Fish in the Bay – March 2025. Baby Fishes & Interesting Oddballs

The Shaduary Shad population explosion ended by early March.  Only a small remnant of stragglers remained in the area. 

Unfortunately, most other fish numbers declined as well.  It’s not completely unexpected.  Fish numbers usually decline a bit in late winter.  March is an in-between month:  Wintertime spawners flee and the big surge in baby gobies has yet to arrive.

• Part 1 of this March report focuses on baby fishes and some of the more interesting oddballs.
• Part 2 will cover bottom fishes and bugs.  

Good News: 

• The non-native Silverside boom has ended. A mere 5 egg-eating demons were seen.  Unfortunately, they will return.  But, at least they are mostly gone for now. 
• Signs of life: Hundreds of baby Anchovies, scores of baby gobies, and a little over a dozen each of baby Herring and baby Striped Bass were caught. Altogether, there were a lot of babies.  And, we were still a month away from traditional “baby fish month” in April.  

Bad News: We found only one (1) small juvenile Longfin Smelt.  The Longfin spawn of 2024-25 appears to have started and ended early, and it looks to have been a weak one.  The long-term impact will not be understood until we count returning Longfins next November.

1. Striped Bass & Shad.

Striped Bass count = 13.  This is the non-native fish we hate to love.  As we pulled up to the Artesian Slough boat launch on Saturday, we were greeted by two fishing parties showing their love for the Bass.  Local anglers know that big Bass can always be hooked at the exact point where highly treated wastewater from the SJ-SC RWF discharges.  This is where the big fish like to hang out.

• This is matter of great pride for those who currently work at, or have ever worked for, the SJ-SC RWF facility.

Sami Araya and Jim Hobbs show the Bass and Carp harvest at Art1.

Only minutes later we confirmed it.  Our first trawl a Art1 pulled up two Bass and a Carp.  The big ones probably got away – We always presume that the biggest bass swim fast enough to evade the trawl net. 

Baby Bass.  All but one other Striped Bass netted during the March weekend were small youngsters, 3 to 5 inches long. 

• I call them “babies.” Technically, they are “juveniles.”
• We also found abundant “Bass food”: Mysids, Shrimp, and small fishes everywhere.  If it weren’t for high summertime temperatures in these marshes, this place would be a Striped Bass paradise.

Shaduary ended as of March:  Threadfin Shad count = 29.  American Shad count = 14.  These were fairly normal numbers for this time of year.

2. Baby Fishes.

Pacific Herring count = 16.  All but one Herring were tiny babies.  Even the one exception was a returning (?) young-of-year.  (We like to think that Herring hatched in Lower South Bay might actually return here.)

Do Herring return to natal waters?  … For some Herring species, the answer is yes!

• Bowden (2013) https://academic.oup.com/icesjms/article/71/3/666/632784
  “There is strong evidence that river herring home to natal rivers. However, some individuals will colonize new areas; using otolith microchemistry, Gahagan et al. (2012) estimated straying rates in Connecticut streams at ∼20% for both species, higher than rates reported for salmon species and American shad.”
• River Herring. https://www.fisheries.noaa.gov/species/river-herring “River herring (alewife and blueback herring) are migratory fish that range along the East Coast from Florida to Maine. They spend most of their life cycle in the marine environment, returning every four to five years to their natal rivers to spawn.”

Northern Anchovy count = 347.  This was the second highest Anchovy number we have seen in a March. – The LSB 2024 Anchovy spawn was a success!  

Similar to the Herring situation, all but a few Anchovies were either juveniles or tiny, nearly transparent, babies.  These babies found “first food” after hatch.  Many have now survived at least three or four months and recruited to a substantial size.  

• This tells us that Lower South Bay hosts a dense and complex microbial food web.
• Multiple studies confirm that Baby Anchovies require dense concentrations of unarmored dinoflagellates (e.g. Gymnodinium) as “first food” and progressively larger organisms as they grow.
• Hunter (1975). “Anchovy larvae fed dinoflagellates Gymnodinium splendens, rotifers Branchionus plicatilis, harpacticoid copepods Tisbe furcata, and brine shrimp nauplii Artemia salina, completed metamorphosis (35 mm) in 74 days at 16°C with a minimum survival of 12.5%. … Growth was comparable to that on a wild plankton diet.”

3. Interesting Oddballs.

Bay Pipefish count = 4.   We rarely catch more than a few dozen Pipefish per year.  They prefer to shelter in submerged marsh vegetation where the trawl net does not go.  Catching a few Pipefish suggests that more are probably hiding nearby.  Like baby Anchovies, Pipefish require tiny food to survive.   

Sacramento Sucker count = 1.  Suckers are strictly freshwater fishes.  Nonetheless, we reliably catch a few individuals each winter, and we seem to be seeing bigger ones as years pass.

“With horizontal mouths designed for suction, Sacramento suckers primarily feed on a diverse diet that includes insect larvae, worms, fish eggs, and vegetation, making them omnivores. They can grow up to two feet in length and weigh nearly four pounds…”  https://www.ebsco.com/research-starters/anatomy-and-physiology/sacramento-sucker 

Pacific Lamprey count = 1.  This was yet another adolescent “Macropthalmia” (Big Eye) Lamprey.  We caught another one just like it a few weeks earlier, a little farther downstream.

We intercept a few young Lamprey each year as they begin their once-in-a-lifetime migration out to sea.  He (or she) grew to this size after five to seven years of life as a small worm-like filter-feeder in upstream creek sediment.

• Lampreys are important indicators of healthy creek conditions far upstream. “If Lampreys are seen, the creeks are clean!”  
• We celebrate whenever we find one of these jawless boneless fishes.

Makayla Marquez, a field investigator and outreach fellow with San Francisco Baykeeper, joined us for the trawls on Saturday (https://baykeeper.org/our-staff/).    She communed with our Lamprey for a moment before releasing it.

• Don’t worry: This Lamprey is not biting Makayla. He uses his mouth to grip to surfaces.  Plus, Lamprey teeth are far too small to break human skin at this young age. 
• Even adult Lampreys are usually reluctant to bite humans. https://www.youtube.com/watch?v=8jNs5G88TiI

Prickly Sculpin count = 2.  Pricklys are catadromous fish.  They spend most of their lives in upstream creeks and migrate downstream for spawning.  These two gravid-looking females will be seeking a suitable male with nesting site to release their batches of eggs. 

• FishBase info – Prickly Sculpin https://www.fishbase.se/summary/Cottus-asper  “Prior to breeding, males move downstream and select a nesting site under boulders or flat rocks. Females aggregate some distance upstream and move down singly to the spawning area. Courtship behavior occurs outside the nest until a female is selected. The pair enter the nesting site, courting continues until eggs are deposited and fertilized. The female then leaves the nest and goes back upstream to feed, while the male spawns with other females or fans and guards the eggs. The male does not feed until the eggs have hatched, moving upstream only in the late summer …”