Fish in the Bay – May 2019, UC Davis Trawls – Just a fun 20mm day in the Bay

20mm trawls on May 11th.   I rode along with Dr. Hobbs on both May 4th, for regular monthly otter trawls, and again on May 11th for this set of 20mm trawls.  In the interest of time, I am reporting more recent 20mm voyage out of sequence, and I Facebook posted many of these images on Sunday.



11 May Jar Graph.


Fish data table from 20mm trawls on 11 May.

Technically, these 20mm trawls are intended to catch young Longfin Smelt in the jars shown above.  Everything else is by-catch. 

Ironically, everything else constitutes the tiny fish and bugs that serve as environmental indicators of a very healthy Bay.  How can we assess how healthy this Bay is if no one trawls? (Rhetorical question.)

  • Good news: contrary to expectations, the tiny fish haul was pretty good. We saw lots of Anchovies, Rainwater Killifish, and Pacific Herring, in that order.
  • Bad News: We MAY HAVE caught only ONE Longfin Smelt (See jar photo far below!).  It is likely that additional baby Longfins will be found from lab analysis of our sample jars, but clearly the abundant fry we expected from recent Longfin spawning either quickly fled out to sea (or deeper Bay) or they got eaten!

1. 20mm Trawling

Ale Zaydahr-Kulka prepping the 20mm net as we waited for Alviso Boat Launch to open.

We started the day as early as possible to catch the morning high tide in Alviso Slough and Pond A21.  Unfortunately, the public launch in Alviso opens at 8 AM, so logistics are tricky. The tide turned on us by the time we were in A21, so only one Pond station could be sampled.


Ale at the launch on Alviso Slough.

Green marsh.  This may put some people off, but as atmospheric CO2 climbs over 415 ppm   … I see green!  Lots of green!  Maybe carbon-sequestering marshes can save us all!

Is it just me, or is the Earth getting greener? …

California Bulrush.  We see effects of a recent wet winter in this photo.  The tall tules with brown flowering tops on the right side are California Bulrush  (  California Bulrush has colonized much further downstream in Alviso Slough, and in Pond A19.  The expansion is a clear reflection of fresher water.

Alkali Bulrush.  In the immediate foreground, and on the other side of Alviso Slough, we see the more typical salt-tolerant Alkali Bulrush (  Even the Alkali Bulrush is looking especially tall and green this year.


Hobbs Lab Junior Specialists, Alyssa Baldo and Ale, deploying the 20mm net in Pond A21

This was the start of our first and only trawl in Pond A21.  You can guess from the appearance of exposed mud banks that we were running out of water as tide receded.  The boat cannot pull a 20mm net in less than 3 feet of water, and we were about 30 minutes away!


Alyssa examining the first 20mm net catch of the day.


2. Megafauna

Megafauna map.



Great Blue Heron on a mud ball.



Great Blue Herons at the mouth of Alviso Slough.

Great Blue Herons seemed to be out fishing in greater numbers than usual this morning.

Plants that tolerate high-salinity Bay water tend to be sparser and shorter.  However, this year salinities at all stations upstream of the main Bay continued to be in the single digits.  Even downstream at the mouth of Coyote Creek, the landscape above the tideline is exceptionally green.


Harbor Seal pup!  I assume mama was teaching her pup to forage along the west bank of Alviso Slough.  Both took notice of us as we trawled past.  The innocent baby was a lot more curious about us.  The mother kept nudging baby to keep moving.


It didn’t help that a boat full of four humans were excitedly watching mom and baby from mid-channel.

Mama seal has taken on the full South San Francisco Bay “Red Seal” hue.  Will baby turn red with age?


A small portion of the main colony of Calaveras Point Harbor seals.

As noted before: Harbor Seals usually watch people when people watch them.


Bald Eagle circling high above the mouth of Alviso Slough.

Bald Eagle.  I am pretty certain this was either mom or dad Bald Eagle from the nest over Curtner Elementary School in Milpitas that I often mention. This is the pair that hatched their 4th and 5th chick in April.  (Albeit, the original dad eagle may have passed away.  Mom eagle apparently remarried.)

