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How humans impact on fisheries
Preview
There
are increasing efforts internationally to balance human activity
with protection of the marine environment. This Fact Sheet
shows the major human direct and indirect impacts on fisheries
resources, some of the efforts to manage these impacts, and
alternative approaches such as aquaculture.
Major
human impacts on fisheries
Human
damage to marine environments is not as not as well publicised
as the depletion of the rainforests, but the sea is also under
threat from our mistakes.
We
often think of fish species in isolation, but each species
is part of a complex ocean ecosystem. There are interactions
between fish, plankton, nutrients, water and air. If we don't
understand how these interactions work, we can upset the relationships
between species or between species and their habitat.
In
New Zealand, it is the job of the Ministry of Fisheries to
manage our fisheries to ensure they remain intact for future
generations. However, everyone has a part to play, for example,
by disposing of rubbish responsibly.
Throughout
history humans have had major impacts on fisheries resources
through:
Fishing
People have been fishing since prehistoric times,
for food, for profit and for leisure, but it is only in
the last few decades that there has been serious concern
about overfishing. Overfishing has been caused partly
by a dramatic increase in the world's population with
a greater demand for marine products. |
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Both
recreational and commercial fishing are now big business.
Some commercial boats can stay at sea for months at a time,
processing 100 tonnes of fish a day as they are caught. The
reported world total marine catch is about 90-100 million
tonnes a year. The actual catch could be up to 50 percent
higher.
At
the same time, there has been an improvement in fish-catching
technology especially in deepwater fisheries (such as using
fish finders to locate fish). Processing, storage, transportation
and marketing systems have also improved. For example, whole
fish can now be packed in ice and sent by plane to arrive fresh
or even live in overseas markets.
Reclamation
Land reclamation can destroy nursery grounds of juvenile
fish and the habitats of shellfish. Many coastal cities, such
as Wellington, Auckland and Christchurch, have reclaimed shallow
marine areas for extra land.
Reclamation
is still continuing around New Zealand, but now environmental
impact reports are required as part of the consent process
before such work can start. Regional councils are required
to prepare coastal plans, setting out what activities and
effects are allowed in their coastal marine area. These requirements
mean that the impact of reclamation on fisheries resources
is now more likely to be taken into account when decisions
are made.
Mineral
exploitation
Oil production and mining of the sea bed and beach sands
can disrupt marine habitats. Mining companies are now much
more aware of environmental impacts than in the past.
Pollution
Dealing with waste products is a worldwide problem. Many
cities and large industries have chosen the "out of sight,
out of mind" option, discharging sewage and waste products
into the sea. Some of the waste products are toxic. In parts
of the North Sea some fish are now so contaminated they're
unfit to eat. Some fish are being born deformed.
The
problem has not reached that scale in New Zealand, but it is
a problem we all need to think about. For example, if you tip
house paint down the drain, where will it end up and what damage
will it do? If a person tips the remains of pesticides into
a stream, what are the likely consequences?
 Rubbish
Rubbish, such as plastic and bits of fishing nets, dumped
at sea or on the foreshore, is a menace to fish, marine mammals
and birds. Fishers are often blamed for this, and while some
probably are still irresponsible, the fishing industry has made
a big effort over the last few years to educate New Zealand
fishers not to dump rubbish. Everyone has a responsibility to
dispose of their own rubbish and not throw it into the sea or
on the beach.
By-catch
When commercial fishers are fishing for a particular species
they may also catch other fish species and sometimes birds
and marine mammals. This is known as by-catch.
Marine
mammals and sea birds are protected under New Zealand law. Over
the last few years the fishing industry and the Government have
taken steps to minimise unwanted by-catch. For example, by using
bird scaring devices on tuna vessels and closing some areas
to set nets to protect dolphins and penguins. There is also
research into devices to allow marine mammals to escape trawl
nets.
By-catch
case study: saving fur seals
Fur seals looking for an easy meal are attracted to hoki being
caught in trawl nets, and can get pulled aboard or drowned.
