Fish in the Bay – May 2019, UC Davis Trawls – Cinco de Mayo

I joined the UC Davis / Hobbs Lab for a regular set of Otter Trawls on May 5th.  Last week’s report covered 20mm trawls (tiny fish and bug trawls) conducted on the 11 May weekend.

Trawl map.


Bay-side station trawling results.


Upstream of Railroad Bridge.


Fish and Bug Matrix – May 2019. … Wet weather fishes are doing well: 

  • Longfin Smelt are having their best year ever! – albeit they fled when temperature rose last month;
  • American Shad and Threadfin Shad seem to be on a similar track: high numbers in Jan thru March, then took off as waters warmed.
  • Pacific Herring recruited well; apparently about a month later than usual.
  • I don’t think of non-native Shimofuri Gobies as wet-weather fish, but their numbers are increasing. This may simply reflect ongoing invasion.

A few dry weather fishes are not doing so good in LSB: California Halibut and California Tonguefish.  These are common coastal fish.  Winter freshwater flushing keeps them away from upstream (in our case southern) portions of the Bay.


1. Shrimp Wars.

Tray of shrimp:  pinkish = young Palaemon, speckled/sandy = young Crangon.

Shrimp Races.  As of May 2019, the official year-to-date shrimp count is:

  • 13,000 native Crangon,
  • 2,993 non-native Palaemon, and
  • 2,056 non-native Exopalaemon shrimp.


Most Crangon we see are young recruits from the 2018-19 brooding event.

Crangon had a huge head-start this year as a result of the 2018 population explosion.  However, after January, Crangon and Palaemon numbers have been nearly neck-and-neck.  Exopalaemon are close behind.


Older Palaemon shrimp from Coy4.  At least two are berried females.  Note reddish color.

Palaemon and Exoplaemon shrimp were a mix of young ones and berried (egg-bearing) females.  As we discovered this winter, Crangon had one big egg brooding event from late-November through roughly February.


2. Lovely day in May began with a tragedy; followed up with a tire.

Please,  mind your fishing gear!  Jon Kuntz spotted this cormorant on Alviso Dock.  It has a fish hook, lure, and weight hooked to its beak.  Jon tried to carefully net it, so he could extract the hook.  But, the Cormorant was too fast.  It jumped to the other side of the slough.  He was weak, but we couldn’t reach him.  … And, we knew, this bird was doomed.  He may be just one double-crested cormorant in a world of fairly common cormorants.  But, we all want to help a bird when we can.  RIP.


A bummed crew cruises down Alviso Slough.


First haul: A tire full of bugs!

Tires are a mixed blessing.  It is literally a heavy lift to bring a tire on deck, and a real pain to extract it from the net and clean it.  Plus, they are a big ugly piece trash in the Bay.  But, tires provide very desirable shelter for tiny bugs and fish.


Prickly Sculpin – 2 views.

Prickly Sculpin. A large Prickly may have been the boss of the tire, or just randomly scooped up near it.  This creek denizen will have to flee back upstream soon as summer salinity rises.  In the bottom photo, you can see how he is using his buccal cavity to absorb oxygen until he finds himself back in water.


Bonus Worms! The tire gave up several intact polychaetes.

I am always looking for these interesting-faced pseudo-legged segmented worms.  They evolved down a line, more-or-less unchanged since the late-Ediacaran Period or early-Cambrian over 550 million years ago (  They were around before land plants or almost any other animal we much know about.


I believe this is a common Nereid polychaete found in many parts around the world:  It is not native here, and not surprisingly this one was found just downstream from Laine’s bait shop and the Alviso boat launch where sports anglers set off for fishing.  It is possible that some of these worms here are escaped bait.  Nonetheless, they populate places all around the Bay and are eaten by most fish and birds.  They are as beneficial as earthworms as far as I know.  Plus, they are edible for humans: eaten by some people in China and Vietnam.


A pair of polychaetes about to go at it – tentaclo a tenaclo.

I was curious to watch how polychaetes interact.  As we motored to the next trawl station, I watched them bump and maneuver around each other.  They didn’t interact a lot, but on occasion, they did seem to recognize their own kind in a defensive sort of way.


Polychaetes are not exactly unattractive.  … once you get to know them a little.


Four-eyed polychaete from Art3 photographed on 10 Feb 2019.

More than one kind of Polychaete?  I took a picture of the worm above a few months ago.  The eyes and facial arrangement look a little different.  I don’t know if it represents a different species or just an older polychaete.


3. Fish


Baby fish season was not quite over.  We were still catching a few tiny fish, but numbers are tapering off.

Bad News:  Only two Longfin Smelt!  Dr. Hobbs and everyone had been hoping that huge catches of Longfins in November thru January, followed by spawning in March, would result in a bumper crop of young Longfin Smelt in the Alviso Marsh Complex (AMC).   Alas!  This was not to be.  Longfins, young and old alike, appear to have vacated the premises.

Good News?? The only good news is that 4-1/2 years of good comparable data indicate that Longfins vacate the area EVERY YEAR by around May. (See Fish and Bug Matrix Chart above).  Presumably, they head out to the deeper Bay or out to sea as temperatures climb.  Where exactly do they go?  How reliably do they return to the same location?  If we don’t know, nobody knows!


