Abstract
Stocks with low market value are rarely included in stock assessments because their catch records are generally lacking, thus adding to the already large number of un-assessed fisheries at a global scale. T his deficiency is more evident in the Mediterranean Sea where stock assessments are relatively fewer. A new method (AMSY) has been recently developed to assess stocks for which only abundance trends from scientific surveys are available. The AMSY method was used in the Aegean Sea to assess the status of 74 fish and invertebrate stocks (50 actinopterygians, 4 sharks, 5 rays, 12 cephalopods, and 3 crustaceans) for which catch data are lacking; 20 of them have medium or high market value and are being targeted by fishing fleets, while the remaining 54 are either not targeted, but by-caught and often discarded, or are not exploited at all. Overall, 31 of the 54 non-targeted stocks (57%) were healthy in terms of biomass (B/Bmsy > 1), whereas only 6 of the 20 targeted stocks (30%) were healthy. Of the 23 unhealthy non-targeted stocks, 12 were near healthy (B/Bmsy > 0.75), compared to only 1 of the targeted stocks, whereas 10 non-targeted stocks (19%) and 10 targeted ones (50%) were outside safe biological limits (B < 0.5Bmsy). Cephalopods and crustaceans were generally in a better status compared to fishes. The results confirm that fishing does not only affect commercial stocks, but it may also affect by-catch stocks. In general, stocks that are targeted by fishing fleets are in a worse status in terms of biomass compared to those that are only occasionally collected as by-catch or those that inhabit environments that are not accessible to fishing fleets.
Highlights
Commercial fish and invertebrate stocks attract the attention of fisheries scientists at a global (Ricard et al, 2012) and regional (Colloca et al, 2013) scale and, as a result, the vast majority of regular assessments have been performed on fish and invertebrate stocks of high commercial interest (Osio et al, 2015)
Out of all fish and invertebrate stocks that are being collected during the experimental Mediterranean bottom trawl survey (MEDITS: Bertrand et al, 2002) and for which no official catch time-series exists, 74 stocks were included in the analysis
The number of stocks assessed in this study triples the number of stock assessments in the Aegean Sea, which sum to 116 stocks accounting for over 95% of the total catch (Stergiou et al, 2007a,b), with the exception of rarely caught species (Vassilopoulou et al, 2007)
Summary
Commercial fish and invertebrate stocks attract the attention of fisheries scientists at a global (Ricard et al, 2012) and regional (Colloca et al, 2013) scale and, as a result, the vast majority of regular assessments have been performed on fish and invertebrate stocks of high commercial interest (Osio et al, 2015). In Greece, the number of stocks that have been regularly and officially assessed is still very low compared to the other European countries of the northern Mediterranean coastline (Osio et al, 2018). One of the reasons for the low number of assessments is the lack of complete fisheries data time-series since 2009 due to administrative and financial constraints, while some of the recent official assessments suffer from various biases, one of which is the mixing of catch time-series from multiple fleets (Tsikliras et al, 2020). The lack of adequate number of assessments is an international issue as un-assessed stocks exceed 80% of total catch, globally (Costello et al, 2012)
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