Bald Eagles generally ignore people no matter how closely we watch them.


American White Pelican far off the mouth of Guadalupe Slough.

American White Pelican. This was one of several seen on 11 May.


3. Tiny fish

20mm net catch at station Coy4.

We caught 95 Northern Anchovies in Alviso Slough and the Bay.  Anchovies were at all stations except the far upstream station Alv1.


Northern Anchovies and some Pacific Herring from Station Alv2

Anchovies and Herring are Humpback Whale food.  We must feed our whales!


Golden-green Anchovies from station Alv2


More golden-green Anchovies from station Alv3


Golden-Green Anchovies from Coy4

Almost all Anchovies were Golden-green.  The exceptions were a few true “Green-backs” at LSB2 and another one in Pond A21.

From the little I know, golden-green is not a typical ocean-going Anchovy dorsal color.  We usually expect our Anchovy ocean migrants to have vivid emerald green-backs, per Hubbs (1925), or distinct peacock blue-backs following more recent observations.  On the other hand, since 2016, we have not been seeing completely “colorless” pinkish or “Brown-backs,” again per Hubbs (1925).

Golden green-backs were caught about this time last year as well.  Many of these shown above are clearly adults.  I speculate that these are Bay residents.  They may be precursors to, or otherwise closely related to, true Brown-backed marsh residents. Time will tell.


“Green-back” Anchovies from LSB2!

These were some of the few “Green-backs” caught on the 11th.  They are not fully “colored-up,” but they are showing the emerald green we expect from ocean-going stock.


Adult and juvenile Anchovies from LSB1.  Two Pacific Herring are at far left.


More juvenile Anchovies from LSB2.

The Hobbs team is catching a lot of juvenile Anchovies in both North and South Bay locations.

Until now, I presumed that Anchovies must be spawning in Alviso Marsh Complex.  But, Dr. Hobbs reminded me that no eggs or yolk-sac larvae have been detected to date.  Like Herring, Anchovies may spawn in Central or North Bay with larvae drifting, then recruiting, in our LSB locations. … more investigation needed!


Juvenile Pacific Herring.  All but a few have “colored-up” to green-backs.


Another juvenile Pacific Herring.

Young Pacific Herring continue to show green dorsal color.  In previous years, young Herring were caught through March, and they were slightly smaller and uniformly brown.  They seem to be staying in LSB a little longer this year, so we are seeing slightly more mature fish.


Prickly Sculpin.

Prickly Sculpin were caught near the mouth of Lower Coyote Creek (Stations Alv2, Alv3, and Coy4).  These are the little sentinels that continue to tell us that we had good creek flushing this year.


Rainwater Killifish with one Pacific Herring and a young, nearly colorless, juvenile Anchovy.

Rainwater Killifish are non-native but very common around California.


Arrow Goby? Or Cheekspot?

Probably a Cheekspot Goby.  From a distance, I would identify this fish as an Arrow Goby.  However, I recently learned that the corner of the mouth of an Arrow Goby should extend back behind the eye.  This mouth is closer to Cheekspot Goby size.


California Tonguefish from LSB2

Once again, I nominate the Tonguefish as “Weirdest fish in SF Bay.”


Baby Bay Pipefish at LSB2.

This baby Bay Pipefish was way downstream from the marsh waters where we usually expect to see it.


Longjaw Mudsucker (Top).  Same Longjaw Mudsucker with a Rainwater Killifish (bottom).

Longjaw mudsucker.  The pattern of black melanophores across its body is the identification key.  With luck, the Mudsucker will grow to several inches.

The Rainwater Killifish is almost adult size.


Longfin Smelt?

Longfin Smelt in the jar.  The fish indicated above appeared to be a Longfin, but it will have to be confirmed in the UC Davis taxonomy lab.  Hopefully, more baby longfins will be teased out from these jar contents.


4. Ship Wreck?

Derelict Boat with Shoreline Amphitheater in background.

Shipwreck.  This old boat on mudflats near Mountain View looks like it has been here for a long time.  Neither Jim Hobbs nor I recall seeing it before.  This could be a new hazard to navigation that broke loose from somewhere nearby.


… May 2019 otter trawl report to follow.


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