Fish in the Bay – 14-15 April 2018 UC Davis Trawls – My friends caught over 2,000 fish and all I got was a turtle!

Hello folks.  I joined UC Davis fish researchers on Sunday April 15th.  Every South Bay fishing weekend I choose either a Saturday or a Sunday to join the Hobbs crew.  It is a calculated choice:  Bay-side usually has bigger fish, Upper Coyote Creek-side is fresher and greener.  Unfortunately, this weekend, I chose unwisely, as you can see in the data below.

Saturday, 14 April – Bay-side trawls

Sunday, 15 April – upstream and east of the Railroad Bridge

I missed the big fishing day on Saturday: 1809 fish!  I also missed the baby leopard shark and some very cool looking jellyfish. Fortunately, Jim Hobbs and crewmates took a few Saturday photos to help tell the story.

Saturday Trawls.  The number of fish caught on Saturday versus Sunday was much higher (1809 versus 200).  In addition, the Saturday catches seem to show interesting trends:

Northern Anchovies are returning.  We may be looking at the first wave of returning springtime Anchovies.  271 were caught out in Lower South Bay.  These are ocean-going greenbacks.  We nearly always catch a few anchovies throughout the year.  (There is a resident population that seems to stay in the Bay.)  But, Anchovy numbers dwindle during cold December through March months.  The main population of Anchovies migrate from ocean spawning areas to Lower South Bay marshes by summer and fall.  The April 14th catch was not huge, but it is the most anchovies seen on a single day since the big Flush in February 2017.  (photo credit: Jim Hobbs’ cell phone)

Pacific Staghorn Sculpin are clogging the net.  I reported over the past two months that we were seeing very tiny baby staghorns in Lower Coyote Creek and restored ponds.  Now we see bigger staghorns, and they are caught in large numbers not seen for several years.  The staghorns were mainly concentrated at the mouth of Alviso Slough on Saturday (1246 of them) and on Sunday in Pond A-19 and at nearby UCoy-2 station.  These locations correspond closely with where we saw baby sculpin in previous months; a strong indication that these are home-grown sculpins.  But, why did this most-numerous fish in 2012-2013 decline in numbers for a few years?  Why the population rebound now in 2018?

Jellyfish invader from the sea!  Dr. Hobbs emailed and Facebook posted this gnarly-looking jellyfish on Saturday.  He hesitates to identify it, so it is recorded as one of 28 “Unknown Jellies.”  In my unprofessional opinion, I think this individual is a Pacific Sea Nettle (PSN). Sea nettles were reported to have invaded the Bay in 2009:  But, UC Davis researchers were not trawling in those days, so we do not know if jellies caught this April are an early warning.  If you read about human swimmers being stung later this year, remember, you saw it here first!   (photo credit: Jim Hobbs’ cell phone)

Also notice several Comb Jellies in the photo.  Comb jellies continued to be caught, but as expected, numbers are tapering down as Bay water temperatures climb.

Good News:  English Sole are up!  Yellowfin Gobies are way down!  Almost all the English Sole (four of them are shown in the photo above) were caught at the mouth of Alviso Slough.  Like the staghorn sculpin, English Sole were numerous several years ago, then they became quite scarce.  Now, once again we are seeing a population boom of baby sole.  However, unlike our sculpin, English Sole spawn on the ocean bottom off the coast:  Young sole are swept into estuaries and coastal lagoons that serve as their nurseries.  The years around the 2015 El Nino warm period appeared to greatly reduce numbers of English Sole in the Bay.  The ocean is cooler, so now they are back.

Another seemingly unrelated data point:  only five Yellowfin Gobies were caught on the April weekend.  (The larger fish in this photo is a spent female Yellowfin.)  There seems to be a declining trend here, and this is the lowest number in over a few years.  Yellowfins are considered “noxious invasive” and are usually the first or second most numerous fish caught in UC Davis trawls in Lower South Bay.  They are an attractive little fish, but I hope this downward trend continues.

Leopard Shark.  A single Leopard Shark was caught at the mouth of Lower Coyote Creek on Saturday, and it was a baby.  (Photo credit, Jim Hobbs)

Beautiful Sunday morning.  Above, Pat Crain returns from checking tide level at the Artesian Slough boat ramp shortly before we launched.

Sunday trawls were pleasant but not nearly as eventful.  You can see in the data that only 200 fish were caught on Sunday.  And, if you look really hard at the data table, you sort of see similar demographics for sculpin and yellowfin gobies, not enough fish to make many conclusions.

