Predictive Models of Cetacean Densities in the California Current Ecosystem, 2020b

To develop improved species distribution models (SDMs) and to update US West Coast cetacean stock abundance estimates, sighting data from NOAA’s Southwest Fisheries Science Center 2018 California Current Ecosystem Survey were combined with previous line-transect survey data collected within the study area to create a robust modeling database spanning more than 25 years (1991–2018). Habitat models were developed based on previously established methods that allow for the incorporation of segment-specific estimates of detection probability and included dynamic covariates from an ocean model calibrated to the California Current Ecosystem study area. In addition, recently-developed techniques for deriving more comprehensive estimates of uncertainty in SDM predictions were used to provide variance estimates for the model-based abundance estimates. SDMs were developed for short-beaked common dolphin (Delphinus delphis delphis), long-beaked common dolphin (Delphinus delphis bairdii), northern right whale dolphin (Lissodelphis borealis), Pacific white-sided dolphin (Lagenorhynchus obliquidens), striped dolphin (Stenella coeruleoalba), common bottlenose dolphin (Tursiops truncatus), Risso’s dolphin (Grampus griseus), Dall’s porpoise (Phocoenoides dalli), sperm whale (Physeter macrocephalus), blue whale (Balaenoptera musculus), fin whale (B. physalus), humpback whale (Megaptera novaeangliae), Baird’s beaked whale (Berardius bairdii), and a “small beaked whale guild” that included Mesoplodonts (Mesoplodon spp.) and Cuvier’s beaked whale (Ziphius cavirostris). Sample sizes were also sufficient to develop the first model-based density estimates for minke whale (B. acutorostrata) in this study area.