Continental-scale hotspots of pelagic fish abundance inferred from commercial catch records
Phil Bouchet, Tom Letessier, Jessica Meeuwig | Aug 24, 2017
Yellowfin tunas (Thunnus albacares) constitute a major target of industrialised fisheries in the Indian Ocean. Photo: David Valencia
Bouchet PJ, Meeuwig JJ, Huang Z, Letessier TBL, Nichol SL, Caley MJ, Watson RA. 2017. Continental-scale hotspots of pelagic fish abundance inferred from commercial catch records. Global Ecology and Biogeography, 26: 1098–1111.
- We used historical commercial fisheries catch records to map the likely location of pelagic fish hotspots in the Commonwealth waters surrounding the state of Western Australia.
- High fish numbers were inferred around a number of large submarine canyon systems including the Argo-Rowley, Ningaloo, Perth, and Bremer canyons.
- Geomorphometrics (measures of seabed complexity) were relatively good predictors of fish abundance, with canyon distribution the most important one in the North bioregion.
- Fish hotspots showed very little overlap with the national network of marine reserves, highlighting a significant gap in current protection.
- Static topography may be a useful blueprint for broad-scale conservation planning in pelagic environments.
Aim: Protected areas have become pivotal to the modern conservation planning toolbox, but a limited understanding of marine macroecology is hampering their efficient design and implementation in pelagic environments. We explored the respective contributions of environmental factors and human impacts in capturing the distribution of an assemblage of commercially valuable, largebodied, open-water predators (tunas, marlins and mackerels).
Location: Western Australia.
Time period: 1997–2006.
Major taxa studied: Pelagic fishes.
Methods: We compiled 10 years of commercial fishing records from the Sea Around Us Project and derived relative abundance indices from standardized catch rates while accounting for confounding effects of effort, year and gear type. We used these indices to map pelagic hotspots over a 0.58-resolution grid and built random forests to estimate the importance of 33 geophysical, oceanographic and anthropogenic predictors in explaining their locations. We additionally examined the spatial congruence between these hotspots and an extensive network of marine reserves and determined whether patterns of co-occurrence deviated from random expectations using null model simulations.
Results: First, we identified several pelagic hotspots off the coast of Western Australia. Second,
geomorphometrics explained up to 50% of the variance in relative abundance of pelagic fishes, and submarine canyon presence ranked as the most influential variable in the North bioregion. Seafloor complexity, geodiversity, salinity, temperature variability, primary production, ocean energy, current regimes and human impacts were also identified as important predictors. Third, spatial overlap between hotspots and marine reserves was limited, with most high-abundance areas primarily found in zones where anthropogenic activities are subject to few regulations.
Main conclusions: This study reveals geomorphometrics as valuable indicators of the distribution of mobile fish species and highlights the relevance of harnessing static topography as a key element in any blueprint for ocean zoning and spatial management.
O FISH WHERE ART THOU …
Pelagic fish hotspots derived from the Sea Around Us data. Hotspot probability was calculated as the frequency with which each grid cell was selected as a hotspot across 100 Bootstrap iterations, with darker tones denoting higher values. Figure: Bouchet et al 2017.
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