Initial experiments to assess short-term survival of discarded plaice (Pleuronectes platessa) caught in trammel nets during winter season

European plaice (Pleuronectes platessa) is a key species in commercial fisheries in the North Sea, Skagerrak, Kattegat, and Baltic Sea. The reformed European Union Common Fisheries Policy includes the possibility of exemptions from the landing obligation for “species for which scientific evidence demonstrates high survival rates”. Discard survival from set-net fisheries is poorly studied. Trials were conducted on two commercial fishing vessels over seven trips from November to February 2017–2018 in the Baltic Sea. The nylon trammel nets had a nominal bar size for the inner/outer wall of 75/350 mm and 85/400 mm. Soaking time was 23–47 h, water depth 7–18 m, and deck temperature was − 0.1–6.0 ◦C. Following commercial practice, the trammel nets were hauled back onto the vessel, after which netting and fish passed through a net hauler onto a steel sorting table where the entire fish catch were manually untangled by the fishers and plaice collected by scientists. We used a storage system for housing the captured fish inside fishing harbours during observations. Catch-damage-index (CDI) and Reflex Action Mortality Predictor (RAMP) scores were used to assess fish condition immediately after capture and at the end of observation periods. All plaice below 40 cm were sampled with a total number of 118 individuals from 13 fleets (several nets joined together). The fish were assessed for short-term survival for 4–10 days with full survival (100%). The majority of fish exhibited no reflex impairments. Minor bruises, fraying, and net marks were frequently observed on captured fish. The overall condition of the fish did not change during observation periods

Discard survival in Trammel net and Danish seine

European plaice (Pleuronectes platessa) is a key species for Danish commercial and recreational fishing. A discard ban in the reformed European Union’s Common Fisheries Policy includes the possibility of exempting from the landing obligation “species for which scientific evidence demonstrates high survival rates”. Although smaller coastal fishing vessels make up a substantial part of the commercial Danish fishing fleet, discard survival in plaice from these vessels is not well studied. To address this issue, a study on discard survival in plaice from trammel net and Danish Seine was established as a cooperation between Aalborg University, Copenhagen University and Foreningen for Skånsomt Kystfiskeri. Methodology was developed to collect, assess and observe discard survival in plaice from trammel net and Danish Seine. Experiments were conducted in 2017 and 2018 from three commercial coastal fishing vessels. Livewells were designed to house captured individuals for up to 11 days for observation of short-term survival rate. Catch-damage-index (CDI) and Reflex Action Mortality Predictor (RAMP) were used to assess fish condition immediately after capture and at the end of the observation periods. Results showed 100% survival rate in plaice from trammel net and 87% survival rate in plaice from Danish Seine. For the majority of fish assessed after capture, reflex impairments were absent and injuries were primarily minor bruises, fin fraying, and net marks. Assessments of injuries and reflex impairments after observation showed the condition of the fish generally did not worsen during the observation periods. The project is financed by the European Fisheries Fund and the Ministry of Environment and Food of Denmark