Abstract
The frequently observed positive relationship between fish population abundance and spatial distribution suggests that changes in distribution can be indicative of trends in abundance. If contractions in spatial distribution precede declines in spawning stock biomass (SSB), spatial distribution reference points could complement the SSB reference points that are commonly used in marine conservation biology and fisheries management. When relevant spatial distribution information is integrated into fisheries management and recovery plans, risks and uncertainties associated with a plan based solely on the SSB criterion would be reduced. To assess the added value of spatial distribution data, we examine the relationship between SSB and four metrics of spatial distribution intended to reflect changes in population range, concentration, and density for 10 demersal populations (9 species) inhabiting the Scotian Shelf, Northwest Atlantic. Our primary purpose is to assess their potential to serve as indices of SSB, using fisheries independent survey data. We find that metrics of density offer the best correlate of spawner biomass. A decline in the frequency of encountering high density areas is associated with, and in a few cases preceded by, rapid declines in SSB in 6 of 10 populations. Density-based indices have considerable potential to serve both as an indicator of SSB and as spatially based reference points in fisheries management.
Highlights
Fisheries managers establish abundance limit and target reference points for commercially exploited fishes to ensure the maintenance of healthy and productive populations and enable the recovery of depleted populations
Given our expectation that the relationship between Spawning Stock Biomass (SSB) and High density areas (HDAs) will be sensitive to the level of tow density considered to be ‘high’, we explore several HDA categories, for which we vary the quantile distribution of biomass per tow by taking the highest 33.3% of the biomass per tow quantile distribution (HDA 33), highest 15% (HDA 15), highest 10% (HDA 10), highest 5% (HDA 5), and highest 2.5% (HDA 2.5)
We find that the reproductive component of marine fish populations is related to their spatial distribution
Summary
Fisheries managers establish abundance limit and target reference points (indicator benchmarks) for commercially exploited fishes to ensure the maintenance of healthy and productive populations and enable the recovery of depleted populations. When relevant spatial distribution information is integrated into fisheries management and recovery plans, risks and uncertainties associated with a plan based solely on the SSB criterion would be reduced. The potential of spatial distribution indicators to signal changes in biomass has been recognized [8] and efforts towards integrating spatial distribution indicators in assessment methods have been made [6,9,10]. We build on those efforts by comparing the functionality of various spatial distribution methods as indicators for SSB in groundfish fisheries management. We assess the potential utility and development of fisheries management reference points based on spatial criteria
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