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Fishery Yields (fishery + yield)
Selected AbstractsMarine reserve effects on fishery profits: a comment on White et al. (2008)ECOLOGY LETTERS, Issue 3 2009Deborah R. Hart Abstract A recent study (White et al. 2008) claimed that fishery profits will often be higher with management that employs no-take marine reserves than conventional fisheries management alone. However, this conclusion was based on the erroneous assumption that all landed fish have equal value regardless of size, and questionable assumptions regarding density-dependence. Examination of an age-structured version of the White et al. (2008) model demonstrates that their results are not robust to these assumptions. Models with more realistic assumptions generally do not indicate increased fishery yield or profits from marine reserves except for overfished stocks. [source] Long 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] Reconciling differences in trophic control in mid-latitude marine ecosystemsECOLOGY LETTERS, Issue 10 2006Kenneth T. Frank Abstract The dependence of long-term fishery yields on primary productivity, largely based on cross-system comparisons and without reference to the potential dynamic character of this relationship, has long been considered strong evidence for bottom-up control in marine systems. We examined time series of intensive empirical observations from nine heavily exploited regions in the western North Atlantic and find evidence of spatial variance of trophic control. Top-down control dominated in northern areas, the dynamics evolved from bottom-up to top-down in an intermediate region, and bottom-up control governed the southern areas. A simplified, trophic control diagram was developed accounting for top-down and bottom-up forcing within a larger region whose base state dynamics are bottom-up and can accommodate time-varying dynamics. Species diversity and ocean temperature co-varied, being relatively high in southern areas and lower in the north, mirroring the shifting pattern of trophic control. A combination of compensatory population dynamics and accelerated demographic rates in southern areas seems to account for the greater stability of the predator species complex in this region. [source] Restoration of sturgeons: lessons from the Caspian Sea Sturgeon Ranching ProgrammeFISH AND FISHERIES, Issue 3 2000D.H. Secor Depletion of sturgeon stocks world-wide has increased interest in aquaculture-based restoration programmes. The Caspian Sea Sturgeon Ranching Programme (SRP) of the former Soviet Union represents a unique opportunity to evaluate expense, benefits and potential ecological and genetic effects of such restoration programmes. The SRP was initiated in the 1950s to compensate for lost spawning habitat in the Volga River and elsewhere. After its completion in 1962, the Volgograd Dam reduced spawning grounds in the Volga River system, the principal spawning tributary of the Caspian Sea, by ,80%. For two of the three commercial sturgeon species (Russian sturgeon, Acipenser güldenstädti, and stellate sturgeon, A. stellatus), yields improved after the imposition of the 1962 moratorium on sturgeon harvests in the Caspian Sea. Volga River fisheries were managed for spawning escapement. Although imprecisely known, the contribution of the millions of stocked Russian and stellate juveniles during 1962,91 was most likely important to sustaining fisheries, although less so (contributing to <30% of the adult stock) than natural recruitment. Apparently, reduced spawning grounds, supplemented with artificial spawning reefs were sufficient to support reproduction and large fishery yields of Russian and stellate sturgeons. For beluga sturgeon, Huso huso, harvests in the Volga River were nearly all dependent upon hatchery stocking. Beluga sturgeon spawning grounds were mostly eliminated with the construction of the Volgograd Dam. Without the hatchery programme, beluga sturgeon in the Volga River and Caspian Sea would in all likelihood have been extirpated. Currently, sturgeons are severely depleted in the Volga River and Caspian Sea due to poaching and lack of co-operation between countries exploiting the species. Aquaculture-based restoration in Russia is now viewed a chief means of rebuilding stocks of Caspian Sea sturgeons. [source] The relationship between the skipjack tuna (Katsuwonus pelamis) fishery and seasonal temperature variability in the south-western AtlanticFISHERIES OCEANOGRAPHY, Issue 1 2003H. A. Andrade Abstract The spatio-temporal distribution of tuna fishing effort has been related to oceanographic circulation and features in several seas of the world. Understanding the relationship between environmental variables and fishery resource dynamics is important for management decisions and to improve fishery yields. The relationship between sea temperature variability and the pole-and-line skipjack tuna (Katsuwonus pelamis) fishery