Fish in the Bay – North Bay Trawls in April 2026.

This is a “North Bay Addendum” to the April 2026 report.  With support from the Wetlands Regional Monitoring Program (WRMP), the UC Davis team has been trawling at many new places in San Francisco Bay twice each quarter for almost a year now.  

• Trawls in the “North Bay,” aka San Pablo Bay, cover four geographic areas based on WRMP “Operational Landscape Units” (OLUs): Napa marshes, Petaluma River, Hamilton Wetlands to Gallinas Creek, and Wildcat + San Pablo Creek. 
• The four geographic areas, in turn, encompass at least nine different creek and river systems as indicated above. 

(A note for WRMP wonks: Each area circled on the map reflects the organization of our trawling effort, not necessarily the exact boundaries of the OLU scheme.)

Comparison with Lower South Bay (LSB) monitoring: North Bay/San Pablo Bay covers a much larger region using a total of only 42 monitoring stations and 5-minute trawl duration.  

• Always think in terms of “Catch per Unit Effort” (CPUE)!

1. Napa Marshes.

The Napa River “mini-delta” is a good example of the last point above. The Napa marsh system alone is roughly the size of our traditional monitoring area in LSB. 

• For Napa, we sample at 12 stations (one day of effort using 5-minute trawls). In LSB, we trawl at 20 stations (plus three more WRMP stations added in 2025 – 2 days of effort using 10-minute trawls).
• Thus, fish and bug raw numbers from Napa must be multiplied by roughly a factor of 4 to make a fair CPUE comparison against LSB catches.  Needless to say, the CPUE correction factor is even greater for the eight other smaller creeks, rivers, and wetlands we survey in North Bay.  

Special Fishes!  Napa hosts some species that are very special to us.

Tule Perch count  = 3.  We caught 3 Tule Perch in Napa Marshes last year at this time, and a total of 30 for 2025.  Napa is the only place where we see this fish. They are more common farther upstream in the Sacramento-San Joquin Delta.  Like many California natives, Tule Perch are the only species of their genus.  https://en.wikipedia.org/wiki/Tule_perch

• Two of these three girls were visibly swollen with babies.  Each female gives live birth to between 10 to 60 young that come out as thin as potato chips.
• We have caught only two small, sickly-looking Tule Perch in LSB in almost 15 years of trawling.  (A small remnant population may still be surviving downstream of Anderson Dam in Coyote Creek.)  But, for all intents and purposes, we no longer see this special fish in LSB. 

Starry Flounder count = 1. (plus 1 more at Wildcat Creek). This compares with ZERO (0) Starries caught in LSB in the same month. Starry populations surge and fall due to factors we still do not understand.  Rainfall and river flow are big ones, but those alone do not explain the current crash.        

Sacramento Splittail count = 1.  We caught ZERO (0) anywhere else this April.  In 2025, 13 Splittail were caught in Napa marshes, 4 more at Sonoma Baylands, and one in Gallinas Creek – 18 total.

• Splittails are another uniquely Northern California fish. They don’t exist anywhere else. Splittail seek floodplains in spring to feed and mate.  As floodplains disappear to development, so do the Spittail.  Splittail went extinct in Clear Lake by 1970.  A Splittail was last seen in Lower South Bay in 1980. We must not lose this fish!  https://en.wikipedia.org/wiki/Sacramento_splittail 

Striped Bass count = 5.  Plus, 2 at Sonoma Baylands, 1 in Novato Creek, 1 at McInnis Marsh, and 2 more near San Pablo Creek.   Striper numbers are still a little low in 2026.  Don’t worry about this one.  Striper numbers will rebound.

Guest visitors.  Two distinguished guests joined us for April trawls.

• Karen Taylor is a senior environmental scientist with CDFW. She has been involved in permitting and restoration of the Napa marshes for roughly 20 years.  She provided a wealth of historical information about each restoration site as she rode along with us for a day of trawling.

