Factors affecting the seasonal distribution and biomass of E. pacifica and T. spinifera along the Pacific coast of Canada: A spatiotemporal modelling approach

Abstract

Euphausiids are a keystone species in coastal food webs due to their high lipid content and seasonally high biomass. Understanding the habitat and environmental drivers that lead to areas of high biomass, or ‘hotspots’, and their seasonal persistence, will support the identification of important foraging regions for mid- and upper- trophic level predators. We quantify the distribution of hotspots of the two dominant species of euphausiid in the north-east Pacific Ocean: Euphausia pacifica and Thysanoessa spinifera, as well as euphausiid larvae (mixed species). The Canadian coast encompasses the northern California Current Ecosystem and the transition zone to the Alaska current, and is a highly productive region for fisheries, marine mammals, and seabirds. We used spatiotemporal modelling to predict the distribution of these three euphausiid groups in relation to geomorphic and environmental variables during the important spring-summer months (April through September) when euphausiid biomass is highest. We quantified the area, intensity, and persistence of biomass hotspots across months according to specific oceanographic ecosections developed for marine spatial planning purposes. Persistent hotspots of both adult species were predicted to occur along the 200 m depth contour of the continental slope; however, differences were predicted on the shallower Dixon shelf, which was a key area for T. spinifera, and within the Juan de Fuca Eddy system where E. pacifica hotspots occurred. The continental slope along the west coast of Vancouver Island was the only persistent hotspot region common between both adult species and euphausiid larvae. Larval distribution was more correlated with T. spinifera than E. pacifica biomass. Hotspots of adults were more persistent across months than hotspots of euphausiid larvae, which were seasonally patchy. The persistence of biomass hotspots of forage species through periods of low overall biomass could maintain trophic connectivity through perturbation events and increase ecosystem resilience to climate change.

The influence of temperature on Pacific hake co‐occurrence with euphausiids in the California Current Ecosystem

“…Columbia while E. pacifica are more likely to form hotspots near the Juan de Fuca eddy system (Evans et al, 2021). Thus, the lower predicted hake-krill co-occurrence near the Juan de Fuca eddy system may relate to species-specific differences in krill aggregations.…”

“…The lack of predicted hake‐krill co‐occurrence in this area may be due to interannual variation in the northern extent of hake migration, or variation in hake distributions near the numerous submarine canyons and shallow banks in the area. There is evidence that hake preferentially consume T. spinifera over E. pacifica (Emmett & Krutzikowsky, 2008; Tanasichuk, 1999), and recent research suggests that T. spinifera hotspots are more often located in northern British Columbia while E. pacifica are more likely to form hotspots near the Juan de Fuca eddy system (Evans et al, 2021). Thus, the lower predicted hake‐krill co‐occurrence near the Juan de Fuca eddy system may relate to species‐specific differences in krill aggregations.…”

Acoustic and visual cetacean surveys reveal year-round spatial and temporal distributions for multiple species in northern British Columbia, Canada

“…The increase in blue whale detections off Gwaii Haanas in September coincides with high primary productivity in the fall, likely fueling high zooplankton abundance. In BC, hotspots of the zooplankton Euphausia pacifica and Thysanoessa spinifera , the most abundant euphausiid species in the northeast Pacific Ocean and preferential prey for blue whales, also peak in September and were highest over the continental slope, particularly off the west coast of HG (data were from April to September 43 ). Our finding that blue whale A-B vocalizations are associated with location, SST and chl-a concentration was consistent with other studies that linked blue whale distribution patterns to seasonally productive waters associated with high chl-a 44 .…”

“…13). Blue whales (38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55), fin whales (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27), and humpback whales (50-2000 Hz) to a lesser extent, were the main contributors to the winter soundscape. Blue whales have a great acoustic power 118 , and their call repertoire includes intense, low frequency, long-duration continuous calls 119 .…”

Canyon Downwelling and Water Mass Influences on Winter Zooplankton Distributions in the Coastal Northeast Pacific

“…), and chaetognaths (Sagitta sp.) (Evans et al, 2021;Mackas, 1984Mackas, , 1992Mackas et al, 1997). The presence of these zooplankton species varies with the water types present (Mackas et al, 1985(Mackas et al, , 2001.…”