Bycatch of brown trout Salmo trutta in a commercial gillnet fishery targeting whitefish Coregonus lavaretus

Abstract

Harvesting one species of fish might lead to unintentional or unwanted catch of non-targeted ones (Alverson et al., 1994;Hall et al., 2000;Pascoe, 1997). Discarded fish can be morbid or die after release and discard can, therefore, be the cause of a decline in fish populations (Davis, 2002). If the bycaught fish belongs to a threatened species or population, bycatch might be a factor hindering population recovery.Gillnetting is globally one of the most common methods of fishing (Watson et al., 2006). Mesh size and type of net is often selected to increase the likelihood of catching a targeted fish species of a certain size. In general, gillnets are specific with respect to the size of fish caught, but when it comes to species selectivity they are not as effective (Hamley, 1975), and in most cases, bycatch cannot be avoided.Whitefishes, Coregonus spp., are target species of fisheries in Europe, Asia and North America (Funge-Smith, 2018). There are multiple species within the genus. The European whitefish.Coregonus lavaretus L., hereafter referred to as whitefish, inhabits and is caught in both fresh and brackish waters (Verliin et al., 2013). Whitefish belongs to the family Salmonidae and is thus related to brown trout, Salmo trutta L., hereafter referred to as trout.These two species often share similar habitats, exhibit the same general body form and both can adapt to an anadromous life history (Jensen et al., 2017). It is, therefore, not surprising that trout commonly occurs as bycatch in gillnet fisheries for whitefish (ICES,