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Fisheries, sustainability & conservation

Fisheries supply a valuable food resource, but are seldom managed in a sustainable manner

Fisheries and fisheries management Setting and enforcing limits Summary Related issues

Fisheries and fisheries management Setting and enforcing limits Summary Related issues

Humans have exploited many different types of resource species in the sea

The graphic includes some of the types of animals exploited by past and present fisheries, including whales, fish (mackerel, cod, tuna, shark), crustaceans (crab and krill), molluscs (squid and clam)

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 When fish are caught on a small scale for subsistence, fishing pressure is too small to be a significant cause of mortality in resource species

Modern fishing equipment means that far more fish can be caught, to supply an expanding market Increasing demand for fish, together with more sophisticated fishing equipment and techniques mean that more and more species are exploited, and greater catches are possible

About 50% of exploited fish stocks are close to their maximum biological production level This means that increasing catch on these species would make the fishery unsustainable - continued fishing would then wipe out the poplulation

A further 25% of exploited fish stocks are over-fished These stocks have already passed the point of no return

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 The study (see next slide) was published in the journal Nature in 2003. It combines numerous surveys of population statistics and fishery data for 62 species of large predatory fish, including species such as tuna, swordfish and marlin The study demonstrates that industrialised trawl fishing typically reduces a stock by 50% in the first five years of the fishery. The authors conclude that globally the population of these fish is 10% of unfished levels

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 Summary Related issues

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 age distribution Population size Population age distribution Growth rate at given ages These quantities are the input variables to simple fishery population models. Mortality would be broken down into natural and fishing-associated mortality Reproductive rate at given ages Mortality rate at given ages

Fishery management is designed to ensure that the fish population does not drop below the value needed to replace caught fish Fishery management aims to achieve several things. Most importantly, it must ensure that sufficient fish reach breeding age and produce enough juveniles to sustain the next generation. Such measures may either limit the overall catch, or set minimum size limits for fish.

Fishery management can use various approaches to regulate a fishery

Set quotas or allowable catch levels Establish ‘no-fishing’ areas Establish a ‘closed season’ Measures aim to stop or restrict fishing, and may aim to conserve part of the population whilst leaving the rest accessible to fishing Set minimum fish size-limit, or specify net mesh size Close fishery entirely

However, fish may be injured even though they are not caught 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 under-sized fish Fishing in coastal seas is often well-regulated - or at least well-policed. However, fishing on the high seas is difficult to police, and waters fall outside national jurisdiction 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 Press and broadcast news often feature stories where species protected by quotas or closed fisheries are being caught but cannot be landed

Finally, measures to protect fish populations may have important social and economic impacts The effects on local communities and economies can often be harsh. Attempts at multinational regulation, for instance by the EU, often result in sub-standard protection because of competing national interests

Fisheries and fisheries management Setting and enforcing limits Summary Related issues

There are several effects associated with fisheries which also give cause for concern: Habitat damage Environmental effects of discarded gear These topics are dealt with superficially, but are important elements in the assessment of the cost and benefit of modern fishery 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 Deliberate dumping of waste is now prohibited on the high seas as well as in most territorial waters. However, marine debris remains a significant problem

Marine birds and mammals, such as dolphins, can drown in nets 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 By-catch is a significant problem for both exploited species and for ‘innocent bystanders’. In a few cases, such as the wandering albatross, fishing-related mortality is the cause for significant population decline 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 Ecosystem-based management regulates one or many fisheries with the primary aim to keep measured impacts of the fishery (-ies) to a defined minimum level. Needless to say, such an approach to multi-species management is very much more complex to both regulate and monitor

Fisheries and fisheries management Setting and enforcing limits Summary Related issues

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

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