Fish in the Bay – Alert! The 2022 Anchovy Spawn has Begun!

The Anchovy population just exploded in Lower South SF Bay.  The monthly totals in April and May were 29 and 52, respectively.  The total number leaped to over 2,600 for the June trawls.  This is the second-highest monthly total we have ever seen.  It is exceeded only by the January 2022 catch of 2,934. 

2022 is already the record-breaking Anchovy year for Lower South Bay (LSB)!


More importantly, these Anchovies have arrived to spawn again.  Adults bearing either eggs or milt were detected at 19 out of 20 stations, from far upstream to the deepest parts of the Bay.  This is Anchovy spawning season. 


The monthly Anchovy picture along with Silversides and Sticklebacks – dreaded egg-eating enemies of the Anchovies.

Monthly catch variability is high.  But, when averaged over all years, two things become very clear:

1) Anchovies arrive to LSB to spawn each year from roughly June through October, and

2) We are experiencing a very large surge in the Anchovy population from 2020 to present.  More importantly, juveniles were a large portion of the high numbers seen in January 2021 and January 2022.  This may indicate that the LSB marshes were a net source of Anchovies for the two most recent years!

But, always watch out for egg-eaters!  Both Inland Silversides (non-native) and Three-spined Sticklebacks (native) are notorious eaters of both eggs and larval fishes.  We saw an enormous explosion of Inland Silversides in late 2020 and a smaller explosion in 2021.  We must keep an eye on Silversides, and we should consider control measures – if needed.


Creek-Side/Slough Trawls on Saturday.

Golden Anchovies at Art1 on 11 June.  Salinity was ~ 4 to 14 ppt.

I continue to study the riddle of Anchovy dorsal colors. Like the other Clupeiforms, Anchovies generally ‘blue-up’ in high salinity and ‘brown-down’ when water is fresher.  But, there are always many exceptions.   


Salinity was 15.3 at Art2.

Spawning-ready Anchovies always seem to seek low-salinity brackish marshes for spawning.  They ‘brown-down’ to golden-green or gold at these locations.  The eggs tend to be pinkest and plumpest.  Like Longfin Smelt in winter, Anchovies are drawn to brackish marshes where production of tiny food is highest.

  • There must be a dinoflagellate connection.  But alas, we cannot see dinoflagellates! 


Dump Slough was the winner for spawning Anchovies in June:  827 were caught at stations Dmp1 and Dmp2.  Only the two UCoy stations came close, with another 687 caught there.  Dissolved Oxygen dipped as low as 2.3 mg/l in upstream sloughs and Pond A19. 

The Anchovies appeared unphased by low DO.  They were energetic, sometimes flipping out of our hands as we attempted to photograph them. But, they became lethargic quickly and started to suffocate when held too long in the tray.

  • We had to measure, count, and return them to the marsh quickly lest they die.
  • Like sharks, Anchovies must swim to survive, at least when DO is this low.    

Do Anchovies seek low Dissolved Oxygen!?!?  More likely these Anchovies are seeking food. High food production, probably as tiny zooplankton, results in high rates of biological respiration, especially during the warm season. Dissolved Oxygen drops as a result, AND the Anchovies move in for the feast.

Deep Thought of the Day: Northern Anchovies are always on the move. They routinely ram-feed and ram-ventilate by charging through the water with mouths wide open.  Ram ventilation seems to be their strategy for exploiting warm upstream marshes.  Low DO may actually trigger Anchovies to swim faster and open mouths wider.


Anchovies at Dmp2. Salinity was 18.7 ppt.  DO readings ranged from 2.6 to 4.4 ppt.

Green-backs at Dmp2.  Salinity was a bit higher and Anchovies were a bit greener at the downstream end of Dump Slough. 


Golden-green in Pond A19.  Salinity was a little lower and the Anchovies were a little more golden in the Pond.    

Scoliosis.  We also found a very bent Anchovy, shown above.  Scoliosis can result from either natural mutation or from exposure to heavy metals or other pollutants.  Since this was the only bent Anchovy out of over 2,600 caught on the weekend, we attribute natural mutation in this case. 

  • It is a wonder that this fish could survive to adulthood with such an extreme spinal deformity.


Halibut and Sticklebacks eat Anchovies and their eggs. 

  • Young Halibut migrate from the Bay to grow big on marsh food.
  • Sticklebacks generally arrive here from the opposite, creek-side direction.
  • Both of these fishes mercilessly attack the burgeoning Anchovy population. Halibut eat the adults, and Sticklebacks feed on Anchovy eggs and larvae. 
  • We caught 10 young Halibut and 57 Sticklebacks on the weekend. Those number are not high, and frankly, we would greatly welcome more of both.


Bay-Side Trawls on Sunday. 

Anchovies at Alv1.  Their backs were golden-green here.  Salinity was 17.4 ppt.


A mix of goldish, greenish, and bluish Anchovies at Alv2.  Salinity was 18.7 ppt.

Anchovies do not like to follow the Clupeiform Color Rule.  Blues, greens, and golds often mix together as they ram-feed and ram-ventilate up and down the sloughs and creek segments.    


Anchovies were generally bluer at the LSB, deep Bay, stations in conformance with higher salinity.


Specimens with eggs or milt were found at every station except Art3.


More Anchovies in Pond A21.


Death from Above!  California Gulls chased us as we sped downstream on the way back to Alviso Marina.  The Gulls know that the marsh is flush with spawning anchovies.  They saw us releasing the catch at Coy2 and Coy3.  They chased us for a long way before they finally gave up.


Words are very unnecessary
They can only do harm.
Depeche Mode – 1990

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