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Fisheries Society Essay

Fish is the major source of food worldwide and the main supply of protein; it is consumed by many people from almost all backgrounds. Fish is obtained by fishing using different types of methods; the techniques used for fishing are both old and new ones, but all of them have negative impacts on both fish and the environment.

Impacts on the environment by wild stock fish harvesting depends on the techniques used for harvesting and the place where the species are found, harvesting techniques are divided into active or passive depending on whether the fishing gear is propelled or towed in pursuit of species or target species move into or forwards the gear. In active gear technique a vessel tows a net trawl or dredge through the water or on the seabed, dredges are used to capture sedentary species that live and feed on benthic habitats while trawls ate towed beneath the water immediately above the seabed.

Trawls and dredges sometimes are designed with ticker chains that disrupt the seabed surface to induce the target species flee upwards into the water column and get trapped into the net or to fluidize the sediment of the sea for the tickler chains to penetrate deeper and harvest the fish deep in the water. Trawling and dredging are meant to reduce the roughness of the seabed to depths above 6cm within the sediment, but on large scale it changes to benthic habitats and the fishing structure of a given community but depends the type of target species, gear used and organisms affected for instance sea urchins are more likely to be fatal.

Gears differ in sizes, they can be large and heavy and can be towed up to approximately 13 km/hr and it take years to recover when an impact occurs, at the same time the gears have a high magnitude although, the disturbance caused by the magnitude depends on benthos and the changes to benthic structure can be permanent, this disturbance cannot be compared to natural physical disturbance. Severity of impacts remains unknown in areas of high-grading, black-market sales ad by-catch where large fish deaths occur. Trawls and dredges rip up the sea bed considering that they are not better placed than purse seine in targeting species.

Gill nets target on fish accumulating both small and large sizes but fish that are too small for mesh swim through while large sizes are not caught; In order to increase the surface area targeting large fish, the length of headline to the length of the stretched net can be set too low, and the net hangs slacks, this makes the net less selective and entangles the fish but as drift nets pelagic shark fish near the surface or mid-water or to catch demersal species with the gill the net sets and gets close to the seabed.

Seals, dolphins, turtles and dugongs can be caught and get killed in gill nets, however this depends on the region and fishery, and sometimes infest them leading to eventual death. Gill nets are hazard to dolphins, whales, turtles, sharks and fish when lost for they remain buoyant and continue fishing untended for a good number of years. Pots and traps affect ecological effects and food web is disturbed as a result of overshing of rock lobster may result in population explosion of sea urchins and consequently the disruption in trophic structures.

The long lines deployed to catch pelagic species, they consist of long lines with baited hooks attached to shorter ones, they catch seabirds and the devices for reducing bird catches fannels and shuts do introduce lines and hooks below the sea surface and the change in prey abundance changes the diet of birds and foraging time; change in food web predator-prey interactions the trophic structure and diversity; for example the over harvesting predator species of sea urchins results in overabundance of sea urchins and the decimation of kelp beds; known as urchin barren grounds it results in loss of habitat structure, loss of primary and secondary production, and all tropic structures and barren areas of sea floor, consequently a fast growing species also may become dominant with increased pressure an lower trophic levels and local extinctions will occur and the target species becomes uneconomical even before depletion occurs. 5. Introduction The use of marine reserve was banned by the fisheries management allowing fleet and gear techniques. However many fisheries have collapsed worldwide as a result, illustrating the vulnerability of fishery resources and showing that these methods are ineffective.

But marine reserves would generally increase yields; especially at the high fishing mortality that occurs in most fisheries, but the most interesting feature or reserves is their ability to provide resilience to overexploitation and therefore reduces the risk of stock collapse and therefore the best management option. Benefits of reserves are increased biomass and individual size within the wild stock, resulting in adult migration and larvae dispersal which replenishes fishing grounds. The use of marine reserve necessitates a thorough understanding of critical habitat requirements, fish movement, the behavior of fish, the relationship between subpopulations and the critical density effect for larvae dispersal.

When marine reserve is properly designed in conjunction with other management practices reserve has the capability of providing better ‘insurance’ against uncertainties in stock assessment, fishing control and management by protecting a part of the population from exploitation, it can be the best strategy to be used both for sedentary and migratory species. The unwanted by catch is one of the main environmental effects of fishing and on a global basis the scale has large effects. UN Food and Agriculture organization (FAO) For instance in 1996, estimated annual global discards at about 27 million metric tones, of an equivalent of approximately 25% of reported annual production from fisheries. However the recent updated figure is taken to be 7.

