Effects of season, target species and codend design on the survival of undersized plaice (Pleuronectes platessa) discarded in the bottom otter trawl mixed fisheries in Skagerrak

TY - JOUR

T1 - Effects of season, target species and codend design on the survival of undersized plaice (Pleuronectes platessa) discarded in the bottom otter trawl mixed fisheries in Skagerrak

AU - Savina, Esther

AU - Noack, Thomas

AU - Karlsen, Junita Diana

PY - 2019

Y1 - 2019

N2 - Unaccounted fishing mortality is recognized as an important determinant in the management of bycatch, and discard survival studies have been conducted in commercial and recreational fisheries around the world. A range of environmental, operational and biological factors affect survival of discarded fish and should be considered when presenting survival estimates. The present study compared discard survival of plaice in the bottom otter trawl mixed fisheries in Skagerrak between (a) seasons, (b) target species and (c) codend designs. In the latter, a horizontally divided codend designed to reduce interactions between spiny Norway lobsters (Nephrops norvegicus) and fish during the fishing process was investigated for its capacity to reduce catch damages and improve fish survival. (a) In winter, survival was significantly higher (75%, Confidence Interval (CI): 61–78%) than in summer (44%, CI: 34–61%). (b) When targeting plaice, survival was significantly higher (73%, CI: 63–83%) than when targeting Nephrops (40%, CI: 14–59%) in winter. (c) Using the divided codend, an improvement in discard survival of undersized plaice was possible when targeting Nephrops, but without a significant difference from the 90 mm diamond mesh standard codend (37%, CI: 14–54%) when fish were caught in the 60 mm square mesh lower compartment (61%, CI: 48–73%). In the 120 mm square mesh upper compartment, survival was significantly higher (94% with CI: 81–100%), but few undersized individuals were caught. When targeting plaice, survival rates did not differ between codends.

AB - Unaccounted fishing mortality is recognized as an important determinant in the management of bycatch, and discard survival studies have been conducted in commercial and recreational fisheries around the world. A range of environmental, operational and biological factors affect survival of discarded fish and should be considered when presenting survival estimates. The present study compared discard survival of plaice in the bottom otter trawl mixed fisheries in Skagerrak between (a) seasons, (b) target species and (c) codend designs. In the latter, a horizontally divided codend designed to reduce interactions between spiny Norway lobsters (Nephrops norvegicus) and fish during the fishing process was investigated for its capacity to reduce catch damages and improve fish survival. (a) In winter, survival was significantly higher (75%, Confidence Interval (CI): 61–78%) than in summer (44%, CI: 34–61%). (b) When targeting plaice, survival was significantly higher (73%, CI: 63–83%) than when targeting Nephrops (40%, CI: 14–59%) in winter. (c) Using the divided codend, an improvement in discard survival of undersized plaice was possible when targeting Nephrops, but without a significant difference from the 90 mm diamond mesh standard codend (37%, CI: 14–54%) when fish were caught in the 60 mm square mesh lower compartment (61%, CI: 48–73%). In the 120 mm square mesh upper compartment, survival was significantly higher (94% with CI: 81–100%), but few undersized individuals were caught. When targeting plaice, survival rates did not differ between codends.

KW - Captivity experiment

KW - Demersal fishery

KW - Discard survival analysis

KW - Landing obligation

KW - Norway lobster (Nephrops norvegicus)

KW - Horizontally divided codend

U2 - 10.1016/j.fishres.2019.105311

DO - 10.1016/j.fishres.2019.105311

M3 - Journal article

VL - 219

JO - Fisheries Research

JF - Fisheries Research

SN - 0165-7836

M1 - 105311

ER -