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Decline in whale shark size and abundance at Ningaloo Reef over the past decade: The world’s largest fish is getting smaller

Citation

Bradshaw, CJA and Fitzpatrick, BM and Steinberg, CC and Brook, BW and Meekan, MG, Decline in whale shark size and abundance at Ningaloo Reef over the past decade: The world's largest fish is getting smaller, Biological Conservation, 141, (7) pp. 1894-1905. ISSN 0006-3207 (2008) [Refereed Article]

Copyright Statement

Copyright 2008 Elsevier Ltd.

DOI: doi:10.1016/j.biocon.2008.05.007

Abstract

Over-exploitation of whale sharks threatens the future of these wide-ranging pelagic fish. A long-term continuous record (4436 sightings) from a large aggregation (300–500 resident individuals) of whale sharks at Ningaloo Reef, Western Australia shows that mean shark length declined linearly by nearly 2.0 m and relative abundance measured from ecotourism sightings (corrected for variation in search effort and environmental stochasticity) has fallen by approximately 40% over the last decade. This population-level result confirms previous predictions of population decline based on projection models parameterised using mark-recapture estimates of survival. The majority of these changes are driven by reductions in the number of large individuals in the population. Phenomenological time series models support a deterministic (extrinsic) decline in large females, although there was some evidence for density dependence in large males. These reductions have occurred despite the total protection of whale sharks in Australian waters. As this species is highly migratory, the rapid change in population composition over a decade (<1 whale shark generation) supports the hypothesis of unsustainable mortality in other parts of their range (e.g., overfishing), rather than the alternative of long-term abiotic or biotic shifts in the environment. As such, effective conservation of whale sharks will require international protection, and collaborative tagging studies to identify and monitor migratory pathways.

Item Details

Item Type:Refereed Article
Keywords:Australia, decline, exploitation, Rhincodon typus, size reduction, whale shark
Research Division:Biological Sciences
Research Group:Ecology
Research Field:Population Ecology
Objective Division:Environment
Objective Group:Flora, Fauna and Biodiversity
Objective Field:Marine Flora, Fauna and Biodiversity
Author:Brook, BW (Professor Barry Brook)
ID Code:116269
Year Published:2008
Web of Science® Times Cited:31
Deposited By:Biological Sciences
Deposited On:2017-05-04
Last Modified:2017-09-14
Downloads:0

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