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Fisheries: balancing the
books
Fisheries supply a valuable food
resource, but are seldom managed in a
sustainable manner
Fisheries and fisheries management
Setting and enforcing limits
Related issues
Summary
Fisheries and fisheries management
Setting and enforcing limits
Related issues
Summary
Humans have exploited many different
types of resource species in the sea
Current annual fish catches total 80-90 million
tonnes, and provide 20% of human protein
consumption
Over 100 million people depend on ocean
fisheries and aquaculture for their livelihoods
Subsistence fisheries usually take
relatively small amounts of fish
This means that the fishery is
sustainable - the fishery does not result
in a long-term decline in the resource
species
Modern fishing equipment means that
far more fish can be caught, to supply
an expanding market
About 50% of exploited fish stocks are
close to their maximum biological
production level
A further 25% of exploited fish stocks
are over-fished
A recent study estimates that ‘industrial’
fishing has reduced the biomass of large
predatory fish to 10-20% of pre-fishery
values, usually within fifteen years
Myers & Worm (2003)
Fishery management should ensure
that fishing does not deplete
populations below sustainable levels,
and should protect endangered
populations
Fisheries and fisheries management
Setting and enforcing limits
Related issues
Summary
Managing a fishery in a sustainable manner
means that catches must be regulated so
that the fish population remains stable
This requires an understanding of the
current status of the population and its
biology
Population size
Population age distribution
Growth rate at given ages
Reproductive rate at given ages
Mortality rate at given ages
Fish populations respond to increasing
intensity of fishing in a predictable way
Recovery of exploited fish populations
depends on how fast new, young fish are
being produced
This depends on how many breeding fish
there are, and how fast and at what age
they breed
A sustainable fishery must ensure
that fishing mortality and
spawning stock biomass are kept
within safe limits
Catch limits can be based on the need to
preserve the breeding population above
the value Blim, and keep fishing mortality
below the value Flim
The ‘Safe Zone’ is bounded by
values of F and B that allow for
natural variability and uncertainty
in data and models
Fishery management can use various
approaches to regulate a fishery
Set quotas or allowable catch levels
Establish ‘no-fishing’ areas
Establish a ‘closed season’
Set minimum fish size-limit, or specify net mesh size
Close fishery entirely
Excluding young fish from the catch is
achieved by using nets that allow small
fish to escape
However, fish may be injured even though
they are not caught
There are several other practical
problems in regulating fisheries
Illegal and unregulated fishing
Inadequate scientific data
Minimum size limits may not be effective in excluding undersized fish
Target species may be caught by other fisheries
Natural environmental variability may make prediction
unreliable
In some cases, catches of individual
species may be prohibited, but there is
no way to prevent them being caught
Supposedly protected fish have to be
discarded, even though they are already
injured or dead
Finally, measures to protect fish
populations may have important social
and economic impacts
Fisheries and fisheries management
Setting and enforcing limits
Related issues
Summary
There are several effects associated with
fisheries which also give cause for concern:
•Habitat damage
•Environmental effects of discarded gear
•Incidental mortality and by-catch
•Ecosystem effects
Large fishing gear and
dynamite-fishing cause
extensive damage to coral
reefs and other habitats
Discarded and lost
fishing gear and
other materials form
a serious hazard for
marine animals
Few fisheries catch only the intended species
Marine birds and mammals, such as dolphins, can
drown in nets
Long-line fishing is a significant cause of population
decline for some seabirds, such as albatrosses
Fishing for small species may catch young stages of
larger protected species, below their minimum size
Fishing can also compete with other
species in the ecosystem
Some modern fishing regulatory measures
aim to maintain the entire local ecosystem in
balance, rather than simply conserving target
species
So, is there an alternative to ‘capture’
fisheries?
Aquaculture would appear to be a more
sustainable alternative to capture
fisheries
Farmed salmon production in 2000 was
about 1 million tonnes, equivalent to 1%
of fish catches
Enclosed stocks can be managed efficiently,
with no incidental effects such as by-catch and
under-sized fish
However, ‘industrial’ net-pen fish culture
does have some serious environmental
and ecological impacts
Waste food and faeces produce intense local pollution beneath
pens
Pesticides and antibiotics used in fish culture may affect the
local ecosystem
Pens are sources of parasites and disease
Escaped fish may displace local populations, or interbreed
Wildlife may become entangled in the pens
Farming carnivorous fish does not relieve
pressure on fished wild stocks
Each kilogramme of farmed salmon requires 3
kilogrammes of fish meal and oil
Fisheries and fisheries management
Setting and enforcing limits
Related issues
Summary
You have seen that Fishing is an important source of
food
Many fish populations have
been reduced by over-fishing
You have seen that Fishery management aims to
provide a sustainable resource
Various methods are used to
regulate fisheries
You have seen that Fisheries affect species other than
the target
Aquaculture is not always a
simple, foolproof alternative to
‘capture’ fisheries
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NOTES for USERS
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