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Testing CPUE-derived spatial occupancy as an indicator forstock abundance: application to deep-sea stocks
Published online by Cambridge University Press: 27 September 2013
Abstract
The status of an exploited population is ideally determined by monitoring changes inabundance and distributional range and pattern over time. Area of occupancy is a measureof the current distribution. Unfortunately, for many populations, scientific abundance anddistribution information is not readily available. To evaluate the reliability ofcommercial fishing data for deriving occupancy indicators that could serve as proxies forstock abundance, we investigated four questions: 1) Occupancy changes with stock biomass,but is this change strong enough to make occupancy a sensitive indicator of populationbiomass? 2) Fishing boats follow fish, but when does such activity alter the positivemacroecological relationship between occupancy and abundance? 3) When does the activity ofpursuing fish adversely affect occupancy estimates derived from catch and effort data? 4)How does uncertainty in fishing effort data affect occupancy estimates? Spatialsimulations mimicking the dynamics of four deep-water fish species showed thatbiomass-occupancy relationships can be weak. Fishers following fish can modify the spatialdistribution of target species, even reversing the sign of the biomass-occupancyrelationship in certain cases, and can affect the reliability of occupancy indicators,which can also be impaired by error in effort data. Using commercial catch and effort dataand abundance indices for deep-sea fish populations to the west of the British Isles itwas found that only for roundnose grenadier might occupancy provide insights into biomasschanges. In conclusion, care should be taken when using occupancy for evaluating rangechanges in cases where fishing might have modified spatial distributions, uncertaincommercial data are used or when the abundance-occupancy relationship is too flat.
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- © EDP Sciences, IFREMER, IRD 2013
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