Fish in the Bay – September 2023, Summer’s End.

A belated September fish report:  I missed September trawls, but Sami, Niko, and Janai sent me some photos.

  • I got great photos of water color from them because everyone was watching the water for any signs of potential H. akashiwo red tide in September.  However, fish photos were a little sparse.
  • For that reason, I am using some October photos (and some October spoilers) to round out the story in this report.

Big stories in September:

  1. No H. akashiwo red tides were observed! LSB marshes once passed the test.
  2. Late summer blooms of non-native Silversides and Shimofuris were observed once again.


Silverside Tsunami.  1,596 non-native Inland/Mississippi Silversides showed up in Artesian Slough in September and to a lesser extent in October. 

Baby Starry Flounder numbers were still high but had dropped off considerably after August.


Shimofuri Explosion.  A disturbing number of Shimofuris were netted at stations Alv1 and Alv2.  This is another late summer Shimo Explosion like the one we saw in 2021.  

Baby Bat Rays.  So far, low salinity in 2023 had made this a fairly bad Bat Ray year.  Then, 35 baby Bat Rays were unexpectedly caught at Coy3.  35 at a single station!  That was a big catch.

Musculista on the move.  The Musculista catch (231 “Asian Date Mussels” in September) was not as big as August, but it was still a lot more of them than we have ever seen prior to 2022. 


1. Non-native Fish Explosions.

Bad News: Both Silverside and Shimofuri Goby populations exploded in Sept.

Silverside Tsunami.  We have caught a late summer explosion of Silversides at upstream stations in most years after 2016. 

  • Technically, non-native Silversides in California are identified as “Mississippi Silverside.” This non-native fish was initially introduced in California in 1967.  It has since spread to practically all inland waters of the state. 
  • There are at least four major varieties of “neotropical” Silversides in North America. Listed from freshwater to marine salinity, they are: Brook Silverside (Labidesthes sicculus), Mississippi Silverside (Menidia beryllina), Inland Silverside (Menidia audens), and Atlantic Silverside (Menidia menidia).
  • Rightly or wrongly, I refer to those we catch in LSB as “Inland Silversides” because we catch them in estuarine brackish salinity consistent with the “Inland” variety. The morphological differences between Mississippi versus Inland Silversides are otherwise trivial (in my opinion), so I am sticking with my story for now. 


Non-native Silversides (regardless of variety) are very bad fish for California:

Two Shimofuri Gobies, Dump Slough, 7 Oct 2023.

Shimofuri Explosion.  Large numbers of Shimos were counted in Alviso and Artesian Sloughs in September.  The Shimo concentration was particularly dramatic at station Alv1.  Something about this location has made it a particular hotspot for Shimos.

  • Shimofuris could have arrived in LSB as early as year 2000. UC Davis data suggests they may have been absent (or nearly absent) in LSB until around 2012, and rare for at least another four years.  Shimo numbers quickly increased after 2016.  They are now our second most common goby after Yellowfins. 
  • Recent UC Davis beach seining studies also found huge numbers of Shimofuri Gobies in adjacent restored or restoring ponds.  


Historic monthly Silverside and Shimo counts from LSB otter trawl monitoring.  Sticklebacks were added for comparison.


Long-term Silverside and Shimo trends are not encouraging.  Counts of both fishes have risen substantially over the last decade.

  • Silversides may compete directly with Three-spined Sticklebacks. Both Silversides and Sticklebacks are well documented as “egg-eaters” of spawning pelagic fishes.  
  • Silversides are a broader threat to almost any fishes that leave tiny eggs or larvae lying around unguarded – like spawning Anchovies or Longfin Smelt.
  • The impact of Shimofuri Gobies is not known. Shimos are only the latest arrivals of at least four non-native gobies in LSB since the 1950s. At the very least, Shimos must compete directly with those other non-natives.   


2. More Baby Fishes for the Nursery: Starries, Longfins, & Bat Rays.


Starry Flounder.  Numbers of young or baby Starries remain high, but they have been dropping off since August: 464 in August, 114 in September, and 52 in October. 

