Fish in the Bay – April 2021: More baby fish.

Trawl map.

April is “Baby Fish Month.”  We caught almost 1,900 unidentifiable baby fish.  Most of these tiny babies were almost certainly non-native Yellowfin Gobies. 

  • This new batch of baby fish adds to the ongoing explosion of young Staghorn Sculpin and English Sole we first saw last month.
  • Unfortunately, the baby Pacific Herring recruitment is over. Our monthly catch dropped from 3,700 Herring babies in March to only 26 in April. Young Herring flee this area quickly after hatch.
  • Shrimp are doing surprisingly well so far this year.
  • Lots of bigger fish are feasting on our baby fish and shrimp bonanza – more below.


Bay-side stations trawling results.

All “Unidentified Gobies” we count are too small for naked-eye identification.  We have learned from history, and occasional checks by macro lens, that the vast majority of these fry are baby Yellowfin Gobies.    

  • English Sole greatly prefer Alviso Slough and downstream Bay-side locations.
  • Staghorn Sculpin were caught at every station!


Upstream of Railroad Bridge.

Salinities 12 ppt and less are again highlighted in blue.  I have not figured out why the creeks continue to exhibit so much freshness given the near absence of rain this winter.  But, freshness is good: most of our native fish and shrimp seek fresher water for spawning and recruitment. 


1. Baby Fish Month. 

Yellowfin Goby closeup: Two yellowfins and two unknown gobies, Pond A19.

“Unidentified Gobies.”  Macro-lens magnification helps us see dark abdomens that distinguish two tiny Yellowfins from the other two gobies in this photo.  A fingertip is shown for size comparison.   


Yellowfin Goby explosion at station Dmp1.

More “Unidentified Gobies” with mysids.  Tiny gobies were mostly caught in ponds and upstream stations away from the main channels.  Yellowfins comprise 90 percent or more of this batch with some other types of gobies mixed in.  

Nonetheless, this group was officially tallied as “Unidentified.”  The photo makes it look deceptively easy to identify them.  In real-time, these tiny wriggling fry are impossible to sort and identify with speed and accuracy.


More baby Yellowfin Gobies alongside Mysids and tiny baby Crangon.

Non-native baby Yellowfins appear to dominate the roughly 1-to-2 centimeter “tiny critter” community in upstream pockets of our trawling area.  They are about the same size as native mysids and baby Crangon, so they must be important food for bigger critters up the trophic web.  


English Sole and Staghorn Sculpin dominate the baby fish community in Alviso Slough.  We can easily see a difference from these “tray-shots.”  Baby gobies probably get eaten pretty quickly after hatch in Alviso Slough this year.


The composition of young fish and shrimp was more diverse in the main channel of Coyote Creek.  In the photos above, I pushed Staghorn Sculpins to the right and the few English Sole to the left to make a crude representative display at each station.

General overview of tiny fish spatial distribution:

  • Upstream dead-end sloughs and Ponds = Thousands of baby gobies.
  • Coyote Creek main channel = A mixed bag of fish and shrimp.
  • Alviso Slough = English Sole and Staghorn Sculpin.


2. Spawning Grounds Update.

In the February blog, we designated the stretch of Coyote Creek between stations UCoy1 and UCoy2 as “Spawning Grounds” because this area is a consistent year-round hotspot for spawning Anchovies, Sculpins, Longfin Smelt among others.

This month we observed more species of spawning (or birthing) fish here and nearby.


Cheekspot Goby at UCoy2.

Cheekspot Goby.  The Cheekspot Goby shown above is one of several that appeared to be full of eggs.

  • This female is desperately seeking a suitable male. She must paste her eggs on the ceiling of his mating cave. 
  • After brief examination, she was immediately released back to Spawning Ground.
  • Most likely, some of the many “unidentified gobies” we count here are baby Cheekspots.


American Shad (top) and Shiner Surfperch (bottom).  Art1, 10 Apr 2021.

American Shad.  Eleven young shad were caught over the April weekend.  American Shad on the East Coast go out to sea for three or four years before returning to their natal streams to spawn.  Our Shad act differently; they return every year whether ready for spawning or not. 

Shiner Surfperch.  Three visibly pregnant Shiner Perches were caught at stations Alv3, Art1, and UCoy2.  These fish are live bearers; their bellies are filled with 10 to 20 developed babies.  The newborns will need tiny food.  The pregnant female shown above is looking for a good upstream place to release her brood.


Longfin Smelt with eggs at Dmp2.

