One of the fundamental challenges in ecology is to quantitatively define a species’ habitat requirements and to evaluate the consequences of changes in habitat conditions to survival, growth, and production. Habitat quality varies in space and time, and can be summarized based on how it impacts organism foraging and growth. In terrestrial systems, these “energy landscapes” have been used to explain how habitat selection and foraging efficiency may be altered by global change. Here, we expand upon this concept by characterizing pelagic habitat quality as an “energy seascape”. We created an energy seascape for the northern portion of the California Current, a highly variable region characterized by large scale climatic patterns such as the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). We compiled vertical profiles of water temperature, dissolved oxygen, and salinity from several sites in the Pacific Northwest. These data were used to calculate an energy seascape based on bioenergetics models for adult Chinook salmon and albacore tuna between 1952 and 2016. We examined changes in energy seascapes in time and space to assess and predict how habitat quality responds to climate shifts.
Results/Conclusions
The energy seascape for salmon decreased by 57 percent after the El Niño event in 1987-1988 as compared to the years before the event. This event heralded the transition from a strong warm phase to a strong cool phase in both the ENSO and the PDO, and also corresponded to a decline in salmon landings. Inter-annual variability in the Chinook salmon energy seascape was related to the temperature regime and also to water column stratification and upwelling strength. Overall, results for Chinook salmon show that: 1) salmon energy seascapes differ both spatially and inter-annually; 2) salmon energy seascapes are limited by both water temperature and dissolved oxygen; and 3) energy seascapes can be used as an indicator for fish habitat quality in the pelagic ocean. Albacore tuna results will also be presented and compared to those of Chinook salmon to make some predictions for the future of these two commercially important fish species under climate change. We suggest that energy seascapes can be used to capture the variability in climatic forcing of ecosystems. Both conservation and ecosystem management can benefit from energy seascapes as a way to quantitatively understand changing habitat requirements in time and space.