  • In most previous years, we only randomly caught a few to several Starries per month at best, so recruitment and growth trends were difficult to see. In contrast, the 2023 Starry count stands at 1,426 at the end of October, and there was a clear surge in baby Starry numbers that began in May.
  • Anecdotally, but very interestingly, we caught a big “mama” Starry at Dmp2 during October trawls. We occasionally catch a big one once or twice during the cool wet season.  We presume this mama is working her way upstream to eventually drop her developing load of eggs.      
  • Successful Starry recruitment relies heavily on returning big mamas like this one. We measured her quickly.  The marsh can’t afford to lose any of these big ones.


The First Longfin of the 2023/24 season caught at Art3 on 9 Sept 2023.

Longfin Smelt.  We caught our first Longfin of the new winter season in September!  It was a young and small one.  (Spoiler Alert:  We caught 93 more Longfins in October!)   The 2023/24 Longfin spawning season has begun!


A tub full of Baby Bat Rays at Alv3 in September.

Baby Bat Rays.  The Bat Ray count jumped to 47 in September.  Most of them were caught in a single haul at Coy3.  We believe this was the largest number of Bat Rays we had ever seen in one catch. 

  • Another spoiler alert: We caught 105 Bat Rays in October. 2023 went from being one of our worst Bat Ray years to a potential record-breaker!


3. Oddball Fishes.

Plainfin Midshipman, aka the “Singing Toadfish.”  This is only the second Midshipman seen in 2023.  Fresher water in 2023 has pretty much kept Midshipmen out of LSB.

Common Carp.  Two more carp were caught at UCoy2 in September and another six were caught in October.  The two carp we caught in August were the first we had ever seen in LSB trawls. 

Nudibranch, aka Enosima Aeloid – (Sakuraelois enosimensis).  Only one Enosima Nudibranch was found in September.  This tiny Nudibranch ranges around 10 to 15 mm in length (length equals roughly the width of a thumbnail – at most).  We never noted them until 2019. Then, a few to several started to show up in late summer trawls during the drought years.  2023 has been relatively fresh, so we have seen few this year.


Spoiler: Four of six Common Carp caught on 7 Oct 2023.


4. Water Colors.

Crew members kept a close eye on water color in September. 

  • A Red Tide bloom killed many thousands of big fishes in SF Bay last year.  Literature indicates that the H. akashiwo organism blooms into red tides under conditions of warmth and pronounced stratification.  The crew was on red alert.
  • A chocolate dark red-brown stain is a conspicuous sign of an H. akashiwo attack.
  • Verdict from photographs: Water appeared greenish-brown or brownish-green at almost all stations. There were no hints of redness, with one exception! …


Odd patch of brown water at LSB2.

An odd patch of (possibly reddish) brown water was observed at LSB2.  Janai was onboard with sample bottles and a microscope at the ready.  She sampled and assessed LSB2 water for microbial content:

The report from Janai:  “The sample appeared to be a healthy-looking mix of plankton both phyto and zooplankton. Copepods and barnacle nauplius, adult copepods, centric and pennate diatoms, polychaete worms, and tintinnid loricas. It was nice to see that there was variety, with no one organism in the overwhelming majority.”


Copepod nauplii at Coy2 –  photographed by Janai on 8 Oct 2023.

The health of our marshes depends on microbial life!


5. Life Goes On.

New old faces.  Sami Araya and Niko Floros are now assuming leadership of the long-term monitoring effort. They have joined the monthly UC Davis trawls of LSB periodically over the past few years.  

  • Seasons and people change, but the project continues.


American White Pelicans flying over Artesian Slough in September.

Ancient Romans watched flights of birds to decipher the will of the gods.  Bird signs were called “auspices.”  Our English word “auspicious” – for a positive or successful future – comes from that. ( 

  • The Roman divination practice was called “augury,”
  • Nowadays, we track the migration of fishes to decipher restoration progress.  Would this be called “fishery?”


My apologies for missing September trawls.  I tried to make up for it in October.

The Greatest Song in the World
This is not the greatest song in the world, this is just a tribute!

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