Fish in the Bay – 10-11 March 2018 UC Davis Trawls – English Sole & Herring are back!

I went out with the UC Davis / Jim Hobbs fish researchers on March 10th.  This is my belated report.  I went out on a Saturday for the Alviso Slough and Bay-side fish survey.

Saturday, 10 March – Bay-side trawls

Sunday, 11 March – upstream and east of the Railroad Bridge

Fish numbers are climbing with arrival of spring, as expected.  Data in the above tables show that warmer season fish are returning, particularly Shad, Herring, a few Anchovies, and surprise to us – English Sole.

I made a couple of changes to the tables:
Total Fish number is summed at upper right of each table.  ( I removed the row that summed total fish species per station to simplify the table.)
b. I continued addition of a row at bottom of each table to show Comb Jellies. ( I also snuck in a single tally of Philine snails at bottom of upper table.) As time goes on, it gets harder to ignore important invertebrates.
c. Physical water quality parameters at top of tables were taken on the surface at end of each trawl.  If there was dramatic difference between surface and bottom readings, I entered both numbers: “Surface/Bottom.”   This makes for a messy table, and I had to use tiny fonts.  But, it is important to note that temperature, salinity, and dissolved oxygen can fluctuate wildly with each tide and diurnal cycle. Stratification is common.  For example, at station COY-3 on Saturday, bottom DO was alarmingly low at 3.6 mg/l, but at the same time and place, surface DO was a very robust 6.9 mg/l.

Trawling begins.  We met at Alviso launch for a pleasant overcast day of trawling.  Hobbs Lab researchers were Jim Hobbs, Micah Bisson, and Malte Willmes.

We started at Pond A21.  Fish survey advance planning includes development of a “Float Plan.”  Lower South Bay is very shallow, and tides rise and fall up to several feet.  Before each trawling weekend, Jim Hobbs works out the timing and sequence of each day’s ten trawling stations with respect to tide.   In this instance, we started a little after 8:00 AM with an ebbing tide, so we had to hit Pond A21 before water level fell too low for Otter Trawls.

In the photo above, the borrow ditch ringing the interior of Pond A21 becomes a narrow and shrinking channel as Malte deploys the net.  The team had to work fast because the ditch was getting shallower by the minute.

Many ducks in front of us; none behind!  The restored ponds host hundreds, if not thousands, of ducks and other waterfowl we can see as we approach.  But, the ducks are wary.  Hunters shoot at them nearby.  As soon as we motor into the pond, “duck heaven” immediately becomes “duck wilderness.”  As they burst into flight, I could make out hundreds of Gadwalls, Northern Shovelers, American Widgeon, a few Mallards, and some Ruddy Ducks.

Disappointing that they flee, but still a wonderful sight.

Herring!  The two trawls in Pond A21 pulled up 70 young Pacific Herring.  (Herring are the small silvery fish interspersed among the three larger shad.)  This is very good news.  The Herring spawn in Lower South Bay coincides with late winter rain and is extremely variable; some years good, some years very small to almost absent.  To my memory, in past years, young herring were caught much further upstream at Upper Coyote (UCOY) stations.  This spring, young herring were abundant in both restored ponds, A21 and A19, and there appear to be more of them.

Herring closeup.

Two larval herring on the back of my hand.  From Dr. Hobbs I learned that larval herring and larval longfin smelt have the same long, snake-like, body shape.  The swim bladder is the distinguishing feature – Longfins have a triangular shaped swim bladder. The Herring bladder is more elongated.

Baby Staghorns – more of them.  We saw very young Pacific Staghorn Sculpin in February, now a few more in March.  These are so small that they must have been hatched very close by.  Around 2012, Staghorns were, by far, the most numerous fish caught in trawls.  Then, they practically disappeared for a few years before becoming common once again.

Longfin Smelt found after we went out in Lower Coyote Creek.  A total of five Longfins were caught on Saturday and five more on Sunday, all in deeper water of Lower Coyote Creek.  We presume the remaining Longfins are seeking cooler water.  Above, Micah studies a captured Longfin and records its vital info.

Two Longfins bagged and tagged.  We must understand why this once-abundant fish flourishes here in Lower South Bay while populations are crashing elsewhere in the Bay-Delta complex.  What is the secret?

English Sole – a big surprise.  For the first time since at least 2014, we caught large numbers of baby English Sole: 54 at COY-2 plus a few more at other stations.  Jim Hobbs tells me that English Sole recruitment is driven by cold ocean upwelling.  We surmise that warmer El Nino years may have depressed numbers of young English Sole.  Now they are back.  ( Photo shows many of the 54 English Sole.  A young Starry Flounder is at top right.)

English Sole harbor some kind of parasite.  There were nasty looking red and flesh-colored bumps on many of the Sole.  Jim Hobbs tells me this is a common affliction amongst Sole.  I tried to scratch off one of the red welts with my fingernail.  It didn’t help.  The parasite is deep in the flesh.  Good news: not all the Sole have this parasite, and it is not visible in any other species here.