in the south-western Atlantic Ocean was investigated in this work. Data from logbooks, satellite images (sea surface temperature), and oceanographic surveys were used in the analyses. Skipjack are caught in warm tropical waters of the Brazil Current (BC). The north,south displacement of fishing effort was strongly associated to seasonal variation of the surface temperature, which was coupled to the tropical BC flow. Oceanographic fronts from autumn to spring and a shallow thermocline in summer probably induces the aggregation of skipjack schools over the shelfbreak, favouring fishing operations. Hypotheses are proposed to explain the relationship between peaks of fishing events and the presence of topographic peculiarities of the shelfbreak. [source] Long-term changes in the trophic level of the Celtic Sea fish community and fish market price distributionJOURNAL OF APPLIED ECOLOGY, Issue 3 2002J. K. Pinnegar Summary 1The intensive exploitation of fish communities often leads to substantial reductions in the abundance of target species, with ramifications for the structure and stability of the ecosystem as a whole. 2We explored changes in the mean trophic level of the Celtic Sea (ICES divisions VII f,j) fish community using commercial landings, survey data and estimates of trophic level derived from the analysis of nitrogen stable isotopes. 3Our analyses showed that there has been a significant decline in the mean trophic level of survey catches from 1982 to 2000 and a decline in the trophic level of landings from 1946 to 1998. 4The decline in mean trophic level through time resulted from a reduction in the abundance of large piscivorous fishes and an increase in smaller pelagic species which feed at a lower trophic level. 5Similar patterns of decline in the trophic level of both catches and landings imply that there have been substantial changes in the underlying structure of the Celtic Sea fish community and not simply a change in fishery preferences. 6We suggest that the reported changes in trophic structure result from reductions in the spawning stock biomass of traditional target species associated with intensive fishing, together with long-term climate variability. 7The relative distribution of fish market prices has changed significantly over the past 22 years, with high trophic level species experiencing greater price rises than lower trophic level species. 8Although decreased abundance of high trophic level species will ultimately have negative economic consequences, the reduction in mean trophic level of the fish community as a whole may allow the system to sustain higher fishery yields. 9Management objectives in this fishery will depend on the relative values that society attaches to economic profit and protein production. [source] Effects of tidal flat reclamation on sediment quality and hypoxia in Isahaya BayAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2006Yoshikuni Hodoki Abstract 1.Ariake Bay, which is located in western Japan, has a large tidal range (>6 m) and a vast tidal flat (200 km2). In the early 1990s, the government-managed Isahaya Reclamation Project began in the western part of Ariake Bay. A 16-km2 area of tidal flat in the inner part of Isahaya Bay was destroyed through reclamation and separated from the sea by a dyke, which created land and a freshwater reservoir. 2.Since the initiation of the project, fishery yields around Isahaya Bay have dramatically decreased. The objective of this study was to clarify the relationship between the work associated with the Isahaya Reclamation Project and the recent environmental deterioration in Ariake Bay, with references to present sediment thickness and organic matter content, and hypoxic water distributions in Isahaya Bay. 3.The organic matter load from the reservoir has increased since the initiation of the reclamation project and has been associated with a thick layer of fine sediment at the bottom of Isahaya Bay. The thickness of fine sediment and the total organic carbon content were higher in Isahaya Bay than in the freshwater reservoir. 4.Based on measurements in August 2001, hypoxic water spread widely in and around Isahaya Bay; the lowest dissolved oxygen (DO) concentration (0.53 mg L,1) was observed just outside the dyke. An analysis based on a two-layered box model using data obtained in August 2001 showed that the DO consumption rate in the bottom layer was high (0.61 mg O2 L,1 day,1), and that 22,41% of the total organic carbon load needed to induce the hypoxic water was derived from the reclamation area. 5.Our findings strongly suggest that enclosed seas may suffer from eutrophic and hypoxic conditions because of their low seawater-exchange rate. A comprehensive conservation programme and environmental assessment including physical and material transport processes in the system is needed to manage the environment of the enclosed sea. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||