Resolving fine-scale population structure and fishery exploitation using sequenced microsatellites in a northern fish

Funding Information Natural Sciences and Engineering Research Council of Canada (NSERC) Strategic Project Atlantic Canada Opportunities Agency and Department of Tourism, Culture, Industry and Innovation grants allocated to the Labrador Institute (MC) Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Genomics Research and Development Initiative (GRDI) Weston Family AwardPeer reviewedPublisher PD

Basin-scale phenology and effects of climate variability on global timing of initial seaward migration of Atlantic salmon (Salmo salar)

Migrations between different habitats are key events in the lives of many organisms. Such movements involve annually recurring travel over long distances usually triggered by seasonal changes in the environment. Often, the migration is associated with travel to or from reproduction areas to regions of growth. Young anadromous Atlantic salmon (Salmo salar) emigrate from freshwater nursery areas during spring and early summer to feed and grow in the North Atlantic Ocean. The transition from the freshwater (parr') stage to the migratory stage where they descend streams and enter salt water (smolt') is characterized by morphological, physiological and behavioural changes where the timing of this parr-smolt transition is cued by photoperiod and water temperature. Environmental conditions in the freshwater habitat control the downstream migration and contribute to within- and among-river variation in migratory timing. Moreover, the timing of the freshwater emigration has likely evolved to meet environmental conditions in the ocean as these affect growth and survival of the post-smolts. Using generalized additive mixed-effects modelling, we analysed spatio-temporal variations in the dates of downstream smolt migration in 67 rivers throughout the North Atlantic during the last five decades and found that migrations were earlier in populations in the east than the west. After accounting for this spatial effect, the initiation of the downstream migration among rivers was positively associated with freshwater temperatures, up to about 10 degrees C and levelling off at higher values, and with sea-surface temperatures. Earlier migration occurred when river discharge levels were low but increasing. On average, the initiation of the smolt seaward migration has occurred 2.5days earlier per decade throughout the basin of the North Atlantic. This shift in phenology matches changes in air, river, and ocean temperatures, suggesting that Atlantic salmon emigration is responding to the current global climate changes

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

Ecology and comparative population dynamics of anadromous Arctic charr, Salvelinus alpinus (Linnaeus 1758), in northern Labrador

Biological characteristics and population dynamics of northern Labrador anadromous Arctic charr (Salvelinus alpinus) were investigated. Univariate and multivariate statistical analyses were performed on nine meristic and thirteen morphometric characters of charr samples from various northern Labrador areas. Variation in meristic characters was slight, although significant differences between samples indicated the discrete nature of the stocks. Differences in growth rate, age at maturity, and movement patterns of tagged fish corroborated results of morphological analyses. -- Biological characteristics including age, growth, movement patterns and aspects of reproduction were examined in Fraser River Arctic charr. No consistent differences in growth rate were found between male and female charr. Upstream migration from the sea began in mid-July with a tendency for larger fish to enter the river first. Average size and age of upstream migrants were 45.1 cm and 8.3 years respectively. -- Biological characteristics of commercially exploited and unexploited Labrador charr populations were examined. Mean age of charr increased with latitude. Commercial exploitation has reduced the proportion of charr greater than 2.3 kg (gutted head-on weight) in commercial catches. Mean length of catches, however, has remained relatively constant in several areas. Total instantaneous mortality rates varied from 0.48 to 0.83 in exploited areas to 0.28 and 0.29 in unexploited populations. -- Comparisons between northern Labrador Arctic charr and charr from other regions are discussed with respect to movement patterns, size, age and reproductive characteristics. Labrador· charr migrated to sea for the first time at smaller sizes (7.8-19.1 cm) but comparable ages (3-7 years) with Arctic charr from other regions. Egg production in Fraser River charr was intermediate between charr from eastern and central Arctic regions, and those from the Western Arctic. Female Fraser River charr were estimated to produce 245 eggs 100g⁻¹. Commercially exploited Labrador Arctic charr populations were generally smaller and younger than exploited charr stocks in the Northwest Territories

Ontogenetic differences in Atlantic salmon phosphorus concentration and its implications for cross ecosystem fluxes

Nutrient transport across ecosystem boundaries by migratory animals can regulate trophic and biogeochemical dynamics of recipient ecosystems. The magnitude and direction of net nutrient flow between ecosystems is modulated by life history, abundance and biomass, individual behavior, and body element composition of migrating individuals. We tested common assumptions applied to nutrient transport models regarding homeostasis of species' body element composition across space and ontogenetic stage. We quantified whole body phosphorus (P) concentration of three life stages of wild Atlantic salmon (Salmo salar L.) from three distinct populations in Newfoundland, Canada, to evaluate the importance of river of origin and life stage as predictors of salmon %P. We found that life stage was a more important predictor of salmon %P than river of origin, and that %P of post-spawn adults migrating downstream to the ocean (i.e., kelts) was more similar to %P of juveniles migrating downstream to the ocean (i.e., smolts) than it was to %P of adults migrating upstream to spawn. We then compared nutrient flux for the three rivers over a 20-year period calculated with body composition values extracted from existing literature and our direct measurements to evaluate how assumptions regarding spatial and ontogenetic homogeneity in salmon %P influenced the observed P fluxes. We demonstrate that assuming equality of kelt %P and adult %P results in an overestimate of net nutrient flux to rivers by Atlantic salmon and the erroneous conclusion that Atlantic salmon populations are unconditional sources of nutrients to their natal watersheds. Instead, Newfoundland's salmon populations are conditional sinks of freshwater P, which is the opposite functional role of Pacific salmon. Our results highlight that a better understanding of intraspecific variation in body element composition of fishes is a prerequisite to determining their role in global biogeochemical cycling