Decline in abundance and apparent survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence

Estimates of abundance and survivorship provide quantifiable measures to monitor populations and to define and understand their conservation status. This study investigated changes in abundance and survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence in the conte...

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Bibliographic Details
Published in:Ecology and evolution 2019-04, Vol.9 (7), p.4231-4244
Main Authors: Schleimer, Anna, Ramp, Christian, Delarue, Julien, Carpentier, Alain, Bérubé, Martine, Palsbøll, Per J., Sears, Richard, Hammond, Philip S.
Format: Article
Language:English
Subjects:
Abundance
Accuracy
Animal behavior
Anthropogenic factors
Aquatic mammals
Balaenoptera physalus
Calves
capture heterogeneity
capture–recapture
Cetacea
Cluster analysis
Clustering
Confidence intervals
Conservation status
Demographic variables
Demographics
Ecosystems
Environmental changes
Environmental conditions
Estimates
fin whale
Heterogeneity
Mortality
Original Research
Polls & surveys
Population
Population decline
Population number
Prey
Ships
Site fidelity
Studies
Survival
survival rate
terminal bias
Trends
Whales
Whales & whaling
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Summary:Estimates of abundance and survivorship provide quantifiable measures to monitor populations and to define and understand their conservation status. This study investigated changes in abundance and survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence in the context of anthropogenic pressures and changing environmental conditions. A long‐term data set, consisting of 35 years of photo‐identification surveys and comprising more than 5,000 identifications of 507 individuals, formed the basis of this mark–recapture study. Based on model selection using corrected Akaike Information Criterion, the most parsimonious Cormack–Jolly–Seber model included a linear temporal trend in noncalf apparent survival rates with a sharp decline in the last 5 years of the study and a median survival rate of 0.946 (95% confidence interval (CI) 0.910–0.967). To account for capture heterogeneity due to divergent patterns of site fidelity, agglomerative hierarchical cluster analysis was employed to categorize individuals based on their annual and survey site fidelity indices. However, the negative trend in survivorship remained and was corroborated by a significant decline in the estimated super‐population size from 335 (95% CI 321–348) individuals in 2004–2010 to 291 (95% CI 270–312) individuals in 2010–2016. Concurrently, a negative trend was estimated in recruitment to the population, supported by a sharp decrease in the number of observed calves. Ship strikes and changes in prey availability are potential drivers of the observed decline in fin whale abundance. The combination of clustering methods with mark–recapture represents a flexible way to investigate the effects of site fidelity on demographic variables and is broadly applicable to other individual‐based studies. Mark‐recapture models showed a decline in abundance and a negative trend in survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence. Divergent site fidelity patterns were shown to violate the assumption of equal capture probabilities and the authors proposed to combine mark‐recapture models with agglomerative hierarchical cluster analysis to deal with capture heterogeneity.
ISSN:2045-7758
2045-7758
DOI:10.1002/ece3.5055