Modeling changes in baleen whale seasonal abundance, timing of migration, and environmental variables to explain the sudden rise in entanglements in California

PLoS One. 2021 Apr 15;16(4):e0248557. doi: 10.1371/journal.pone.0248557. eCollection 2021.

Abstract

We document changes in the number of sightings and timing of humpback (Megaptera novaeangliae), blue (Balaenoptera musculus), and gray (Eschrichtius robustus) whale migratory phases in the vicinity of the Farallon Islands, California. We hypothesized that changes in the timing of migration off central California were driven by local oceanography, regional upwelling, and basin-scale climate conditions. Using 24 years of daily whale counts collected from Southeast Farallon Island, we developed negative binomial regression models to evaluate trends in local whale sightings over time. We then used linear models to assess trends in the timing of migration, and to identify potential environmental drivers. These drivers included local, regional and basin-scale patterns; the latter included the El Niño Southern Oscillation, the Pacific Decadal Oscillation, and the North Pacific Gyre Oscillation, which influence, wind-driven upwelling, and overall productivity in the California Current System. We then created a forecast model to predict the timing of migration. Humpback whale sightings significantly increased over the study period, but blue and gray whale counts did not, though there was variability across the time series. Date of breeding migration (departure) for all species showed little to no change, whereas date of migration towards feeding areas (arrival) occurred earlier for humpback and blue whales. Timing was significantly influenced by a mix of local oceanography, regional, and basin-scale climate variables. Earlier arrival time without concomitant earlier departure time results in longer periods when blue and humpback whales are at risk of entanglement in the Gulf of the Farallones. We maintain that these changes have increased whale exposure to pot and trap fishery gear off the central California coast during the spring, elevating the risk of entanglements. Humpback entanglement rates were significantly associated with increased counts and early arrival in central California. Actions to decrease the temporal overlap between whales and pot/trap fishing gear, particularly when whales arrive earlier in warm water years, would likely decrease the risk of entanglements.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animal Migration / physiology*
  • Animals
  • Aquaculture / methods*
  • Balaenoptera / physiology
  • California
  • Climate
  • Ecosystem
  • Humpback Whale / physiology
  • Models, Theoretical
  • Pacific Ocean
  • Seasons
  • Temperature
  • Whales / physiology*

Grants and funding

JJ, NN, KBI, and the biologist collecting data on the Farallon Islands received support from the Paul Angell Family Foundation, Bently Foundation, Boring Family Foundation, California Sea Grant, Campini Foundation, David and Lucile Packard Foundation, Elinor Paterson Baker Trust, Firedoll Foundation, Faucett Catalyst Fund, Giles W. and Elise G. Mead Foundation, Hellman Family Foundation, Kimball Foundation, Marisla Foundation, Moore Family Foundation, National Fish and Wildlife Foundation, Pacific Life Foundation, Resources Legacy Fund, RHE Charitable Fund, Thelma Doelger Trust, The Volganeau Foundation, and the many Point Blue donors who have helped fund wildlife monitoring on the Southeast Farallon Island. KBI also received support from the Council on Ocean Affairs, Science, and Technology (COAST), the American Cetacean Society – San Francisco Chapter (ACS), and the Estuary and Ocean Science Center Scholarship and Student Association.