Influence of salmon lice (Lepeophtheirus salmonis Krøyer) on vertical distribution of sea trout (Salmo trutta)
The aim of our study is to gain more knowledge about the habitat use of the sea trout (Salmo trutta) and salmon post-smolts (Salmo salar) while in the ocean, which a field that it is requested more information on in the report published by IMR in 2016 which identified the knowledge gaps that needs to be filled to properly implement the new management system of Norwegian Aquaculture ratified in January 2017 (Karlsen et al. 2016). The goal of the study is to document how the trout uses freshwater through vertical positioning for coping with osmotic stress caused salmon lice. The impact of salmon lice on the depth preference and vertical behaviour of sea trout and salmon is mostly unkown. Although, earlier studies indicate that sea trout may change their vertical behaviour according to the parasite, the complex interactions between other environmental factors have not been explored. Furthermore, recently Wright et al. (2016) suggested that early sessile stages of lice might die in short exposure to freshwater, while older stages of lice may survive for a longer period of time. Thus, early and late infestation may lead to differential responses to optimal use of freshwater. We seek to explore how the upper layer of freshwater may impact the infestation levels and impact the vertical behaviour of the indviduals. The behaviour will be quantified by using a field experiment with acoustic telemetry that tracks the vertical behaviour of individual fish in respect to light intensity, salinity, temperature, and intensity of infection, size of the individual and skin damage.
Repeated trials with will be conducted at Herdla outside of Bergen. Fish with natural infestations of lice and without lice will be individually tagged and released into a ~4 meter deep keep net. The keep net will be placed in a bay with a natural stratification. On half of the infested fish salmon lice will be removed. The lice on the fish will be counted before and after the trial. Tags will be surgically implanted into the abdomen of the fish using standardized methods in fish telemetry. No other non-invasive methods are possible to get accurate behavioural tracking of individual fish at the level which are needed to disentangle the behavioural effect on lice infestation and sublethal effects of lice on trout. In total 120 trout and 120 salmon will be used in the experiment where 60 fish will be tagged with acoustic telemetry and 60 fish will be tagged with less invasive passive integrated transponders (PIT). The data sampling will be coordinated with the annual salmon lice surveillance (NALO) at Herdla. Trout will be collected in trap-nets, while salmon will be provided by Voss hatchery. For trout natural lice infestations on trout will be used as parasite treatment, while for salmon artificial infestations will be used. The fish will monitored daily and will only be kept in the keep net for a maximum 10 days.
Repeated trials with will be conducted at Herdla outside of Bergen. Fish with natural infestations of lice and without lice will be individually tagged and released into a ~4 meter deep keep net. The keep net will be placed in a bay with a natural stratification. On half of the infested fish salmon lice will be removed. The lice on the fish will be counted before and after the trial. Tags will be surgically implanted into the abdomen of the fish using standardized methods in fish telemetry. No other non-invasive methods are possible to get accurate behavioural tracking of individual fish at the level which are needed to disentangle the behavioural effect on lice infestation and sublethal effects of lice on trout. In total 120 trout and 120 salmon will be used in the experiment where 60 fish will be tagged with acoustic telemetry and 60 fish will be tagged with less invasive passive integrated transponders (PIT). The data sampling will be coordinated with the annual salmon lice surveillance (NALO) at Herdla. Trout will be collected in trap-nets, while salmon will be provided by Voss hatchery. For trout natural lice infestations on trout will be used as parasite treatment, while for salmon artificial infestations will be used. The fish will monitored daily and will only be kept in the keep net for a maximum 10 days.