3 million metric tones and this large reduction in bycatch is thought to be the result of use of more selective gears, introduction of by catch and discard regulations and their enforcement and increased utilization of the catch with improved processing technologies and expanding market opportunities; the bycatch varies between different fisheries, for demersal finfish fisheries account 36% of global discards while shrimp fish fisheries account for 27%, whilst together. These fisheries represent 22% of total landings. But on the contrary low by catch levels are associated with purse seines, hand lines, jig, trap and pot fisheries. 6. Introduction

Stock enhancement bypasses early density dependent on food, habitat and predation and density independent factors like water, temperature, patterns of migration, oceanographic and conditions of early stages of life. There is dramatic decrease in mortality when compared to wild populations. Restocking has biological, disease, genetic, environmental, ecosystem and socio-economic impacts risks and the level of each risk vary significantly between species and releasesing sites, depending on stocking a sessile versus mobile species, native versus exotic; confined versus open water; type of predator prey interactions that is associated with the activity variables. Success of stocking will depend on pre-release conditioning and carrying out pilot studies to determine optimal release times, sites and size.

Expansion of market over the short term after successful introductions as a result increases pressures on wild stock in case of less successful introductions and on sustainable environmental, genetic and economic perspectives the gains are not significant. Competition between wild fish and farmed stock depends on the density of fish and availability of resources which are directly influenced by stocking. The genetically homogenous reared fish dilutes the wild gene and thus introducing unfavorable genetic traits into wild stocks like in the case of Black bream from Moore River into swan increased susceptibility to disease and reduced growth rate of wild stocks.

Restocking pollutes the environment and it affects farmed stock and the native species decreases due to competition for food any resources as seen with Galaxiidue as a result of introduction of rainbow trout, how one of the most seriously ‘threatened species’. The bacteria, viruses or parasites into the receiving environment with largely unknown potential effects wild stock like more than 30 world populations of wild salmon have been wiped out by gyradactylus salaries that were released from hatcheries. Consequently invasion by exotic species from hatcheries environment had lead to altered tropic structures, although diagnostic technologies prior to release and rise of quarantine stations may reduces chances of spreading diseases but it relies on knowing what pests or diseases to test so it is which in itself is uncertainty.

The higher exploitation rates resulting from stocking results in over exploitation of remaining wild populations, which eventually endangers the viability of wild stock and diminished genetic pool. At the same time the structures involved with aquaculture can provide a habitat for invasive species which can eventually get transported on boats, and recess that service aquaculture sites and the invasive species are transported across regions. In addition there is lack of success in attempting to stock oceanic species inculcating that stock enhancement for marine fin fish should be confined to estuaries. Lastly evaluation of stocking programmes takes a good number of years after which changes in environmental, ecological or financial issues late resulting in long-term viability diminishing. Conclusion

Fishing causes phenotypic change in target species in heavily fished stocks, and the breeding population matures earlier and this allows species to continue smaller females generally produce fewer, less viable eggs with lower spawning and recruitment rates resulting in a smaller less fecund population. Certain conditions for restocking and resources are needed to be available like sand, sea grass or reef for the optimum survival of fingerlings. Survival depends on critical resources of food and habitat, and therefore requires knowledge of carrying capacity of site. Summery Impacts on the environment by wild stock fish harvesting depends on the techniques used for harvesting and the place where the species are found; harvesting techniques are divided into active or passive depending on whether the fishing gear is propelled or towed in pursuit of species or target species move into or forwards the gear.

In active gear technique a vessel tows a net trawl or dredge through the water or on the seabed, dredges are used to capture sedentary species that live and feed on benthic habitats while trawls ate towed beneath the water immediately above the seabed. Trawls and dredges sometimes are designed with ticker chains that disrupt the seabed surface to induce the target species flee upwards into the water column and get trapped into the net or to fluidize the sediment of the sea for the tickler chains to penetrate deeper and harvest the fish deep in the water Stock enhancement bypasses early density dependent on food, habitat and predation and density independent factors like water, temperature, patterns of migration, oceanographic and conditions of early stages of life. There is dramatic decrease in farmed mortality when compared to wild populations.

Restocking has biological, disease, genetic, environmental, ecosystem and socio-economic impacts risks and the level of each risk vary significantly between species and releasesing sites, depending on stocking a sessile versus mobile species, native versus exotic; confined versus open water; type of predator prey interactions that is associated with the activity variables. Success of stocking will depend on pre-release conditioning and carrying out pilot studies to determine optimal release times, sites and size. Expansion of market over the short term after successful introductions as a result increases pressures on wild stock in case of less successful introductions and on sustainable environmental, genetic and economic perspectives the gains are not significant. Competition between wild fish and farmed stock depends on the density of fish and availability of resources which are directly influenced by stocking.

The genetically homogenous reared fish dilutes the wild gene and thus introducing unfavorable genetic traits into wild stocks like in the case of Black bream from Moore River into swan increased susceptibility to disease and reduced growth rate of wild stocks.

References Beverton R. J. H. & Holt S. H. (1993). On the dynamics of exploited fish populations . Fish and Fisheries Series 11, Chapman & Hall, London. Hilborn, R & Walters, C. J. (1992). Quantitative Fisheries Stock Assessment. Choice, Dynamics and Uncertainty. Chapman & Hall, N. Y. Murphy B. R. & Willis D. W. (1996). Fisheries Techniques, 2nd Edition.. American Fisheries Society, Maryland, USA.


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