• Chris Janousek is an associate professor of ecology and wetlands restoration at Oregon State University.  He evaluates the health of our least-disturbed and restoring marshes for the Wetlands Regional Monitoring Program.
  • Chris only rode with us for a few stations.  He needed a ride to the Napa wilderness so he could download data from his remote field instruments. We dropped him off in the tall weeds near station Mud1 and picked him up about 3 hours later. He was refreshed and invigorated after a few hours in the marsh.      

2.  Petaluma River.

Yellowfin Goby count = 3.  Surprisingly, these were the only Yellowfins caught in North Bay in April.  In contrast, we caught hundreds of them, mostly tiny babies, just a few weeks earlier in LSB and at Eden Landing. 

• “Traditional Baby Fish Month” in LSB brought us many baby Yellowfins in early April. These Petaluma Yellowfins were adults at advanced stages of spawning readiness.  Perhaps ‘Baby Fish Month’ arrives a week or two later up here???
• Both females appeared gravid.  The big-headed male looked long and skinny, like a guy who might have spent his last few weeks guarding eggs and young without eating.       

Shrimp Alley – Petaluma River.  We consistently catch high numbers of shrimp at our four stations at Petaluma.  We also occasionally greet a small commercial shrimper who collects here.  Raw shrimp numbers at Petaluma seem pitifully small until we remember that the numbers only reflect 5-minute trawls at 4 stations versus 10-minute trawls at 20 stations in LSB.  This is another example that highlights the importance of thinking in terms of CPUE.

• The simplest CPUE conversion adjustment would be 10 minute trawl in LSB/5 minute trawl in Petaluma X 20 stations in LSB/4 stations in Petaluma = CPUE adjustment for Petaluma of 10X.  
  In other words, multiply each Petaluma bug count by 10. 

• Holy Kamolicans!  By this crude CPUE calculation, the Petaluma count was 3,590 Crangon and 1,420 Palaemon.  Those numbers are twice to three times higher than what we saw in LSB’s Shrimp Alley two weeks earlier! 

• However, stations outside of Shrimp Alley in LSB add little to overall shrimp counts.  Perhaps only the 5 stations in LSB’s Shrimp Alley should be compared. That shrinks the CPUE factor to 2.5.  But even with the smaller adjustment, the Petaluma numbers remain comparable to LSB April counts, e.g. 898 Crangon/355 Palaemon in Petaluma versus 696 Crangon/674 Palaemon in LSB’s Shrimp Alley.       
  

“Shrimp Alleys” are extremely important.  They represent the detrital zone where nutritious material settles to the bottom as freshwater flushes into the salty estuary.  Shrimp are just a macroinvertebrate manifestation of the largely microscopic biological web that seemingly ‘bubbles up’ near the foot of healthy flowing creeks and rivers. Fishes of all sizes exploit these Alleys as food sources. 

• So far, only Petaluma River seems to host an Alley that consistently rivals the one we have at the mouths of Guadalupe River and Coyote Creek in LSB.  Novato and Gallinas Creeks also show some potential, but they are not quite so robust.

3.  Gallinas Creek.

Gallinas Creek is one of our next best hopes as a potential Shrimp Alley.  Many good signs are here: Lots of baby Anchovies in the Bay-side channel, an occasional Longfin Smelt upstream during the spawning season, and plenty of tiny bugs on the bottom – to include tiny colonial animals like Hydrozoan and Mossy Bryozoan that are typical features elsewhere.  The 2025 springtime mysid bloom here was the biggest we witnessed in the entire Bay.  These different critters indicate that tiny food is here.

• But alas, shrimp counts remain low and inconsistent.  In April, only 19 Crangon and one Palamon were netted.  This was disappointing!

