Intermittent upwelling impacts zooplankton and their gray whale predators at multiple scales

Coastal upwelling dynamics influence the abundance and distribution of marine zooplankton; however, knowledge of how intermittent upwelling patterns impact nearshore prey retention and predator foraging is limited. The Pacific Coast Feeding Group (PCFG) of gray whales forage between northern California and southern British Columbia from early June through the end of November. In Port Orford, Oregon, a subregion of the PCFG foraging range, gray whales demonstrate selection preference for prey patches consisting of elevated zooplankton abundance. Using a 6 yr data set, we characterized the influence of oceanographic conditions on zooplankton relative abundance and gray whale foraging effort in this subregion. Here, we tracked gray whale movements using a theodolite (263 tracklines) and simultaneously quantified prey availability through GoPro camera drops (n = 520) off a research kayak between July and August from 2016-2021. Boosted regression tree models assessed the influence of broad (seasonal) and fine (days to weeks) temporal scale upwelling metrics, sea surface temperature, and kelp condition on daily zooplankton abundance and gray whale foraging effort. Results show that at both temporal scales, environmental factors impact ecological response, with zooplankton abundance and gray whale foraging effort maximal at moderate values of upwelling and relaxation, highlighting the importance of intermittent upwelling. These findings document the role of intermittent upwelling on zooplankton availability and whale foraging effort in a nearshore system, which can improve conservation management of this region.