Fish in the Bay – May 2025, WRMP San Pablo Bay Trawls, Part 1.

New WRMP San Pablo Bay trawls.  The UC Davis OGFL crew performed fish assessments of restored marsh areas around San Pablo Bay in April and May.  These trawls are part of the expanded Wetland Regional Monitoring Program (WRMP) that now takes us to new places around the northern fringes of San Francisco Bay.

• This part covers the Napa River marshes.  Parts 2, 3, and perhaps 4(?) will report similar results from Petaluma, Gallinas, and the Wildcat/San Pablo City areas. 
• Time is short.  This WRMP-inspired expansion represents roughly a tripling of UC Davis fish monitoring efforts in SF Bay.  We are already two months behind for blog reports!  Deep thoughts must wait. 
• Just fish facts and first impressions for now.

April.

• The first set of trawls of Napa marshes in April found large numbers of tiny baby Longfins at most stations. 
• Catches of Tule Perch and Prickly Sculpin also signaled that Napa River must be providing a strong reliable source of freshwater here.

May.

• Longfins largely petered out by May.  This is to be expected.  Adults stage to spawn in upstream marshes from November, at earliest, to March, at latest.  The young fry might hang out for a month or two after the spawn.  By summer, the fry must flee to cooler saltier waters.
• Tule Perch and Prickly Sculpin numbers increased by May.  This again suggests a robust source of freshwater from Napa River. 
• Striped Bass numbers also increased.  This is another good reason for small fishes, like baby Longfins and baby Herring, to flee this area.

Also note:  Two additional stations were added in May, Pond 3-1 and Pond 3-2, but the catches there had little effect on fish or bug totals.

1. Beautiful Fishes.

The catch at Steamboat Slough (station STE1) on 20 May:

• Top tray – Striped Bass. 
• Middle tray – Sacramento Sucker. 
• Bottom tray – Tule Perch

BTW: I was not present for these North Bay trawls in April or May.  Most of these photos were taken by Sami.  He has an excellent eye for fish photography.
 

Striped Bass counts = 7 in April; 20 in May.  Our old acquaintances, the Striped Bass, were well represented in Napa marshes in both April and May.  Many had suspiciously fat bellies.

Tule Perch count = 3 in April; 17 in May.  Tule Perch are part of the “Surfperch” family that ranges along the California coast.  Of the several members, they are the only species that live mostly in freshwater marshes.  – Surfperch  https://en.wikipedia.org/wiki/Surfperch 

Sacramento Sucker count = 1.  Only one native Sucker was seen in April.  Suckers are strictly freshwater fishes.  Salinity was around 5.5 ppt where he was caught.  More Suckers must live upstream!

More Tule Perch in May.

Tule Perch are ubiquitous natives in the Sacramento-San Joaquin Delta and around the fringes of north San Francisco Bay. 

• We are particularly interested in this fish.  Tule Perch have been all but extirpated in Lower South Bay (LSB).  A small surviving remnant population may still exist in downstream of Anderson Dam in San Jose.  (We last observed a Tule Perch in LSB in 2019!!!) 

Sacramento Splittail count = 1 in April; 13 in May.  Splittail are another California native fish of which those of us who live in LSB know little about. 

• According to reports, Splittails were last seen in Lower Coyote Creek, LSB, in 1980. 
• Fortunately, Splittail are still present and healthy-looking in North Bay marshes!

2. Little Pelagic Fishes.

Baby Herring at Mud2 on 22 April.

Pacific Herring count = 19 in April; 0 in May.  Adult Herring stage for their big annual spawn in San Francisco Bay in late winter.  Herring fry usually show up in March or April.  These young Herring stick around for a month or two before migrating out to the cooler deep blue sea. 

Longfin count = 424 in April; 2 in May.  These young recruits must have hatched a few weeks earlier.  There must be another Longfin spawning place just a little farther upstream. 

• Tiny glassy baby Longfins are hard to see.  Invisibility is their main defense at this stage of life.  Most will be eaten despite their invisibility.

Two Longfins caught in May.

Longfins recruit in Napa marshes.  This is very good news!

3. Gobies & Sculpins.

Shimofuri Goby count = 13 in April; 7 in May. 

• Shimos shown here appear to be males in breeding colors: bright white epaulettes, puffy cheeks, and many conspicuous spots on cheeks. 

Prickly Sculpin count = 11 in April; 27 in May.  Pricklys are a catadromous species.  They migrate downstream from freshwater creeks to spawn.  They can be a good indicator of rainwater flushing.

4. Starries.

Starry Flounder count = 0 in April/5 in May.  Starries were the only flatfishes seen. 

5. Bugs.

Corbula clam count = 492 in April; 80 in May.  The vast majority of Corbula in April were picked up at station P2A1.  By May, Corbula appeared to have spread to other stations, but overall numbers decreased dramatically.

• Corbula are an extremely destructive non-native clam.  

Mossy Bryozoan.  (No count).  We find these balls of mossy byozoan at downstream ends of flowing rivers in LSB.  They look like fist-sized Brillo pads. In reality, they are filter-feeding colonies of near-microscopic animals.

• What is their ecological impact?  Investigation continues.

Crangon shrimp count = 775 in April; 553 in May.  Baby shrimp, along with tiny pelagic fishes and baby gobies, are essential food for bigger fishes. 

• Much more to say about the inverts, but this is no time for mindless speculation.  Many new North Bay marshes have now been opened for our exploration!  
• We must move on.

Drain You, 1994   https://www.youtube.com/watch?v=dUb69RIqfO8&list=RDz2unV6W8D1s&index=2