Sea trout (Salmo trutta) area use and harvest selection: different traits lead to different fates

Abstract

The sea trout (Salmo trutta) is a popular target for recreational fishing along the coast. Harvest selection is known to often fish out large individuals in a pop- ulation, selecting for small size and early maturation in populations. However, selection of behavioral traits through fishing has been overlooked for a long time. In Tvedestrandfjorden, a marine protected area (MPA) has been established in order to protect fish with a none-fishing zone in the middle of the fjord and a buffer zone on each side where only hook-and-line fishing is allowed. A total of 59 sea trout individuals were implanted with acoustic transmitters and their movement in Tvedestrandfjorden was tracked for 18 months. The data was analyzed using capture-mark-recapture analysis. The fish were assigned one of four possible fates during this period: alive, dead, dispersed or harvested. The results showed that there were differences in habitat use between the four groups, and that it was possible to point to behavioral trends in each group both for short- and medium-scale migrations. The behavior of the fish could be con- nected to their fates in ways which made sense. In most cases, temperature had a positive effect on migration activity. The surviving group which did not dis- perse showed clear trends of staying more inside the notake area than the other groups, and were thus probably protected by the regulations within this area. This shows that the MPA does have a protective effect for sea trout, but may also cause selection for the behavioral traits found in this particular fate group, ultimately leading to adaptation of a more stationary and less bold behavior.