Longfin Smelt.  Only 9 Longfins were caught. This very plump egg-bearing female was picked up along with three smaller adults at Dmp2.  April is very late in the Longfin spawning season, so this was a surprise.


3. Big Fish Prowl the Nursery.

Bat Rays.  Eighteen Bat Rays were caught.  All but one were captured at the deep LSB stations.  We should see more of them as the season warms up.


Striped Bass.  32 Striped Bass is a fairly typical haul for an April.  Full fat bellies indicate that these miniature barracudas were feasting on baby fish.


More well-fed Stripers at upstream stations.

Starry Flounder.  We have been catching an average of exactly one (1) Starry Flounder per month since late 2018.  This is a very low number, but it has been steady.


White Sturgeon.  This young Sturgeon was captured and released at UCoy1:  810 mm/ 32 inches standard length.  We saw another Sturgeon a little further downstream on sonar the following day.  Coyote Creek was full of Sturgeon food in April.


Young Halibut at Alv2.

California Halibut.  We continue catching about a dozen young Halibut per month this year. 


Baby Halibut at UCoy2

Smaller Halibut are usually caught at upstream stations.  They move downstream in search of bigger prey as they grow.


Leopard Sharks.  These two newborns were caught at Coy3 and Coy4.  Unlike most fish, Leopard Sharks are born live.  At this size, these babies must be only days old.  They could be members of the same liter! 


4. Beautiful Birds Prowl this Nursery Too.

Clockwise from top left: Caspian tern, Lesser Scaup (blue-billed duck), Clark’s Grebe, Eared Grebe.

These diving birds eat small fish, shrimp, clams, and worms.


Top: Ruddy Duck and Canvasback.  Bottom American White Pelicans and Gulls.


5. Jellies in Lower South Bay.

Pacific Sea Nettle at LSB2.

Pacific Sea Nettle.  Pacific Sea Nettles are common along the Pacific coast, but rarely drift this far into the Bay.  It has been at least a few years since we saw one of these.  This is an exceptionally beautiful and graceful jelly.


Ctenophores (Comb Jellies) at LSB2

Ctenophores!  Ctenophore numbers jumped from roughly 50 each month in February and March to over 3,600 in April!  Every once in a while, Ctenophores (Comb Jellies) bloom in Lower South Bay. They are hermaphrodites that reproduce like crazy when food is available.  


Another Booger.  I still do not know the identity of these 3-inch by 1-inch jelly-like organisms!


6. Bryozoan Reef Seen on Sonar.

Our Bryozoan Reef has been located on sonar!  Over the past year, we have been seeing more hard chunks of Encrusting Bryozoan near station LSB1.  Tiny Bryozoan animals form hard shell communities nearly identical to a coral reef. 

Bryozoan “zooids” and Coral “polyps” are different, unrelated animals.  Nonetheless, chunks of Encrusting Bryozoan look and feel like coral to my untrained eye.  They even look like a rough coral scape on sonar!

We found the reef!  From fish-finder/sonar view, a rough reef-scape appears to line the west slope of the deep channel in LSB. 

Encrusting Bryozoan has been found on ancient shells at LSB stations since trawling began ten years ago, but the big chunks seem to be a new and growing phenomenon. 


Orange-striped Anemones have broken loose!  Until this winter, we have only spotted them at deep LSB stations.  This spring, we continue finding specimens far upstream. 

These tiny anemones must be native Diadumene franciscana, aka “the San Francisco Anemone.”  They are about the size of the nail on your pinky finger. 


7. Shrimp Wars.

Shrimp are doing very well this year despite lower than average rain.  Total April shrimp counts were:

  • Native Crangon: 5676
  • Non-native Palaemon: 3526
  • Non-native Exopalaemon: 281

All Crangon were young recruits.  This is another mystery because adult brooding Crangon females were late to arrive and relatively few in number between December and February.  Where did all these Crangon babies come from? 


Crangon nigricauda (Black-tails).   A little farther downstream, an interesting pocket of Black-tails persists near station Alv3.  Black-tails are the saltier cousins of our more familiar Brown-tail / Crangon franciscorum shrimp.

Crangon at all other stations were overwhelmingly the Brown-tail variety.


A mix of native and non-native shrimp at station Dmp2.

All three types of shrimp were generally concentrated at upstream creek and slough stations.  Very few shrimp were found in the Ponds or at deep LSB locations.  This was probably influenced by their respective brooding and recruitment cycles:

  • All Crangon were young recruits.
  • At least a plurality of Palaemon and Exopalaemon were brooding females full of eggs.

Good News!  We are having a very good shrimp year so far!

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