In Norway, 29 fjords and 52 rivers have been designated for protection in order to prevent the infection of important populations of wild salmonids with salmon lice of farm origin. We evaluated the effect of this protection on the lice infection pressure for wild salmonids based on lice counts performed on wild-caught sea trout and Arctic charr inside onethird of these protected fjords (known as 'National Salmon Fjords'). Results indicate that these areas may provide a certain extent of protection against lice of farm origin, but their configuration will play a key role in their success. When the size and shape of a protected area are such that fish farms are kept at a minimum distance (calculated here as at least 30 km, but this distance is likely site-dependent), wild fish seem unaffected by the direct lice infection pressure imposed by fish farms. In contrast, the effects of small protected fjords were strongly dependent on the production pattern of the aquaculture industry in the surrounding area, and we found a clear correlation between lice levels on wild salmonids and lice production in nearby salmon farms. To establish more precise management practices, both in National Sal mon Fjords and other fjord systems along the Norwegian coast, the development and validation of accurate distribution and abundance models for the dispersion of planktonic lice larvae is needed; this could also be the basis for an area management system based on 'maximum sustainable lice loads' or 'lice quotas.'

The abundance and distribution of salmon lice Lepeophtheirus salmons originating from fish farms in a northern Norwegian fjord during the summer of 2010 was investigated by means of a numerical model, underpinned by field observations. In order to evaluate the robust-ness of the simulated distribution of the lice, we reran the simulation several times, changing the vertical responses of the lice to environmental cues such as light and turbulence, in addition to altering their vertical swimming velocity. The model was able to realistically reproduce the observed currents and stratification in the region. The simulated distribution of lice was not sensitive to different implementations of surface light nor to the light sensitivity level of the lice. However , the vertical swimming velocity and a mixing parameter influenced both their vertical distribution and horizontal dispersion. The aggregation of lice along land was influenced by their response to turbulent water. The simulated infectious stages of the lice were transported on average 20 to 45 km from their release site. The simulated concentrations of infectious lice varied in synchronisation with lice infestations observed on wild fish in the area. Less than 1% of the simulated lice reached a farm site. The ratio between internal and external exposure ranged from 7 to 57%. Farms in the north of the fjord system were more exposed to lice released in the south than vice versa. KEY WORDS: Salmon lice · Lepeophtheirus salmonis · Dispersion · Fjord · Aquaculture management · IBM · Model

Salmon lice Lepeophtheirus salmonis Krøyer may affect survival and growth of anadromous salmonids through physiological stress and/or behavioural changes. Using acoustic telemetry tracking, we investigated the behaviour of 30 infected sea trout Salmo trutta throughout the summer in a fjord with very high salmon lice infection pressure. Most of the tracked sea trout adopted a movement pattern expected to suppress salmon lice infestation, as they showed a strong preference for fresh or brackish water, spending most of the time close to a river outlet or even migrating into the river. Highly infested sea trout preferred shallower depths, associated with lower salinity. The fish lost to predation stayed further away from the river outlet than nonpredated fish, and were likely subjected to a stronger infection pressure. Half of the tracked group were treated with a salmon lice prophylaxis, emamectin benzoate. The effect of treatment on infestation was monitored in a separate group held in a sea cage and found to be moderate; the mortality in this group was associated with infestation by motile lice stages. In contrast, treatment was not found to have an effect on tracked fish behaviour. It is likely that some physiological and behavioural responses to high salmon lice infection pressure may be present even after a prophylaxis treatment, in particular when the treatment is given after exposure to salmon lice infection. We conclude that increased salmon lice infection pressure associated with altered salmon farming practice may have the potential to influence the marine behaviour and growth of sea trout.

The escape of fish from sea-based aquaculture facilities is regarded as a potential environmental threat and is one of the biggest challenges the industry has faced in recent years. In addition to preventing escapes by improving farming operations and procedures, effective and operational routines are needed for recapturing fish should an escape occur. This study investigated the post-escape dispersal of juvenile Atlantic cod Gadus morhua L. from commercial sea cages in coastal Norway using acoustic telemetry. It also assessed the efficacy of different techniques (e.g. cod pots, fyke nets, and gill nets) for recapturing escaped fish. Results suggest that escaped juvenile cod can experience a high size-related predation pressure immediately after escape due to high numbers of large fish aggregating around the cages. Consequently, the escapees rapidly disperse from the farms and seek shelter in littoral areas. Once in shallower waters, they stay relatively close (<10 km) to the farm during the first 2 mo following an escape. This suggests a high potential for recapture if the effort is focused on the littoral area and not in the immediate vicinity of the farm. No escapees were caught using live recapture methods, and a low number of recaptures (< 5%) were achieved with gill nets deployed in littoral areas. Moreover, high by-catch rates and a subsequent high workload suggest this method may be inappropriate for the recapture of escapees.

Salmon louse Lepeophtheirus salmonis Krøyer infection levels in both wild sea trout Salmo trutta L. and sentinel Atlantic salmon Salmo salar L. smolts were investigated inside and outside a temporary protected zone with limits on fish farming in the intensively farmed Romsdalsfjord system. Wild sea trout outside the protected zone had higher prevalence and significantly higher abundances than those inside the zone. Furthermore, sentinel caged Atlantic salmon smolts confirmed significant differences in infection pressure: Eresfjord (non-farmed inner part of the protected zone) had the lowest infection risk, a moderate risk was found in Langfjord (intermediately farmed middle part of the protected zone), while Karlsøyfjord (intensively farmed area outside the protected zone) had the highest infection risk. No clear bias between the near-shore and pelagic areas of the fjord were found, although significant differences between pelagic and near-shore cages were occasionally observed. Results show that small sentinel cages can be used as an alternative method to monitor the infection pressure in a fjord system. Overall, our results indicate that wild salmonids may benefit from the protection zone. However, the infection level on wild sea trout inside the temporary protected zone was higher compared to completely farm-free fjords in Norway, and infection levels likely to have a negative physiological impact on wild sea trout were found. This may indicate that the zone is too small to have the necessary protective effect against salmon lice.