AS FISH in shallow waters become scarcer, commercial fishing boats are
increasingly forced to go after deep-water fish. But the habits of species that
live deep down cannot be studied using conventional methods, which involve
tagging fish, and this makes it hard to get the information needed to ensure
these new fisheries are managed sustainably.
Now engineers in Iceland have come up with a device that promises to remedy
the problem. Star-Oddi, a marine equipment manufacturer based in Reykjavik, has
developed equipment that tags fish at depths down to 1000 metres.
Researchers need to track fish to map their daily movements and seasonal
migrations. Such information is needed, for example, to ensure that fishing
boats don鈥檛 catch too many fish of a certain age group. It is also important for
determining whether fish found in international waters spend most of their time
in waters belonging to a particular country, which means the fish are the
property of that country.
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Researchers study these movements in shallow-water fish by catching large
numbers of them, fitting them with tags that log depth, temperature, time and
other data, and then releasing them. If one of these fish is later caught,
fishermen return the tags and researchers can use the data recorded on them to
piece together where the fish travel and at what age.
The pressure of the deep ocean makes tagging more difficult, as deep-water
fish are likely to die if brought to the surface. But the Iceland fish tagger
makes this unnecessary, says Sigmar Gudbjornsson, an engineer with
Star-Oddi.
The refrigerator-sized device is installed in a hole cut into the rear end of
a trawl net (see Diagram).
A video link monitors fish swimming into a trap built
into the device. When a fish is in the trap, researchers trigger a series of
linked metal fingers that immobilise it against the side. A mechanical arm makes
a tiny incision in the fish and inserts a tag. The fish is then released.
The process takes about 15 seconds, and Gudbjornsson estimates that it should
be possible to tag 500 to 1000 fish per day. Early tests have been geared toward
the commercially important deep-sea perch, also known as the redfish. But the
equipment can be configured to tag a variety of fish.
鈥淚t will be a great asset to the whole scientific community, if it works,鈥�
says Tom Laidig, a fisheries biologist at the US National Marine Fisheries
Service in Tiburon, California. 鈥淎ny data that you鈥檙e missing adds error to the
management that you do.鈥