Term
| decline of species with a wide spectrum of life histories and habitats: |
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Definition
–Atlantic cod
–Peruvian anchoveta
–Southern bluefin tuna
–Swordfish
–Sablefish
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Term
| Over past decade conservationists have begun to worry about the possibility that... |
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Definition
| fish populations may be unable to recover from severe declines and fishes may become extinct as a result of fisheries |
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Term
| economic effects of population declines in fisheries |
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Definition
–Poorest of the world’s countries (per capita GDP< $5,000 US): fisheries supply 40% of their protein.
–Richer countries: diminished fisheries do not lead to starvations but enormous disruptions to livelihoods: loss of 40,000 jobs in eastern Canada when northern cod stocks collapsed and fishery closed in 1992.
concerns are raised when populations fall below levels that provide adequate yields
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Term
| global status of exploited fish populations |
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Definition
•The global marine catch peaked in 1988 at 78 mill. Tonnes and has since declined to 69 mill. Tonnes.
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•The FAO (Food and Agriculture Organization) report that half the major fish stocks are fully exploited and very close to their maximum sustainable limits, with another quarter overexploited or depleted.
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Only the remaining quarter of the world’s fish stocks are considered to be under or moderately exploited. |
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Term
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Definition
•There are severe problems in estimating how many fish species have become extinct because of the difficulties of sampling aquatic habitats sufficiently well to be sure that a fish has truly disappeared from its entire range.
•Funding agencies do no longer pay for basic taxonomy and collecting trips, thus:
–Lack of sampling effort
–Taxonomic uncertainties
making it difficult to determine if populations have gone extinct
all known cases of recent extinctions of fishes (since AD 1500) are freshwater species
•We know that there are 34 species whose taxonomic status is clear and for which surveys have been adequate and they are extinct. (overhead T.1)
•When Lake Victoria’s (East Africa) cichlids are included, as well as other unresolved cases of known extinctions, the total is 164 species.
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Term
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Definition
•Habitat Alteration
•Introduced Species
•Overfishing
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Human activities have been held responsible for all known cases of recent extinctions, it is not a coincidence that most documented extinctions have occurred in freshwater fish.(overhead |
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Term
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Definition
•Dams
•Channels
•Siltation
•Water extraction
Habitat destruction is also the most important threat to birds, mammals and plants.
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Term
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Definition
•Introduced species pose a major threat to native fishes.
•In 1998 data was compiled on 1,354 introductions of 237 alien fish species into inland waters.
•For 72 species it was possible to document the outcome of the introductions in terms of impacts in the environment, including native fish species.
•Twenty five of the introduced species had harmful impacts.
•Harmful impacts of the 25 introduced species:
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–Reduction or elimination of native fish populations.
–Introduction of parasites to native fishes
–Physical disturbance of habitat
–Severe depletion of native fishes due to predation
–Escapes of farmed fishes that interbreed with native populations.
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Term
| escaped farm fish that interbreed with native fish |
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Definition
•Example: in Norway 20-30% of spawning Atlantic salmon are of farmed origin.
•Studies have shown genetic differences between farmed and wild salmon in important fitness traits:
–Farmed salmon were competitively inferior to wild fish, with a lifetime reproductive success of 16% of that of wild fish.
–Males inferior at courting females, about one third as often as wild males, and obtaining only 24% reproductive success of wild males.
–Farm fish contributed to a reduction in production of wild fish of 30%.
Genetically modified very large fish may interfere with spawning success of wild fish by displacing them during spawning |
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Term
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Definition
•This threat increases if we consider secondary activities related to it, such as introduction of alien species for harvesting purposes.
•The best example is Lake Victoria in East Africa:
–Introduction of the Nile perch (Lates niloticus) to a fishery in L. Victoria.
This predatory species has had a devastating impact on rock-dwelling cichlids. Provided a boom fishery for a while. Now overfished
•The direct impacts of fishing and the indirect impacts related to fishing often combine with various forms of habitat degradation to threaten species.
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•These problems are particularly acute in freshwater bodies and coastal zones, as they are recipients of virtually every form of human waste.
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•In North America, multiple factors were implicated in 82% of extinctions of 27 species and 13 subspecies during the last 100 years.
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Term
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Definition
•Direct exploitation has caused the collapse of many targeted fish stocks.
