Continental‐scale hotspots of pelagic fish abundance inferred from commercial catch records

Abstract

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, large‐bodied, 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 0.5°‐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.

True blue: Temporal and spatial stability of pelagic wildlife at a submarine canyon

“…These results add to growing evidence that Perth Canyon is a habitat that supports relatively high abundances of pelagic fishes (Bouchet et al 2017) and aggregations of wildlife, including the pygmy and Endangered Antarctic blue whale Balaenoptera musculus intermedia (Double et al 2014, Nanson et al 2018). Our finding that the Perth Canyon pelagic assemblage is relatively spatiotemporally stable adds to the location’s ecological importance and suggests that strong, year‐round protection (i.e., IUCN II or above) could have major conservation outcomes for pelagic wildlife.…”

“…We considered an identical set of candidate explanatory variables (depth, aspect northing, rugosity, longitudinal curvature, cross‐sectional curvature, slope, slope variance, topographic position index, fractal dimension, and sea surface temperature mean and variance), in addition to daytime remote‐sensed chlorophyll a (mg/m 3 ), derived from 8‐day AQUA MODIS composite images available at 4 km resolution (Bouchet and Meeuwig 2015). Rugosity was included as a variable due to its well‐understood influence on surface productivity and prey availability, via upwelling, eddy formation, and diurnally migrating species (Rennie et al 2009, Bouchet et al 2017, Maggs et al 2019). Temperature and chlorophyll a values were sourced from the Environmental Data Connector (http://www.pfeg.noaa.gov/products/EDC/) and both seasonal means and variances calculated.…”

“…Sharks and other pelagic wildlife such as the black marlin Istiompax indica may display natal or regional philopatry, revisiting the same locations over time (Jorgensen et al 2010, Howey‐Jordan et al 2013, Rogers et al 2015). Mobile species also tend to migrate along prescribed highways (Horton et al 2017, Sequeira et al 2018) and use submarine canyons and other locations of topographical complexity as reliable and predictable foraging grounds (Bouchet et al 2017, Boerder et al 2019, Gilman et al 2019).…”

Submerged Carbonate Banks Aggregate Pelagic Megafauna in Offshore Tropical Australia

“…It also complements a growing body of research documenting the Timor Sea as a conspicuous and globally significant epicenter of biodiversity (Tittensor et al, 2010;Moore et al, 2017). Marine organisms commonly form predictable aggregations at sites of abrupt topography such as submarine canyons or seamounts (Nur et al, 2011;Aïssi et al, 2012;Garrigue et al, 2015;Bouchet et al, 2017;Sutton et al, 2019). The combined importance of seabed backscatter and water depth in our models suggests that the region's carbonate banks may play a similar role in attracting pelagic megafauna.…”

Transferable, predictive models of benthic communities informs marine spatial planning in a remote and data‐poor region

“…This result is significant because it suggests that positive conservation outcomes could be achieved in some situations on the basis of relatively rudimentary ecological knowledge, and is particularly pertinent given the rapid implementation of large, remote MPAs and the impediments to collecting ecological data in the marine realm. Our results suggest that predictive models such as these could provide important tools to identify key habitats, or biodiversity "hotspots," to maximize the effectiveness of large, remote reserves (see also Bouchet et al, 2017).…”