Ghost fishing in Raet National Park: estimating the impact on Atlantic cod and three species of wrasse
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Loss of fishing gear have been a problem for as long as fishing has occurred in the ocean. As modern fishing gear are made up of mostly synthetic materials, it will stay intact and continue to fish for a long time after it has been lost, while slowly degrading and end up as marine litter. Fish and other animals caught in the gear become victims of ghost fishing. Despite the increasing attention worldwide, there is still a lack of small-scale local studies. This study aimed to find the impacts ghost fishing have on four species of fish in Raet National Park in Southern Norway. Atlantic cod (Gadus morhua) and the wrasse species Ballan (Labrus bergylta), goldsinny (Ctenolabrus rupestris) and corkwing (Symphodus melops) are commercially important species fished for in Southern Norway. The Skagerrak coastal cod have been victim of a strong fishing pressure, showing clear signs of the populations being depleted. The number of fish caught in retrieved ghost fishing gear in Raet during the period June 2020 to March 2022 formed the basis for estimating yearly mortality of fish caught in ghost fishing gear. This mortality was compared to that of commercial landings for cod and wrasse, in addition to the estimated yearly mortality of cod caused by recreational fishers. The results show that in the worst case scenario, the number of cod caught in ghost fishing were 11936, close to the 15670 individuals landed yearly in commercial fisheries. Recreational fishers are responsible for the most catches, with 31418 individuals estimated caught each year. For wrasse, the mortality from ghost fishing is seemingly low compared to that of commercial fishery, although between 7794 and 31178 individuals are estimated caught by ghost each year. The results indicate that ghost fishing is selective for smaller cod than the minimal landing size in the commercial fishery and that the median of ghost fishing is smaller than that of commercial and recreational landings, while ghost fishing is selective for larger individuals of wrasse than the minimum landing size in the commercial fisheries and median size of the commercial landings. The study found clear differences in the effectivity of different ghost fishing gear, where wrasse traps stood out as the most effective with the highest catch per unit of both cod and wrasse. Large monthly variations were also found, with August being a month with high catch per unit values for both cod and wrasse. November was the month with highest catch per unit for wrasse, indicating that lost wrasse traps continue to pose a risk to the species beyond the wrasse fishing season. The results indicate the need of change in regulations of fishing wrasse with traps, that ghost fishing in the worst case is a big threat to local coastal species and that there is a need for further, targeted ghost gear retrieval in Raet National Park.