MV Sapphire pelagic
trips often combine seabirding with research into shark movements via a tagging
program. The two activities are complementary since chum is used to attract
both seabirds and sharks. Seabirders may be lucky enough to witness a shark
being tagged.
We have been tagging Blue Shark around the Isles of Scilly since
August 1996. In this time we have tagged and released 131 Blue Sharks and two
Porbeagle Sharks. We have had 13 recaptures of Blue Shark:
When
a Blue Shark is caught its weight is recorded and a numbered tag inserted just
below the dorsal fin. Upon subsequent recapture the shark again will be weighed
so that the growth rate can be determined for the period that the shark was at
liberty. Also, by recording the location of each capture we can understand more
about shark movements. If a number of anglers catch the same shark, then we are
able to produce a more definite migration pattern. Furthermore, if a non-gravid
female is caught and later recaptured gravid, then we know that between times
the shark has mated. Using this information, a breeding-area could be set up
where both angling and commercial fishing is prohibited.
Tagging
in previous years has already shown that the majority of Blue Sharks caught
around the British Isles are females, whereas the majority caught off the
eastern seaboard of the USA are males. This could well have something to do
with breeding, which further tagging would confirm.
Shark
tagging plays an important role in conservation. There is not a never-ending
supply of stock that anglers and commercial fishermen can continue to exploit.
Fish in general, and sharks in particular, are very slow to reach maturity.
Comparatively speaking, they breed late in life. Continual slaughter of stocks
will hasten the demise of these truly unique creatures.
Shark
species management on the part of the national fisheries bodies is
non-existent. Tagging hopes to highlight some of the problems and provide the
scientific means by which to introduce shark species management.
Contact
Paul Whittaker psmwhittaker@hotmail.com
for details of the Shark Trust.
