Fish in the Bay – 14 January 2018 UC Davis Trawl – Longfin Smelt WITH EGGS!

Happy belated New Year! …

The UC Davis / Hobbs crew surveyed Alviso area sloughs and marshes on 13 & 14 January.   The 13th was sunny and a bit warm after rain the previous week.  Sunday, the 14th was cloudier and cooler.  Suffice it to say, it’s winter-fish time.

January brings good weather for ducks and duck hunters.

Winter freshwater flushing is critical for recruitment of certain fish we are seeing in greater numbers this year: American Shad, Threadfin Shad, Starry Flounder, Prickly Sculpin, and Longfin Smelt, as I have mentioned before.  But, there is a bit of a downside:  Fish and bug populations tend to drop right after the rains.

You can imagine that sharp fluctuation in water quality causes many species to “scoot or die.”    On the other hand, freshwater flushing is a natural stressor that helps keep many of our native species in top survival shape.  Non-native invaders didn’t evolve in this system, so, at least in theory, they are at a competitive disadvantage.

Christine Joab at Central Valley Water Board sent me this link to an interesting paper that documents rapid changes in the Bay benthic organism populations as waters change from salty to fresh:

You can imagine that similar seasonal and extreme climate driven shifts must also happen in all biotic communities; benthic, phyto, zooplankton, fish, even marsh plants.  Wet season is a bit of a biotic doldrum period.  January is an annual low point in fish populations.  You can see on the charts that fish got even scarcer as the Hobbs crew moved upstream on Sunday.

Saturday – Bay Side:

Sunday: – Upstream Side:

The beginning – where 1.4 million people discharge treated wastewater.  I started my Sunday, waiting for the UC Davis crew at our SJ-SC RWF discharge point.  This is the exact point where roughly 100 million gallons per day of treated wastewater flows into our outfall channel.  Cold morning air made mist rise over the warmer effluent.

It is amazing how quickly life colonizes here.  Literally within seconds of discharge, tiny bug larvae become so dense that coots move in to browse in winter.  In summer, clouds of mosquito fish proliferate by feeding off the same bugs.  California bulrush grows so dense you can’t walk through it year-round.

Jim Hobbs, Levi Lewis, and Pat Crain set up trawling equipment, notes, and navigation settings in preparation for launch.  I have to admit, there is a tremendous amount of logistical preparation for these boat trips of which I am blissfully unaware.

Black-crowned Night Herons.  As we motored down Artesian Slough against a slow incoming tide, I was instead focused on the hundreds of Black-crowned Night Herons blinking back at us from the misty canebreak.  At times, these Coyote Creek boat trips remind me of Disneyland’s Jungle Cruise when I was a kid; exceptions being that these animals are real, and I don’t have to stand in line waiting for the boat.

Winter doldrums.  This is what the marsh in Pond A19 looked like on Sunday.  This is a sad looking time of year.

American Shad & Threadfin Shad.  Catches this day were light compared to other times of the year.  The big winner was American Shad.  Yes, this is a non-native fish, but after 120-odd years, let’s just consider them naturalized citizens.  The Hobbs crew caught a total of 221 American Shad over the weekend; last year they caught between 10 to 20 on a comparable weekend.  The story was similar for Threadfins:  22 this January weekend; zero to two was typical catch last winter.  This is an ongoing biological echo from the February Freshwater Flush of 2017.  American and Threadfin shad babies recruited last year because of the giant freshwater pulse and have now returned as young adults.

Anchovy and Stickleback countershading.  Anchovies are the summer/fall fish.  They like it hot and salty.  So, we see hundreds or thousands up to November, but they are scarce in January.  The photo also shows the only Three-spined Stickleback caught this weekend.  Evidently these two very different species, anchovies and sticklebacks, show the same color changes with the seasons.  What is up with this?  In summer, sea-going anchovies display vivid green backs and Sticklebacks show practically the same bright green color. Now in winter, the backs of both species wash out to dull blueish-gray.  Some fish change color as indication of spawning readiness.  Some change color as a camouflage response.  Which factor is causing these two different species to undergo the same color change?