•Causes where fishing alone has caused the collapse:
–Georges Bank haddock and cod on both sides of the Atlantic
–Decline of the sablefish (Anoploma fimbrae) off the coast of the US. Stocks reduced by half over a period of 27 years. (overhead F.1f)
–Sturgeon (Acipenser sturio) is now only captured rarely in Europe.
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Term
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Definition
―They were the fish food that contributed to 70% of the fish consumed in the 7th-8th centuries around the Southern Baltic Sea.
―By the 11th century this species was extinct in the Netherlands, and by the 12th c. all captures were reserved for kings (they were so rare).
―International trade restricted by CITES (Convention of International Trade in Endangered Species) since 1983.
―Species listed under the IUCN Red List (International Union for Conservation of Nature) as critically endangered.
―All other species of sturgeons and paddlefishes (Acipenseriformes) are threatened by multiple factors: overexploitation for caviar, habitat loss through dams, channelization, degradation of spawning habitat and pollution.
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―To date:
―One species and one population of Acipenseriformes are listed as extinct.
―Six species are critically endangered
―Ten species are endangered
―Seven species are listed as vulnerable.
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Term
•The totoaba (Totoaba macdonaldi):
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Definition
•A marine fish that is listed under the US Endangered Species Act.
•The totoaba is a huge species of croaker (Scianidae) that occurs only in the North half of the Gulf of California.
•Each year fish migrated in huge shoals following the coast to spawning grounds at the mouth of the Colorado River.
•Fish were 2 m. long and weighed 100 kg.
•Caught originally for swimbladders to be sent to the far east for thickening soups, the rest of the fish was discarded.
•In 1930s CA developed a marked for the meat: 2,300Tm/yr. in 1942
•They were easy to catch, shoals could be pitched forked out of the water.
•Gillnet fisheries began the real decline, only 59 Tm in 1975.
•After the crash, Mexico has banned to catch totoaba but the totoaba are
–incidental by-catch in gillnets
–juveniles are caught by shrimp trawlers
–The nursery estuarine habitat has been transformed from brackish to saline due to the abstraction of water from the Colorado River upstream for irrigation.
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It is relatively easy to track declines of important target fishery species, but it is much more difficult to document declines in non-target species, or species of minor commercial importance.
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Term
| What Renders Species Susceptible to Overfishing? |
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Definition
1.When catchability remains high as population size decreases.
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2.When targeted fish are highly valuable
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3.When fish are susceptible to capture as non-target species
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4.When the fishes life histories result in low productivity
–Species with long generation times, low natural mortality rates and slow body growth.
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1.When per capita recruitment decreases as population size decreases:
•Depensation, called the “Allee Effect” in terrestrial systems, occurs when there is a positive relationship between individual productivity and population size.
•In fisheries, depensation might occur due to a reduced ability to aggregate and find mates, reduced fertilization success, or increased predation rates.
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Term
| Conservation Meets Sustainable Use |
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Definition
•Conservationists traditionally worry about preventing extinction, whereas resource managers in fisheries or forestry traditionally ignore extinction risk, and worry about high sustained yields.
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•Most of the world’s exploited fish species are not being assessed or managed
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•Extinction cannot be ruled out for many species with the characteristics listed in the previous slide.
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•Many conservationists point to the repeated failure of fisheries management to maintain adequate populations, even when fisheries are under control of single nations.
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Term
| What lead to species conservation? |
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Definition
•Cod and haddock are in the Red List of Threatened Species (IUCN 1996) as “vulnerable to extinction”.
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•Traditional management practice suggests that populations should decline about 50% of virgin population sizes in order to maximize productivity.
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•It is difficult to distinguish between “real” decline and population fluctuations in many marine fishes.
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•Our models of fish populations are not sensitive to the variability in natural systems and we should use them only as snapshots of the status of populations.
•The high fecundity of many exploited fish species has been taken to imply that such stocks have high potential to bounce back from low numbers.
•However, there is little support for this assumption: little evidence of recovery for more than 90 stocks studied.
•Recoveries were slower than expected even when data are restricted to stocks in which fishing mortality during the recovery phase is extremely low.
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Term
| what is needed to safeguard biodiversity? |
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Definition
•Marine reserves
•Use of the Precautionary Principle and reference points:
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–Taking account of uncertainty
–Being cautious with new fisheries
–Not using lack of information as an excuse for inaction
–Using reference points:
•Benchmark population sizes
•Mortality rates not to be exceeded
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•Targeted management at key points in the life history of fishes:
–Identification of critically important ages, stages, habitats and sexes (this type of approach is still in its infancy).
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