Linking oceanic variability, euphausiid hotspot persistence, and marine predator distribution along Canada's west coast.

Abstract

Understanding patterns of habitat use across trophic levels and the physical drivers of multispecies aggregations is essential to inform ecosystem-based management. To achieve this, we quantified the spatial distribution and co-occurrence of hotspots (defined using the Getis-Ord statistic) for euphausiids and nine of their commercially important fish and whale predators on the west coast of Canada during summer. We first developed fine-scale spatiotemporal distribution models of euphausiids and Pacific hake using high-resolution acoustic data from coast-wide surveys conducted between 2007 and 2018. We found that the spatiotemporal distribution of hotspots of euphausiids and hake was variable between years with low direct overlap (apart from 2017). The summer of 2015, during the 2014-2016 marine heatwave event, was a particularly anomalous year, as euphausiids and hake showed spatial mismatch in their biomass hotspot distributions. For the other eight predator species, predictions from published species distribution models were used to identify spatial hotspots as an average across years. Co-occurrence patterns were associated with the depth gradient across the shelf and slope and along the canyon and sea valley systems that characterize the Pacific coast of Canada. One assemblage was associated with the deeper parts (200-1000 m+) of the continental slope (euphausiids, hake, redbanded rockfish, sablefish, Pacific ocean perch, and humpback and fin whales) and a different assemblage (redstripe and yellowtail rockfish, and dogfish) was associated with the shallower shelf regions. Important ecological areas with co-occurring multispecies hotspots occurred along the west coast of Vancouver Island, the sea valleys of Queen Charlotte Sound, and the northwest coast of Haida Gwaii. Our results identify areas where multiple species aggregate, which can inform better management and hopefully protection of these regions that support complex food webs, commercial species, and large predators, and are therefore essential for overall ecosystem health.