Catch quality of Northeast Atlantic cod (Gadus morhua) caught by bottom trawl and gillnet – Effects of changes in gear design and fishing practices

• Main Author: Jensen, Tonje Kristin
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UiT The Arctic University of Norway 2022
• Subjects: VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920; DOKTOR-002; atlantic cod; Gadus morhua; Northeast Atlantic
• Online Access: https://hdl.handle.net/10037/26896

Cod caught with bottom trawls and gillnets have often been associated with poor and variable quality, and little is known about how changes in gear design and fishing practices may influence the quality of fish caught by these two fishing gears. It is difficult, if not impossible, to improve catch quality if fish are damaged during the capture process. Therefore, preventing the deterioration of the catch during the capture process is of utmost importance in improving the quality of caught cod. This thesis studied the effects of changes in gear design and practice in bottom trawl and gillnet fisheries on the catch quality of Northeast Atlantic cod ( Gadus morhua ). Paper I evaluated the improvement in catch quality of cod caught using a dual sequential codend compared with a conventional codend by evaluating residual blood levels in cod fillets as measured by hemoglobin concentration. No significant differences were found in the residual blood levels of fish caught by the two different codends. Whether the use of a dual sequential codend mitigated the effect of postponed bleeding compared with a conventional codend was also investigated. It was found that postponed bleeding influenced the residual blood levels in caught cod, and that this effect was similar whether the fish were caught using the conventional or sequential codends. Another solution that potentially could improve catch quality is to turn the direction of the codend netting 90 degrees (T90) perpendicular to the towing direction. Paper II compared the amount and severity of external catch-related damage and the residual blood levels in muscle between cod caught using a conventional codend configuration (a sorting grid followed by a diamond-mesh (T0) codend) and a T90-codend without a grid. No significant differences were found between fish caught by the two different trawl configurations. Paper III compared the color and amounts of residual blood in cod loin captured by trawling both with and without buffer towing. Further investigation looked at ...