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Life history trait variation within a species promotes regional-specific strategies that optimize fitness in a particular environment. Capelin (Mallotus villosus) is an important forage fish species with a circumpolar, temperate distribution, but has increased in relative abundance in Arctic regions recently. To examine for region-specific life history strategies, we compared life history characteristics (length, body condition, age of sexual maturity and growth) of spawning male capelin collected from the eastern Canadian Arctic, in Pangnirtung Fjord, Nunavut (66°N; July 2014 and June-July 2015) with a sub-Arctic location on the northeast coast of Newfoundland (49°N; July 2014 and 2015). First year growth was higher for sub-Arctic relative to Arctic capelin. In contrast, body condition (regression of total length versus mass) was lower for capelin in the Arctic compared to the sub-Arctic population. The age structure of spawning males suggested that Newfoundland capelin reached sexual maturity earlier, as the youngest spawners in Newfoundland were age 2+ (median age: 3+) relative to Pangnirtung where the median spawning age was 4+ (maximum age 5+). Overall, Arctic capelin were generally characterized by lower growth, especially in the first year, later age of reproduction, and lower body condition, relative to the sub-Arctic population. These differences may be the result of limited gene flow on the northern margins of this species’ geographical distribution. They also support previously reported genetic distinction among the sub-Arctic and Arctic clades in the North Atlantic. [ABSTRACT FROM AUTHOR]

Climate change is expected to drive shifts in abundance and distribution of marine forage fishes and possibly result in dietary overlap among sub-Arctic and Arctic species. Stable isotopes of carbon and nitrogen (δ13C, δ15N) were used as a proxy of dietary niche breadth and overlap between co-occurring, immature capelin (Mallotus villosus) and polar cod (Boreogadus saida) collected in the western Canadian Arctic, Darnley Bay, NT, during August 2013. Stable isotope ratios were determined from muscle tissue to quantify the range of δ13C and δ15N, along with dietary niche breadth metrics (standard area ellipses and total area) and niche overlap between lipid-extracted and nonextracted muscle tissues of capelin and polar cod. Lipid extraction influenced the values of δ13C, δ15N, and C:N ratio in polar cod, but only δ13C in capelin tissue. Lipid extraction influenced the interpretation of dietary niche breadth and extent of overlap between co-occurring species, such that overlap of capelin within the niche of polar cod increased (from 53.0 to 89.7%) when lipids were extracted. We recommend the use of lipid extraction to standardize δ13C values when assessing dietary niches and extent of overlap between co-occurring fishes that differ in lipid content. Species-specific lipid normalization equations for δ13C ratios provided in this study can be used to correct δ13C ratios from nonextracted tissues of polar cod in future research. Overall, the high degree of dietary niche overlap between immature capelin and polar cod in the western Arctic suggests there is a high potential for competition between these fishes while immature. [ABSTRACT FROM AUTHOR]

Trophic interactions among seabirds and capelin (Mallotus villosus), a key forage species off Newfoundland and Labrador, are examined. During the 1990s, estimates of relative year-class strength of capelin were similar to estimates in the 1980s, capelin spawned later and matured younger, mean fish size was smaller, and there were large-scale distributional shifts of capelin. Most of these changes were linked to below-normal sea temperatures during the early 1990s, but the changes have persisted even though temperatures have returned to normal. Seabirds bred later in the 1990s and changed diets and foraging strategies. Off eastern Newfoundland, the breeding success of black-legged kittiwakes declined during the early 1990s owing to a suite of factors, including their inability to dive to capture capelin, the late arrival of capelin inshore and predation by gulls. Common murres and puffins did not suffer breeding failures because they could dive and catch capelin at depth. Off Labrador, black-legged kittiwakes experienced breeding failures because of the lack of capelin while common murres were able to find alternate prey and bred successfully. The diets of gannets in the 1990s contained a higher proportion of cold-water prey than in earlier periods when warm-water prey predominated. The population sizes of all seabird species remained stable or increased, with the exception of gulls. Increasing populations of seabirds are related in part to their lessened mortality from gillnets since the closures of the eastern Canadian groundfishery in 1992, whereas declining populations of gulls can be related to reduced food availability from fishery discards and offal. This food limitation has led gulls to switch much of their foraging effort from scavenging to predation on seabird adults and chicks before capelin arrive inshore. Crown Copyright 2002 Published by Elsevier Science Ltd on behalf of International Council for the Exploration of the Sea. All rights reserved. [Copyright &y& Elsevier]

Focuses on the decrease in sea birds population around offshore oil platforms in the North-west Atlantic Ocean. Contribution of oil drilling structures on bird mortality rate; Effect of hydrocarbon development in the region on the breeding of sea birds; Need to implement monitoring of potential avian impacts of offshore hydrocarbon platforms in the region.