October Report – Big Bass & Guitarfish Month.

In response to concerns about fish kills from the July-September Red Tides in Central and South San Francisco Bay, I am releasing this October Fish in the Bay report ahead of the September report, which is still in draft. 

With the change in the seasons, is now clear that no significant fish kills were detected in Lower South Bay through the recent Red Tide crisis.  But, how and why warm and nutrient-rich Lower South Bay escaped the Red Tide threat is still unknown.


October Report – Big Bass & Guitarfish Month.

We just finished the October trawls of LSB on 2 October.  I left the boat with the strong impression that the October fish totals were fairly dismal:  

  • The monthly catch numbers of Anchovies dropped from over 1,100 in September to only 254 for October.
  • Goby numbers dropped between August and September but held pretty steady by October.
  • Ironically, the catch of Silversides (a highly undesirable non-native fish) jumped up from 52 in September to 448 in October.


However, the numbers actually look pretty good when compared to previous seven Octobers.  

  • The October 2022 Anchovy catch, and all the other fish catches, were well within recent historic norms!
  • And, we caught unusually high numbers of BIG Striped Bass, and more Arrow/Cheekspot Gobies and Speckled Sanddabs than usual.
  • As I review the data, it looks like we had yet another fairly kick-ass month, all else considered.


The numbers were fairly good on Saturday.


The upstream Anchovy catch on Sunday seemed disappointing only because the previous two years were so abnormally good. 


1. We caught Big Bass in October.

Striped Bass that we catch in monthly trawls are usually younger and less than half this size.

Striped Bass.  18 bass were caught.  That is not a particularly high monthly total, but it is the most we have ever caught in an October!  And, these bass were bigger than we normally see.



4 of 5 Big Bass at Coy1.  Did these ‘Brackish water Barracudas’ eat our Anchovies???


Local anglers were also having good luck catching bass on the October weekend.


2. Sharks, Rays, & Guitarfish.

4 Leopard Sharks & 12 Bat Rays were caught in October.


2 of 4 Baby Guitarfish caught on Saturday. (A total of 5 were caught for 2022.)

Guitarfish explosion.  We caught 4 baby Shovelnose Guitarfish on Saturday.  Until now, we have never caught more than one baby in a single year.  High salinity during a drought year may have encouraged a few more mama Guitarfish to deliver their babies in LSB this summer. 


3. Baby Anchovies were detected early this year.

A larval Anchovy at LSB1.

Several Larval Anchovies were caught in October.  Larval Anchovies indicate possible recruitment success for this summer’s Anchovy spawn.  Each tiny fish has only a few days to find first food after it absorbs its yolk sac.  Critical ‘First Food’ for Anchovies consists of nutritious and digestible unarmored (naked) Dinoflagellates – the same organisms that occasionally cause Red Tides.  

  • More likely than not, delicate soft cells of Heterosigma akashiwo (a Raphidophyte, https://en.wikipedia.org/wiki/Raphidophyte) also serve as essential First Food – assuming H. akashiwo is not in crazy Red Tide mode.   


4. Did non-native filter feeders help ameliorate a potential late summer Red Tide bloom???

(Note: I am not aware that the non-native filter-feeders listed below directly feed on Red Tide-producing Dinoflagellates or Raphidophytes, like H. akashiwo, to any substantial degree.  But, in great numbers, the rapid-blooming filter-feeders could be helping to control runaway plankton blooms that, in turn, feed Dinos and Raphis into a Red Tide frenzy.) 


Musculista senhousia.  We detected a substantial surge in Musculista mussels:  100 in Sept and 86 in October.  The previous high number was 25 this past July.  I looked at data back thru 2019:  we always caught ZERO to a dozen, at most, in prior monthly trawls. 

  • I was not present during September trawls and seriously thought that 100 Musculista might have been a misidentification. Then, I saw them for myself in October.
  • Could unusually high phytoplankton concentrations have stimulated explosive recruitment and growth of this filter-feeder? https://www.cabi.org/isc/datasheet/107753#tosummaryOfInvasiveness   
  • Musculista senhousia (aka. Arcuatula senhousia) is a notorious invader on the West Coast and in other regions, but it does serve some important ecosystem services. It is a mixed blessing.  https://invasions.si.edu/nemesis/species_summary/79577 


Tunicate numbers jumped from 93 in September to 1,623 in October.  Most were caught in Alviso Slough and they were larger than usual. 

Tunicates (aka Sea Grapes, aka Mogula manhattensis) are another type of rapid-blooming filter-feeder we occasionally find exploding across Lower South Bay when conditions favor them.  Apparently, conditions were especially favorable in Alviso Slough where dense colonies of extra-large tunicates seem to have popped up within just a few weeks by October. 


Eastern Mud Snails also seemed to be more conspicuously abundant in Alviso Slough than usual. 

Granted, non-native Eastern Mud Snails are ALWAYS abundant near the waterline.  Our trawl catches from the channel bottoms only give a very rough approximation of their numbers. 

  • These snails feed on benthic diatoms as well as other phytos that settle from the water column.
  • Eastern Mud Snail recruitment could be another first-line biome response to explosive phytoplankton growth.


Do these filter-feeding critters help or hurt the maintenance of a healthy microbiome in Lower South Bay? … Food for thought!

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