Trawl Fishery Bycatch in Marine Protected Areas of the Northern Persian Gulf: A Case Study of Dayyer-Nakhiloo and Mond

doi:10.21203/rs.3.rs-3124939/v1

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Trawl Fishery Bycatch in Marine Protected Areas of the Northern Persian Gulf: A Case Study of Dayyer-Nakhiloo and Mond

https://doi.org/10.21203/rs.3.rs-3124939/v1

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This study investigates the composition of bycatch and the maturity status of some commercial fish caught by fishing boats equipped with shrimp trawls in the Dayyer-Nakhiloo and Mond marine protected areas in Bushehr, located in the north of the Persian Gulf. Cruises were conducted by fishing boats equipped with 27-foot length and 115-horsepower engines between August 18th and September 20^th in 2020 and 2021. The trawl nets were made of polyamide (PA) and had mesh sizes of 50 mm in the body and 40 mm in the bag (STR). After 32 haulings, a total of 37 aquatic species were caught as bycatch. Greater lizardfish (Saurida tumbil), largescale tonguesole (Cynoglossus arel), blue swimming crab (Portunus segnis), whipfin silver-biddy (Gerres filamentosus), spotted sicklefish (Drepane punctata), elongate sole (Solea elongata), and orange-spotted grouper (Epinephelus coioides) were the most frequently caught species in all seasons. The results of the bycatch weight showed that the highest and lowest amounts of bycatch weight were observed in the 18^th and 3^rd fishing operations in the Mond region, respectively, with 234 kg and 4 kg. Similarly, the highest and lowest amounts of catch per unit effort (CPUE) were observed in the 18th and 9th fishing operations in the Mond region, respectively, with 234 kg h^-1 and 3.25 kg h^-1. The bycatch to shrimp ratio (r) was computed as 2.32:1. The results of species dominance showed that Acanthopagrus arabicus (9.4%), Scomberomorus commerson (7.75%), and Saurida tumbil (6.05%) had the highest percentage of abundance during the study period. Length frequency data of commercial fish caught showed that Parastromateus niger (44.19%) and Acanthopagrus arabicus (33.81%) had the highest percentage of mature fish in the specimens, while Scomberomorus commerson and Epinephelus coioides had the highest percentage of immature fish (100%). Overall, the present study indicates that bottom trawling by fishing boats in Dayyer-Nakhiloo and Mond marine protected areas poses a threat to the biodiversity of the Persian Gulf. An efficient management approach is therefore essential to promote responsible fisheries in the region.

Trawl fisheries

Bycatch

Marine protected area (MPA)

Bushehr

Persian Gulf

The fishing industry in the Persian Gulf is very important due to its ancient history. The high diversity of aquatic species in this aquatic ecosystem and the benefits of fisheries have attracted the attention of the beneficiary countries (Paighambari et al. 2019). The main target species in the Persian Gulf include shrimps, tuna fish, and various species of Perciformes (Farrokhi et al. 2014; Eighani et al. 2014). Unfortunately, the stocks of valuable commercial fish have decreased in the Persian Gulf in recent years. The lack of proper management, the lack of long-term planning for the restoration of stocks, the lack of sufficient monitoring of fishing, inflation, and the unfavorable economic situation of fishermen can be considered effective factors involved in the current situation (Moradi et al. 2013; Paighambari et al. 2017). The mortality of long-lived marine species with low reproductive rates is a major problem in species conservation and affects the sustainability of fisheries in the seas (Hall et al. 2000). The amounts of bycatch obtained in different fishing methods depend on the used fishing gear. In general, the highest amount of bycatch is observed in the trawl method. The large volume of discarded by-catch and increasing awareness of the pressure on the environment by trawl nets have caused a high level of dissatisfaction among the fishing communities in the Persian Gulf (Daliri et al. 2013).

The presence of non-target species with commercial value (incidental) and non-commercial value (discard) is the most important fishing challenge in areas with high diversity such as tropical areas (Hall et al. 2005; Rezende et al. 2019). Several factors such as hauling depth, net hauling time (day or night), water physicochemical factors, bed type, net hauling duration, and other factors are effective in the catch composition of caught species by trawl nets (Gorelli et al. 2016). Ecological factors can affect catch per unit effort (CPUE), catch composition, and length frequency of caught species (Samanta et al. 2018; Rezende et al. 2019). The selectivity of the trawl net as an active and pursuit fishing tool is weak and often depends on the target catch (Andrew and Pepperell 1992).

