Survival rates for Nephrops norvegicus discarded from Northern European trawl fisheries

Abstract

When discarded from bottom trawl fisheries, survival of Nephrops norvegicus may be sufficiently high that this species can be exempted from the EU Landing Obligation. In three studies, Nephrops were sampled from trawlers in northern European waters, and the fate of individuals monitored for a minimum of 13 days in onshore tanks. Winter estimates of captive survival (means ± 95% confidence intervals), including immediate mortality during catch sorting, were 62 ± 2.8% for the West of Scotland, 57 ± 1.8% for the Farne Deeps (North Sea), and 67 ± 5.4% for the Skagerrak. The Farne Deeps fishery is not active in summer, but captive survival rates in summer in the other two areas were reduced to 47 ± 3.4% for West of Scotland and 40 ± 4.8% for the Skagerrak. Linear modelling of the West of Scotland and Skagerrak data suggested that higher survivals in winter were related to colder water or air temperatures, although temperatures during captive observation may also have had an impact. Net modifications in the Skagerrak study had an effect on survival, which was higher for Nephrops sampled from nets equipped with the more selective Swedish sorting grid compared to Seltra trawls.

Accounting for environmental and fishery management factors when standardizing CPUE data from a scientific survey: A case study for Nephrops norvegicus in the Pomo Pits area (Central Adriatic Sea)

“…Nevertheless oxygen is not the only environmental parameter that could affect Nephrops catch rates; salinity stress conditions as hypercapnia and salinity fluctuations may as well alter abundance of recruits [ 135 ]. However, literature on salinity influence on Nephrops is poor and mainly focusing on survival studies, generally showing an increase in mortality in low salinity ranges (around almost 15 in Harris and Ulmestrand [ 50 ]; and from about 24 to 29 in Fox et al [ 136 ]). Within this study, in both models slight variations in salinity ranges resulted in relevant impacts on CPUE values, despite the measured range being really narrow.…”

Inclusion of recreational fishing in data-limited stocks: a case study on Norway lobster (Nephrops norvegicus) in Norway

“…Throughout its range, Nephrops has mostly been fished with bottom trawl, a gear with substantial impacts on bottom habitats as well as high rates of bycatch and discard (ICES 2021). Exemptions from landing obligations have been sought and, in some cases, granted for several Nephrops fisheries based on evidence of discard survival (Fox et al 2020;Mérillet et al 2018). Although empirical evidence is limited, trap fishing for Nephrops likely reduces bycatch and discard rates (Jansson 2008) and increases discard survival (Valentinsson and Nilsson 2015) due to better selectivity and less harmful handling.…”

Enhancing onboard post-catch vitality of discard Norway lobster (Nephrops norvegicus) for more sustainable Mediterranean trawl fishery

“…This refrigeration can be carried out by simple means such as contact with the ice in the container (all trawlers carry ice compulsorily to keep the commercial catch cool for sale) well in advance until the manoeuvres are finished. This practice would improve the post-release survival of trawling of N. norvegicus, especially during the warm months, when their mortality has been shown to be higher both in the Mediterranean and in the Atlantic (Méhault et al 2016, García-de-Vinuesa et al 2020, Fox et al 2020. In this trawl fishery, the amount of catches under the MCRS is very low (ca.…”