Effects of salmon lice on wild salmonid populations; filling in knowledge gaps

The LicePop project will provide new empirical knowledge that is essential for understanding how and to what extent salmon lice from fish farms affect wild salmonid populations. The project consists of three work packages: WP1) Test the tolerance levels for salmon lice in wild salmonids by laboratory studies; WP2) Determine natural adaptations of wild salmonids to reduce infection levels by behavioural studies in the wild; WP3) Determine whether, or to what extent, salmon lice reduce or regulate wild populations of salmonids by modelling. In the years 2013 through 2015, we have studied the physiological responses of salmon lice on wild caught sea trout? both with natural and artificial infestations (WP 1). Samples of fish have been taken before, during and after the end of the study and analysis of blood (stress/osmoregulation) and tissue (gene expression: immune response and the degree of seawater tolerance) has been performed. Salmon lice infestation on fish in 2014 was high and caused high mortality so the experiment had to be terminated after 12 days. We took care of this in 2015 so we collected fish earlier before the lice load on the fish had increased. In addition, similar experiments at the Institute of Marine Research at Matre is currently underway and will be supplemented with our data. Collection of fish and laboratory experiment is presented in this link: www.youtube.com/watch?v=SqA4PL40ATE&feature=youtu.be In WP 2, we addressed sea trout behaviour in the Etnefjord in Hardanger, Western Norway, and how the behaviour may be influenced by the infection pressure of salmon lice. Salmon farming in the Hardangerfjord is regulated by fallowing legislation, which means that all the fish farms in the fallowing zone closest to the Etnefjord should be abandoned for at least a month every second spring. We developed testable hypotheses relating to the potential influence of salmon lice on sea trout behaviour (premature return) and survival, and tested these by tracking fish using acoustic telemetry in three consecutive years with expected high-low-high (2012-2013-2014, respectively) infection pressure. We found clear support for this hypothesis, with sea trout staying generally closer to the river outlet in 2014 and 2012 (high infection pressure) as opposed to 2013 (low infection pressure). The potential reduction in sea trout growth opportunities resulting from premature return might have population-regulating effects through reduced fitness and through a reduced likelihood of a seawater migration in general. By sampling male and female salmon lice parasitizing wild adult Atlantic salmon and sea trout, we found that salmon lice of both sexes typically were smaller on sea trout than salmon of a similar size (WP 3). The clear differences in salmon lice dynamics between salmon and sea trout will have considerable consequences for modelling and interpretation of host-parasite interaction, and specifically in assessing the infestation dynamics between wild sea trout and farmed salmon. Further, in WP 3, we assembled data and developed statistical models to test for an association between the abundance of adult salmon returning to rivers along the Norwegian coast and the exposure to salmon lice infection pressure from farms that the wild salmon experienced during their early postsmolt life-history stage. The salmon lice infection pressure data were generated for each salmon population for the years 2002-2013 from reported salmon lice infestation data covering all marine salmon farms along the Norwegian coast. Our initial analysis, using a hierarchical mixed-effects multi-stock model used salmon lice infection pressure for the month of May and separately for the month of June. That analysis indicated that there was a signal between salmon abundance and salmon lice infection pressure, which is most pronounced for the June salmon lice data. We then followed up with a refined estimate of salmon lice infection pressure that is calculated for the appropriate outmigration month for each population (May in the south, average of May-June in the middle, and June in the north). This analysis also indicated that there was an association between salmon lice infection pressure and salmon abundance. However, we believe that the effect of ocean fisheries, which is variable spatially, has not been adequately accounted for in these analyses. The next steps are to assemble the fisheries data to revise the salmon abundance data to a better estimate of overall recruitment per river. We are currently in the process of assembling that dataset, and will analyze the data using similar hierarchical model, but which will be modified to include nested random effects for river identity and the spatial scale of fisheries catches.

This project will provide new empirical knowledge that is essential for understanding how and to what extent salmon lice from fish farms affect wild salmonid populations. Questions raised in this study are: Q1) To what extent do lice from farms occur on w ild fish? i.e. to what extent do farms increase abundance of lice on wild fish; Q2) How many lice does a wild fish tolerate under natural conditions before its viability is compromised; Q3) To what extent are wild fish able to combat lice infection throug h adaptations aimed at reducing infestations; Q4) To what extent can sea lice reduce or regulate wild populations of salmonids. These questions will be answered through a combination of field and laboratory studies and through modelling of population effe cts. The project consists of three work packages: WP1) Test the tolerance levels for sea lice in wild salmonids - by laboratory studies; WP2) Determine natural adaptations of wild salmonids to reduce infection levels - by behavioural studies in the wild; WP3) Determine whether, or to what extent, sea lice reduce or regulate wild populations of salmonids - by modeling.