Nearly 18% of Gray Whales Entering San Francisco Bay Die There, Sonoma State University Study Reveals

Alarming Findings from Sonoma State University-Led Research on Gray Whale Mortality

Gray whales, the majestic migrators of the Eastern North Pacific (ENP), are facing unprecedented challenges as climate change disrupts their traditional foraging grounds in the Arctic. A groundbreaking study led by graduate student Josephine M. Slaathaug from Sonoma State University's Department of Biology has revealed that nearly 18% of these whales entering San Francisco Bay do not survive the visit. Published on April 13, 2026, in Frontiers in Marine Science, the research highlights how vessel strikes and malnutrition are turning this urban waterway into a deadly trap. 88 86

From 2018 to 2025, researchers cataloged 114 unique gray whales in the Bay using photo-identification techniques, matching unique scars and pigmentation patterns. Shockingly, 21 of these individuals were later confirmed dead in the region, yielding a minimum mortality rate of 18.2%. This figure likely underestimates the true toll, as many carcasses sink or decompose before detection. Of the examined carcasses—70 in total—43% showed blunt or sharp force trauma indicative of vessel collisions. 88

The study, co-authored by Sonoma State professor Daniel E. Crocker and collaborators from The Marine Mammal Center and Cascadia Research Collective, underscores the vulnerability of these 'mystery whales' not affiliated with known foraging subgroups like the Pacific Coast Feeding Group (PCFG) or Sounders. Only 7% matched these groups, suggesting most are traditional ENP migrants desperately seeking food.

Climate Change: Driving Gray Whales into Urban Danger Zones

Gray whales (Eschrichtius robustus) undertake one of the world's longest migrations, traveling 10,000-14,000 miles round-trip from Baja California breeding lagoons to Arctic feeding areas. They rely on amphipod-rich benthic sediments for 90% of their caloric intake during summer foraging. However, marine heatwaves and sea ice loss have decimated prey populations, leading to a 52% population decline since 2016 and the NOAA-declared Unusual Mortality Event (UME) from 2019-2023, with 690 strandings. 0

This nutritional stress manifests as 'skinny whales'—emaciated individuals with visible bones and sunken heads—prompting opportunistic foraging along the migration route. San Francisco Bay, not historically a stopover, saw its first seasonal influx in 2018. Peak entries occurred in 2025 with 36 whales, often in groups of 10+, lingering for weeks (average minimum stay 27.6 days in 2023). 88 Slaathaug notes, "San Francisco Bay is a highly trafficked waterway, and the Golden Gate Strait serves as a bottleneck." Foggy conditions exacerbate visibility issues for low-profile surfacing whales. 86

Co-author Rebekah S. Lane from the Center for Coastal Studies emphasizes, "The climate crisis is driving starving gray whales into busy San Francisco Bay, where they are hit and killed by vessels." This shift illustrates broader ecosystem disruptions, with implications for marine mammal conservation worldwide.

The Research Methods: Photo-ID and Necropsy Insights from Sonoma State Team

Slaathaug's master's thesis at Sonoma State formed the backbone of this study. Data came from vessel-based surveys using a 7.6m rigid-hull inflatable boat equipped with DSLR cameras and Mysticetus software for real-time photo-ID. Surveys targeted central Bay from February-June, supplemented by citizen science submissions, whale-watch logs, and U.S. Coast Guard reports. Flank, dorsal, and fluke features enabled cataloging 114 whales, with 503 matches to external databases. 88

Carcass matching required ≥3 unique marks and >60% skin visibility. Necropsies, funded by NOAA grants, revealed causes: vessel trauma in 43% of cases. Statistical models in R (linear mixed-effects for stay length, multinomial logistic for mortality predictors) showed subgroup affiliation reduced death risk, but overall, ENP whales fared poorly.

This rigorous, multi-year effort exemplifies interdisciplinary higher ed research, blending Sonoma State's biology expertise with field conservation at The Marine Mammal Center.

