Fish in the Bay – February 2025. Shaduary Continues.

Good news? Or Bad News?  Shad population explosion has spilled over into February. 

• January counts broke previous records: 533 American Shad & 232 Threadfin Shad.
• In February, American Shad numbers dropped closer to seasonal norm: 156. But once again, Threadfins broke all records: 245 !!!  

Bad News: Longfin Smelt numbers remain low.  Only 50 were caught. 

Non-native Inland/Mississippi Silversides remain present in upstream sloughs, but their numbers dropped from 535 in January to a more acceptable 91 this month.

Very good news:  Post El Nino Halibut recruitment is holding steady, and Crangon shrimp brooding continues. 

1. Non-native Fishes.

Common Carp count = 1.  The single Carp we caught in February was a golden beauty.  She was foraging a short distance downstream from the Regional Wastewater Facility.  

• She cannot stray far from fresh water! Carp tend to disintegrate in salty water. When we find them in saltier water downstream, they generally have big open sores on their sides, missing fins, etc.  It’s not a pretty sight!  
• We immediately released this one where we found her.

Striped Bass count = 4.  Four Bass caught in February are shown above alongside some Shad and a baby Halibut.   A single small adult Striper was from Artesian Slough.  Three youngsters measuring 85-95 mm (roughly 3.5 inches) were picked up a short distance away in the main stem of Coyote Creek.

It’s still Shaduary!

American Shad count = 156.  This month’s count would have been an annual record in any year prior to the Big Flush of February 2017.   

Threadfin Shad count = 245.  Half of all Threadfins and over a third of the American Shad were caught in Artesian Slough alone.  I have long suspected there is something magical in this water. … The magical ingredient is probably Shad food! 

• American Shad eat zooplankton and small fishes: “small aquatic insects and crustaceans such as copepods and dipterans (flies, midges, and mosquitoes)” according to Google AI and many other sources.
• Threadfin Shad eat both phytoplankton and zooplankton in roughly equal amounts according to the Missouri Dept of Conservation: https://mdc.mo.gov/discover-nature/field-guide/threadfin-shad

Mississippi / Inland Silverside count = 91.  In a good year, we expect to see many spawning Longfin Smelt at these upstream stations.  Presence of egg-eating demon Silversides is a very bad sign here.

What about Shad???  Are Shad in local sloughs a good thing?  Or, a bad thing?  Threadfin Shad are one of four indicators of “Pelagic Organism Decline” (POD) in Suisun Bay and the Delta.  Their catch numbers crashed after 2002. 

• Baxter et al (2008)  “The four primary pelagic fishes of the upper estuary (delta smelt, longfin smelt Spirinchus thaleichthys, striped bass Morone saxatilis, threadfin shad Dorosoma petenense), …  Fall Midwater Trawl abundance indices for these four pelagic fishes began to decline sharply around 2000, …  By 2004, these declines became widely recognized and discussed as a serious management issue, and collectively became known as the Pelagic Organism Decline (POD).”  https://www.waterboards.ca.gov/waterrights/water_issues/programs/bay_delta/pelagic_organism/docs/pod_ieppodmt_2007synthesis_011508.pdf

Good thing?  Shad were introduced to California by Dr. Livingston Stone in the late 1800s as part of his dream to someday feed the world.  Shad are highly edible for both humans and game fishes.  The introduction was highly successful; American Shad became a valued game fish along with Striped Bass (also introduced by Dr. Stone.)  https://www.adirondackalmanack.com/2016/02/livingston-stone-leading-19th-century-fisheries-expert.html

Bad thing?  Both American and Threadfin Shad have been present long before LSB trawls began in 2010, but we never counted more than a few dozen per month or much more than 100 per year until 2017 – The year of the big flushing rain – the February Flush of 2017.  Shad numbers quadrupled in 2017 and have remained relatively high ever since. 

• Do Shad compete with other native species in LSB? –  If we don’t know, who does?

2. Colorful Clupeiforms

Blue and green Clupeiforms.

Herring Count = 1.  We caught a yearling Herring at Coy4.  (Another adult Herring was caught later in February during Broodstock trawls.)  

• The spawn is on! Herring spawning season began in January farther north – closer to Richardson Bay near Sausalito.     https://thelostanchovy.com/2025-herring-spawn-report/
• Here in Lower South Bay, we catch only a few wandering individuals, and occasionally, many baby Herring around March. This strongly suggests that at least a few Herring may spawn in LSB.
• A video of a big Herring catch in north Bay from 2023: https://www.youtube.com/watch?v=GH58Nt_o-mU
• In LSB, we celebrate if we catch just ONE adult Herring like those shown in these videos. https://www.youtube.com/watch?v=yNzUBqRHaf8&t=72s  

Blue and Green Shad.  As always, Shad blue-up to a cyan hue of “Rivulet” or slightly greener “Thermal Spring” on the Kudela Lab/Sherwin Williams color scale when salinity is above 18 or 19 ppt. 

• The Shad brown-to-green threshold is still a bit uncertain: Shad at Alv2 blued-up to green (“mélange green”) when salinity was 12.3 ppt.  But, they remained brownish (“different gold”) in Pond A19 where salinity was 12.2 ppt. 
• Perhaps the brown-green threshold for Shad is exactly 12.25 ppt? Or, is it temperature dependent?  Investigation continues!

3. Longfin Smelt

Longfin Smelt count = 50.  This is the lowest February count since 2020. Only 13 were caught that year.  But. for further context, Longfin numbers were lower in 2018 and every year prior. 

• We had hoped that high Longfin spawning season counts in 2019 and 2021-24 had become the new normal. Disappointing results in early-2025 are showing us that our Longfin status still remains very precarious.
• We must not lose this fish!    