 Another small semi-related problem.  The southern shores of San Pablo Bay are at least moderately infested with European Green Crabs.  These highly invasive bad crabs can overwhelm ecosystems by eating almost everything within claw-range, including shrimp food and the shrimp themselves!   https://en.wikipedia.org/wiki/Carcinus_maenas 

4.  Wildcat & San Pablo Creeks.

California Halibut count = 1 at Wildcat, plus one more in Napa Marshes.  (This compares against 58 Halibut caught in LSB earlier in the month. Halibut tend to recruit in warmer water. Hence, we catch a lot more of the young ones in LSB.) 

Most of our Wildcat and San Pablo Creek trawling area consists of shallow, flat-bottomed waters near the shore just north of City of Richmond. Fish and bug counts tend to be low, but we always catch at least a few interesting natives plus the occasional Striped Bass. 

Flocks of Scaup, a common diving duck, and a few Surf Scoters, were hanging out here during the early months of 2026.  They must either be feeding on benthic critters or they simply enjoy loafing in this relatively protected embayment. (Sorry, no photos of Scaup or Scoters. They are shy birds that fly away as our boat approaches.)        

The most interesting feature of the Wildcat/San Pablo area is the variety of seaweeds we collect here.  Last year, we were concerned and careful to minimize potential disruption of all algae.  But, we quickly realized that this red, green, and brown vegetation grows all over this area. 

• These seaweeds grow very fast.  They completely disappeared during winter months.  Total die-back!  Then in April, Kaboom!  Seaweeds returned more abundant than ever.  Conclusion, this place is a summertime seaweed garden!   (Maybe the same conditions that foster these weeds in summer also attract diving ducks in winter???  – More investigation is needed!)
• Most of these are very common weeds.  We find Ulva, Cryptopleura, Gracilaria, and Ceramium almost everywhere else.  But other types, like Turkish Towel (aka Chondracanthus https://en.wikipedia.org/wiki/Chondracanthus_exasperatus), Fucus, and now non-native Sargassum, seem to grow only in this Wildcat/San Pablo trawling area.     
• I discussed some of these weeds around this time last year.  They are just as fascinating this year as they were back then – see section 4 of the May 2025 report.    https://www.ogfishlab.com/2025/06/10/fish-in-the-bay-may-2025-wrmp-san-pablo-bay-trawls-part-4-wildcat-san-pablo-marshes/ 

5.  Anchovies & Jellies.

Baby Anchovies!  Our limited monitoring of both North and South SF Bay suggests that “baby Anchovies,” the juvenile recruits from the previous year’s spawn, tend to congregate off the western edges of the Bay.  … Or is this just an artifact of our limited trawling range and experience?

• Whether coincidence or not, we netted an astonishing catch of over 2,000 Anchovies in the Port of Redwood City in South Bay in early April.  And then, just two weeks later, our highest baby Anchovy counts were again at stations along the western edge of San Pablo Bay (albeit these North Bay numbers were a small fraction compared to Redwood City.) 
• 276 Anchovies were picked up on the west side from Hamilton to Gallinas In contrast, only two baby Anchovies were caught along the northern shore from Napa River to Novato Creek, and only 35 more were found at Wildcat/San Pablo. 
• But why would baby Anchovies prefer the western side of the Bay?  Winds, currents, and/or temperature could be factors.  Or, more directly, those factors may influence the near-microscopic soft and squishy foods that baby Anchovies need.  

Tiny Jellies.  We found many small, nearly transparent jellies in April.  They were about the size of Ctenophores but were clearly medusa (bell-shaped) types.  We do not know if these were young of some larger type of jelly or simply a midget-sized species.

• Dr. Hobbs suggested that they may be young Hydrozoans of either Maeotias marginata or Polyorchis penicillatus varieties.  The small size and transparency of these tiny ones made it nearly impossible to discern identifying features.  We caught adult specimens of both hydrozoan types in North Bay just last year. 