As also noted earlier in December, anchovies are looking really skinny this winter.  They must be stressed out.

More Anchovies. Anchovies are a filter feeding fish that eats near microscopic diatoms and zooplankton as a rule.  But, Dr. Hobbs has found them with corophium (small amphipods) in their stomachs.  By all rights, they should have no problem feeding on mysids here, and we found fairly abundant mysids at several stations.  But, obviously, the skinny anchovies caught on Sunday were not eating much.

The batch of anchovies below, caught in Pond A19, were showing a little more of the robust green-back color.  They were still pretty skinny though.

Bugs!  Like the fish, and plants, bug numbers, including shrimp, were low, as is typical after winter rains.  But, we continued to see a fair number of very fat, very juicy mysids in Coyote Creek and the ponds.  In the photo below, mysids appear as grayish strings of dots between the yellow Synidotea.

I tried to capture a magical moment when Synidotea meets mysid.  Not a bad shot.

The muted misty light makes clear-bodied mysids really pop out in a photo.

I read somewhere that eyestalk length and shape is the main way that experts identify mysid species.  Maybe someone out there can tell me which mysid species this is?

More fish.  This was some of the catch from Upper Coyote Creek station, one of the bigger catches of the day.  Lots of shad with five young starry flounder under them.  We are now past the main young starry flounder season, so their numbers tapered off after fall.

This young starry had a large bite scar.  We found several smallish fish with big wounds this day.  It is a reminder that there are much bigger fish in these waters, but they swim fast enough to keep out of the trawling nets.

Longfin Smelt. The more gratifying surprise was appearance of Longfin Smelt.  These are California natives that were designated as a State threatened fish in the Delta in 2009.  Last year, shortly after the February Freshwater Flush, Dr. Hobbs’ finally confirmed that this fish spawns here in Lower Coyote Creek.  But spawning only occurs when water is cold enough and fresh enough.  On this weekend, the Hobbs crew caught a total of 54 Longfins.  This compares to 10 or less in a typical winter month in previous years.

These first two were caught near the end of Artesian Slough.

Longfin closeup.  Longfins are not a particularly charismatic fish.  I showed this photo to one of senior facility operators.  “Oh, looks like a bait fish,” he sniffed.  He is correct.  The main ecological role of most little smelt is simply to be eaten by bigger fish.  That doesn’t diminish their ecological importance.  Just that their ecological role is largely invisible to most humans.

Nine longfins caught in Pond A19.  You can see in the data that most longfins hang out in restored ponds.  But, this year the news was so much better …

Longfins with Eggs!!!  Jim Hobbs identified spawning-ready Longfins on both Saturday and Sunday.  On Saturday he also identified some “spawning-spent” females (Females with flabby bellies indicating they had dropped their loads of eggs.)  Again, restored salt ponds are where most of the spawning appears to occur.

Jim Hobbs documenting his Longfin find on Facebook.

Another Longfin with eggs!  Last spring, Dr. Hobbs caught juvenile and larval longfins, confirming that these fish are spawning in LSB.  This year he nailed it!  These are ripe ready mama longfins on the verge of dropping eggs.

This female with eggs is being taken back to the UC Davis lab for analysis.

Levi Lewis transfers a batch of tiny bugs to a collection jar.  As usual, the UC Davis crew also collected mysid net and Clarke-bumpus net samples to quantify densities of different zooplankton size-categories.

Smaller nets catch tiny bugs.  This is the whole array of mysid net jars collected on the January weekend sampling.  This is a quick-easy evaluation of where the bugs are.  Small clear-bodied bugs = mysids (generally).  Really tiny, almost microscopic, brownish bugs = copepods.  Based on eyeball evaluation, I will make a leap and say … freshwater creek and wastewater treatment plant sources favor copepods.  Salty downstream areas and restored ponds attract and nurture mysids.  But, don’t take my word for it!  This is strictly an eyeball examination.

As always, so much more could be shown and said.  I will save the rest for another time …

Jim Hobbs after a weekend of trawling.



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