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Inferring population trends for the world's largest fish from mark-recapture estimates of survival

Bradshaw, Corey J. A., Mollet, Henry F. and Meekan, Mark G. (2007). Inferring population trends for the world's largest fish from mark-recapture estimates of survival. Journal of Animal Ecology,76(3):480-489.

Document type: Journal Article
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IRMA ID A00003xPUB65
Title Inferring population trends for the world's largest fish from mark-recapture estimates of survival
Author Bradshaw, Corey J. A.
Mollet, Henry F.
Meekan, Mark G.
Journal Name Journal of Animal Ecology
Publication Date 2007
Volume Number 76
Issue Number 3
ISSN 0021-8790   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-33846539616
Start Page 480
End Page 489
Total Pages 10
Place of Publication Oxford, England
Publisher Blackwell Publishing
Field of Research 0602 - Ecology
HERDC Category C1 - Journal Article (DEST)
Abstract 1. Precise estimates of demographic rates are key components of population models used to predict the effects of stochastic environmental processes, harvest scenarios and extinction probability. 2. We used a 12-year photographic identification library of whale sharks from Ningaloo Reef, Western Australia to construct Cormack-Jolly-Seber (CJS) model estimates of survival within a capture-mark-recapture (CMR) framework. Estimated survival rates, population structure and assumptions regarding age at maturity, longevity and reproduction frequency were combined in a series of age-classified Leslie matrices to infer the potential trajectory of the population. 3. Using data from 111 individuals, there was evidence for time variation in apparent survival (phi) and recapture probability (p). The null model gave a (phi) over cap of 0.825 (95% CI: 0.727-0.893) and (p) over cap = 0.184 (95% CI: 0.121-0.271). The model-averaged annual (phi) over cap ranged from 0.737 to 0.890. There was little evidence for a sex effect on survival. 4. Using standardized total length as a covariate in the CMR models indicated a size bias in phi. Ignoring the effects of time, a 5-m shark has a (phi) over cap = 0.59 and a 9 m shark has (phi) over cap = 0.81. 5. Of the 16 model combinations considered, 10 (63%) indicated a decreasing population (lambda < 1). For models based on age at first reproduction (alpha) of 13 years, the mean age of reproducing females at the stable age distribution ((A) over bar) ranged from 15 to 23 years, which increased to 29-37 years when alpha was assumed to be 25. 6. All model scenarios had higher total elasticities for non-reproductive female survival [E(s(nr))] compared to those for reproductive female survival [E(s(r))]. 7. Assuming relatively slow, but biologically realistic, vital rates (alpha = 25 and biennial reproduction) and size-biased survival probabilities, our results suggest that the Ningaloo Reef population of whale sharks is declining, although more reproductive data are clearly needed to confirm this conclusion. Combining relatively precise survival estimates from CMR studies with realistic assumptions of other vital rates provides a useful heuristic framework for determining the vulnerability of large oceanic predators for which few direct data exist.
Keywords Australia
Leslie matrix model
Ningaloo Reef
Rhincodon typus
vital rates
whale shark
south africa
northwestern pacific
reproductive biology
elasticity analysis
sexual segregation
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