Fish in the Bay – April 2025, Traditional Baby Fish Month.

Spring is here – technically it arrived on March 20th.  Returning warmth is slowly awakening the marshes … just in time for another ‘baby fish month.’

• Fish counts are climbing but only partly due to the baby goby explosion we have come to expect each April.
• Unfortunately, we also counted a near record number of ecosystem-killing Corbula clams – to be discussed further in Part 2 of the April report.

April was designated “Traditional Baby Fish Month” in Lower South Bay (LSB) several years ago.  We counted hundreds to thousands of tiny “Unidentified” baby gobies in three out of four Aprils between 2014 through 2017.  Each baby goby explosion was accompanied by a subsequent spike in young Yellowfin Gobies a month or two later.  

• Undoubtedly, baby Yellowfin Gobies account for most of these April ‘baby fish month’ increases.
• In 2018, the baby goby surge arrived late (in July), but goby babies were back on schedule in Aprils of 2019, 2021, 2022, 2024, and now again in 2025.

However, this current Baby Fish Month 2025 was a bit of a bust.  Only 308 babies were seen this April.  That is much lower than average.  Only counts in 2015 (13) and 2018 (11) were lower.  (There was no ‘baby fish month’ count in April 2020 due to COVID-19 hiatus.)

Weak ‘baby fish month’ hypothesis #1: The recent “Shimofuri-Shokihaze Seesaw” could be a wildcard in local goby world. 

• The Shimofuri population spiked hugely in late 2021 and 2023. We believe that an anomalous baby goby spike in October 2024 was also largely comprised of Shimofuris.
• Shokihaze numbers declined rapidly in mid-2021 and stayed low as Shimofuris temporarily replaced Yellowfins as our #1 goby. Now, Shokihaze numbers surged to 82 this month – their highest number since May 2021 and the Shimofuri count dropped to only eight. 
• Does this ‘Shimo-Shoki Drama’ affect overall Yellowfin population dynamics??? More discussion about this as well in Part 2 of this report.

• As usual, most “Unidentified” baby gobies were observed at upstream stations.
• Bad News: Huge numbers of Corbula clams showed up in the main stem of Coyote Creek (stations Coy1 & UCoy2).  

Staghorn Sculpin numbers unexpectedly jumped.  This month’s count (438) is the largest we have seen since May 2023 – before El Nino in early 2024.

English Sole counts also jumped.  The April total (90) is also the highest seen in LSB since May 2023. 

• Both Sculpin and Sole are documented “La Nina fishes.”  These population swings are not random coincidence!

More bad news:  Large numbers of Corbula clams were collected at upstream stations in Alviso Slough as well. 

Also note: UC Davis OGFL adjusted the historical trawling schedule due to initiation of the new Wetlands Regional Monitoring Program (WRMP) in other parts of the Bay.  –  LSB stations were trawled a day earlier than the rest of Lower South Bay in April.  All other fish monitoring procedures and protocols remain the same.

1. Baby Gobies.

Unidentified / Baby Goby count = 308.  As mentioned above, this was the third, or perhaps fourth, weakest “Baby Fish Month” we have measured since 2014. 

• Baby gobies at stations Art1 and Dmp2, shown above, were too small to identify even under the macroscopic lens.
• However, babies at Dmp1 were beginning to display the classic ‘red, white, and blue’ (actually pink, grey, and clear) pattern that seems to characterize Yellowfin Goby babies.

Restored Pond A19 was the ‘Unidentified / Baby Goby’ winner.  229 baby gobies were counted in Pond A19 – versus only 79 everywhere else. 

• We have seen this over-and-over again for the past several years: restored ponds A19 and A20 account for most of the most baby fish recruitments, whether they be baby gobies, Longfin Smelt, or Herring.
• Also note: baby gobies are about the same size as baby Crangon and Mysid ‘shrimp.’ These baby gobies (mostly Yellowfins) are likely providing a similar (not the same!) food source for larger fishes.

Unidentified / baby gobies in Pond A19 also displayed the classic ‘red, white, and blue’ (a.k.a. pink, grey, and clear) body color of baby Yellowfins.  The pattern is easy seen in magnified photographs – but much harder to see in wriggling baby fishes measuring only 10 to 17 mm. 

Weak ‘baby fish month’ hypothesis #2: Yellowfin goby spawning and recruitment peaks over a narrow period each spring.  Monthly trawls may present a “hit-or-miss” opportunity. 

• Appearance of some gravid Yellowfin females in April suggests that some Yellowfin spawning has not yet occurred.     

2. Baby Herring & Easter Eggs.

Easter eggs!  We caught bunches of Herring eggs at both LSB stations!  Twenty (20) young Herring were picked up farther upstream. 

