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Spatiotemporal variation in pup abundance and preweaning survival of harbour seals (Phoca vitulina) in the St. Lawrence Estuary, Canada (2023)
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Renaud, Limoilou-Amelie; Pigeon, Gabriel; Van de Walle, Joanie; Bordeleau, Xavier; Hammill, Mike O.; Pelletier, Fanie — 2023-06-02 <p class="MsoNormal"><span lang="EN-CA">Marine mammal populations worldwide greatly benefitted from conservation measures put in place since the 1970s following overexploitation, and many pinniped populations have recovered. However, threats due to bycatch, interspecific interactions or climate change remain, and detailed knowledge on vital rates, population dynamics and their responses to environmental changes is essential for efficient management and conservation of wild populations. In this study, we quantified pup abundance and survival of individually marked harbour seal (<em>Phoca vitulina</em> Linnaeus, 1758) pups during the preweaning period at Bic Island and Métis sites in the St. Lawrence Estuary from 1998 – 2019. We used mark-recapture models to evaluate competing hypotheses regarding variation in daily preweaning survival rates and capture probability during the pups’ first 30 days of life. Pup abundance increased from 76 (95% CI: [59, 101]) to 323 [95% CI: 233, 338] in the past two decades at Bic Island and from 66 [95% CI:47, 91] to 285 [95% CI: 204, 218] at Métis. Preweaning survival was generally higher at Bic (0.73 [95% CI: 0.58,0.82]) than at Métis (0.68 [95% CI: 0.52,0.79]). We hypothesize that differences between habitats and human disturbance contribute to lower preweaning survival at Métis, but behavioural studies are needed to understand the impacts of disturbance on mother-pup interactions during the nursing period. </span></p>
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Data from: Spatial distribution of fishes in a Northwest Atlantic ecosystem in relation to risk of predation by a marine mammal
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Swain, Douglas P.; Benoît, Hugues P.; Hammill, Mike O. — 2016-03-23 1. Numerous studies have shown that, at spatial scales of metres to several kilometres, animals balance the trade-off between foraging success and predation mortality by increasing their use of safer but less profitable habitats as predation risk increases. However, it is less clear whether prey respond similarly at the larger spatiotemporal scales of many ecosystems. 2. We determine whether this behaviour is evident in a large marine ecosystem, the southern Gulf of St. Lawrence (sGSL, 75 000 km2) over a 42-year period. This ecosystem is characterized by a recent increase in the abundance of a large marine predator, the grey seal (Halichoerus grypus Fabricius), by more than an order of magnitude. 3. We compared changes in spatial distribution over the 1971–2012 period between important prey of grey seals (Atlantic cod, Gadus morhua L.; white hake, Urophycis tenuis Mitchill; and thorny skate, Amblyraja radiata Donovan) and non-prey fishes. Distribution was modelled using generalized additive models incorporating spatially variable effects of predation risk, density dependence and water temperature. 4. Distributions of cod, hake and skate were strongly related to risk of predation by seals, with distribution shifting into lower risk areas as predation risk increased. Non-prey species did not show similar changes in habitat use. Spatial variation in fish condition suggests that these low-risk areas are also less profitable for cod and skate in terms of food availability. The effects of density dependence and water temperature were also important in models, but did not account for the changes in habitat use as the risk of predation increased. 5. These results indicate that these fish are able to assess and respond to spatial variation in predation risk at very large spatial scales. They also suggest that non-consumptive ‘risk’ effects may be an important component of the declines in productivity of seal prey in this ecosystem, and of the indirect effects at lower trophic levels.

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(Author: Hammill, Mike O.)

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