Mammals Blog

Harbor seals are year-round residents of San Francisco Bay Area waters. But they don't just stay in the water. They also need safe places to come ashore to rest, shed their fur, and raise their young. They “haul out” in several coves, lagoons, and estuaries along the coast, and at many sites within the San Francisco Bay.

It’s tough for a park to conserve wildlife habitat and support sensitive species when no one is quite sure what creatures live there. Nor is it easy to learn what lives where when so many species' superpowers include avoiding human observation. Early on, such challenges weighed on biologists working at Rancho Corral de Tierra, which became part of Golden Gate in 2011. But now, answers are on the horizon. In August 2023, we launched the San Mateo Wildlife Inventory project.

On one memorable nighttime visit to Redwood Creek in Muir Woods, I met with several National Park Service and US Geological Survey biologists to learn about and photograph their bat research. Turns out it’s a good place to catch bats that like to hunt along the creek for mosquitos, flies, and beetles. In the last few moments of sunlight, we set up four mist nets (loose, nearly invisible mesh nets) over different parts of the creek and crossed our fingers.

Visitors to Bay Area coastlines might spot cautious, curious harbor seals snoozing on rocks or sandbars any time of year. But annual harbor seal monitoring efforts focus on the pupping and molting seasons, from March to July. This is when the seals spend greater amounts of time hauled out of the water. With the 2023 pupping season peak now past, we have counted fewer pups than average across all Marin County haul out sites.

Through acoustic monitoring, winter mist netting, and summer radio telemetry, researchers have started to describe Bay Area bats’ habitat preferences, roosting sites, and more. But there’s a whole other black hole of bat knowledge that they’re just now beginning to peer into: bat migrations. This fall, the team started leveraging an automated wildlife tracking system for the first time to better understand bats’ journeys as they migrate through—and beyond—local parks.

Researchers studying pinnipeds (seals and sea lions) have long noted marine algae sometimes growing on their fur. But few had studied the phenomenon. Dr. Floyd Hayes, struck by a few seals in Bodega Bay with large mats of algae on their backs, decided to investigate. He and researchers from the San Francisco Bay Area Network and Point Reyes National Seashore found that at least eight genera of photosynthetic algae attach to six different pinniped species.

After a long hiatus due to concerns of the unknown risk of transferring COVID-19 from humans to bats, the Marin Bat Monitoring Project team was finally able to safely resume the bat-handling portion of our research this summer.

Last year, COVID-19 meant that biologists weren’t able to do their usual harbor seal surveys at park sites throughout Marin County. The few surveys they were able to do left them with more questions than answers. Namely, where did a large portion of Drakes Estero’s seal population disappear to? This year, the monitoring team hoped to find clues. But with the 2021 season now wrapping up and countywide harbor seal counts below average, some of the mystery remains.

Since 2017, One Tam partners have been collaborating with USGS to conduct the first countywide bat monitoring program in Marin. This October, we dove in to the results from last winter's roost site monitoring, and discussed the implications of what park researchers have learned from three years of bat monitoring.

The evolutionary record from previous climate perturbations indicates that marine mammals are highly vulnerable but also remarkably adaptable to climatic change in coastal ecosystems. Consequently, national parks in the Pacific, from Alaska to Hawaii, are faced with potentially dramatic changes in their marine mammal fauna, especially pinnipeds (seals and sea lions).