Fish in the Bay – 2 September 2017 UC Davis trawl – American Shad & Bat Rays

A fishing update:  I went with the Hobbs crew on the deeper water Bay side on 2 September.  It is always interesting to see the bigger and weirder fish community just a few miles downstream: more sharks and rays if nothing else.

Saturday – Bay side:

Sunday – Upstream side:

This was another low Dissolved Oxygen weekend. Take a look at the numbers on Sunday:  DO was in the 3’s almost across the board!  Nonetheless, fish abundance and diversity remained more or less the same as the preceding two months.  If I may be so bold to say: native Northern Anchovies and Three-spined Stickleback and non-native Inland Silversides and Yellowfin Gobies don’t seem to care about DO within ranges we see in this area.

A public service announcement: The Mercury and PCBs Watershed Permit is due for 5-year reissuance this December. ( )  The current permit contains a provision:   Dischargers shall continue to implement and participate in programs to reduce mercury and PCB-related risks to humans from consumption of San Francisco Bay/Delta fish.”  This is why you should see “Fish Smart” posters advising which Bay fish tend to be more contaminated at local boat launches and fishing sites.  Also check the OEHHA website here:

I check at least once per year that notices are posted at Alviso Marina.

After checking the signs, I joined the Hobbs team bright and early at Alviso Marina.  Even early in the morning, it was stifling hot on 2 September.  We could tell by 8:00 AM that it was going to be hot – a triple-digit day on the water.

First trawl:  a big giant board and lots of Silversides and American Shad.   The first trawl was disrupted when a large sunken plywood board got tangled the net.  This forced an early termination, at 5 minutes, of a normally 10-minute trawl.  Nonetheless, a lot of fish got scooped up (977 Silversides alone!) along with marsh roots and muck.

I presume many of the fish were attracted to the many Corophium amphipods that were present, or maybe other food.

Shipworms!  The photo below show some calcareous tubes embedded in the plywood board. These tubes were formed by “Shipworms” more formally known as “Toredo worms” which are actually a type of long skinny clam, go figure!

American Shad.  29 young American Shad that were caught in this interrupted trawl.  Dr. Hobbs tells me that this time of year it is normal see them, but this might be a better than usual year.  The February Freshwater Flush probably helped them. Adults spawn upstream in rivers and creeks.  After a year or two of growth, young American Shad congregate in estuaries, acclimate to salt water, then spend the next 3 to 5 years in the ocean.

American Shad like the restored ponds: another 28 of them were caught in Pond A21 on Saturday.  On Sunday, 68 American Shad were caught in Pond A19.  American Shad can grow over 2 feet in length (75 cm says the Moyle book).  They were transplanted to California from New York shortly after 1871.  And, they continue to be a popular and very delicious sportfish here after 140-odd years. No one will complain if we have more shad this year.

Prickly Sculpin. A few Prickly Sculpin continue to be caught.  These are lingering artifacts from the Freshwater Flush.  There are fewer now as this year’s cohort migrates upstream – or gets eaten!

Starry Flounder.  2017 continues to look like a good year for local Starry Flounder recruitment.  Seven of the 21 Saturday Starrys were caught in this first trawl.  On Sunday most of the 54 Starrys were picked up from the main stem of Coyote Creek, particularly the upper side near Newby Island.  Now that I look at all the summer data, I will go out on a limb and state that young starrys like to hang out in the creek channels.  Fewer are seen in the ponds.

Anchovy.  Anchovies started to show up as we proceeded downstream on Alviso Slough and especially in Pond A21.  About 200 anchovies were caught each day on Saturday and Sunday with most caught in restored ponds.  Anchovies are found year-round in Lower South Bay, but they greatly favor salty water in late summer.  Hobbs trawl numbers show that November 2016 was “peak anchovy” for the past year and January through April was the nadir.  Even 200 each day seems to be on the low side for September.  All the Anchovies caught on Saturday appear to be ocean-going greenbacks. I have a hunch (just a hunch) that local resident brownback anchovies got hammered by all the freshwater this past spring.

Threadfin Shad. This is the other shad we started seeing further downstream.  This fish looks very similar to the American Shad exept for a deeper body and the epynomous “threadfin” on his dorsal fin.

Bat Rays.  It was a good day for bat rays.  34 were collected on Saturday.  13 bat rays were netted at station Alviso 3, the downstream end of Alviso Slough, along with one leopard shark and almost 800 corbula clams.  We watched as Micah Bisson filled the tub with flapping mad bat rays, each one armed with serrated stinger.  Then, it seemed to occur to everyone at once: how do we remove 13 angry bat rays from the big tub?

Emily and Micah then took turns grabbing and measuring rays, one-by-one.


It’s more fun than it looks.

This young bat ray has stinger exposed.

Only one Leopard Shark was caught on this weekend.  The February Freshwater Flush was very stressful to elasmobranchs, and there were signs of shark and ray die-off at that time.  It is good to see that sharks and rays are still around and hopefully healthy.

Bad News: Potamocorbula (Corbula) clams.  These were some of the 794 corbula clams collected at the ALV3 Alviso Slough station.  There were some big ones here – up to an inch across which is quite big for a corbula.  Jim Hobbs speculates that the bat rays may have been feeding on this corbula patch.  No stomach content analysis was performed on the rays or the shark, so we can’t know for certain.

Good News: Shrimp. Bat rays feed on a variety of benthic critters, so they could have been feasting on some of the many hundreds of  Palaemon and Crangon shrimp that were pulled in.  Even better news: the numbers of native Crangons generally exceeded non-native Palaemons in the Saturday trawls.

Red Algae.  Lower South Bay does not have much submerged aquatic vegetation, so I take an interest when I see it.  These were two specimens of red algae.  James Downing helped me make the tentative identifications above.

Longjaw Mudsucker.  Only one Mudsucker was caught this weekend, but he was a beauty.  He has the elongated maxilla (upper jaw) that gives him his name.  Check out his “long jaw.”  He is a mudsucker alpha male from Pond A21.

Don’t let the happy face fool you!  This guy is a brute.

Baby gobies.  As typical, we saw a lot more gobies.  These were some babies, probably Shokihazes.


Staghorn Sculpin.  We always see at least a few Staghorn Sculpin. They haven’t been so numerous the last few years, but they continue to be present.  Some people use these as bait, which seems like a waste of a perfectly good fish to me.

The small colony of harbor seals near Calaveras Point: they are always lounging there – watching us as we zip by.

It was an unusually hot day. I have to admit, it was good when the day was over and we could get out of the heat.


Leave a Reply