CHASES - Consequences of land-use change and human activity on anadromous salmonids and the ecosystem services that they provide

Informations

Funding country

Norway

Acronym

-

URL

-

Start date

1/1/2016

End date

12/31/2020

Budget

866,781 EUR

Fundings

Abstract

Brown trout may live the entire life in freshwater (resident trout) or occasionally migrate to sea (sea trout). In theory, individuals should migrate to the sea if such behavior increases their life-time reproductive success. It has been shown that differences in migration strategies not only concern whether individuals remain resident or migrate, but within the seaward migrating group of trout, large differences in distance migrated away from the river can often be found. Some individuals stay close, while others migrate far away. Within the CHASES project, we have mapped physiological differences between brown trout that reside in freshwater and estuaries or migrate to sea, and between short- and long-distance migrating sea trout. Seaward migration is a behavior that can be expected when the benefits for the individual fish by doing so are higher than the costs. Consequently, one can expect that this behavior will be changed or disappear if conditions for sea trout at sea are so poor that they lose reproductive potential by migrating to sea. During the project we found that (i) the nutritional status differed among fish adopting different migratory tactics, with long-distance migrants being in poorer condition than the short-distance migrants; and that (ii) within migratory groups, nutritional status was negatively correlated with duration of the marine residency. Further, our data suggest that sea trout from watercourses with good conditions for overwintering, like lakes, stay for a shorter time at sea than individuals from smaller rivers and streams. Finally, females seem to migrate further away, and stay longer at sea, than males. Analyses of swimming depth of sea trout showed that habitat, time of day (day v. night), season, seawater temperature and body length at the time of tagging influenced the depth use. The swimming depths of sea trout coincided with the depths known as water layers used by salmon lice larvae Lepeophtheirus salmonis, which are parasites spreading from open net pen salmon farms, causing elevate mortality in sea trout in many farm-intensive areas. In general, this and other studies of sea trout behavior illustrate how the trout utilize coastal areas commonly influenced by anthropogenic factors such as aquaculture, harbors and marine constructions, marine renewable energy production or other human activities. This suggests that the marine behavior of brown trout and its susceptibility to coastal anthropogenic factors should be considered in coastal zone management plans. Growth during the marine migration has strong implications for reproductive potential and ultimate fitness of sea trout. Hence, the effects of anthropogenic factors on marine growth are important when evaluating population responses and implementing management measures. Temporal changes in growth patterns of sea trout from three Norwegian and two Irish watercourses were examined, covering time spans of 25 to 65 years within each watercourse. Elemental chemistry Ba:Ca profiles and visual reading of fish scales were used to estimate smolt length and life-time growth after first sea entry. Reduced growth after the first sea entry coincided with periods of nearby (<14 km) salmon farming activity in impacted watersheds in both countries. Increased Ba:Ca levels were also recorded during these periods, likely indicating reduced residency in marine habitats caused by premature return to freshwater and estuaries. An increase in estimated size at first sea entry coincided with salmon farming activity, for groups of fish sampled after the sea migration, which suggests a size-selective marine mortality related to fish farming, with the smallest individuals experiencing a larger mortality. Sea trout is an important resource for the community in many areas. The species is important for recreational fishing and in some areas also for tourism. As a part of the CHASES project, the value of sea trout as an ecosystem service was evaluated. The results indicated that the most important ecosystem services delivered by recreational sea trout fisheries are social-cultural ecosystem services at the level of individual fishers; fishing sea trout most likely has important social functions. Further, we found that fishers are prepared to accept stricter management measures that reduce catches but allow fishing to continue. To obtain understanding and acceptance of scientific results in the community, interactions between scientist and the society are important. Our results from two surveys support the supposition that fisheries scientist-society interactions are of variable quantity and quality, and that information exchange and mutual learning could be significantly improved. To strengthen this within the CHASES project, several meetings have facilitated the contact between the researchers and fishery managers, landowners, aquaculture industry and other with large interests in the coastal zone.