In the past, the objective of fisheries management strategies was to increase fish catch to provide food for the growing world population. However, the current global view of fishing has shifted, as it is now widely recognized that aquatic resources and fishing stocks have significantly declined (Watson and Pauly 2001). In the Persian Gulf, bottom trawl nets are commonly used for shrimp fishing in coastal areas. However, during the tiger shrimp fishing season in the Motaf fishing ground, many commercial and non-commercial fish are caught below standard size by bottom trawl nets, causing irreparable damage to their stocks. One important issue related to the bycatch obtained by trawl nets during the shrimp fishing season is the study of LM50, which refers to the length at which 50% of the fish have matured. Sustainable exploitation of aquatic species is achieved when the length frequency of fish caught by fishing gear is higher than the LM50 of the species, as this ensures the species' reproduction and regeneration abilities are maintained. Several studies have investigated the bycatch composition of shrimp trawl nets in the southern waters of Iran, highlighting the importance of this issue (Moradi et al. 2013; Nasaj nejad et al. 2013; Daliri et al. 2013; Eighani et al. 2014; Farrokhi et al. 2014; Gerami and Abdollahi 2015; Paighambari et al. 2017; Paighambari et al. 2019). This study aimed to investigate the bycatch composition and maturity status of important commercial fish caught by shrimp trawl nets of fishing boats in Dayyer-Nakhiloo and Mond fishing grounds. This research is crucial in promoting sustainable fisheries management in the region.

The fishing operations in Dayyer-Nakhiloo and Mond MPAs were carried out using shrimp trawl nets made of polyamide with mesh sizes of 50mm in the body and 40mm in the bag (Knot to opposite knot) between August 18 and September 20 in 2020 and 2021. Fishing boats with a length of 27 feet and a 115-horsepower engine were used for sampling operations. The head and foot ropes of the nets were 14m and 15m long, respectively. In total, 32 net haulings were performed during the study period, with trawling times ranging from 0.5 to 2.5 hours and a mean of 1.48 ± 0.57 hours. The trawling speed was between 2.5-3 knots, and the trawling operations were carried out in relatively calm sea conditions. After the net was pulled up, the target species were separated from the bycatch. To determine the bycatch composition, 5% of the catch was randomly selected, and the isolated aquatic animals were identified using valid keys at the genus and species level (Bianchi 1985; Carpenter et al. 1997). However, it was not possible to separate some aquatic animals based on their size and number, and they were therefore considered as discarded fish.

The catch per unit effort (CPUE) was calculated using the following equation (Sparre and Venema 1998):

CPUE = C_w/t

Where C_w is the catch weight per each net hauling (kg) and t is the time of each net hauling (hours).

The amount of bycatch was calculated using the following equations (Andrew et al. 1995):

r = µb/µs

B = rs

Where r is the ratio of bycatch to the target species, µb is the mean by catch per unit effort of fishing, µs is the mean catch of the target species per unit of effort fishing, B is the total bycatch during the fishing season, and s is the total landing rate of the target species in the fishing season.

Sturges formula was used to determine length interval that would have stable class size frequencies (Zar 2010). That is,

R = (Max-Min) + 1

K = 1 + 3.3 log n

C = R ÷ K

Where R is the range of the measured fork lengths, K is the number of categories based on a sample size of n, and C is the class width.

Data analysis

All statistical analyzes of this study were performed by Excel 2013 and SPSS version 21.

Table 1 shows the bycatch composition, presence, and absence of fishes caught by shrimp trawls in Dayyer-Nakhiloo fishing grounds. The study identified 37 aquatic species in the bycatch composition of used trawls. Seven species, including Greater lizardfish (Saurida tumbil), Largescale tonguesole (Cynoglossus arel), Blue swimming crab (Portunus segnis), whipfin silver-biddy (Gerres filamentosus), Spotted sicklefish (Drepane punctata), Elongate sole (Solea elongata), and Orange-spotted grouper (Epinephelus coioides), were observed as permanent catch species in all seasons. The highest and lowest amounts of bycatch weight were observed in the 19^th fishing operation in the Mond region, which were 465 kg and the 7^th fishing operation in the Dayyer-Nakhiloo region, which was 8.9 kg, respectively. Additionally, the highest and lowest amounts of catch per unit effort (CPUE) were observed in the 19th fishing operation in the Mond region and the 7^th fishing operation in the Dayyer-Nakhiloo region, which were 310 kg h^-1 and 17.8 kg h^-1, respectively. The ratio of bycatch to target species (r) was 3.193 and the total amount of bycatch weight during the fishing season was 3025.19 kg, as shown in Table 2.

