Behaviour and survival of wild Atlantic salmon Salmo salar captured and released while surveillance angling for escaped farmed salmon

In many Norwegian rivers, spawning stocks are surveyed for escaped farmed salmon with surveillance fishing by rod and reel after the recreational angling season. However, the benefits of surveillance fishing depend on the ability of wild salmon to return to the spawning stock. To evaluate the impacts of surveillance fishing, we captured, radio-tagged and released wild Atlantic salmon Salmo salar in the River Lakselva, Norway, in a surveillance fishery occurring just prior to the spawning period. Among 39 salmon captured, 36 wild fish were tagged and released, whereas 3 were not released (1 bleeding from the gills, 1 farmed, 1 farmed and bleeding). Surviva

Proxy Measures of Fitness Suggest Coastal Fish Farms Can Act as Population Sources and Not Ecological Traps for Wild Gadoid Fish

Background: Ecological traps form when artificial structures are added to natural habitats and induce mismatches between habitat preferences and fitness consequences. Their existence in terrestrial systems has been documented, yet little evidence suggests they occur in marine environments. Coastal fish farms are widespread artificial structures in coastal ecosystems and are highly attractive to wild fish. Methodology/Principal Findings: To investigate if coastal salmon farms act as ecological traps for wild Atlantic cod (Gadus morhua) and saithe (Pollachius virens), we compared proxy measures of fitness between farm-associated fish and control fish caught distant from farms in nine locations throughout coastal Norway, the largest coastal fish farming industry in the world. Farms modified wild fish diets in both quality and quantity, thereby providing farm-associated wild fish with a strong trophic subsidy. This translated to greater somatic (saithe: 1.06–1.12 times; cod: 1.06–1.11 times) and liver condition indices (saithe: 1.4–1.8 times; cod: 2.0–2.8 times) than control fish caught distant from farms. Parasite loads of farm-associated wild fish were modified from control fish, with increased external and decreased internal parasites, however the strong effect of the trophic subsidy overrode any effects of altered loads upon condition. Conclusions and Significance: Proxy measures of fitness provided no evidence that salmon farms function as ecological traps for wild fish. We suggest fish farms may act as population sources for wild fish, provided they are protected from fishing while resident at farms to allow their increased condition to manifest as greater reproductive output.Funding was provided by the Norwegian Research Council Havet og kysten program to the CoastACE project (no: 173384)

Pan-Holarctic assessment of post-release mortality of angled Atlantic salmon Salmo salar

Recreational Atlantic salmon Salmo salar fisheries are culturally and economically important, but confronted with global population declines, catch-and-release has frequently replaced harvest in these fisheries. Many studies have evaluated the effects of catch-and-release angling on Atlantic salmon; however, studies typically focused on a single system and had small sample sizes. Using data from Atlantic salmon catch-and-release studies conducted in 12 rivers throughout the pan-Holarctic range of wild Atlantic salmon, we modeled delayed mortality data using logistic regression. The model was based on 512 salmon (75 ± 15 cm TL) captured and released with electronic tags (i.e. radio or acoustic transmitters), which permitted the determination of fish fate after release (delayed mortality). The percentage of salmon categorized as survivors after release was high (93%). Salmon with longer body length tended to be played for longer durations (R2 = 0.60) but there was no significant effect of fish length or playing time on mortality. Water temperature at capture emerged as a significant predictor of delayed mortality of salmon. Individuals captured by flies had significantly higher survival (96%) compared to lure (86%) and natural bait (85%) caught salmon. Data from throughout the range of Atlantic salmon confirm that fish captured by anglers adhering to best practices have high probability of surviving catch-and-release angling