Narrowing down the number of species requiring detailed study as candidates for the EU Common Fisheries Policy discard ban

Abstract

By 2019, the Common Fisheries Policy will prohibit discarding in all European fisheries of any pelagic, demersal or shellfish species for which removals are managed by TACs and quotas or minimum sizes. However, the regulation allows for exemptions from the prohibition for species for which scientific evidence demonstrates high survival rates associated with discarding. Producing reliable evidence of high survival typically requires long and costly studies involving tagging or captivity. This paper proposes to use the capacity to resist air exposure, a key stressor for discarded animals, as a proxy for survival that can be used to prioritize candidate species for more in-depth discard survival studies. The time required to induce mortality (TM) in air-exposed fish was estimated for ten discarded species under commercial fishing conditions for two artisanal French otter trawlers in the Bay of Biscay and in the English Channel. European seabass, plaice, sole and skates had extended TM values on average, suggesting that these species are good candidates. The three species observed in both regions (plaice, sole and skates) had larger TM values in the English Channel experiment compared to the Bay of Biscay experiment. Among the four measured external conditions that could influence TM (air temperature, fish length, tow depth and tow duration), the air temperature was the most important and the factor that most distinguished the two experiments. Highlights► Discard survival was investigated in small-scale bottom trawl fisheries. ► Mortality due to air exposure was used as a proxy of discard survival potential. ► Air exposure mortality was higher in the Bay of Biscay than in the English Channel for three common species. ► High survival potential was demonstrated for sole, plaice, seabass and skates.

Comparative assessment of two proxies of fish discard survival

“…The resulting RI scores were significantly different between seasons only for seabass and plaice, and were very low for catshark (less than 10% on average), followed by sole and seabass (around 20% on average), and around 38% for plaice and skates. Although the relationship between the scores and discard survival rate were not established, these results indicate that the vitality of these species was not strongly impacted by these apparently rather favorable fishing conditions (shallow bottoms, short air exposures, light catch weights), in accordance with most of the previous discard survival studies for catshark (Revill et al, 2005;Rodríguez-Cabello et al, 2005), skates (Depestele et al, 2014;Ellis et al, 2017;Enever et al, 2009;Mandelman et al, 2013), seabass (Lewin et al, 2018;Morfin et al, 2017b), plaice and sole (Depestele et al, 2014;Methling et al, 2017;Uhlmann et al, 2016). the difference between seasons was significant for a given trait, light grey for March and black for July, and otherwise coloured grey for both seasons.…”

“…Indeed, the most important reported influential factors for these species were related to the gear or mesh size (Enever et al, 2010), or at much larger ranges conditions of tow durations (Depestele et al, 2014;Enever et al, 2009) or air exposure (Methling et al, 2017). Furthermore, the levels of deviance explained were consistent with the relative survival potential of the species which has been assessed independently (from catshark, followed by skates, sole, plaice, and seabass ; Morfin et al, 2017b), as the species with an intermediate survival potential are expected to be more sensitive to external conditions than the species highly resistant or poorly resistant.…”

Determining long‐term changes in a skate assemblage with aggregated landings and limited species data

“…For example, in France, skates smaller than 45 cm total length cannot be landed (JORF, ) and are therefore discarded at sea. As skates have been considered to be amongst the fish species that might survive discarding (Depestele, Desender, Benoit, Polet & Vincx, ; Knotek, Rudders, Mandelman, Benoit & Sulikowski, ; Morfin, Mehault, Benoit & Kopp, ), discarding rather than landing all catches may have helped reduce fishing mortality. If this effect is sufficiently large, it should lead to an increase in biomass, although with some delay (Collie, Rochet & Bell, ).…”

What can be expected of a T90 extension piece to improve selectivity in bottom trawl multispecific fisheries in the Bay of Biscay?

“…As this species constitutes the third most discarded species (in tons) in the coastal bottom trawl fisheries of the Bay of Biscay (Cornou et al 2016), this escape would allow fisherman to avoid lengthy sorting periods while later discarding the fish. Moreover this species shows particularly low survival probability when exposed to air on deck (Morfin et al 2017); their direct escape at sea from the gear would be highly beneficial for the species stock. Finally, because the catch is mostly composed of individuals below 15 cm, these immature fish (Mahé al.…”