Reviews in Fish Biology and Fisheries 10: 493–514, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
Over-exploitation of a broadcast spawning marine invertebrate: Decline of
the white abalone
Alistair J. Hobday
, Mia J. Tegner
& Peter L. Haaker
CSIRO Marine Research GPO Box 1538, Hobart, Tasmania 7000, Australia (E-mail: Alistair.Hobday@
Scripps Institution of Oceanography, La Jolla, CA 92093-0227, USA;
of Fish and Game, Long Beach, CA 90802, USA
Accepted 15 June 2001
Abstract page 493
Case study: White abalone 495
Biology of white abalone
Current status of white abalone: Fishery-independent data
Review of the white abalone ﬁshery
Alternative hypotheses: Did factors other than over-exploitation cause decline of white abalone?
Failure to detect post-exploitation decline
Failure to detect pre-exploitation warning signals
Recommendations for abalone recovery and future management 510
Implications for broadcast spawners 511
Key words: endangered species, episodic recruitment, minimum legal size, recruitment failure
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.