al. 2017). Currently, the above-mentioned species as well as Upeneus spp., Parupeneus forsskali, Scarus ghobban, Sphyraena flavicauda, and occasionally S. rubrum, are landed in the southeastern Aegean Sea (Kondylatos, pers. com.).

The most significant limitations of this study are the relatively restricted temporal extent of the field data and the exclusion of unpublished data from citizen science initiatives. However, this is a baseline study that can be periodically updated with new information from the ongoing Greek multiannual program on fisheries data collection, the international scientific literature, and any additional sources that may become available in the future. The compilation of Greek commercial fisheries monitoring and scientific surveys data and the up-to-date systematic review of the international scientific literature resulted in a substantial update of the distribution and importance of fish NIS for commercial fisheries in the North Aegean Sea. The analysis of the fisheries monitoring data revealed new (first records), more accurate (systematically collected across space and time), or more comprehensive (in terms of horizontal and bathymetric extent) information than the existing scientific literature, highlighting their significance as an important source for biological invasions research.

Acknowledgements

The authors thank the Ministry of Agriculture and Food, which is responsible for the Multiannual Union Programme for the Data Collection in the Fisheries and Aquaculture sectors (EU MAP) and the staff involved in commercial fisheries sampling and the scientific survey MEDITS, which is part of the EU MAP programme.

Chrysoula Gubili was supported by the Operational Programme of Fisheries and Sea (OPFS) 2014-2020, Greece, and the European Maritime and Fisheries Fund (EMFF) and the project “Monitoring and control of invasive alien species in Greece using innovative techniques under current and future climate conditions – INVASION” (MIS 5049543).

The authors also thank the anonymous reviewers for their careful reading of the manuscript and their many insightful comments and suggestions.

Funding

Competing interests

The authors have no relevant financial or non-financial interests to disclose.

Ethics approval

Not applicable

Consent

Not applicable

Data availability

Restrictions apply to the availability of the field data. These data may be shared upon reasonable request to the corresponding author, if appropriate.

Authors’ contribution statements

Study conception and design was performed by Athanasios Evangelopoulos. Material preparation, data collection and analysis were performed by Athanasios Evangelopoulos, Dimitrios Karampetsis, Aris Christidis, Chrysoula Gubili, and Argyrios Sapounidis. Aris Christidis, Angeliki Adamidou, Nikolaos Kamidis and Emmanouil Koutrakis participated in and/or coordinated fieldwork. The first draft of the manuscript was written by Athanasios Evangelopoulos and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Alien fish species in the North Aegean Sea: a review of their distributions integrating unpublished fisheries data

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Abstract

Figures

Introduction

Materials and Methods

Study area

Systematic review of the scientific literature

Preparation and compilation of field data

Data analysis

Species identification verification with DNA barcoding

Results

Fish NIS distributions and establishment status in the study area

Spatio-temporal patterns in the distributions of alien fish species

Fish NIS effects on commercial fisheries

Static nets

Bottom trawl

Purse seine

Other gear

Discussion

Distributions of alien fish species in the study area: current state

Fish NIS effects on commercial fisheries in the study area

Declarations

Acknowledgements

References

Supplementary Files

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