Table 3 presents the numerical percentages of fish caught by shrimp trawl nets of fishing boats in Dayyer-Nakhiloo and Mond fishing grounds. The results show that different fish species were dominant during each stage of fishing. In the first stage, Scomberomorus commerson (12.29%), Acanthopagrus arabicus (7.62%), and Lutjanus johnii (6.38%) were the dominant species, respectively. In the second stage, Pampus argenteus (11.97%), Pelates quadrilineatus (10.72%), and Saurida tumbil (9.23%) were the dominant species, respectively. In the third stage, Acanthopagrus arabicus (14.72%), Scomberomorus commerson (9.75%), and Cynoglossus arel (9.4%) were the dominant species, respectively. In the fourth stage, Acanthopagrus arabicus (14.72%), Cynoglossus arel (7.65%), and Terapon jarbua (7.65%) were the dominant species, respectively. Additionally, the results of species dominance showed that Acanthopagrus arabicus (9.4%), Scomberomorus commerson (7.75%), and Saurida tumbil (6.05%) had the highest percentage of abundance during the study period.

Table 4 presents the descriptive statistics of commercial fishes caught by shrimp trawl nets of fishing boats in Dayyer-Nakhiloo and Mond fishing grounds. The statistics include the mean, standard deviation, minimum, and maximum values of fish length, weight, and age for each species caught during the study period. Table 5 shows the comparison of mature and immature caught commercial fish. Parastromateus niger (44.19%) and Acanthopagrus arabicus (33.81%) had the highest percentage of mature fish, while Scomberomorus commerson (100%) and Epinephelus coioides (100%) had the highest percentage of immature fish.

The length classes of different fish species caught by shrimp trawl nets of fishing boats in Dayyer-Nakhiloo and Mond fishing grounds are presented in Figure 2. The results show that for Pampus argenteus, the length class of 19.4-22 cm with 27.08% (13 fish) had the highest frequency percentage, while the length class of 30.2-32.8 cm with 2.08% (1 fish) had the lowest frequency percentage. For Parastromateus niger, the length class of 16.7-19.9 cm with 23.55% (20 fish) had the highest frequency percentage, while the length class of 35.9-39.1 cm with 2.32% (2 fish) had the lowest frequency percentage. For Platycephalus indicus, the length class of 35.4-31 cm with 32.56% (14 fish) had the highest frequency percentage, while the length classes of 48.9-44.5 cm and 53.4-49 cm with 2.33% (1 fish) had the lowest frequency percentage. For Lutjanus johnii, the length class of 24-19.3 cm with 38.71% (24 fish) had the highest frequency percentage, while the length classes of 43-2.38-5 cm and 57-3.51 cm had the lowest frequency percentage (1.61%, 3 fish) among all other length classes. Finally, for Pomadasys kaakan, the length class of 28.8-23.2 cm with 28.36% (19 fish) had the highest frequency percentage, while the length classes of 51.6-46 cm and 57.3-51.7 cm with 4.48% (3 fish) had the lowest frequency percentage.

The length classes of different fish species caught by shrimp trawl nets of fishing boats in Dayyer-Nakhiloo and Mond fishing grounds are presented in Figure 3. The results show that for Acanthopagrus arabicus, the length class of 27-23.1 cm with 29.52% (62 fish) had the highest frequency percentage, while the length class of 37-33.8 cm had 0% frequency percentage. For Otolithes ruber, the length class of 23-18.6 cm with 41.32% (31 fish) had the highest frequency percentage, while the length class of 41.5-37 cm had 1.33% frequency percentage. For Scomberomorus commerson, the length class of 33-30.8 cm with 25.43% (44 fish) had the highest frequency percentage, while the length class of 19.2-17 cm had 3.47% frequency percentage. For Sparidentex hasta, the length class of 31.25-18 cm with 25.49% (13 fish) had the highest frequency percentage, while the length class of 52.7-47.4 cm had 1.96% frequency percentage. Finally, for Epinephelus coioides, the length class of 22.8-26.1 cm with 23.4% (11 fish) had the highest frequency percentage, while the length class of 36.4-39.7 cm had 2.13% frequency percentage.

