A Synthesis of Tagging Studies Examining the Behaviour and Survival of Anadromous Salmonids in Marine Environments

This paper synthesizes tagging studies to highlight the current state of knowledge concerning the behaviour and survival of anadromous salmonids in the marine environment. Scientific literature was reviewed to quantify the number and type of studies that have investigated behaviour and survival of anadromous forms of Pacific salmon (Oncorhynchus spp.), Atlantic salmon (Salmo salar), brown trout (Salmo trutta), steelhead (Oncorhynchus mykiss), and cutthroat trout (Oncorhynchus clarkii). We examined three categories of tags including electronic (e.g. acoustic, radio, archival), passive (e.g. external marks, Carlin, coded wire, passive integrated transponder [PIT]), and biological (e.g. otolith, genetic, scale, parasites). Based on 207 papers, survival rates and behaviour in marine environments were found to be extremely variable spatially and temporally, with some of the most influential factors being temperature, population, physiological state, and fish size. Salmonids at all life stages were consistently found to swim at an average speed of approximately one body length per second, which likely corresponds with the speed at which transport costs are minimal. We found that there is relatively little research conducted on open-ocean migrating salmonids, and some species (e.g. masu [O. masou] and amago [O. rhodurus]) are underrepresented in the literature. The most common forms of tagging used across life stages were various forms of external tags, coded wire tags, and acoustic tags, however, the majority of studies did not measure tagging/handling effects on the fish, tag loss/failure, or tag detection probabilities when estimating survival. Through the interdisciplinary application of existing and novel technologies, future research examining the behaviour and survival of anadromous salmonids could incorporate important drivers such as oceanography, tagging/handling effects, predation, and physiology

Using movement, diet, and genetic analyses to understand Arctic charr responses to ecosystem change

Arctic charr Salvelinus alpinus are a commercially and culturally valued species for northern Indigenous peoples. Climate shifts could have important implications for charr and those that rely on them, but studies that evaluate responses to ecosystem change and the spatial scales at which they occur are rare. We compare marine-phase habitat use, long-term diet patterns, and trends in effective population size of Arctic charr from 2 areas (Nain and Saglek) of Nunatsiavut, Labrador, Canada. Tagged charr in both areas frequently occupied estuaries but some also used other habitats that extended to the headland environments outside of their natal fjords. Despite the relatively small distances separating these study areas (&lt;200 km), we observed differences in habitat use and diet. Northern stocks (including Saglek) were more reliant on invertebrates than southern stocks (e.g. Nain), for which capelin and sand lance were important prey. The use of coastal headlands also varied, with Saglek charr occupying these environments more frequently than those from Nain, which only used these habitats in 1 year of the study. Long-term commercial catches also indicate that the tendency for Nain charr to stay within fjords varies annually and relates to capelin availability. Despite the demonstrated capacity to alter diet and habitat use to changing environmental conditions, notable declines in effective population size were associated with the regime shift of the 1990s in the northwest Atlantic. Collectively, these results demonstrate that behavioral plasticity of Arctic charr may be insufficient to deal with the large environmental perturbations expected to arise from a changing climate.</jats:p

Precocial male maturation contributes to the introgression of farmed Atlantic salmon into wild populations

The escape of domesticated Atlantic salmon Salmo salar from aquaculture facilities represents a continued threat to the genetic and demographic stability of wild salmon stocks. Escaped farm-origin salmon have been shown to hybridize with wild conspecifics, yet the long-term genetic impacts are generally unknown. Theoretically, life history variation, specifically precocial maturation of male hybrids, could fast-track introgression, but evidence for this has been sparse. Here, we used empirical and experimental data to examine the role of precocious male maturation in introgression. We examined hybrid class composition using juvenile sampling and genetic assignment over a 5 yr period following an escape event in southern Newfoundland, a region with high rates of natural male precocial maturation. Initially following the escape, the proportion of first-generation (F1) hybrids was high and then decreased annually, contrasting the proportion of backcross wild individuals, which increased over time. The presence and temporal distribution of backcross wild individuals supports the hypothesis that high rates of precocial maturation can fast-track the long-term impacts of escaped farmed salmon on wild populations via interbreeding. This was experimentally tested using lab-created wild, farmed, and F1 parr released and recaptured from a Newfoundland river to assess levels of precocious male maturation. Observed rates of maturation of F1 hybrids were high and similar to wild parr (77 vs. 73%, respectively), indicating that most F1 hybrids mature precocially. Our results suggest that rates of precocial male maturation should be explicitly considered in risk assessments evaluating the genetic impacts of escaped farmed salmon on wild populations.</jats:p

Model-based evaluation of the genetic impacts of farm-escaped Atlantic salmon on wild populations

Genetic interactions (i.e. hybridization) between wild and escaped Atlantic salmon Salmo salar from aquaculture operations have been widely documented, yet the ability to incorporate predictions of risk into aquaculture siting advice has been limited. Here we demonstrate a model-based approach to assessing these potential genetic interactions using a salmon aquaculture expansion scenario in southern Newfoundland as an example. We use an eco-genetic individual-based Atlantic salmon model (IBSEM) parameterized for southern Newfoundland populations, with regional environmental data and field-based estimates of survival, to explore how the proportion of escapees relative to the size of wild populations could potentially influence genetic and demographic changes in wild populations. Our simulations suggest that both demographic decline and genetic change are predicted when the percentage of escapees in a river relative to wild population size is equal to or exceeds 10% annually. The occurrence of escapees in southern Newfoundland rivers under a proposed expansion scenario was predicted using river and site locations and models of dispersal for early and late escapees. Model predictions of escapee dispersal suggest that under the proposed expansion scenario, the number of escapees is expected to increase by 49% and the highest escapee concentrations will shift westward, consistent with the location of proposed expansion (20 rivers total &gt;10% escapees, max 24%). Our results identify susceptible rivers and potential impacts predicted under the proposed aquaculture expansion scenario and illustrate how model-based predictions of both escapee dispersal and genetic impacts can be used to inform both aquaculture management decisions and wild salmon conservation.</jats:p