Recent Spike: Six Deaths in Early 2026 Signal Ongoing Crisis

Just weeks before publication, six gray whales perished in SF Bay from mid-March to early April 2026, mirroring patterns since 2018. Additional strandings—a malnourished whale in Oregon and one in Washington's Willapa River—highlight range-wide distress. In 2025 alone, 70 regional deaths were recorded, 30 from vessel strikes. 87

Named individuals like 'Oreo' (TMMC-1-66) and 'Ladybug' illustrate tragedies: Oreo struck near Crissy Field, Ladybug necropsied with trauma. Sub-lethal injuries compromise future survival, compounding malnutrition effects.

Sonoma State University's Role in Marine Mammal Research

Sonoma State University, located in Rohnert Park, California, has emerged as a hub for cetacean studies through its Biology Department. Slaathaug's NSF Graduate Research Fellowship-funded work, supervised by Prof. Daniel E. Crocker—a veteran in marine physiology—demonstrates how public universities contribute to urgent conservation science. Crocker's prior research on elephant seal diving and stress responses informs whale health assessments.

Funding from California State University’s Council on Ocean Affairs, Science, and Technology (CSU COAST) supported surveys, bridging academia and fieldwork. This study, stemming from Slaathaug's Marine Mammal Center internship, highlights grad student-led innovation addressing real-time ecological crises. 129

Such projects position Sonoma State as a leader in applied marine biology, training future researchers amid declining populations.

Photo by Mohit Kumar on Unsplash

Vessel Strikes: The Primary Killer in Busy Bay Waters

San Francisco Bay's 100,000+ vessels annually—cargo ships, ferries, fishing boats, kayaks—create a high-risk zone. The Golden Gate bottleneck funnels traffic past foraging whales. Necropsies confirmed vessel trauma in 9/11 matched cases; overall, 43% of 70 carcasses bore propeller scars or fractures.

Fog reduces visibility; whales' low profile (surfacing briefly) evades detection. Studies on humpbacks show 10-knot speed limits cut strikes by 80%.The full open-access paper details necropsy protocols. 88 Voluntary NOAA guidelines exist, but enforcement lags.

• High-speed ferries: Primary threat due to routes overlapping hotspots.
• Recreational vessels: Increasing with tourism.
• Cargo ships: Propeller gashes common in strandings.

Malnutrition and Ecosystem Shifts: Root Causes Exposed

Arctic prey crashes from 2018 'The Blob' heatwave persist. Gray whales lost 46% body mass during migration, arriving emaciated. Bay foraging targets crabs/amphipods, but yields insufficient calories. Thin whales (skinniness score >2) dominate sightings, with no calves observed—critical for rebound.

Range expansion risks novel threats; low interannual resights (3.5%) suggest failed adaptation. PCFG/Sounders thrive better, hinting behavioral learning absent in ENP migrants.

Conservation Recommendations: Speed Zones, Tech, and Collaboration

Slaathaug advocates dynamic 10-knot zones February-June, AI detection (e.g., WhaleSafe), ferry rerouting. Expand Biologically Important Areas; mandate necropsy tows for photo-ID matching. Lane stresses, "Route changes and speed restrictions significantly reduce mortality." 86

• Implement mandatory slow zones via Port authority.
• Enhance reporting apps for sightings.
• Fund university-led monitoring (e.g., Sonoma State's expansions).
• International Arctic protection to restore prey.

Success in other areas (e.g., Santa Barbara) proves feasible.

Stakeholder Perspectives: From Researchers to Regulators

The Marine Mammal Center's Barbie Halaska notes necropsy challenges. NOAA monitors UME closure but urges vigilance. Local ports (Oakland voluntary 10-knots) collaborate, yet gaps remain. Conservationists push lawsuits over inaction. 87

Sonoma State's work empowers policy; Crocker's expertise aids modeling.

Broader Implications for Marine Ecosystems and Higher Ed Research

Gray whale plight signals biodiversity crisis; prey loss cascades to fisheries. Universities like Sonoma State exemplify vital roles in citizen science, training MS/PhD students for NOAA careers. Future studies: drone thermal imaging, genetics for subgroup ID.

As populations hover near historic lows, adaptive strategies must evolve.

Photo by Aavron delos Santos on Unsplash

Future Outlook: Hope Through Science and Action

With NSF/CSU backing, Sonoma State's trajectory promises continued leadership. Urgent: Enforce protections before 2027 migration. Public awareness via apps fosters stewardship. Recovery possible if Arctic rebounds and Bay risks mitigated—gray whales' resilience endures.