The Persian Gulf is known for its high diversity of marine life, similar to other tropical regions (Garcia-Caudillo et al. 2000). Shrimp trawl nets often result in high levels of bycatch, including small fish, immature commercial fish, large fish, and other aquatic animals (Valinssab et al. 2006). The catch rate and size composition of these aquatic animals can vary seasonally and even daily, influenced by various biotic and abiotic factors such as prey and predator presence, temperature, salinity, and substrate type (Tonks et al. 2008; Gerami, 2015). Effective catch management requires complex models that consider multiple criteria, including cognitive and biological dimensions, socio-cultural factors, and economic and livelihood status (Jentoft 2000; Hilborn 2007). The conditions of mangrove and adjacent habitats, such as algal, grassy, sandy, and mud beds, are also important factors affecting the distribution and abundance of different aquatic species (Vahidi et al. 2020; Hajializadeh et al. 2020). Therefore, it is essential to consider these factors in the management and conservation of marine resources to ensure their sustainable use for future generations.

A total of 37 aquatic species were observed as bycatch in the used trawls. Among them, seven species, including Greater lizardfish (Saurida tumbil), Largescale tonguesole (Cynoglossus arel), Blue swimming crab (Portunus segnis), whipfin silver-biddy (Gerres filamentosus), Spotted sicklefish (Drepane punctata), Elongate sole (Solea elongata), and Orange-spotted grouper (Epinephelus coioides), were caught permanently in all seasons. During the study period, Acanthopagrus arabicus (9.58%), Scomberomorus commerson (7.89%), Cynoglossus arel (7.48%), and Saurida tumbil (6.16%) were the most abundant species. In the study by Nassaj nejad et al. (2012) on the catch composition of traditional shrimp trawlers, they identified 73 aquatic species belonging to 51 families in the Lifeh-Booseif fishery ground. The catch included 20% target catch (Penaeus semisulcatus, Metapenaeus affinis, and Parapenaeopsis stylifera), 22% bycatch, and 58% discarded fish. According to Eighani et al. (2013) in Hormuz Island, the ratio of target catch (shrimp) to bycatch was 2:8 in 2010 and 3:77 in 2011 in bottom trawls. Farrokhi et al. (2013) identified 103 species belonging to 64 families in the trawl nets used during the shrimp fishing season in the fishing grounds of Hormozgan province. The catch composition included 86.26% bycatch and 13.74% shrimp, with a ratio of bycatch to the target of 6.27%. These studies highlight the need for sustainable fishing practices that minimize bycatch and ensure the conservation of marine resources for future generations. The implementation of bycatch reduction technologies, such as modified fishing gear and exclusion devices, can help reduce bycatch and increase the efficiency of fishing operations.

In the study by Paighambari et al. (2015), 57 aquatic species belonging to 43 families were identified during the shrimp fishing season in the fishing grounds of Bushehr and Hormozgan provinces. In Hormozgan province, the percentages of target catch (shrimp) and bycatch were 13.77% and 86.24%, respectively. In Bushehr province, the percentages of target catch and bycatch were 6.52% and 93.48%, respectively. According to the study by Paighambari and Daliri (2012), the catch composition of the trawl nets in the Bushehr coast included 12.5% shrimp and 87.5% bycatch, and the ratio of shrimp to bycatch was 7:1. Additionally, Eighani and Paighambari (2013) reported that the catch composition of the trawl nets included 76% bycatch and 24% shrimp. The majority of bony fishes caught in shrimp trawl nets are demersal species, which are one of the most important commercial fish groups in the Persian Gulf (Logerwell et al. 2018). Unfortunately, overfishing and increased fishing pressure on these species have led to a significant decrease in their populations. This pressure on non-commercial species can also disturb the balance of the ecosystem (Hall and Mainprize 2005). Therefore, it is essential to implement sustainable fishing practices that minimize bycatch and ensure the conservation of marine resources for future generations.

The maturity percentage of 10 commercial fish caught showed that Parastromateus niger (52.33%) and Acanthopagrus arabicus (33.81%) had the highest percentage of mature fish during the study period. Additionally, Scomberomorus commerson (100%) and Lutjanus johnii (96.77%) had the highest percentage of immature fish.

Pomadasys kaakan belongs to the Haemulidae family, which is one of the most important fish families in the Persian Gulf and Oman Sea. Its catch rate is much higher than that of other species in this family. Pomadasys kaakan lives around rocks, open sandy beds, estuaries, and mouths of brackish water rivers (Mos and Mos 2022). The results of a study showed that 14.58% and 85.42% of Pomadasys kaakan caught were mature and immature, respectively. These fish reach sexual maturity at a total length of 35 cm (Vahabnezhad et al. 2021).

