Fish in the Bay – May 2025, WRMP San Pablo Bay Trawls, Part 3 – Gallinas Creek to Hamilton Wetlands.

May 22, 2025 Jim Ervin
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Fieldwork, Fish in Lower South Bay, News

This is part 3 of the San Pablo Bay series.  We continue our journey around San Pablo Bay. This time we moved just south of the Petaluma River area described in Part 2.  Once again, this post summarizes results from fish monitoring trawls in both April and May.

  • We are still in unfamiliar territory.  This blog post is as much about the new places we visit as the creatures we meet here.  

April results:

  • Many Mysids – Like Petaluma in the previous post, the Hamilton-to-Gallinas marshes appeared to support a robust Mysid bloom in April.  Mysids are the “secret sauce” for pelagic fish recruitment.
  • 274 Baby Anchovies & 41 Baby Herring – These are the highest Anchovy/Herring totals so far in the San Pablo Bay series.  We caught ZERO Anchovies in Napa marshes in April, only 10 near Petaluma, and only 35 in Lower South Bay (LSB) in the same month.
    • Hamilton-to-Gallinas marshes were clear baby Anchovy & Herring winners in April.      
  • Baby Fish Month – In April, we caught 137 baby gobies here, 11 in Petaluma, 1 in Napa, 264 at Eden Landing, and 308 in LSB – mostly in upstream segments. (Remember, all trawls performed outside of LSB are 5-minute duration.  LSB trawls are 10-minutes each.  Multiply North Bay and Eden Landing trawl results by two for a rough “Catch Per Unit Effort” (CPUE) comparison with LSB.)   
    • These April results indicate that South SF Bay (LSB + Eden Landing) may support higher Goby recruitment.

May results:

More Mysids – The Mysid total increased to 9070 in May.  High totals in Hamilton and Gallinas areas contributed to most of the jump. 

1. Hamilton Wetlands.

Alex Lama at station Ham1 on 23 April 2025.  Big white buildings in the background are former aircraft hangars of Hamilton Air Force Base.

Hamilton Wetlands is the northmost restoration area in this segment.  It was part of an Air Force Base from the 1920s until the mid-1970s and then an Army Airfield until 1988.  Now, it is a restoring wetland.

  • Hamilton Wetlands Restored! – 2014  https://scc.ca.gov/2014/04/28/hamilton-wetlands-restored/  “On Friday, April 25, 2014, the Coastal Conservancy and Corps of Engineers took the final step in the restoration of Hamilton Airfield to tidal marsh habitat, breaching the levee that has separated Hamilton from the Bay for over a century.  Bay waters flowed in and the crowd cheered!  Hamilton is a 648-acre wetland restoration project in Novato along the Marin shoreline.  Formerly an Army Airfield, the site was cleaned up and then filled with 5.6 million cubic yards of dredged material, mostly from the Port of Oakland, to raise the elevation and speed conversion to tidal marsh habitat.”  
  • Marin County wetlands rise again in Hamilton airfield restoration – 2014. https://www.sfgate.com/bayarea/article/marin-county-wetlands-rise-again-in-hamilton-5430696.php “Schuchat said the conservancy will now turn its attention toward restoring 1,850 acres north of the airfield, … It is part of what he called a “renaissance” of bay wetlands restoration going on right now, including 900 acres at Sears Point in Sonoma County, 600 acres in Vallejo, 10,000 acres of former salt ponds in the Napa-Sonoma Marsh and 15,000 acres of salt ponds in the South Bay.”

At this point, Hamilton Wetlands is primarily a large open-water lagoon (at high tide at least.)  It is a hunting ground for young adult Striped Bass.

Striped Bass count = 15 in April, 5 in May.  Half of all Bass from Hamilton to Gallinas were caught at the four “Ham” stations.  Food production is high here. Bass follow the food. 

California Halibut count = 4 in April, 6 in May.  Halibut shown above were the only two caught in Hamilton Wetlands.  All the others were netted farther south at Gallinas Creek or China Camp stations.

  • Young Halibut recruit in shallow marshes and gradually migrate out into the deeper bay and coastal ocean as they grow.

Northern Anchovy count = 274 in April, 63 in May.  Anchovy numbers decreased from April to May as baby Anchovies that hatched late in 2024 grew up and moved on.  A new cohort of summertime spawning adults was starting to show up by May.    

  • Most Anchovies in this region, in both April and May, were caught at “Outside” stations, e.g. HamO, MCIO, MilO, and ChiO.  It will be interesting to follow the Anchovy spawn in this area over the rest of the warm season.

Mysid Count = 7401 in April, 9070 in May.  The Gallinas-to-Hamilton OLU is a significant Mysid factory.  These tiny shrimp-like bugs feed almost every type of fish at every age.  

  • Big Mysid blooms were observed at stations Ham3, Gal1, and Gal2 in May. 

2. McInnis Marsh.

We sample McInnis Marsh restoration areas from a single “outside” station: MICO.  Some of the restoration work is either in progress or still planned according to county websites.

English Sole count = 0 in April, 5 in May.  Five Sole were found at station MICO in May and nowhere else in this area.  Baby Sole arrive in the Bay around December to January.  They retreat back to the ocean as summer approaches.

Pacific Herring count = 41 in April, Zero in May.  (Herring not shown here – 11 of the 41 in April were caught at MICO.)     

3. Miller Creek.

Miller Creek carries treated wastewater discharged by the Las Gallinas wastewater treatment plant. Results here were at least good, or better than most other upstream stations in this area. 