• I could find only one photo possibly showing many tiny eyes (bottom left corner in the collage above).  That could indicate that some or all of these blooming jellies are Polyorchis, aka “the Red-Eyed Medusa.” https://inverts.wallawalla.edu/Cnidaria/Class-Hydrozoa/Hydromedusae/Polyorchis_penicillatus.html

We pay close attention to jellies.  Blooms of the wrong kind of jelly can indicate serious problems associated with nutrient enrichment. On the other hand, good native jellies, like Ctenophores for example, can provide extremely beneficial control over zooplankton population booms.

6.  Other Interesting Stuff.

Trash and Treasures.  On a small boat, we don’t have much capacity for hauling trash.  But, there are always at least a few pieces that are either so ugly or so useful that we can’t resist. As long as they can be safely and easily accessed, we try to take them with us. 

• Milk crates are particularly high-value items. We never have enough of them aboard for storing gear.

Beggar Birds of Loch Lomond.  We launch from Loch Lomond in San Rafael when we trawl the Wildcat/San Pablo area.  The birds are a charming feature of this harbor.  They have learned to expect fish treats from anyone who remotely looks like an angler.  

• Loch Lomond is a great place to get close-up photos of some of the most beautiful birds in SF Bay. 

• And again, as I said last year, if you meet these birds, feed them only fish!  Do not feed them unhealthy sugary or salty processed foods!   

Wild birds everywhere else.  Riding on a noisy boat creates a particular near-constant frustration.  Beautiful birds are always on the horizon.  They usually scatter long before we get within range for decent photography.  At certain spots, birds are brave enough to support our approach.  They watch us warily as we train telescopic eyes on them. With luck, we capture good enough images.    

• Terns are pretty much everywhere this time of year. Mostly Caspians in the north and Forster’s Terns farther south in LSB.  We passed by an attractive pair of Forster’s as we motored into Novato Creek in April.  They sat unperturbed on a channel marker as we drifted by.
• Ospreys make nests in some lighted channel markers around the Bay.  They mostly choose the “green” (starboard) markers.  We suspect this is because the green signs are square and give better wind protection compared to triangle-shaped red signs on the port side of channels.
  • Conservation management tip: if you want more Ospreys nesting in the Bay, provide better wind protection at the top of channel markers.  Who knows?  It might work.
• Willets, Dowitchers, and Avocets at Sob3. Over the last year, we noticed that shorebirds tend to sit tight on a small sand spit at station Sob3. 
  • Different birds in different seasons: Avocets in winter, Willets and other brown birds in the warm season. The birds eventually flush if we get too close, but they circle and immediately touch down again after we pass.  They never appear to be actively feeding.  They seem to just stand and socialize here. 
  • The same birds elsewhere in the Bay are much less inclined to let us approach so closely.  There is something special about this small patch.     

7.  Supplemental Tables – North Bay 2025 Fish & Bug Counts (not counting Napa & Sob).

A special treat for data hounds.  The tables below summarize 2025 fish and bug data from the rest of North Bay/San Pablo Bay.  They are in the same format and style as the Napa and Sonoma tables that were included in the January report – see section 3 “Big Data.”   https://www.ogfishlab.com/2026/01/01/fish-in-the-bay-wrmp-napa-sonoma-wetlands-review-2025/

• The tables are organized by river or stream counterclockwise around San Pablo Bay:  1) Petaluma-Novato-Hamilton, 2) Miller-Gallinas-Wildcat, and finally a small strip summarizing LSB downstream stations for comparison.  
• I highlighted some particularly high totals of good things (desirable native fishes and bugs) in green, and bad things (undesirable non-native bugs) in red.   

After staring at the tables for hours, I decided that 1) six trawling events at each station is still not enough data to make firm conclusions, and 2) the good versus bad critters are still largely a matter of opinion.   

It’s a giant puzzle.  All pieces constantly move and interact with each other.  Do not be intimidated.  We will figure this out!

Travis Japan – ‘Moving Pieces’ -Dance Practice- 
https://www.youtube.com/watch?v=_l9-XviFots&list=RD_l9-XviFots&start_radio=1