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Figuring
fish: A guide to marine fisheries research
Preview
Most people agree that we should try to conserve our fisheries
resources. To do this successfully we need information about
the fish that live in our waters. This information is collected
by fisheries scientists, and passed on to the Ministry of
Fisheries.
The
Government uses this information to set limits on how much fish
from different species can be caught each year. The fishing
industry also uses fisheries research information, for example,
about farming aquatic species.
What information is collected
Research is aimed at:
How
it is collected
Unlike animals in a paddock, which are easy to count, some fish
can be very difficult to track down. Some species live in waters
more than 1000 metres deep, and most fish move over quite large
areas. For this reason, fisheries scientists based at The National
Institute of Water and Atmospheric Research (NIWA) use a number
of different techniques for researching fish, including:
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Trawl
surveys
This involves catching fish with a trawl net. The scientists
carefully record what they catch and note any changes
when they fish the same area at a later date.
Acoustic
surveys
Using high-tech sonar equipment to find schools of fish
and estimate their total weight.
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RV Tangaroa - deepwater research vessel |
scientists
measuring and tagging fish |
Tagging
Catching fish, tagging them and releasing them. When fishers
catch tagged fish they return them to the scientists,
providing useful information about the movements of the
fish and how fast they grow. |
Underwater
filming
Using underwater videos or still cameras, scientists get a first-hand
look at what is beneath the sea's surface. Fish are filmed up
to 1200 metres below the sea's surface where it is cold and
totally dark, except for the light produced by many of the organisms
that live there (bioluminescence.)
Egg
production
Most fish reproduce by gathering into large groups and releasing
eggs and milt (sperm) into the water. By collecting samples
of eggs from the water with special plankton nets, scientists
can work out how many spawning fish are in the area.
Removing
the otolith (ear bone) from a fish The "growth
rings" on the ototlith tell us much about the age
and growth of the fish. |
Age
and growth
Some fish grow fast and live only four or five years (eg,
flounder). Other fish, eg, orange roughy, grow very slowly
and live for over 100 years. Scientists can work out the age
of fish by counting the rings on the scales or on the otolith,
a part of the fish's inner ear.
Catch
sampling
Scientists survey samples of fish caught by commercial fishers,
recording information such as the sex and size of the fish.
Biochemistry
Scientists can find out more about different fish species
by looking at their "genetic fingerprint" in the
laboratory. This technique has been used to catch out people
selling a cheap type of fish fillets as something much more
expensive!
Catch-effort
Comparing the size of the commercial fish catch with how much
effort (eg, days at sea) is needed to catch them, gives information
about the size of the fish stock.
Modelling
Computer models are used to help predict what will happen to
fish stocks, depending on how heavily they are fished and on
changes in the environment.
Aquaculture
and enhancement
Marine farming, or aquaculture, is a valuable industry. In New
Zealand, aquaculture is based around greenshell mussels, Pacific
oysters and chinook salmon. Scientists are carrying out research
to help marine farmers. Other species being investigated for
marine farming include dredge (Bluff) oysters and paua.
Although
New Zealand's unpolluted waters are suitable for aquaculture,
nature can play some unkind tricks. From time to time over
the last decade shellfish around New Zealand have been contaminated
by naturally occurring algae, and farmed shellfish cannot
be harvested while the toxic algal bloom lasts.
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A mussel farm
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Enhancement
takes place when stocks of fish and shellfish are boosted
by releasing young into the wild. Enhancement has been very
successful with Tasman Bay scallops. Scientists are also looking
at enhancing paua, oysters and snapper.
For more
information click on any link below.
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