  • Many mysids, five young Herring, and four Striped Bass were caught at station Mil1 in April. 
  • In May, the fish count included “Unidentified Gobies/Larval fishes” and a female Bat Ray who was seeking a safe place to give birth to her litter of pups. 

The treatment plant is managed by the Las Gallinas Valley Sanitation District.  https://www.calopps.org/las-gallinas-valley-sanitary-district 

“Las Gallinas Valley Sanitary District (LGVSD) is located in the Las Gallinas Valley between central San Rafael and Novato. In 1955, our original wastewater treatment plant was constructed to address health problems associated with failing septic tanks in Santa Venetia. … Major plant expansions were built in 1958, 1972 and 1984. The latter increased capacity to 2.92 million gallons per day.  Today, LGVSD serves 32,000 customers in the northern San Rafael area and manages approximately 105 miles of collection lines.” 

The outside station of Miller Creek (MilO) hosted Crangon Shrimp, baby Gobies, and baby Anchovies in April.  Four young Starry Flounder and more baby Anchovies were caught there in May.

4. Gallinas Creek.

Catches in Gallinas Creek and the offshore station ChiO were more diverse and interesting.  The vast majority of baby Anchovies (204) were caught at ChiO in April.  Baby White Croakers were observed here in both April and May.  A Sacramento Splittail and a baby Brown Rockfish were caught here as well. 

Another big female Bat Ray was netted at station Gal2 in May.  Sami and Alex removed a small fishing lure that was snagged in her mouth.

  • She was really big: 730 mm standard length!  Like the other mama Bat Rays, she was looking for a safe place at the mouth of Gallinas Creek to birth her young. 

Mysid and Corbula Clam counts were higher at Gallinas than most other stations in both April and May.  Microscopic food must be abundant here.

5. A New Hydrozoan.

Maeotias marginata count 1 in April, 8 in May.  At first glance, these plum-sized jellies look like jumbo-sized ctenophores (Comb Jellies).  They reveal their true shapes in the photarium as “bouncing bells” – medusa-type jellies.  

New Creature of the Month!  The UC Davis crew tentatively identified these as Maeotias marginata, a hydrozoan. Maeotias look strikingly similar to Polyorchis penicillatus that we sometimes in LSB. (Polyorchis is the “Red-eyed Medusa,” also a hydrozoan.)  These new Maeotias jellies have no red eyes and a slightly different shape. 

  • Sealifebase – Maeotias marginata.  https://www.sealifebase.se/summary/Maeotias-marginata  “Distribution:  Black Sea: Sea of Azov. Introduced in Atlantic and Pacific Oceans. …
    Biology: This is a true brackish water species (Ref. 128415). Medusae released in late spring and early summer and rest on the bottom to feed on small crustaceans (Ref. 2376).”
  • Maeotias per Wikipedia. https://en.wikipedia.org/wiki/Maeotias  “Maeotias marginata, commonly known as the Black Sea jellyfish or brackish water hydromedusa …  It has been recorded in several other estuarine locations around the world and is regarded as an invasive species.

    … specimens have also been found in the Netherlands (1962), France (1971) and the Pacific coast of North America, where it was found in the estuaries of the Petaluma and Napa Rivers flowing into San Francisco Bay in 1992 and 1993, and has since become established.

    M. marginata can reproduce both sexually and asexually, by budding. All individuals found in the Napa and Petaluma River population are male, and must have been produced asexually following the original introduction of perhaps a single male polyp.”
  • Bay Nature – Exotic Jellies in the Bay – 2009. https://baynature.org/article/exotic-jellies-in-the-bay/  “On a hot July afternoon last year, UC Davis graduate students Alpa Wintzer and Mariah Meek dipped glass jars and nets into Suisun Slough at Suisun City’s public dock in Solano County. They were capturing Maeotias marginata, small gelatinous creatures that look and act like jellyfish but technically aren’t (they’re hydrozoans, not true jellies). These jelly look-alikes, ranging in size from a large pea to a silver dollar, seemed to be everywhere and are beautiful to watch. They pump their bell-shaped bodies to the surface of the water, flip over, and float down, capturing zooplankton as their tentacles gently sway in the currents.

    … Originally hailing from the Black Sea, they were likely brought here in ballast water in the 1950s and have since made themselves at home in the Suisun Marsh and Napa and Petaluma Rivers.”

6. China Camp.

This station is named “China Camp” (ChiO) due to its location, but it could be thought of as “GalO.”  It is the “outside” station of Gallinas Creek.  13 of 20 White Croaker, Six of 10 Halibut, and both of the only Longfins in April/May were caught here.

  • China Camp State Park.  https://www.parks.ca.gov/?page_id=466 
    “A Chinese shrimp-fishing village thrived on this site in the 1880s. Nearly 500 people, originally from Canton, China, lived in the village. …  Fishermen by trade in their native country, they gravitated to the work they knew best. Over 90% of the shrimp they netted were dried and shipped to China or Chinese communities throughout the US.”
  • China Camp State Park per Wikipedia.  https://en.wikipedia.org/wiki/China_Camp_State_Park
    “In the late 1800s, the Chinese American fishermen of China Camp would catch 3 million pounds (1.4 million kilograms) of shrimp per year, … In 1914, a new net, the trawl, was invented, which made it possible for the Quans to resume their commercial shrimp fishing enterprise and process 5,000 pounds of shrimp per day.” 

Sadly, our six trawls of the Gallinas Creek basin, three each in April and May, netted only 798 Crangon shrimp; perhaps two pounds!!!  What more can we do to restore the historic productivity here? 

  • All Crangon were released after counting.

Fieldwork, Fish in Lower South Bay, News
Fieldwork, Fish in Lower South Bay, News