Endangered Fish Finds New Habitat at Muir Beach Lagoon

By Science Communication Specialist Jessica Weinberg McClosky, San Francisco Bay Area Inventory & Monitoring Network

December 2023 - Aquatics Intern Matt Millado was surveying turtles at Muir Beach Lagoon this summer when he spotted a small fish he didn’t recognize. So he brought the fish to Aquatic Ecologist Darren Fong to take a closer look. Fong could tell that the fish was some kind of goby—and perhaps even a federally endangered tidewater goby (Eucyclogobius newberryi). So, they snapped a photo to send to experts for their identification advice.

Tidewater gobies live in brackish (somewhat salty) wetland habitats. Coastal lagoons are perfect. But scientists had not seen them before in Muir Beach Lagoon despite decades of fish surveys there. Eager to confirm the goby’s identity, Fong and Millado returned to the lagoon with a seine net to see if they could catch one. They caught several! Fong was able to confirm that the little, elongated fish were in fact tidewater gobies. They took better photos, collected a voucher specimen, and returned their fishy friends to the lagoon.

Fong hopes that genetic analysis of the voucher sample will help solve the mystery of where the tidewater gobies came from. At no more than two inches long and at home in calm waters, they are not exactly strong swimmers. But tidewater gobies can survive being swept out to sea. When this happens, some may find their way back into nearby coastal lagoons or wetlands. Tomales Bay’s Giacomini Wetlands and Rodeo Lagoon host the most likely source populations for Muir Beach Lagoon’s newest residents.

If tidewater gobies love lagoons and can occasionally disperse along the coast, one might wonder: Why had no one found them in Muir Beach Lagoon before? Tidewater gobies are endangered today primarily due to habitat loss from human development and land use. Muir Beach Lagoon was probably lost to the gobies during the 20^th century when much of the surrounding area was filled in and re-shaped to accommodate cattle grazing.

Scientists suspect the gobies’ return has to do with the recent restoration work at Muir Beach. One major component of the restoration was expansion of the small tidal lagoon. This created additional open water habitat with aquatic vegetation that benefits other threatened and endangered species too—like California red-legged frogs and juvenile coho salmon. Improving habitat for some tends to improve habitat for many. These gobies were fortunate to find a much healthier lagoon ecosystem at Muir Beach than what they would have encountered 10 or 15 years ago.

The San Francisco Bay Area Network’s coho and steelhead monitoring team will help Fong keep track of the new Muir Beach Lagoon goby population as part of its regular monitoring work. Everyone is excited and hopeful that the charming little fish will persist. Getting some habitat back following such widespread habitat loss is a big deal. There is also relief in knowing that the gobies have their eggs in one more basket, so-to-speak. If one population were to suffer a die-off—maybe due to an algae bloom or a drought—there will be another nearby to help replenish it.

For more information

• Visit the Pacific Coast Science & Learning Center's Tidewater Goby page
• Contact Aquatic Ecologist Darren Fong or Fishery Biologist Michael Reichmuth

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