• Female Herring lay strings of sticky eggs on eelgrass or other attached bottom substrates. Males follow close by to fertilize the eggs.
• Herring spawned here in LSB! – or at least attempted to do so.
  • Catch and Sushi Series Ep.6: Herring Eggs. https://www.youtube.com/watch?v=zH1SDqLImtw
  • 2024 – The herring spawn is on: Vancouver Island coast turns jade green https://hashilthsa.com/news/2024-03-20/herring-spawn-vancouver-island-coast-turns-jade-green

More Herring eggs.  Dense strings of Herring eggs stuck to the net at station LSB1 on April 8^th.  The eggs must have been deposited along the bottom only days earlier since we could see no signs of developing embryos. 

Egg color.  Most eggs were clear-to-greenish which is typical for Herring eggs.  But, some eggs were distinctly orange. – See video link above: Orange or brownish may indicate mature or rotten eggs.      

• Wikipedia – Pacific Herring. https://en.wikipedia.org/wiki/Pacific_herring “Clupea pallasii is considered a keystone species because of its very high productivity and interactions with many predators and prey. Pacific herring spawn in variable seasons, but often in the early part of the year in intertidal and subtidal environments, commonly on eelgrass, seaweed or other submerged vegetation.”

3. Striped Bass.

Striped Bass count = 31.  This was the most Bass we have seen in a single month since 2021.  Many of them had fat bellies!

Weak ‘baby fish month’ hypothesis #3: Are bigger fishes eating our baby gobies?

Staghorn Sculpin count = 484.  All of these were young Staghorns.  It has been almost two years since we have seen so many Staghorns.  Just a month ago, we counted only 39, and fewer than a dozen each month for most of the previous year.

• Where did they come from? How did they show up so suddenly? 
• Staghorns have big mouths. They can easily eat baby gobies. 

4. Anchovies & the Birds who eat them.

Anchovies & two young Herring in Pond A21, 10 April 2025.

Northern Anchovy count = 35.  April is a hit-or-miss month for Anchovies in LSB.  The local midget-sized E. mordax nanus returns to begin the spawning season in late spring.  Sometimes, Anchovy counts surge into the hundreds in April.  Sometimes, we don’t see the wave until May or June.

Tern photos taken on Sami’s cell phone.

Forster’s Tern count = ??  On both April 9^th in Artesian Slough and again on the 10^th in Coyote Creek, we watched Terns dart overhead.  These small, fast-moving acrobats were easier to observe over calm water during the hour or so it took us to trawl and process catch at stations Coy2 and Coy3 on the 10^th. 

• Every once in a while, each bird in turn (no pun intended) would slow down, hover for a second, and then plunge into the water. It was hard to see what they were eating, but occasionally we could just barely discern small anchovy-sized fish in their bills. 
• Our trawl at the bottom of the channel netted twelve Anchovies at Coy3 and none at Coy2. The Terns were much more effective catching Anchovies at the surface. 

Forster’s Tern nesting season begins soon.   The Terns are now evaluating the suitability of Lower Coyote Creek to support brooding chicks.  – No Tern will invest time and energy to incubate a brood that may starve!

• Male Forster’s seduce females via ritual feeding.
  • Cornell lab- all about birds. https://www.allaboutbirds.org/guide/Forsters_Tern/lifehistory “Soon after arriving in breeding areas in spring, Forster’s Terns begin courtship displays. Male and female of a new pair make coordinated flights high in the air, using exaggeratedly slow wingbeats, circling and rising until the male begins to descend, wings raised above the horizontal and bill pointed downward. The female follows, just above the male, who sometimes carries a fish for this display. Often, another male with fish will join the pair. Another flight display involves the male hovering, with tail spread, low over the colony, bearing a fish. Males regularly offer fish to females at these times in “courtship feeding” displays.”

• Herring and Anchovies are on the Forster’s Tern menu. The Terns are finding good food here!

These Terns now nest in Pond A16.  This pond is managed to optimize bird habitat – another salt pond restoration success!  https://www.southbayrestoration.org/document/establishing-forsters-tern-sterna-forsteri-nesting-sites-pond-a16-using-social-attraction 
“35 Forster’s tern nests were recorded during the second year of social attraction implementation in 2019. These 35 nests represent a re-establishment of a Forster’s tern nesting colony to Pond A16 for the first time in 8 years.” 

5. Harbor Seals.

Another photo from Sami’s cell phone.

Harbor Seals at Calaveras Point.  We generally see 30 to 35 Harbor Seals lounging at the Calaveras Point seal rookery throughout the year.  (More are likely present.  We can only count those we see from a distance.) Most of the population is comprised of one to three groups of females and youngsters.  Each “harem” is jealously guarded by an aggressive male.

• Seal counts vary depending on tides: High tide = few seals; Low tide = maximum seals.
• Seal pups start showing up in March. As usual, we scanned the shoreline for pups as we trawled station Coy4.  Camouflage coloring and the pups tendency to hug close to their moms makes these newborns hard to spot.  Plus, we can only search from far away – a closer approach risks unnecessarily alarming Seal moms.  
• In April, several new pups were spotted on the muddy beaches of Calaveras Point. – April pups are larger. They are more independent and easier to see. 

A belated Happy Easter!

Here Comes Peter Cottontail – https://www.youtube.com/watch?v=q7UXYvR