Pampus argenteus is considered a coastal species that is found in shallow waters and estuaries (Lestari and Chodrijah 2020; Salim et al. 2020). This fish is considered one of the most important economic fish in the north of the Persian Gulf, and its stock is located between the countries of Iran, Iraq, and Kuwait. The economic importance of this species has caused its intense exploitation. The stock of this species has undergone many fluctuations in the Persian Gulf, which has led to a decrease in the catch of this species (Kazemi et al. 2022). The results of a study showed that 29.17% and 70.83% of Pampus argenteus caught were mature and immature, respectively. These fish reach sexual maturity at a total length of 24.1 cm. The reproduction time of this fish is from April to September, and this species has two spawning peaks in May and August (Almatar et al. 2004).

Parastromateus niger is primarily a marine species, but it can also be found in brackish water and migrates to estuarine areas (Froese and Pauly 2019). This species has a global catch of about 75 thousand tons, and Indonesia is the largest producer, catching about 34 thousand tons (FAO 2022). A study showed that 44.19% and 55.81% of Parastromateus niger caught were mature and immature, respectively. These fish reach sexual maturity at a total length of 23 cm. The average catch of this species has increased in all the southern provinces of Iran during the last two decades. However, the fishing status of this species has changed to overfishing in 2017, so it is in the red status in Bushehr province. Lutjanus johnii is one of the dominant species of the Lutjanidae family in Iranian waters (Rawat et al. 2022). The study showed that 3.23% and 96.77% of Lutjanus johnii caught were mature and immature, respectively. These fish reach sexual maturity at a total length of 39 cm. This valuable demersal species lives in rocky and coral areas and is distributed from the seashore to a depth of 80 meters. Lutjanus johnii is a predatory species that may be caught with trawl nets when hunting in non-reef areas. This fish is mainly caught with pots and hook (Osuka et al. 2022). Otolithes ruber is a benthopelagic and amphidromous fish. This species feeds on organisms from the bed, column, and water surface (Riede, 2004). The Sciaenidae family has a wide distribution in the tropical waters of the Indian, Atlantic, and Pacific Oceans and includes species living in saline and brackish waters (Nelson et al. 2006; Dadzie 2007). Otolithes ruber is mostly observed in areas with a muddy bed and estuaries of tropical coastal waters. This species is found in coastal waters at depths between 10 and 40 meters (Sasaki 2001). The results of a study showed that 32% and 68% of Otolithes ruber caught were mature and immature, respectively. These fish reach sexual maturity at a total length of 28 cm (Eskandari et al. 2011).

Scomberomorus commerson is a fish species that can be found in a variety of habitats, from the edge of the continental plateau to shallow coastal waters, typically at depths ranging from 10 to 70 meters (Collette et al., 2001). This fish is widely distributed and is an important species for commercial, traditional, and recreational fishing (Claereboudt et al. 2005). However, a study showed that 100% of the caught Scomberomorus commerson were immature, and these fish reach sexual maturity at a total length of 86.3 cm (Niamaimandi et al. 2015). Narrow-barred Spanish mackerels migrate from the eastern Arabian Sea and the Indian Ocean to the Persian Gulf to spawn at the beginning of spring. Spawning of these fish has been observed in May and June in the Oman Sea and in June and July in the Persian Gulf. Platycephalus indicus is a fish species with a wide distribution in the Persian Gulf and Gulf of Oman. The study showed that 4.65% and 95.35% of Platycephalus indicus caught were mature and immature, respectively. These fish reach sexual maturity at a total length of 45.7 cm (Ho, 2005). This fish is one of the most popular fish in southern Iran and belongs to the Platycephalidae family. It can be found in very shallow waters, estuaries, mouths of rivers, and up to 25 meters deep. Some species are also found in coral reef and rocky areas (Mousavi-Sabet et al. 2015; Akita and Tachihara 2019). P. indicus is caught with hand fishing nets in shallow coastal waters and by trawl nets in deep areas (Mousavi-Sabet et al. 2015).

