The influence of aquaculture unit proximity on the pattern of Lepeophtheirus salmonis infection of anadromous Salmo trutta populations on the isle of Skye, Scotland

Abstract

A total of 230 anadromous Salmo trutta (brown trout) were sampled in five sheltered coastal fjords (or sea lochs) on the Isle of Skye, Scotland, U.K., in 2016 at varying distances from active Atlantic salmon Salmo salar farms. Statistical models were developed to investigate potential correlations between salmon lice Lepeophtheirus salmonis burdens on S. trutta hosts and their proximity to S. salar farm cages. Significant correlations were found between lice burdens and fish fork length and proximity to the nearest S. salar farm. The probability of the presence of L. salmonis on fish hosts increased with fish host size and with distance from the nearest S. salar farm, but total lice burdens were highest in fish sampled near S. salar farms and decreased with distance. The proportion of different life-cycle stages of L. salmonis were also dependent on S. salar farm proximity, with higher juvenile lice numbers recorded at sites near S. salar farm cages. These results highlight the complexity of the relationship between S. trutta and L. salmonis infections on wild fish and emphasize the requirement of further research to quantify these effects to better inform conservation and management strategies, particularly in areas of active S. salar farm facilities.

Environmental influences on life history strategies in partially anadromous brown trout (Salmo trutta, Salmonidae)

“…Sea lice induce ionoregulatory dysfunction, physiological stress, anaemia, reduced feeding and growth, changes in post-smolt behaviour, increased susceptibility to secondary infections, reduced disease resistance and ultimately mortality of individual sea trout (Finstad & Bjørn, 2011;ICES, 1997;Poole, Nolan, & Tully, 2000). On the other hand, in farm-intensive areas, sea lice levels on wild sea trout are typically higher (Gargan et al, 2003;Moore et al, 2018;. On the other hand, in farm-intensive areas, sea lice levels on wild sea trout are typically higher (Gargan et al, 2003;Moore et al, 2018;.…”

“…Sea lice infestations in these areas regularly exceed more than 0.35 lice per gram of fish mass, initiating physiological disturbance to the trout with weight range from 16 to 70 g (Wells et al, 2006(Wells et al, , 2007. The sea lice levels on wild sea trout are particularly high within 30 km of salmon farms, but elevated lice infestations extend beyond this distance (Gargan et al, 2003;Moore et al, 2018;Serra-Llinares, Bjørn, Finstad, Nilsen, & Asplin, 2016;Serra-Llinares et al, 2014;Tully, Gargan, Poole, & Whelan, 1999). The sea lice levels on wild sea trout are particularly high within 30 km of salmon farms, but elevated lice infestations extend beyond this distance (Gargan et al, 2003;Moore et al, 2018;Serra-Llinares, Bjørn, Finstad, Nilsen, & Asplin, 2016;Serra-Llinares et al, 2014;Tully, Gargan, Poole, & Whelan, 1999).…”

“…Sea lice-induced effects on sea trout may in extreme cases lead to local loss of anadromous trout and a transition to entirely resident trout populations (discussed in Poole et al (2007) with reference to the Burrishoole sea trout stock). However, recent studies showed the complexity of the relationship between brown trout and sea lice infestations in the wild (relationship between size of trout and distance of farm cage) and emphasized the requirement of further research to quantify these effects (Moore et al, 2018).…”

“…Wild adult sea trout in farm-free areas exhibit relatively low sea lice levels (Gargan, Tully, & Poole, 2003;Schram, Knutsen, Heuch, & Mo, 1998). On the other hand, in farm-intensive areas, sea lice levels on wild sea trout are typically higher (Gargan et al, 2003;Moore et al, 2018;. Sea lice infestations in these areas regularly exceed more than 0.35 lice per gram of fish mass, initiating physiological disturbance to the trout with weight range from 16 to 70 g (Wells et al, 2006(Wells et al, , 2007.…”

“…At higher lice levels, mortality may occur (Taranger et al, 2015). The sea lice levels on wild sea trout are particularly high within 30 km of salmon farms, but elevated lice infestations extend beyond this distance (Gargan et al, 2003;Moore et al, 2018;Serra-Llinares, Bjørn, Finstad, Nilsen, & Asplin, 2016;Serra-Llinares et al, 2014;Tully, Gargan, Poole, & Whelan, 1999). Therefore, sea lice in intensively farmed areas negatively impact wild sea trout through a suite of primary and secondary impacts reducing marine growth and survival of sea-run fish Shephard, MacIntyre, & Gargan, 2016).…”