Introduction & Objectives

Cetacean distribution, density, and abundance in the Southern California Bight were assessed through visual and acoustic surveys during thirteen California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises. The CalCOFI marine mammal monitoring program examines seasonal and inter-annual patterns in density, abundance, and distribution on a longer continuous time scale and with a higher rate of sampling than previous cetacean surveys off the California coast, particularly for the winter and spring periods, for which there are currently few data available. 

Technical Approach

Visual monitoring incorporated standard line-transect protocol during all daylight transits, while daytime acoustic monitoring employed a towed hydrophone array during transits and sonobuoys deployed at oceanographic sampling stations. 

Progress & Results

Cetacean distribution, density, and abundance in the Southern California Bight were assessed through visual and acoustic surveys during four California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises from fall 2022 to summer 2023. Visual monitoring incorporated standard line-transect protocol during all daylight transits, while daytime acoustic monitoring employed sonobuoys deployed at oceanographic sampling stations. Visual effort included 534 observation hours covering 4,104 kilometers. A total of 352 sightings were made, which included 12 different cetacean species. Acoustic effort included 233 sonobuoy deployments.

Fin whales and humpback whales were the most frequently sighted mysticetes. Humpback whales were observed year-round, while fin whales were observed in the fall, winter, and summer. Blue whales were observed during summer and fall. Gray whale sightings only occurred during winter and spring, and minke whales were sighted fall, winter, and spring. Short-beaked and long-beaked common dolphins were the most frequently encountered odontocetes, while bottlenose dolphins were also observed somewhat regularly. Seasonally, short-beaked common dolphins were most abundant in winter and spring, whereas long-beaked common dolphins were most abundant in summer and fall. Sightings of Pacific white-sided dolphins only occurred in the spring, whereas Risso’s dolphins were encountered in the winter and spring. 

From July 2016 – July 2019, visual effort included 1,010 observation hours covering 19,295 kilometers. A total of 913 sightings were made, which included 13 different cetacean species. Acoustic effort included 682 sonobuoy deployments and 329 towed array deployments. 

Blue whales, fin whales, and humpback whales were the most frequently sighted mysticetes. Blue whales were primarily observed during summer, while fin whales and humpback whales were observed year-round. Gray whale sightings only occurred during winter and spring, and minke whales were only sighted in summer. 

Short-beaked and long-beaked common dolphins were the most frequently encountered odontocetes, while Risso’s dolphins, Pacific white-sided dolphins, and bottlenose dolphins were also observed somewhat regularly. Seasonally, short-beaked common dolphins were most abundant in winter and spring, whereas long-beaked common dolphins were most abundant in summer and fall. Sightings of Pacific white-sided dolphins peaked in the spring, whereas Risso’s dolphins were never encountered during spring cruises. 

Beaked whale echolocation clicks were only detected on one occasion in towed array recordings collected between 2008 and 2019. The low acoustic encounter rate of beaked whales in this dataset may be linked to the continuous use of shipboard echosounders during CalCOFI cruises. 

Publications:

Becker, E.A., K.A. Forney, B.J. Thayre, K. Whitaker, R. Hoopes, J.M. Jones, J.A. Hildebrand, and J. Moore. 2025. Evaluating seasonal vs. spatial extrapolation for cetacean distribution models in the California Current
Marine Mammal Science 41(4):e70030.

Becker, E., K.A. Forney, B.J. Thayre, A.J. Debich, G.S. Campbell, K. Whitaker, A.B. Douglas, A. Gilles, R. Hoopes, and J.A.Hildebrand. 2017. Habitat-based density models for three cetacean species off Southern California illustrate pronounced seasonal differences. Frontiers in Marine Science 4:121. doi: 10.3389/fmars.2017.00121

Soldevilla, M.S., S. Baumann-Pickering, D. Cholewiak, L.E.W. Hodge, E.M. Oleson, and S. Rankin. 2017. Geographic variation in Risso's dolphin echolocation click spectra. 

Journal of the Acoustical Society of America 142:599-617.
Campbell, G.S., L. Thomas, K. Whitaker, A.B. Douglas, J. Calambokidis, and J.A. Hildebrand. 2015. Inter-annual and Seasonal Trends in Cetacean Distribution, Density and Abundance off Southern California. Deep-Sea Research II 112:143-157.