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Commercial Fishery (commercial + fishery)
Selected AbstractsLong term effects of cormorant predation on fish communities and fishery in a freshwater lakeECOGRAPHY, Issue 2 2001Henri Engström Cormorant impact upon natural fish populations has long been debated but little studied because of the requirements of sound data that are often hard to fill. In this study I have monitored fish community composition/abundance before and after a cormorant colony was established in a high productive lake, Ymsen, of south-central Sweden. Data on fish abundance before cormorant establishment enabled me to control for changes in fish densities prior to cormorant colonisation. To control for possible changes in fish populations caused by factors other than cormorant predation (i.e. large-scale regional changes due to climate) data were compared with a control lake, Garnsviken, with no cormorants. Since Lake Ymsen also harbour an important commercial fishery, cormorant impact upon fishery yields was evaluated. The most important fish species in the diet of the cormorants were ruffe (75% by number), roach (11%) and perch (10%). Except for perch, commercially important fish made up a very small fraction of the cormorant diet. Eel, the most important fish for the fishery, was absent in the cormorant diet, pikeperch constituted 0.2% and pike 1.5%. Estimated fish outtake by the cormorants was 12.8 kg ha,1 yr,1 compared to 8.6 kg ha,1 yr,1 for the fishery. Despite considerable fish withdrawal by the cormorants, fish populations did not seem to change in numbers or biomass. The present study indicates that cormorant impact upon fish populations in Lake Ymsen was small and probably in no case has led to declines of neither commercial nor of non-commercial fish species. Still, the number of breeding cormorants in Lake Ymsen, in relation to foraging area, is among the highest known for Swedish lakes. [source] Spatial and temporal trends in abundance of Atlantic salmon, Salmo salar, in Newfoundland with emphasis on impacts of the 1992 closure of the commercial fisheryFISHERIES MANAGEMENT & ECOLOGY, Issue 6 2004J. B. Dempson Abstract Closure of the Newfoundland commercial Atlantic salmon, Salmo salar L., fishery in 1992 was the most restrictive measure introduced to help rebuild depressed local stocks of salmon. Here, the effects of the closure are evaluated by analysing trends in abundance since 1984, and estimates of survival in both freshwater and marine environments derived from enumeration of salmon at fish counting facilities. While freshwater production of smolts generally has been maintained, marine survival rates remain low (2,10%), and highly variable. Overall, total stock size differs little from that prior to the closure of the commercial salmon fishery. Spawning escapements have increased by a factor of 2 or 3 in some rivers, but in other areas total returns are lower on average than those prior to the fishery closure. Factors other than exploitation are contributing to lack of stock recovery, resulting in continued conservation concerns. [source] Developing co-management in an artisanal gill net fishery of a deep hydro-electric reservoir in Sri LankaFISHERIES MANAGEMENT & ECOLOGY, Issue 5 2002S. NATHANAEL Abstract Victoria, is a recently (1984) impounded, deep, hydro-electric reservoir in Sri Lanka with an established commercial fishery. Participatory appraisal of the fishing community revealed decreasing reliance on fishing income with many fishermen moving away to supplementary occupations because of declining fish catches. Illegal fishing and theft of fishing gear resulting from open access, difficulties encountered in enforcing fisheries regulations and the need for fishermen to find alternative sources of income during low water levels are the major management problems. The top,down centralized management approach previously practised was ineffective in addressing any of these issues. Therefore, the possibilities and limitations for introducing co-management as an alternative management strategy were discussed. Financial hardship coupled with perceived benefits through state sponsored welfare schemes caused a positive attitude change among fishermen, making them respond favourably to fishery management. Establishing a licensing system for controlled access, ensuring greater user-group participation through equitable distribution of state sponsored benefits among members, attempting to enforce penalties for illegal fishing linked with surprise checks to enforce management regulations, and obtaining stakeholder perceptions regarding management issues are some of the recent steps taken by the Fishermen's Co-operative Society which would positively contribute towards developing effective co-management in this reservoir. [source] The Role of Fish Communities in Water Quality Management of a Large Shallow LakeINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 5 2003István Tátrai Abstract Management measures of Lake Balaton such as wetland reconstruction at the main inflow to the lake along with the "unplanned" commercial fishery led to great changes in the density and biomass of fish populations. There was no significant difference in CPUE data between the two, eastern and western, basins. Biomass of total fish stock in Lake Balaton has decreased substantially, 2,3 times between 1991,1999, and ranges between 120,194 kg ha,1. Bottom-up effects are more important than the top-down effects due to the impact of internal nutrient load. Changes in the biomass and thus the activity of omnivorous fish in the lake lowered the intensity of various indirect effects and feedback mechanisms causing changes in the nutrient metabolism of the lake. Intensified fishery effort in Lake Balaton did not result in an increased stock of piscivores. The ratio of piscivores and omnivores remained at 5% during the whole study period. Despite this low piscivores to omnivores ratio, the water quality has improved in all basins. [source] Estimating food consumption of marine predators: Antarctic fur seals and macaroni penguinsJOURNAL OF APPLIED ECOLOGY, Issue 1 2002I.L. Boyd Summary 1Estimating food consumption is central to defining the ecological role of marine predators. This study developed an algorithm for synthesizing information about physiology, metabolism, growth, diet, life history and the activity budgets of marine predators to estimate population energy requirements and food consumption. 