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Over-exploitation of a broadcast spawning marine invertebrate: Decline of the white abalone


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Hobday, AJ, Tegner, M and Haaker, PL 2001 , 'Over-exploitation of a broadcast spawning marine invertebrate: Decline of the white abalone' , Reviews in Fish Biology and Fisheries, vol. 10, no. 4 , pp. 493-514 , doi: 10.1023/A:1012274101311.

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Marine invertebrates have long been considered to be resistant to overfishing. However, a growing number
of exploited taxa have declined substantially and even disappeared from parts of their former range. We consider
the case of the white abalone (Haliotis sorenseni); the first marine invertebrate proposed for the US endangered
species list. This high-value species was one of five abalones targeted in the California and Mexico fisheries; it
is now rare and protected from fishing. The biological characteristics of this deep-living abalone indicate that
it was particularly vulnerable to over-exploitation; reduction of density or group size is now known to lead
to declines in fertilization success and recruitment failure. Warning signs of potential problems existed both
pre- and post-exploitation but were not recognized. In particular, serial depletion was not detected because
catch was not analyzed spatially, perhaps because total landings were reasonably stable for the short period of
exploitation. Recent submersible surveys led to estimates that white abalone now number less than 2,600 animals
or 0.1% of the estimated pre-exploitation population size. Densities and estimated population sizes are less
than 100 animals, at all but one location. Alternate explanations for the decline in abundance were considered
and only exploitation-linked factors, such as sub-legal mortality and illegal fishing, were likely contributors.
Episodic recruitment appears to be a characteristic of broadcast-spawning, long-lived species and may make them
particularly vulnerable to over-exploitation. Management strategies based on size limits that allow a few years
of spawning prior to reaching minimum legal size are insufficient. Sustainable fisheries will require multiple
protected areas to preserve brood stock aggregations necessary for successful fertilization.

Item Type: Article
Authors/Creators:Hobday, AJ and Tegner, M and Haaker, PL
Keywords: endangered species, episodic recruitment, minimum legal size, recruitment failure
Journal or Publication Title: Reviews in Fish Biology and Fisheries
ISSN: 0960-3166
DOI / ID Number: 10.1023/A:1012274101311
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