Fish in the Bay – 7 August 2016 UC Davis trawl – Stickleback are up. Staghorns are down.

Hello again folks,

I don’t normally go out fishing with the UC Davis / Jim Hobbs crew so frequently, but this is a special summer.  I went out again on August 7th, and this is mainly a continuation of the Anchovy and Stickleback Story.

For those who do not know: Dr. Hobbs launches from the Alviso boat launch on Saturdays to perform trawling surveys in Alviso Slough, Pond A21, and Lower South Bay (LSB ).   On Sundays, he launches from our San Jose-Santa Clara Regional Wastewater Facility boat launch to survey Lower Coyote Creek, Pond A19, and Artesian Slough.  Usually I try to alternate between Saturday and Sunday runs because you see a different mix of critters depending on which side is surveyed.  But, these last few months I stuck with Sunday, upstream surveys.

The Salt Pond Restoration Project has commissioned almost 20 trawls per month since July 2010.  That equates to almost 1600 trawls over the 6 year period!   The map below shows rough location of the usual trawls. Stations are named by location: LSB = Lower South Bay, COY = Coyote Creek, ALV = Alviso Slough, ART = Artesian Slough, UCOY = Upper Coyote Creek, DMP = “Dump” (next to Newby Island Landfill).

On this weekend, almost 3500 fish and buckets of bugs were netted, hand-counted, and for the most part, returned to the bay, no worse for wear.  Below is Jim Hobbs counting specimens, Emily Trites keeping score.

What we saw:  You can’t take a single weekend of trawling results and make a lot of sense out of it.  But, let’s try anyway:  Two spreadsheets below show results from August 6th and 7th – Saturday, deeper in the Bay, and Sunday, in upstream Coyote Creek and marsh shallows.  The sheets give you a sense for where populations of roughly 20 species of fish were hanging out this past August weekend.

Fish species are listed on vertically.  Trawl locations are indicated along the top.  Physical parameters of Dissolved Oxygen, Salinity, and Temperature at each station are also shown.  Fish respond to salinity and temperature.  The three fresh to brackish loving fish; Inland Silverside, Rainwater Killifish, and Three-spined Stickleback, are rare, if not absent, as salinity increases.  Conversely, Leopard Sharks or Bat Rays are rare or absent in fresher locations.  Other species, like some gobies, are less affected by salinity.

Bay-side fish

Upstream, fresher water fish

Sunday upstream trawling catches a lot more fish.  Almost all of the extra upstream fish in both July and August were Anchovies and Three-spined Sticklebacks.

A two fish mystery: As I mentioned last month, for two years or so, trawls netted NO STICKLEBACKS.   Now we again see thousands.  Where did they go?  How and why did they come roaring back?  Also notice only seven Staghorn Sculpin were caught between 6 and 7 August.  In 2012 and 2013, Staghorn Sculpin were the most numerous fish in Ponds and Coyote Creek.  We caught hundreds in single trawls.  Where did they go?  Historic surveys strongly suggest that sculpin shall return. But, what makes these species come and go from one year to the next?

Striped Mullet: seen in Artesian Slough in July and August, but not netted. (These are 18-inchers!)

The El Nino Fish – We saw mullet, but didn’t catch any:  Large fast swimming fish evade otter trawl nets.  We know larger fish range through this area, but strong swimmers outrun the net.  The same is true of the hundreds of Striped Mullet we saw in Artesian Slough this past month.  Mullet are a warm-ocean sea-going fish that showed up in the Bay and Delta in late 2014 with warm El Nino sea surface temperatures.  On Sunday, we saw dozens of 12-to-18-inch Mullet leaping as we motored down Artesian Slough.  How many did we catch in the net: ZERO!

More Anchovies:  Anchovies are our main summertime fish.  Most anchovies are found in upstream sloughs and restored ponds; the feeding grounds where they fatten up and get ready for fall spawning.

Jim Hobbs continues to see two varieties, or races, of anchovy in Lower South Bay.  This phenomenon was first documented by Carl Hubbs in 1925.  The Bay resident “race” is smaller and pinkish and presumably reproduces in the Bay.  The larger, green-backed, race is believed to spend more time at sea.  In this instance, we can see that females of both races have near fully developed egg sacs and are getting close to spawning readiness on August 7th.

Fish Otoliths: Dr. Hobbs’ specialty is removing and analyzing fish otoliths.  All vertebrates have calcium carbonate ear stones called “otoliths.”  Fish have a big pair behind the eyes and two smaller pair.  A polished anchovy otolith shows daily growth rings under a microscope.  By counting rings, then subtracting the number from the catch date, the UC Davis team can get a close estimate to the date the fish hatched!  Like tree rings, the width of each ring gives information about daily and seasonal growth rates.

