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

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


Posted on 28 July 2011

TitleDecline in whale shark size and abundance at Ningaloo Reef over the past decade: The world’s largest fish is getting smaller
Publication TypeJournal Article
Year of Publication2008
AuthorsBradshaw, CJA, Fitzpatrick BM, Steinberg CC, Brook BW, Meekan MG
JournalBiological Conservation
Volume141
Issue7
Pagination1894 - 1905
Date Published07/2008
ISSN00063207
Keywordsbiodiversity, whale sharks
AbstractOver-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.
URLhttp://www.sciencedirect.com/science/article/pii/S0006320708001791
DOI10.1016/j.biocon.2008.05.007
Short TitleBiological Conservation
Refereed DesignationRefereed