Acanthopagrus arabicus is an important species of the Sparidae family, which is commercially and economically important in East Asia and the Persian Gulf (Vahabnezhad et al. 2017). The Sparidae family is found in temperate and tropical regions and inhabits coasts and continental plateaus (Esmaeili et al. 2014). A study showed that 33.81% and 66.19% of Acanthopagrus latus caught were mature and immature, respectively, and these fish reach sexual maturity at a total length of 24.4 cm (Vahabnezhad et al. 2017). Epinephelus coioides belongs to the Serranidae family and lives in middle depths of water and in rock areas (Tavakoli-Kolour et al. 2022). This fish is usually observed up to 100 meters of water depth and is caught by bottom trawls, pots, and hooks (Grandcourt et al. 2005). The study showed that 100% of Epinephelus coioides caught were immature, and these fish reach sexual maturity at a total length of 27.5 cm (Myers 1999). Researchers suggest that fishing nets should target fish species above LM50 size and prevent damage to non-target fish stocks (Boopendranath et al. 2012; Gerami and Abdollahi 2014). Excessive fishing pressure can reduce fish stocks over time and decrease the population to a minimum, which can disturb the continuation of life and reproduction for aquatic populations (Ardakani 2000). Shrimp trawling, in particular, is very destructive due to catching immature fish and can destroy the species composition and structure of aquatic populations over a long period (Schratzberger et al. 2002).

In summary, this study highlights the negative impacts of bottom trawling by fishing boats equipped with shrimp trawls on the biodiversity of the Persian Gulf in the Dayyer-Nakhiloo and Mond marine protected areas. The bycatch composition and maturity status of some commercial fish caught during the study period were also investigated. The results showed that a total of 37 aquatic species were caught as bycatch, and several species had a high percentage of immature fish in the specimens. An efficient management approach is therefore required to promote responsible fisheries in the region and reduce the threat to the biodiversity of the Persian Gulf.

Acknowledgement

I would like to express my appreciation and gratitude to the Deputy of Graduate Studies at the University of Hormozgan and the Fisheries Organization of Bushehr Province for their collaboration in conducting my thesis. Their support and assistance were invaluable in completing this research.

Ethical Approval

No live animals were used in this study, which exclusively relied on data collected from fishing vessels' catches upon unloading at nearby ports.

Competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper.

Authors' contributions

Khosrow Darvishi: Conceptualization, Methodology; Ehsan Kamrani: Conceptualization, Supervision, Formal analysis; Mohsen Safaei: Data curation, Supervision, Formal analysis; Moslem Daliri: Supervision, Formal analysis, Writing – Review & Editing; Fereydoon Owfi: Methodology

Funding

This research did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors.

Availability of data and materials

All data generated or analyzed during this study are included in this article.

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Table 1 Bycatch composition, presence (+) and absence (-) of fish caught by shrimp trawl nets in Dayyer-Nakhiloo and Mond fishing grounds, Bushehr Province

Scientific name	Family	August 2020	September 2020	August 2021	September 2021
Saurida tumbil (Bloch, 1795)	Synodontidae	+	+	+	+
Upeneus sulphureus Cuvier, 1829	Mullidae	+	-	+	-
Lagocephalus inermis (Temminck & Schlegel, 1850)	Tetraodontidae	-	+	+	+
Cynoglossus arel (Bloch & Schneider, 1801)	Cynoglossidae	+	+	+	+
Platycephalus indicus (Linnaeus, 1758)	Platycephalidae	+	-	-	+
Maculabatis gerrardi (Gray, 1851)	Dasyatidae	+	-	+	+
Gasterosteus aculeatus Linnaeus, 1758	Gasterosteidae	+	-	+	-
Rhynchobatus djiddensis (Forsskål, 1775)	Rhinidae	-	+	+	-
Sepia pharaonis Ehrenberg, 1831	Sepiidae	+	+	-	+
Pennahia aneus (Bloch, 1793)	Sciaenidae	+	-	+	-
Brachirus orientalis (Bloch & Schneider, 1801)	Soleidae	+	-	+	+
Portunus segnis (Forskål, 1775)	Portunidae	+	+	+	+
Pseudosynanceia melanostigma Day, 1875	Synanceiidae	+	-	+	-
Chiloscyllium punctatum Müller & Henle, 1838	Hemiscylliidae	+	+	+	-
Pelates quadrilineatus (Bloch, 1790)	Terapontidae	+	+	-	+
Terapon jarbua (Forsskål, 1775)	Terapontidae	+	+	-	+
Gerres filamentosus Cuvier, 1829	Gerreidae	+	+	+	+
Carangoides talamparoides Bleeker, 1852	Carangidae	+	-	+	-
Alepes kleinii (Bloch, 1793)	Carangidae	+	+	-	+
Thryssa vitrirostris (Gilchrist & Thompson, 1908)	Engraulidae	+	-	-	+
Drepane punctata (Linnaeus, 1758)	Drepaneidae	+	+	+	+
Leiognathus equula (Forsskål, 1775)	Leiognathidae	+	-	+	-
Solea elongata Day, 1877	Soleidae	+	+	+	+
Netuma thalassina (Rüppell, 1837)	Ariidae	+	+	-	+
Otolithes ruber (Bloch & Schneider, 1801)	Sciaenidae	+	-	-	+
Pomadasys kaakan (Cuvier, 1830)	Haemulidae	+	-	+	+
Sparidentex hasta (Valenciennes, 1830)	Sparidae	+	+	-	+
Sphyraena jello Cuvier, 1829	Sphyraenidae	-	+	+	-
Lutjanus johnii (Bloch, 1792)	Lutjanidae	+	-	-	+
Lethrinus nebulosus (Forsskål, 1775)	Lethrinidae	-	+	-	+
Acanthopagrus arabicus Iwatsuki, 2013	Sparidae	+	-	+	+
Pampus argenteus (Euphrasen, 1788)	Stromateidae	-	+	-	-
Parastromateus niger (Bloch, 1795)	Carangidae	+	-	+	-
Scomberomorus commerson (Lacepède, 1800)	Scombridae	+	-	+	+
Scomberomorus guttatus (Bloch & Schneider, 1801)	Scombridae	-	+	+	+
Epinephelus coioides (Hamilton, 1822)	Serranidae	+	+	+	+
Uroteuthis duvaucelii (D'Orbigny, 1835)	Loliginidae	+	-	+	-

