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Effort Data (effort + data)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Declining catch rates of reef fish in Aldabra's marine protected area

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2009
Pierre A. Pistorius
Abstract 1.Fish landings from a small-scale subsistence fishery at Aldabra, Seychelles, were monitored from late 1995 to early 2007 to describe the predominant species caught, catch per unit effort (CPUE) and patterns in yield over time. 2.During this period a total of 19.5 tons of piscivores were caught, varying between 0.99 and 2.46 tons per annum. Effort data allowing for estimation of CPUE were available for 259 fishing trips and from 1998 onwards. 3.Over the study period, and in order of importance, Lutjanus bohar, Variola louti, Lethrinus nebulosus, Epinephelus multinotatus and Epinephelus polyphekadion made up over 80% of the total catch in terms of biomass. Using a general linear model, including fishing location and season as predictor variables, it was shown that CPUE declined significantly over the study period. Annual CPUE varied between 3.0 and 5.1 kg h,1 per person. 4.Throughout the period fishing pressure was low, and largely limited to the subsistence fishery. It is argued that changing catch rates are likely to have been independent of direct anthropogenic influences but a result of reef degradation following the 1998 bleaching event. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Environmental and spatial effects on the distribution of blue marlin (Makaira nigricans) as inferred from data for longline fisheries in the Pacific Ocean

FISHERIES OCEANOGRAPHY, Issue 6 2008
NAN-JAY SU
Abstract Blue marlin is distributed throughout tropical and temperate waters in the Pacific Ocean. However, the preference of this species for particular habitats may impact its vulnerability to being caught. The relationship between spatio-temporal patterns of blue marlin abundance and environmental factors is examined using generalized additive models fitted to catch and effort data from longline fisheries. The presence of blue marlin, and the catch rate given presence, are modeled separately. Latitude, longitude, and sea-surface temperature explain the greatest proportion of the deviance. Spatial distributions of relative density of blue marlin, based on combining the probability of presence and relative density given presence, indicate that there is seasonal variation in the distribution of blue marlin, and that the highest densities occur in the tropics. Seasonal patterns in the relative density of blue marlin appear to be related to shifts in SST. The distribution and relative abundance of blue marlin are sufficiently heterogeneous in space and time that the results of analyses of catch and effort data to identify ,hotspots' could be used as the basis for time-area management to reduce the amount of blue marlin bycaught in longline fisheries. [source]

Spatial correspondence between areas of concentration of Patagonian scallop (Zygochlamys patagonica) and frontal systems in the southwestern Atlantic

FISHERIES OCEANOGRAPHY, Issue 5 2005
EUGENIA BOGAZZI
Abstract It has been hypothesized that the geographical location of scallop beds in extensive shelf regions mirrors hydrographic structures (e.g. frontal systems) that favor the retention/concentration of pelagic larvae. Large, discontinuous concentrations of the Patagonian scallop (Zygochlamys patagonica) are known to have occurred recurrently (for more than 30 yr) at certain geographical locations over the extensive Patagonian shelf. These stocks, exploited since 1996, currently support one of the most important scallop fisheries in the world. Here, we investigate whether those aggregations are spatially coincidental with major frontal systems. Several pieces of information were used: historical survey data documenting the geographic distribution of the Patagonian scallop beds, catch and effort data from the commercial fleet, oceanographic data on frontal systems, and remote sensing imagery. We found that large-scale aggregations do match the location of three major and very different frontal systems in the southwestern Atlantic: the Shelf-Break Frontal System, the Northern Patagonia Frontal System, and the Southern Patagonia Frontal System. We describe the three frontal systems and their associated scallops fishing grounds and discuss which processes can contribute to sustaining the productivity of the scallop grounds in each case. [source]

Chronic fishing disturbance has changed shelf sea benthic community structure

JOURNAL OF ANIMAL ECOLOGY, Issue 3 2000
M. J. Kaiser
Summary 1.,Bottom fishing using towed nets and dredges is one of the most widespread sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively fished areas. Nevertheless, to date it has been difficult to attribute habitat and benthic community changes to fishing effort at a spatial scale that is truly representative of commercial fishing activities. 2.,In this study we present convincing evidence that chronic bottom-fishing disturbance has caused significant and widespread changes in the structure of two distinct soft-sediment benthic assemblages and habitats. 3.,Our study compared the benthic fauna found in areas that have been exposed to either high or low levels of bottom-fishing disturbance over the past 10 years. We were able to validate the fishing effort data in some areas using scars in the shells of a long-lived bivalve mollusc (Glycymeris glycymeris) which result from fishing disturbance. Shell scars occurred most frequently in bivalves collected from the area of highest fishing effort. 4.,Multivariate analyses and the response of abundance/biomass curves indicated that chronic fishing has caused a shift from communities dominated by relatively sessile, emergent, high biomass species to communities dominated by infaunal, smaller-bodied fauna. Removal of emergent fauna has thus degraded the topographic complexity of seabed habitats in areas of high fishing effort. The communities within these areas currently may be in an alternative stable state. [source]