Striped Bass.  These were caught at most of the upstream stations on Sunday.  These fish looked particularly well-fed and healthy. This fish was from Artesian Slough.

The three bass above were caught in Pond A19.

Green water.  Waters were conspicuously green most of Sunday, but particularly in Artesian Slough.  Here near the mouth of Artesian, Jim Hobbs is holding up a sample.  We presume this greenness reflects awesome phytoplankton productivity that is ultimately feeding the fish nursery around us.  If we could understand these phytos, we could probably feed the world.

More Staghorn Sculpins.  These were the most numerous fish caught both Saturday and Sunday.

Judging from the photos, the staghorns all look to be young and pretty close to the same age class; just a few months old.

Native Crangon Shrimp.  Crangon shrimp (AKA: Grass Shrimp) numbers are up.  This is probably due to the wetter seasons in 2017 and 2018.  Crangons do best when there is a strong freshwater flush in winter.  They were relatively scarce during the dry years prior to and during the last El Nino.  Now they are back.  These look to be blacktails, (Crangon nigricauda) as opposed to regular Crangon franciscorum.  In my experience, I always have trouble distinguishing the two.  Whenever, I see blacktails there seems to be a gradient from slightly dark in the tail, all the way to very black tail.  I am not convinced this is a completely separate species.  But, the sandy spots showing here are larger and darker than I see in C. franciscorum.  I have much to learn.

Non-native Exopalaemon and Palaemon shrimp.  Although less numerous than Crangon, Many of the Exo’s and Palaemon shrimp were full of eggs.  This photo shows an Exopalaemon literally dripping with eggs.

Mysids.  We continue to see large numbers of mysids most parts of the year.  These tiny shrimp-like organisms are a fundamental food for most small fish.  Tasty boneless protein pills.  It bears repeating: a healthy mysid population leads to a dense and diverse fish habitat.

Starry Flounder & English Sole.  This pair was caught in Pond A19.  The top fish was one of two Starrys caught.  The bottom fish is a slightly larger English Sole.  Pat Crain pointed out the rough skin on the Starry.

Starry Flounder have breeding tubercles.  Rough sand-papery nodules form on Starry Flounder skin to indicate mating readiness.  This is a common trait in many species of fish.  Cyprinids (true minnows, including carp and gold fish also develop tubercles.)  Both Starry Flounder caught on Sunday were showing tubercles.  Two surprises for me:  1) Until then, I had never heard of tubercles, and 2) I was surprised that a Starry Flounder could spawn at such small size.

Bay Goby.  This fish was recorded as “Unidentified Goby,” but Dr. Hobbs tentatively at first, and more positively later, determined that this is likely a Bay Goby.  This was a big find for the day because Bay Gobies are quite rare in the Alviso Marsh Complex.  Trawling surveys in the mid-1980s found them to be fairly common, but UC Davis/Hobbs surveys since 2010 have only caught half a dozen.  They are still common further north in the Bay, just absent here.  A good theory for why they became scarce is the proliferation of several non-native gobies in recent decades that may out-compete them:  Yellowfins, Shokihazes, Shimofuris, and Chameleon.  Of the non-native gobies, Yellowfins are the largest and most numerous by far … until these last few months.

Turtle!  As mentioned in the title, and indicated in the Sunday data sheet, this turtle was caught in the first trawl in Artesian Slough on Sunday.  There is no doubt that this is a non-native softshell turtle.  It could be an Asian variety, but I am fairly convinced this is a Texas Spiny Softshell Turtle:  This is one of four I have seen in the general area over the past year or two.

We have no turtle policy!  This turtle caused some brief consternation on the boat.  On the one hand, being non-native, there was an inclination not to release it.  On the other hand, this was the first trawl of the day, so somehow the turtle would have to be constrained for several hours in some humane way.  There is a small consideration that UC Davis and Hobbs Lab have permits to take certain species for research: removal or eradication of non-native turtles is not specified.  Also consider that many, and at times most, of the fish caught are also non-native.  This turtle is residing in an area in which thousands of non-native Inland Silversides, Rainwater Killifish, Largemouth Bass, Striped Bass and various Gobies are typically caught in a single beach seine.   One would ask, if we are taking the turtle, why are we not also taking the voracious striped bass or noxious yellowfin gobies?

In the end, we decided to release.  Just one more non-native species we … ummm, like?  (Full disclosure: for better or worse, I voted for release.)


Leave a Reply