The issue
A key definition of selective fishing refers to
a fishing method's ability to target and capture
organisms by size and species during the fishing
operation allowing non-targets to be released
unharmed.
In a fishing area a range of species and sizes
normally occur together, both fish and non-fish.
When encountered by a fishing gear, they will be
captured at different rates, depending on the gear
design and its mode of operation. Various gears are
known to be more selective in this regard than
others. A purse seine has a poor selective
performance, as it will catch most of the
surrounded individuals. No gear is known to be one
hundred percent selective for a given species or
size range of individuals. Most gear and methods
fall into a group that has some selective
performance, and their ability to select targets
can be altered through modification of design and
operation methods.
The catch in many fisheries thus consists of a
mixture of targets and non-targets. What does or
does not comprise targets depends to a large extent
on the market and whether there are regulations in
place prohibiting capture of species or certain
sizes of organisms. Non-targets are often
synonymous with bycatch, a concept defined
differently by various people. A generic definition
often used is that bycatch refers to the capture of
any species, size of species, or sex of species
that is not the primary target(s) of a fishing
activity. Bycatch, as a choice of the fisher, may
be retained or discarded, alive or dead.
The significance of the discard depends on
biological, ecological, or socio-economic factors.
The nature of discards can possibly be classified
into four categories: (1) population status, (2)
socio-economic, (3) ecological and (4) public
concerns. These factors most frequently form the
basis or regulatory actions taken by management
agencies.
The total global discard is difficult to
estimate, but one assessment came up with a level
of 27 million tonnes for the period 1988 through
1990. A 1996 FAO Technical Consultation in Tokyo
concluded, however, that the 27 million tonnes
might be an overestimate, elaborating different
reasons.
Besides bycatch of fish and fishlike species,
other animals might incidentally be captured with
fishing gears. Such includes among others various
species of whales, turtles and seabirds. Although
bycatch of such organisms seldom is a threat to
their population size, public concerns make it
necessary to reduce such bycatch.
Possible solutions
Improved selectivity can be achieved in
different ways, by modifying the gear design and/or
operation and by using alternative fishing gears.
In trawls and gillnets mesh size is a well- known
measure to regulate the size of captured organisms.
For mobile gears, like trawls and seines, improved
selectivity can also be achieved by using square
meshes in the codends and by inserting filtering
grids in front of the codend. Successful separation
of targets and non-targets species can also be
achieved by using grid devices. The principles for
such selectivity are detailed in the referenced
documents.
Successful technical solutions have also been
found to reduce capture of non-fish species like
mammals, turtles and seabirds. The capture of
dolphins in the purse seine fishery for tuna has
been reduced to an insignificant level by using a
combination of technical changes, rescue
techniques, education of fishers and management
actions. Bycatch of turtles in the tropical shrimp
fishery can be avoided by using a turtle excluder
device (TED), which is a rigid or soft (netting)
structure inserted in the aft part of a trawl, in
front of the codend proper. Incidental capture of
seabirds in longline fisheries can be significantly
reduced by underwater setting of the line, night
setting and scaring the seabirds away from the
baited hooks.
Recent actions
At international level the most prominent action
to reduce bycatch during fishing is the ban on
large size driftnetting on the high seas (UN
General Assembly resolution 1990). The FAO Code
of Conduct for Responsible Fisheries of 1995 is
a major international document addressing the
problem with selective fishing. The most recent
international contribution is the International
Plan of Action for Reducing Incidental Catch of
Seabirds in Longline Fisheries adopted by the
FAO Committee on Fisheries in 1999. FAO has
recently developed a project (with GEF funding), to
enhance the capability of developing countries to
reduce environmental impact of tropical shrimp
trawling through the introduction of bycatch
reduction technologies and change of
management.
At national and regional levels regulations,
minimizing unwanted bycatch and discards are being
introduced. These include minimum mesh sizes,
mandatory use of selective devices like TEDs and
sorting grids, areas closed for fishing, etc. Many
countries are putting a great deal of effort into
research and development aimed at improving the
selectivity of fishing gear and methods that
presently capture much of the unwanted catch.
Outlook
Concerns about bycatch are expected to increase
in the future, and therefore focus will continue to
be on the development of selective technologies. It
is expected that better knowledge of organism
behaviour (which should be treated separately) and
technological developments will increase the
success of such developments.
|