Table 2 Weight and CPUE of fishes caught by shrimp trawl nets of fishing boats in Dayyer-Nakhiloo and Mond fishing grounds, Bushehr Province

Location	Time	Bycatch weight	Bycatch CPUE	r = μb/μs	B = rs (Kg)
Dayyer -Nakhiloo	1	46	30.67	3.19	30.25.2
	2	96	38.4
	3	22	14.67
	4	70	140
	5	21.5	43
	6	13.5	27
	7	8,9	17.8
	8	50	25
	9	210	210
	10	120	120
	11	44	22
Mond	1	79	39.5
	2	99	99
	3	111	111
	4	60	30
	5	65	43.33
	6	82	32.8
	7	73,6	147.2
	8	15,6	31.2
	9	200	133.3
	10	180	120
	11	45	30
	12	24,5	12.25
	13	30	15
	14	110	73.33
	15	113	75.33
	16	88	58.67
	17	69	34.5
	18	222	148
	19	465	310
	20	38	38
	21	85	56.67

Table 3 Numerical percentage of fish caught by shrimp trawl nets of fishing boats in Dayyer-Nakhiloo and Mond fishing grounds, Bushehr Province

Scientific name	August 2020	September 2020	August 2021	September 2021	August 2020	September 2020	August 2021	September 2021
Scientific name	N (%)	W (%)	N (%)	W (%)	N (%)	W (%)	N (%)	W (%)
S. tumbil	3.87	0.54	9.23	2.34	7.34	1.05	5.05	0.86
U. sulphureus	1.70	0.33	0	0	2.27	0.52	0	0
L. inermis	0	0	0.75	0.82	1.57	1.35	2.61	2.29
C. arel	4.33	0.52	8.98	1.67	9.27	1.15	7.65	1.14
P. indicus	4.49	3.52	0	0	0	0	2.93	2.31
M. gerrardi	2.17	15.79	0	0	0.35	2.63	1.95	16.29
G. aculeatus	2.01	0.08	0	0	1.92	0.09	0	0
R. djiddensis	0	0	0.5	1.1	0.17	0.32	0	0
S. pharaonis	1.39	5.54	2.49	14.53	0	0	2.44	11.27
P. aneus	2.17	0.44	0	0	4.02	0.87	0	0
B. orientalis	4.33	1.31	0	0	2.45	0.76	3.42	1.22
P. segnis	1.86	0.38	6.48	1.85	2.97	0.74	1.30	0.29
P. melanostigma	0.31	0.27	0	0	0.87	0.91	0	0
C. punctatum	1.86	6.51	2.24	11.53	3.32	14.45	0	0
P. quadrilineatus	4.18	0.34	10.72	1.26	0	0	5.86	0.56
T. jarbua	4.33	0.61	8.73	1.78	0	0	7.65	1.27
G. filamentosus	2.94	0.24	1.5	0.2	3.85	0.34	4.07	0.41
C. talamparoides	2.17	0.87	0	0	4.55	1.89	0	0
A. kleinii	2.63	0.22	6.98	0.95	0	0	1.63	0.16
T. vitrirostris	3.25	0.1	0	0	0	0	2.93	0.13
D. punctata	2.01	0.34	2.74	0.73	4.55	1.01	2.44	0.58
L. equula	1.39	0.19	0	0	2.62	0.37	0	0
S. elongata	1.55	0.23	4.49	1.04	2.97	0.57	3.75	0.67
N. thalassina	0.93	0.34	3.24	1.65	0	0	4.56	2
O. ruber	4.95	1.6	0	0	0	0	7	2.76
P. kaakan	3.25	3.36	0	0	3.32	4.21	4.4	5.92
S. hasta	2.48	2.81	5.74	11.2	0	0	1.95	2.68
S. jello	0	0	2.74	1.53	2.8	1.26	0	0
L. johnii	6.35	5.39	0	0	0	0	3.26	3.22
