2.1. Equation
Like the other ecological footprint components, the Marine footprint (MF) assesses the marine resources' productivity and availability by comparing it against human consumption during a given period at a specific scale.
This indicator is given by Eq. 01, expresses the ratio between the primary production required PPR and the primary production PP of Algeria's fishing area; both expressed in the same weight unit (Pauly and Christensen, 1995; Talberth et al., 2006; Jóhannesson et al., 2018). Defined as a percentage of the PPR, the MF is the fraction of the actual proportion of primary production available for production (De Leo et al., 2013).
\(MF=\frac{PPR}{PP}\) Eq. 01
The estimate of the PPR, given in metric tons of carbon per unit area, is directly related to the fish catches, which are converted into the equivalent yield. This conversion is provided by the following equation Eq. 02.
\(PPR=CC\times DL\times {\left(\frac{1}{TE}\right)}^{(TL-1)}\) Eq. 02
Where CC represents the carbon content of the wet weight of the fish given in tonnes.
The trophic levels of the species (TL), inventoried on fishbase.org
The transfer efficiency rate set at a constant of 10%.
The reduction rate (DR) for all by-catch and discarded or unreported fish of 27% (Pauly and Christensen, 1995).
The inventory of PPR by species is included in Appendix 01
Due to data scarcity, the primary production PP figure was drawn from the literature (Table 01), assuming that these different studies match various areas of the total fishing area in Algeria.
Table 01
Primary Production studies considered
Year
|
Season
|
Area
|
Method
|
Data
|
Author
|
1964
|
Year
|
Algiers bay
|
Sampling
|
120 gC/m² at 3 miles
|
Tellai Salah
|
2017
|
Seasonal and annual
|
Stratified area of the Mediterranean
|
Satellite esti-mates of chlorophyll a,
|
Near the Algerian coast 266 gC/m²
|
Kessouri et al.
|
2022
|
Yearly records 2002–2016
|
Algerian Bassin (zone 18)
|
Satellite imagery
|
125 ± 56 gC/m²
|
Salgado-Hernanz et al.
|
Primary production, which represents the production of organic carbon by phytoplankton photosynthesis, shows high spatial variability in the Mediterranean and is subject to a marked seasonal cycle, with a maximum of the primary output from December to March and a minimum from June to September, in addition to high inter-annual variability (Kissouri et al., 2017; Salgado-Hernanz et al., 2021). Most PP estimates are based on satellite measurements of chlorophyll quantities to quantify the phytoplankton density, thus direct production proportion (Perry, 1986; Kassar, 2011; Uitz et al., 2012).
Tudela (2003) defined minimum and maximum thresholds based on the average trophic level TLc of the fishery considered and the PPR estimated from its fishing landings to assess the effects of fishing on the marine ecosystem. Thus, an unsustainable fishery would result from high TLc and high %PPR values. Thus, sustainably fisheries would be described by values of TL comprised between 3.0 and 4.1 and %PPR between 0.3 and 14.7 (De Leo et al., 2014).
2.2. Study Area
Algerian total fishing area is estimated at 9.5 million hectares (Simmonnet, 1961; Hansal, 2013), extending from its international boundaries with the neighboring countries (Fig. 01).
The Algerian legal text governing the fishing activity defines the different fishing zones' coordinates (Akrour and Grimes, 2021). According to these texts and using ArcGIS, the different fishing zones have been defined (Fig. 02). Therefore, the PP values are crossed with the three main fishing areas, namely
-
The coastal fishing zone,
-
An area comprising both the coastal fishing zone and the offshore fishing zone.
-
The total Algerian fishing area.