Abstract
The recent establishment of the “landing obligation” under the reformed EU Common Fishery Policy has the twofold objective of reducing the excessive practice of discarding unwanted catch at sea and encouraging more selective and sustainable fisheries. Within this context, the awareness of the spatial distribution of potential unwanted catches is important for devising management measures aimed to decrease discards. This study analyzed the distribution of Hot Spot density areas of demersal fish and crustaceans below the Minimum Conservation Reference Size (MCRS) in four different southern European seas: continental Portuguese coast, Catalan Sea, South of Sicily, Liguria and northern Tyrrhenian Seas using both bottom trawl survey data and information on the spatial distribution of commercial fisheries. Critical areas for discarding were identified as zones where the highest densities of individuals below MCRS were consistently recorded throughout a series of years. Results clearly showed a patchy distribution of undersized individuals in each investigated area, highlighting the overlap between high density patches of both discards and fishing effort. The present findings provide a relevant knowledge for supporting the application of spatial-based management actions, such as the designation of Fisheries Restricted Areas (FRAs), in order to minimize the by-catch of undersized specimens and improve the sustainability of demersal fisheries.
Highlights
Unwanted Catches (UCs) are common and critical problems in fisheries worldwide, as they can alter marine biodiversity and at the same time could worsen overexploitation of commercial species (Kelleher, 2005)
The present study provides a large scale assessment of the distribution and temporal persistence of areas with high density of individuals below Minimum Conservation Reference Size (MCRS) of important commercial demersal species, based on a time series of bottom trawl surveys data
The most important result of the analysis is the first evaluation of the importance of different areas in the Mediterranean Sea and the Atlantic waters off the Continental Portuguese coast as potential source of discards for species subjected to the landing obligation in bottom trawling, due to MCRS in the Mediterranean or TAC for the Atlantic area
Summary
Unwanted Catches (UCs) are common and critical problems in fisheries worldwide, as they can alter marine biodiversity and at the same time could worsen overexploitation of commercial species (Kelleher, 2005). UCs constitute the portion of the total catch that is returned to the sea, and typically include undersized individuals of commercial species and non-marketable species or with low market value (Alverson et al, 1994; Kelleher, 2005; Bellido et al, 2011). The quantity of the UCs mainly depends on the characteristics of fishing grounds (e.g., geographic area, type of habitat, abundance of either juveniles of commercial species or non-commercial species etc.) and on the fishing gears used (Catchpole et al, 2005; Kelleher, 2005). In the Mediterranean Sea, demersal trawling is responsible for about 50 percent of the total discard produced (STECF, 2006), highlighting the low level of selectivity of this sector (FAO, 2016), while a lower discard rate characterizes other gear belonging to industrial pelagic fishing, such as the pelagic trawl or purse seine. “the decision of discarding part of the catch is a choice that fishermen take, and is mainly driven by economic reasons or fishing regulations” (Batsleer et al, 2013; Condie et al, 2014)
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