L. nebulosus	0	0	2.99	2.58	0	0	1.47	1.1
A. arabicus	7.59	12.38	0	0	14.51	25.14	12.7	25.21
P. argenteus	0	0	11.97	32.71	0	0	0	0
P. niger	5.73	7.23	0	0	8.57	12.93	0	0
S. commerson	12.23	27.04	0	0	9.62	22.11	6.35	15.17
S. guttatus	0	0	2.49	1.72	2.8	1.32	1.14	0.53
E. coioides	1.08	1.16	4.99	8.82	1.92	2.84	1.47	1.97
U. duvaucelii	0.46	0.33	0	0	1.4	1.15	0	0

Table 4 Descriptive Statistics of commercial fishes caught by shrimp trawl nets of fishing boats in Dayyer-Nakhiloo and Mond fishing grounds, Bushehr Province

Fish species	Count	Min	Max	Mean	SE	Q25	Q50	Q75	SKEW	Kurt
P. argenteus	48	14	43	24.21	0.95	19	23	27.625	1.01	0.75
P. indicus	43	21	49.5	34.03	1.00	30	34	38	0.12	-0.10
S. hasta	51	15	49.5	30.11	1.24	22.5	28.5	37	0.36	-0.76
L. johnii	62	14.5	46	23.16	0.88	18.5	21	25.625	1.32	1.41
P. kaakan	67	17.5	56	30.49	1.19	22.5	28	36	0.88	0.06
A. arabicus	210	14	41	22.08	0.34	17.5	22	25.5	0.44	0.49
O. ruber	75	14	45.5	22.35	0.72	18.5	20.5	24.5	1.79	3.49
S. commerson	173	17	35	27.79	0.37	23.5	28.5	32	-0.39	-1.13
E. coioides	47	18	49	31.40	1.21	24.5	30	37.5	0.55	-0.63
P. niger	86	11	42	25.45	0.89	18.5	23.75	33.625	0.19	-1.24

Table 5 The percentage of commercial mature and immature fishes caught by shrimp trawl nets of fishing boats in Dayyer-Nakhiloo and Mond fishing grounds, Bushehr Province

Fish species	N	Mature N	Mature (%)	Immature N	Immature (%)	Reference
P. indicus (Linnaeus, 1758)	43	2	4.65	41	95.35	Ho, 2005
O. ruber (Bloch & Schneider, 1801)	75	24	32	51	68	Eskandari et al., 2011
P. kaakan (Cuvier, 1830)	67	20	29.85	47	70.15	Vahabnezhad et al., 2021
S. hasta (Valenciennes, 1830)	51	-	-	-	-	-
L. johnii (Bloch, 1792)	62	2	3.23	60	96.77	Osuka et al., 2022
A. arabicus Iwatsuki, 2013	210	71	33.81	139	66.19	Vahabnezhad et al., 2017
P. argenteus (Euphrasen, 1788)	48	7	14.58	41	85.42	Al Mattar et al., 2004
P. niger (Bloch, 1795)	86	38	44.19	48	55.81	Rawat et al., 2022
S. commerson (Lacepède, 1800)	173	-	-	173	100	Niamaimandi et al., 2015
E. coioides (Hamilton, 1822)	47	0	0	47	100	Myers, 1999

No competing interests reported.

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Trawl Fishery Bycatch in Marine Protected Areas of the Northern Persian Gulf: A Case Study of Dayyer-Nakhiloo and Mond

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