Longfin Smelt, Juvenile Herring and Anchovies less than 40mm are easily confused.  I indicated in bright RED, in the chart above, two instances where tiny fish looking like Longfins were identified or confirmed.   Hopefully, the alternate weekend 20mm trawls will uncover additional larval Longfin Smelt and lifecycle clues.


Staghorn Sculpin family portrait:  a large adult with two pair of juveniles of different ages from Alviso Slough.

Staghorn Sculpin.  April seems to be the main month for baby sculpin recruitment.  But, we continued to catch a large number of tiny sculpin in early May, both Staghorn and Prickly.


Juvenile flatfishes from LSB.

Butter Sole and other flatfishes. The Butter Sole and California Halibut were taken back to UC Davis for lab identification.  The Speckled Sanddab is the only fish in this group that is approaching adult size.

Confirmation of the Butter Sole was a surprise.  This is a new fish for Lower South Bay.  Butter Sole are endemic up and down the West Coast.  I presume this juvenile drifted in from its normal range outside the Bay.


Yellowfin Goby juveniles from Pond A21.

Yellowfin Gobies. These noxious invaders are a little down this year.  But, they are by no means out.  Many that we saw in May were young.  Tiny yellowfin gobies, too small to positively identify, are usually recorded as “Unidentified Goby.”


Yellowfin Goby juvenile, approximately 50mm, 2 views.

It gets easier to distinguish tiny gobies and other fish once they grow past 30 to 50 mm.  Small yellowfins are primarily identified by mouth size.  The maxilla (upper mouth corner) does not extend to a point below the eye.


Cheekspot Goby adult, approximately 40mm, 2 views.

Cheekspot gobies. Aside from a greater amount of melanophore pigmentation, Cheekspots also have a mouth extending to just below the eye.  Or, another way to look at it, the snout is shorter.


Left: Cheekspot Goby.  Right: juvenile Shokihaze Goby.  Below: young Shimofuri Goby.

Some Cheekspot gobies have darker pigmentation.  I was hoping to find examples of Arrow Gobies for comparison, but the mouth size of all specimens so far tells me they are Cheekspots.

Someday soon, I hope to find a clear example of an Arrow Goby with mouth extending well under, or behind the eye.


A very colorful adult Shimofuri Goby.

Shimofuri Gobies vs Chameleon Gobies.  According to literature: Shimofuri Gobies are most easily distinguished from Chameleon Gobies by the terminal stripe on the anal fin.  Orange = Shimofuri; White = Chameleon.  So …. what does it mean when our adult Shimos have alternating white-orange-white striped anal fins????  Is this a new hybrid?  Investigation continues!


Northern Anchovies from Coy4

Northern Anchovies.  Only 17 Anchovies were caught on the 4-5 May weekend.  Interestingly, 95 were caught in 20mm trawls just a week later on 11 May.  Not only that, but the 11 May Anchovies were a different color: Golden-green!  Photos above show most Anchovies on 4 May ranged from green to blue-green, and a few young showed slight signs of blue.


Anchovies from different stations.

More Anchovies from 5 May.  Green was the predominant color.  Two shown above were golden-green.  Just one week later, all but a few anchovies were uniformly golden-green.  (See previous Fish in the Bay report.)

I believe that a different Anchovy population came into the Alviso Marsh Complex between 5 and 10 May.  The increase in numbers alone suggests that.  However, we cannot yet rule out the possibility that warming temperatures may influence dorsal color, e.g. dark green may turn golden-green as water temperature rises???


Pacific Herring juvenile from Alv2.

Pacific Herring.  2019 was another good year for Pacific Herring recruitment. Again, young Herring were very colorful this year.


Jon Kuntz showing a Leopard Shark pup.

Only one small Leopard Shark was caught.  At 16 to 17 ppt, the main part of LSB was still very fresh for sharks and rays.


4. A couple of odd things.


  • Top photo shows a cluster of egg capsules glued to a dead clam shell. The capsules look similar to those made by some types of whelks or oyster drills (carnivorous snails).
  • Bottom photo shows fish eggs that were picked up either at LSB2 or Coy2. They look superficially similar to jacksmelt eggs shown last month, but a fish egg expert would have to identify them.


Another Orange-striped Green Anemone.  I saw a few if these in January and again in March.  They may have been present in previous years, but I never noticed them before.  The photo also shows what I believe is an early stage of encrusting bryozoan colony development.  These are tiny coral-like animals.  Their hard shells eventually encrust and consolidate loose gravel and oyster shell material on the bottom.


5. Harbor Seal disturbance experiment.

Harbor seal attention span = 6 seconds!  The seals are OK!   Sarah Allen at National Park Service recently sent me the Pacific Harbor Seal 2016 Annual Report

I was elated to read that San Francisco Bay harbor seals are doing well.  However, I was dismayed to discover that “head alerts” are counted as Harbor Seal disturbance.  I take photos from at least a few hundred feet away.  Even so, the seals often look at me (head alert).  Many other small boats pass by Calaveras point each day as well.  Personally, I don’t think the seals are very disturbed by this.  But, I had to test.

In this example, I snapped two photos of seals six seconds apart.  Normally, I would only feature the first photo of seals looking at me.  But, for purposes of documenting Harbor Seal disturbance, I added the second photo of the same group.  Clearly, these seals saw us, and they were bored!


Happy belated Cinco de Mayo.


Comments are closed.