Fish in the Bay – 7 May 2017 UC Davis trawl – Sharks can’t tolerate fresh water but lots of other critters like it!

Folks, regarding those sharks …  Shark die-off in San Francisco Bay is trending in the news:

The concern is real. SF Bay supports some of the nicest and most charismatic sharks found anywhere (in my opinion). At least through October last year, Hobbs caught Leopard sharks, Bat rays, Smoothhound sharks, and one baby Guitar fish (a type of ray) in Lower South Bay.  All were caught well downstream, in salty water near or in the main body of the Bay.

This was my shark & ray collage from the LSB trawl survey on October 1st, 2016.


No dead sharks were spotted in Lower South Bay on May 6th or 7th.  Jim Hobbs/UC Davis surveyed fish populations by otter trawl this weekend.  He did not catch any sharks or rays living or dead. I asked Hobbs about the current shark and ray die-off.  He thinks it is mainly a freshwater issue.  The Bay rapidly turned fresh this year after mid-February rains.  Sharks and rays had two choices: flee the Bay or die.

Many types of sharks and rays loiter in estuarine systems, to the extent that salinity is high enough because that is where food is found.  But, that can be a dangerous game.  When the rivers surge elasmobranchs (word of the day! It means sharks, rays, skates & sawfish) need to find a quick way out of the estuary.

Fungus brain rot, mentioned in the news articles, may be the operative shark killing mechanism, and human management of drainage ditches and stormwater basins may exacerbate this menace to sharks, but Bay water freshness is likely the current underlying shark killer (in Hobb’s opinion and mine).

This weekend, the main body of LSB was between 14 to16 parts per thousand (ppt) salinity (seawater is about 35 ppt).  That is still pretty fresh.  And, salinity in the upper sloughs and ponds continues to be in the low single digits.  This is way too fresh for sharks.

 Freshwater in LSB increased fish diversity by at least 4 or 5 species.  … (Yes, sharks aside.)


Sacramento Sucker caught in March. (It is a native carp-like fish):

Sacramento Suckers.  On Saturday, the Hobbs crew caught 17 Sacramento Suckers in Alviso Slough.  You may recall that four were caught last month and a few more in February.  Until this year, Sac Suckers had never been caught in Hobbs’ Lower South Bay trawls.  They must have come down from the rivers as the Bay freshened up.

Tule Perch!!!  On Sunday, 7 May, we caught a heavily pregnant tule perch in Pond A19.  First time ever!!! I checked historic trawl data from 1981 to 1986:  Tule Perch was never recorded in these types of trawls. This California native is still common in lowland rivers & the Delta, but not as common as it once was.

According to Peter Moyle’s 2002 edition of Inland Fishes of California: “The [tule perch] population in Coyote Creek, Santa Clara County, was long thought to be extinct but was rediscovered in 1998 as a tiny population below Anderson Dam.”

Not extinct!  Hopefully, this population is growing.  As you can see, this Tule Perch was ready to pop out live babies. (She was returned to the pond immediately after photo.)


A baby Walleye Surfperch was caught in the Coyote Creek bypass (AKA “Dump Slough”).   This baby was probably born in a brood of a dozen or more.  This is a native sportfish, but like the other fish mentioned, not typically seen here.  Three of these were caught in trawls in the 1980s, none in more recent times.

This web site describes some of the more common types of surfperches:

This interesting Bay Nature article from 2013 describes some of the many California native fishes, their natural history, and current management issues:  I hate to admit my ignorance, but I did not know there is a small East Bay Parks aquarium in Alameda:  I will have to visit it.



Longfin Smelt.  Juvenile Longfin Smelt continue to be caught.  Four were caught on Saturday: two in Pond A21, one in Alviso Slough, and one in the Bay.  On Sunday, we caught two Longfins in the upper sloughs.  As the bay warms, we expect these young Longfins will be scooting out to colder waters soon.

This juvenile longfin was caught immediately downstream from our wastewater treatment plant in nearly 100% treated wastewater.



Prickly Sculpins.  When I started riding on UC Davis trawls in 2012, we caught one or two prickly sculpins.  Since then, they seemed to disappear.  Pricklys are common and range widely in California in both fresh and salt water.  We just didn’t see them here for the last 4 or 5 years.  Now they are back!  157 were caught last month and 106 more this month in the upper sloughs and ponds.

According to Moyle’s book: prickly sculpins tend to lay eggs in streams.  The fry “are swept downstream to large pools, lakes, and estuaries, where they assume a planktonic existence for 3-5 weeks. Soon after settling down to the bottom …  [after which] they start a general upstream movement …”  Moyle notes that prickly sculpin populations can be threatened by even low barriers in streams that block upstream movement of small fish. (p.348).  This suggests that recent dry years reduced local creek flows to the point that prickly spawning migration was substantially blocked.  The rains came, and BOOM! … pricklys are back in business!


Pacific Herring. This is a marine fish that seeks fresh water to spawn. 34 were caught in April, and four more this month. The Otter Trawls usually only catch a few during wet months.


Striped Bass.  We caught lots of healthy looking young striped bass. I think the weekend count was 60 of them.  On the negative side, they are non-native and voracious predators.  On the positive, they are an important sport fish and have been in California for well over 100 years.  Get used to them.



More mysids.  If you have been following my photo posts for very long, you may be thinking you have seen enough mysid photos.  Wrong!  Mysids are so incredibly important for young fingerling-sized fish diets.  If I see mysids, I take photos.

Yikes!  I just noticed that larval fish amongst the mysids could be another uncounted longfin!


Conclusion.  I can’t speak with authority on shark deaths, but what I see in nearby sloughs confirms that the freshwater flush of 2017 triggered profound changes to local aquatic life.  I suspect that some native species are particularly adapted to extreme climate swings like this. Hopefully, some of the many non-native fish and benthic invaders are not so well adapted.


Bonus Bald Eagle!  At one point as we motored up Coyote Creek on our Sunday trip, Dr. Hobbs looked up in the sky and said, “What the heck is that!” as a large bird-like shape passed over us.  I lost composure, and shouted, “That’s my freaking Bald Eagle!”  I was only able to get this fuzzy shot as he sailed away from us over Pond A19 looking for prey.  This is one of the pair that hatched an eaglet in Milpitas last month.


I can’t top bald eagles!  So, I will stop now.


Jim Ervin
Compliance Manager
San Jose-Santa Clara Regional Wastewater Facility



Leave a Reply