The IUCN/SSC Shark Specialist Group
Shark News 6: March 1996
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Editorial
I apologise for the lateness of this issue of Shark News, originally
targeted for distribution in February. No need to bore you with a list
of reasons for the delay- suffice it to say that the excuses are generally
feeble ones, but I must also point out in our defence that editing this
newsletter is an entirely voluntary effort; both editors and contributors
are unpaid. We hope to produce the next issue, Shark News 7, in June,
back on schedule. The intention is that it will go out well before the
next official meeting of the Shark Specialist Group in August. See the
next column for more information about this meeting.
This issue, No. 6, concentrates on a theme which was originally
aired in August-early September 1995 on the American Elasmobranch
Society's internet discussion list, elasmo-l. The discussion was first
stimulated by reports of a 'sudden' decline in spiny dogfish Squalus
acanthias catches off the Mt Desert Island Biological Laboratory, near
Bar Harbor, ME (north-west Atlantic) - was this a localised effect or
more widespread phenomenon? Bob Hueter suggested that this could
be another example of localised 'hole-punching' of a shark stock,
defined as localised depletion which is followed by poor recovery
within that locality, even though the core of the population may be
in relatively good shape. His hypothesis to explain this was that
individual sharks are more site-fixed in their migratory habitats than
they are generally given credit for. Once individuals programmed to
live in a certain segment of the range are removed, it takes a relatively
long time for others to stray into the under-utilised habitat. This effect
had been seen in the 1980s Florida sports fishery. The general trend
in the north-west Atlantic has been for localised depletion to be
followed by broad-scale depletion.
This subject was taken up by several correspondents who had
noticed localised stock depletion in other species, including
commercially fished school or soupfin shark Galeorhinus galeus and
bull shark Carcharhinus leucas taken in KwaZulu-Natal shark nets. In
contrast, the tiger shark Galeocerdo cuvier did not show any localised
depletion when taken in beach protection programmes in Queensland
and Hawaii. While this effect can be explained by the very small
home range of bull sharks, it was noted by Sheldon Dudley that a
migratory species, the ragged tooth shark Carcharias taurus, has
shown localised depletion in areas where it only occurs for part of the
year. A very similar pattern is seen for some basking shark Cetorhinus
maximus fisheries (see p. 4). It appears likely that small groups of
some species of shark return separately to particular locations each
year, in a manner similar to salmon or turtles homing to highly
specific breeding, nursery, or feeding grounds.
It will be necessary to study local and long-distance shark
movements and the degree of mixing of localised stocks in more
detail to test these hypotheses. The implications of these observations
for the conservation and management of sharks through protected
areas or protected species designation require careful consideration.
The next (June) issue will be on the general theme of shark and ray
tagging programmes. Please contact the editors NOW if you have any
suggestions or contributions for relevant news items, articles, potential
contributors or other recommendations. I am particularly interested
in featuring a range of examples of tagging programmes, considering
the quality of data they have produced, how this has advanced
scientific knowledge, and how sports angling tagging programmes
may have changed attitudes towards elasmobranch conservation. On
the down side, some readers may feel that tagging induced mortality
is unacceptably high in some tagging programmes - this subject must
also be considered. Please note, however, that for reasons of space and finance
we cannot print everything that we are sent and material
is subject to editing for flow, sense and to address our readership
appropriately.
Sarah Fowler
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