2Two species of marine predators (Antarctic fur seal Arctocephalus gazella and macaroni penguin Eudyptes chrsolophus) that feed on krill in the Southern Ocean were used as examples to test the algorithm. A sensitivity analysis showed that estimates of prey consumed were most sensitive to uncertainty in some demographic variables, particularly the annual survival rate and total offspring production. Uncertainty in the measurement of metabolic rate led to a positive bias in the mean amount of food consumed. Uncertainty in most other variables had little influence on the estimated food consumed. 3Assuming a diet mainly of krill Euphausia superba, annual food consumption by Antarctic fur seals and macaroni penguins at the island of South Georgia was 3·84 [coefficient of variation (CV) = 0·11] and 8·08 (CV = 0·23) million tonnes, respectively. This was equivalent to a total annual carbon consumption of 0·35 (CV = 0·11) and 0·72 (CV = 0·23) G tonnes year,1. Carbon expired as CO2 was 0·26 (CV = 0·06) and 0·65 (CV = 0·19) G tonnes year,1 for fur seals and macaroni penguins, respectively. The per capita food consumption varied depending upon sex and age but, overall, this was 1·7 (CV = 0·22) tonnes year,1 for Antarctic fur seals and 0·45 (CV = 0·22) tonnes year,1 for macaroni penguins. 4The algorithm showed that the seasonal demand for food peaked in both species in the second half of the breeding season and, for macaroni penguins, there was a second peak immediately after moult. Minimum food demand occurred in both species during the first half of the breeding season. 5As both Antarctic fur seals and macaroni penguins compete for krill with a commercial fishery, these results provide an insight into the seasons and stages of the life cycle in which competition is likely to be greatest. [source] The reproductive biology and ecology of the Port Jackson shark Heterodontus portusjacksoni in the coastal waters of eastern AustraliaJOURNAL OF FISH BIOLOGY, Issue 10 2008D. M. Powter The reproductive biology and ecology of the Port Jackson shark Heterodontus portusjacksoni was investigated at three locations on the central and southern coast of New South Wales (NSW), Australia from January 2002 to December 2005 using underwater visual census surveys and samples obtained from a commercial fishery. Adults displayed sexual dimorphism in total length (LT) at sexual maturity, with males maturing between 762 and 772 mm LT and females between 902 and 905 mm LT. The mean ovarian fecundity was estimated at 16 offspring per female but was unrelated to female LT. Male gonado-somatic (IG) and hepato-somatic (IH) indices and female IG declined from July to November as did maximum ovarian follicle diameter and the diameter of the three largest follicles. Adults were absent from inshore reefs between December and July. Hence, H. portusjacksoni has a synchronous annual breeding season in NSW, which occurs between July and November (the austral winter to spring), with a peak in oviposition from August to October. Heterodontus portusjacksoni copulatory and ovipository behaviour are reported for the first time. Copulation was observed and involved oral grasping of the female's pectoral fin by a single male, which wrapped his body around hers to insert one clasper. Ovipositing females appeared to search crevices in the reef prior to delivering a single capsule, which was washed into the crevice by water movement, with the female departing very soon after oviposition. This study represents the first rigorously quantitative analysis of H. portusjacksoni reproductive biology and ecology in NSW waters. [source] Government perspective, statutory protection and the direction of future research and co-operation in the context of the marine environmentAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2002T.W. Eggeling Abstract 1.The Falkland Islands Government is proud of the successful development of its commercial fishery and sees no reason why it should not continue to be managed in a responsible and sustainable way. However, it recognizes that the fishery is vulnerable to over-fishing, changes in the migration patterns of the principal commercial species and the health of world markets. 2.To widen its economic base, the Falkland Islands Government is seeking to promote farm diversification and eco-tourism, to further develop its commercial fishery, and to encourage offshore oil exploration and development in areas under its jurisdiction. 3.It recognizes the value and importance of its wildlife populations and habitats but sees no reason why economic development and environmental protection should be mutually exclusive, provided that suitable measures are adopted to control development and protect the environment, a precautionary approach is applied, all potential risks to the environment are carefully assessed and remedial measures taken to avoid or minimize any adverse impacts. Extensive new legislation has already been enacted, baseline survey work undertaken and further environmental research commissioned. 4.The Government accepts that additional wildlife habitats and populations need to be afforded environmental protection through designation as National Nature Reserves (NNR) and Marine Nature Reserves (MNR) and thereafter managed effectively. It recognizes that much more environmental research needs to be carried out and, to that end, is willing to seek expert guidance on the future direction of that research, to co-operate with other governments or organisations in the carrying out of that research and to contribute financially to further environmental research in and around the Falkland Islands. Copyright © 2002 John Wiley & Sons, Ltd. [source] | |||||||||||||