BAD INVADER!  Philine Snails, AKA: New Zealand Sea Slugs, Tortellini Snails, Snotball Snails, etc.  Far out in the middle of Lower South Bay, eighteen Philines were scooped up. These are non-native predators of other snails and bivalves.  In fact, Jan Thompson in a 2010 paper mentioned that Philine could be one of many predators that limit nuisance Corbula clam populations in Lower South Bay.

Jan cited a Gosliner 1995 paper that documents arrival of Philines to SF Bay in Summer of 1992.  Philines are presumed to be ballast water invaders:

However, the Hobbs team only sees these nasty snotballs deep in the center of Lower South Bay.  Meanwhile, Corbula clams consistently reside at the mouth of Alviso, Artesian, and Coyote Sloughs where freshwater meets salt water.  I think Philine and Corbula rarely meet here, but I don’t know the population distributions in North Bay.

Another nickname for Philine snails is “inside-out snails.”  They say that the shell of this gastropod is deep inside the flesh.  I borrowed a pocketknife from Hobbs and cut one open.  I was hoping to find a tiny black spiral shell.  Nope!  Instead, I found this three-sided structure bound by connective tissue.  What a disappointment: It doesn’t have a cute shell, it doesn’t appear to be killing Corbula, it is truly good for nothing.  Photo above shows results of my Philine autopsy.

GOOD (Resident) INVADER!  Comb Jellies, AKA: Ctenophores.  The Hobbs team caught large numbers of Comb Jellies in February; not quite as many in March.  Since December 2015, I have noticed these to appear in winter.  Jim Hobbs’ theory is that they need cold temperatures.  Lower South Bay summer warmth keeps them out.  They are native to the Bay, and more frequently seen in North Bay.  As voracious eaters of zooplankton, Comb Jellies could be a huge hazard to Lower South Bay, but their effect seems to be fairly benign here.

An article from 2016 describes how researchers learned to culture Comb Jellies at Monterey Aquarium.  It also tells many amazing facts about them.  Knowledge gained from studying Comb Jellies may well save us all:

They look like crystal clear water drops when pulled out of muddy brown Bay water.  Comb Jellies are arguably the most beautiful organisms on earth.

Comb Jellies can threaten survival of pelagic fishes, particularly Anchovies. Ctenophores compete with Anchovies for the same food and even consume young Anchovies and eggs.  The 1982 Ctenophore invasion of the Black Sea is well documented:  In 2016, the invasion appears to have spread to the Adriatic Sea off Italy:

Anchovies.  I am going to go way out on a limb and speculate that one reason Anchovies risk Humpback Whales and other dangers to swim into the Bay each warm season is because Ctenophores can’t compete with them here.  These marshes are highly productive and too warm for comb jellies, hence an Anchovy paradise.  Just a thought.

In any case, Northern Anchovies are showing up in slightly greater numbers.  (There are always some year-round residents.)  Some have vivid green backs which we presume indicate ocean-going Anchovies.  Brown-backs (sometimes pinkish) are known to be resident-spawning.  But, we also see clear or gray-backed Anchovies – who knows?

Bonus Fish!  There was so much more that was worth discussing, but too little time and space for now. A short summary:

Shimofuri Goby.  I believe this was an apex alpha male Shimofuri.  Fabulous specimen worthy of a poster.  You can imagine the commotion on the boat when we pulled this big boy up.  Even Malte took a photo of this special fish.

Bat Ray.  Only one baby bat ray was caught way out in the middle of LSB.

American Shad.  I noticed that American Shad caught way out in the Bay are much more colorful than those caught in the Ponds.  Same fish!  Same day!  Look at the blue-green backs of these beauties!

Not so colorful.  This batch of American and Threadfin Shad was caught in Alviso Slough.  See what I mean?  You have to go out in the Bay to see colorful shad.

Shiner Surfperch.  This was one of two Shiner Surfperch caught in March. They are not super rare, but not as common here as they used to be in the 1980s.

White Croaker.  A single very tiny baby White Croaker was caught at COY-4 on Saturday.  This fish is common along the California coast, and was once common in Lower South Bay.  Hobbs trawls tend to catch one or two PER YEAR nowadays in Lower South Bay.  We have no idea why this fish is so rarely seen here now.

White Sturgeon.  This is Jim holding the one Sturgeon caught on Sunday.  I was not there to see it, so this was “the big one that got away” for me.

Harbor Seals.  As we slowly trawled the mouth of Lower Coyote Creek, I trained my telephoto on the colony of Harbor Seals lounging in the mud near Calaveras Point.  Many of them were looking back at us.

I even saw a few slide into the water as we passed.  It appears that these seals recognize a trawling rig.  Or, maybe they raid the catch of any passing anglers.  It occurred to me that with a bucket of fish and a couple of beach balls, I might be able to teach these guys some tricks.  (Just joking!)

In any case, that’s more than enough for now.

Leave a Reply