How humans impact on fisheries

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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 Indirect impacts Alternative approaches: aquaculture and enhancement

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.

Fishing Reclamation Mineral exploitation Pollution Rubbish By-catch   By-catch case study: fur seals

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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.

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.

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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?

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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.

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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.

Plywood sheets Sheets of ply used as a moving barrier to herd seals along deck.
Nets Circular nets that can be 'pursed' using two closing lines are best to remove large animals from enclosed areas, eg, fish bins.
Fire and deck hoses High pressure hoses can move animals without causing injury.
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.
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.

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.

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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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