Jim Hobbs holding a bag of anchovies for further study at UC Davis fish labs.

Sticklebacks: For over 20 years, I never regarded Sticklebacks as anything more than a tiny, drab, insignificant fish with nasty spines. Now that we again catch buckets full of them, I started to take a closer look.

Estuarine and ocean-going sticklebacks are heavily armored, with three back spines, two pectoral spines (one showing against my thumb) and one spine near the anal vent. The spines make them unappetizing to salmonid predators. 

This species readily adapts to environmental change.  Stickleback populations stranded in freshwater lakes rapidly lose spines and armor when no longer exposed to sea-going predators.  This makes me think that the two races of anchovies might be similarly responding to the different environmental pressures between the open ocean and Bay. 

Take 20 minutes to review the below YouTube videos – you will never disrespect a Stickleback again!

Some of the females below show full bellies when they are ready to lay eggs, or flabby bellies if they had just spawned.  Now that I really look at them, they sparkle like jewels in the sunlight. 

Males show red color under the jaw to indicate spawning readiness. 

Mysids: Using a finer mesh net, Dr. Hobbs continued to find mysids in July and August.  This continues Salt Pond Restoration Project observations of mysids first recorded in 2012: Buckmaster and Hobbs (2012)  That study identified two species of mysid:  Neomysis kadiakensis (blooming in spring through summer), and Alienacanthomysis macropsis (forming a smaller winter bloom).

Mysids caught in July and August were small and not overwhelmingly plentiful.  Jim Hobbs’ comment:  “I haven’t had a chance to look at these mysids under the scope, but I think what we are seeing are juvenile stages of kadiakensis.”

Couple more baby pipefish:  The Clarke-Bumpis net again caught at least two baby pipefish along with many copepods and other small organisms.   Last month, I thought this was a complete oddity.  Now I am thinking that July/August must be baby pipefish season.

Corbula: We saw scattered numbers of corbula clams, which is not unusual.  The photo shows two live Corbula compared to an empty Macoma shell.  Native Macoma petalum clams live at least several inches deep in the mud, so otter trawl nets almost never catch a live one – shells only.  In contrast, Corbula rest on the mud surface and get scraped up into the net.

Corbula (AKA Potamocorbula, or Corbula amurensis, or Amur River Clam) are public enemy #1 in Suisun Bay and the Delta.  This clam invaded the North Bay around the summer of 1987 and caused populations of phytoplankton to plummet.  In Lower South Bay, Corbula seem to be controlled by lack of seasonal food from strong river flushing possibly in addition to competition with local Macoma clams and filter feeding amphipods.  Fish and duck predation also keeps Corbula populations down.

I thought that El Nino year rain may have encouraged this year’s Corbula recruitment until Jan Thompson at USGS corrected me on this point:  Corbula have a wide tolerance for salinity, from 2 to 30 ppt.  Fresher water should tend to impede them.  More likely, additional rain encouraged phytoplankton blooms which, in turn, stimulated Corbula recruitment and growth.  “Corbula amurensis Conceptual Model” written by Jan Thompson and Francis Parchaso in 2010 summarizes everything I know about Corbula and is worth reading:

A new mussel (new to me anyway):  The mussel above, Musculus senhousia (AKA Musculista) ( ), is an example of ongoing invasions.

Cloern 2001, citing Cohen & Carlton 1995 (, noted that SFB recruits an astounding number of non-native species: ” … San Francisco Bay has been colonized by 212 exotic species of plants and animals, and the invasion continues at the current rate of one new species every 24 wk.”  This particular mussel has been in SF Bay since at least the 1940s and is a significant phytoplankton grazer in South Bay.  Like the Corbula clam, musculista populations seem to be kept in check; by competition with other bivalves and predation by local fish and ducks.

Summertime Sturgeon:  Speaking of clam and mussel predators, we got a rare surprise on Sunday when Hobbs netted this young white sturgeon in Coyote Creek.  Sturgeon tend to avoid the warmth and low DO of this stretch of the creek in late summer. Availability of food must have tempted it to stick around.

Pond A19 gets greenest in summer.  Practically all exposed mud is covered by a dense algal mat.  Patches of spartina (cordgrass) are slowly spreading across the pond. This is what 265-acre Pond A19 looked like on August 7th, 2016 about two hours past low tide.

This was A19 at low tide on March 8th, 2006:  at that time, it was 265 acres of salty gypsum bottom.  Good for nothing! – except possibly racing jet cars, I suppose.  What a difference a decade makes!


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