Up
until the New Zealand Marine Mammals Protection Act was passed
in 1978, New Zealand fur seals were largely unprotected. They
had been heavily exploited by commercial sealers from the
late 1700s to 1812. Fur seals were still being killed well
into last century, largely prompted by fishers complaining
that they were depleting fish stocks.
Fur
seals are still in danger, however, as by-catch from hoki
fisheries, a problem recognised in 1989. The total kill for
that season was estimated at 800 fur seals.
In
1989 the then Ministry of Agriculture and Fisheries (MAF)
set up a technical working group to investigate the interaction
between commercial fisheries and marine mammals. The recommendations
of the group were taken up by the Fishing
Industry Association, which published a code of practice
in 1991 (and updated annually) to help minimise seal deaths.
That year the number of seals caught declined to 202.
Measures
include using spotters to quickly assist seals that get entangled
in nets, reducing the use of lights at night (these attract
seals) and better reporting of seal capture.
How
to handle seals on fishing vessels
Suggested methods for handling fur seals accidentally
brought on board trawlers include the following:
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Plywood
sheets
Sheets of ply used as a moving barrier to herd seals
along deck.
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Nets
Circular nets that can be 'pursed' using two closing
lines are best to remove large animals from enclosed
areas, eg, fish bins.
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Fire
and deck hoses
High pressure hoses can move animals without causing
injury.
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Choker
poles
Use carefully to control the head of large seals, while
another crew member lifts the hind flippers. Ensure
that the fixed loop is not overtight on the seal's neck
or injury could occur.
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Handling
small animals
Lift small seals by the hind flippers, supporting the
animal's weight across the arm while keeping a firm
hold on the foreflipper close to the body. Keep the
seal's body straight with the head away from you.
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Indirect
human impacts on the marine environment
Some
human impacts on ocean ecosystems and fisheries resources
are not so obviously and directly the results of particular
human activities. Nevertheless, global warming and ozone depletion
will have real effects on the marine environment.
Global
warming
A changing climate will alter sea levels, temperature
and salinity, current direction and strength, nutrient
levels and the nature and distribution of the boundaries
between water masses. These changing conditions will change
the distribution, reproduction and growth of many fish
species. |
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Ozone
depletion and ultraviolet radiation
UV-b is the most harmful component of ultraviolet radiation.
A higher level of UV-b radiation is reaching the earth because
of the reduction in the ozone layer. Scientists have not yet
been able to predict reliably the effects of this on marine
life, but there is increasing worldwide concern about the
impact on plankton and marine ecosystems.
The
eggs and larvae of most fish, shellfish and crustaceans live
at or near the surface where they are exposed to increasing
levels of UV-b. This could reduce growth and survival rates
at these life stages. Some fish species have spawning periods
that avoid the season of most intense UV-b.
Increased UV-b could also result in fishery losses indirectly
through effects on the planktonic food chain. Based on one
assessment, a five percent decrease in plankton (estimated
for a 16 percent ozone depletion) could lead to a six to nine
percent fish-yield reduction.
Other
effects could include altered patterns of predation, competition
and diversity if species resistant to UV-b replace more UV-b-sensitive
species.
Alternative
approaches: aquaculture and enhancement
Aquaculture
Aquaculture is fish or shellfish farming. In New Zealand,
salmon, mussels and oysters are successfully farmed. Elsewhere,
including Ecuador, the Philippines, China and Japan, aquaculture
is already a large producer of fish. As fish in the wild become
scarcer and the world's population continues to grow, aquaculture
will become more important.
Enhancement
Enhancement involves releasing hatchery-reared young into
the wild or providing additional protection to naturally spawned
juveniles in order to increase fish stocks. This is not done
on a wide scale, because of cost. However, scallops and salmon
are 'enhanced' in New Zealand, with research being done on
snapper, rock lobster and eel enhancement.
For more
information click on any link below.
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