Incidental bycatch of northern fulmars in the small-vessel demersal longline fishery for Greenland halibut in coastal Norway 2012–2014

Abstract

With seabird populations in rapid decline, understanding and reducing anthropogenic mortality factors is essential. One such factor is incidental bycatch in fisheries. Here we analyze bycatch in the small-vessel demersal longline fishery for Greenland halibut outside the coast of Northern Norway in 2012–2014, by means of self-reporting from fishers and independent observers. A sample of killed birds were analysed for sex, age, reproductive status and condition. Nearly all were northern fulmars. Estimated total bycatch for this fishery for the 3-year period was about 312 birds (SE ≈ 133) using a stratified estimator. Bycatch rate per 1000 hooks was estimated to approximately 0.031 (SE ≈ 0.012). Exploring per trip bycatch rates utilizing generalized linear mixed models, we found no convincing trends of environmental, spatial and temporal variables in explaining bycatch. However, trips using longlines with non-swivel hooks had a more than 100-fold larger bycatch rate (mean ≈ 0.760, SE ≈ 0.160) than those using swivel hooks (mean ≈ 0.008, SE ≈ 0.002). Further, trips with external observers had higher bycatch estimates (mean ≈ 0.75, SE ≈ 0.16) compared with trips where bycatch was registered by the fishers (mean ≈ 0.02, SE < 0.01). Of the analysed birds, about two-thirds were adult birds and males dominated (71.1%). A majority were in good or moderate condition. The findings suggest that the incidental bycatch in the Greenland halibut fishery along the Norwegian coast is more limited than previous studies indicated, and that the use of swivel hooks can significantly reduce such bycatch. However, the impacts on the red-listed, diminishing population of fulmars breeding in mainland Norway should be assessed further and requires a method to assign killed birds to regions/colonies. Also, gaining a better understanding of what triggers events with extreme bycatch numbers is important to reduce the problem further and to improve bycatch modelling.