4. Oddball Fish & Bugs.

Jacksmelt count = 1.  This is another common native fish that we rarely see in LSB.  Or at least, we don’t think we see it.  The differences between native Jacksmelt and Topsmelt are very subtle and easy to miss.  Jim Hobbs personally examined this specimen for confirmation.

• Jacksmelt, Topsmelt, and Inland/Mississippi Silversides are members of the Atherinopsidae / Silverside family. Technical identification depends on very specific placement of the two dorsal and single anal fins.  https://marinespecies.wildlife.ca.gov/jacksmelt/the-species/
• On the practical level, non-native Silversides have a yellowish tail. Native Jacksmelt and Topsmelt show a clear or slightly bluish tail.  Also, young Jacksmelt have slightly larger eyes compared to Topsmelt. (Jim Hobbs perscom)
• More confusion: None of these “Silverside smelts” are “true smelts” of the Osmeridae family – like Longfin Smelt or Delta Smelt.

Upogebia / Mud Shrimp count = 2.  One Mud Shrimp (Upogebia major) was caught at each of stations Coy2 and Coy3.  But, what does this mean?

1. Best scenario: Upogebia are now very common under adjacent fringing marsh.  These ecosystem engineers are highly beneficial for nutrient cycling and subsurface oxygenation. They occasionally stray out into the mid-channel of Coyote Creek where we snag them.
2. Worst scenario: Unfavorable marsh conditions could be forcing Upogebia up and out of their deep burrows and into Coyote Creek.
3. Comical scenario: Frustrated sturgeon anglers could be tossing out excess bait at the end of the day.  (We hope this scenario is unlikely.  a) The local bait shop is not known to sell Upogebia as bait, and b) Upogebia are delicious and expensive.  – Who would throw away a perfectly good Upogebia?)

Upogebia at Coy2 – a second look.

Polyorchis plus Ctenophores at LSB1 on 1 Feb 2025.

Polyorchis count = 2.  We had not seen a Polyorchis (Red-eyed Madusa) for a couple of years.  Then we caught four in January.  Now we have two more this month. 

Ctenophore count = 157.  Like Polyorchis, all but a few Ctenophores (Comb Jellies) were found at LSB stations.  These creatures require fairly high salinity for long-term survival.

Polyorchis plus Ctenophores at LSB1 on 1 Feb 2025 – a second look.

Ctenophores occasionally show up in LSB, usually from December through May.  They arrive on a seemingly random boom-and-bust cycle:  We saw several hundred per month in early 2018, almost none in 2019, thousands each month in March-April2020 and again in April-May 2021, then practically none from 2022 thru 2024.  Now, here they are again!   

5. Baby Anchovies & ‘Scrubbing Bubbles’ at LSB stations.

Topsmelt, Baby Anchovies, & Ctenophores at LSB2, 1 Feb 2025.

Northern Anchovy count = 228.  Almost all Anchovies caught in February were tiny babies at LSB stations.  A few random adults were netted farther upstream. 

• Without a doubt, these babies originated from the LSB Anchovy spawn of the previous season. Some of these babies may have hatched as late as November or December 2024?? – judging from their small size.    

Ctenophores = ‘Scrubbing Bubbles’ = Cleanup Crew!  These grape-sized jelly creatures follow the food.  

• Ctenophores eat tiny, near microscopic, zooplankton that are the primary consumers of phytoplankton.
• Think of Ctenophores as original biological ‘scrubbing bubbles’ – metaphorical embodiments of the Dow Bathroom Cleaner mascots created in 1968: ‘They work hard so you don’t have to!’ https://en.wikipedia.org/wiki/Scrubbing_Bubbles

Baby Anchovies also depend on the tiniest of zooplankton as their main food source.  Within a few days after hatch, baby Anchovies require unarmored/naked dinoflagellates as ‘first food.’  They need increasingly larger zooplankters as they grow.

Ctenophores are well documented “circuit breakers.”  When zooplankton threaten to over-consume phytos, ‘scrubbing bubbles’ come to the rescue! 

• Deason and Smayda (1982) https://academic.oup.com/plankt/article-abstract/4/2/203/1465985 “Ctenophores may control phytoplankton blooms indirectly through their predation on herbivorous zooplankton and directly by the nutrient excretion accompanying such grazing. This evidence that a planktonic carnivore two trophic steps removed from the phytoplankton regulates the latter’s dynamics in Narragansett Bay is analogous to reported regulation of benthic algal (kelp) dynamics by the sea otter, lobster and various crabs through their predation on herbivorous sea urchins.” 
• Mcnamara et al (2013) https://www.sciencedirect.com/science/article/abs/pii/S0272771413002059 “Field data suggested significant top-down control of mesozooplankton and microplankton during peak abundances of adult and larval ctenophores, respectively. Abundances of dinoflagellates and ciliates declined by 45–56% and 83–97%, respectively, during highest larval abundances in 2008 and 2009. Furthermore, the dramatic reduction of mesozooplankton by adult  leidyi resulted in a cascading effect on microplankton. A relationship between high adult M. leidyi/low mesozooplankton with high microplankton abundances was identified, and preceded an increase in ctenophore larvae. These data suggest that blooms of M. leidyi result in a direct feedback system, wherein intense feeding activity by adults on mesozooplankton releases certain microplanktonic taxa from predation pressure, enhancing prey conditions for larval ctenophores.” 

We can learn to make sense out of this complexity!

Learn to Fly – Foo Fighters Rockin’1000 Official Video  https://www.youtube.com/watch?v=JozAmXo2bDE