Fish in the Bay – November 2020: Cold Snap – Winter Arrives.

Trawl map.

November trawls confirmed that winter arrived in Lower South Bay: 

  • Total fish counts dropped from over 7,900 in October trawls to only 703 in November!
  • Anchovy Spawn ended abruptly: only 12 Anchovies were caught – about half were juveniles.
  • Silverside population crashed from almost 7,000 in October to only 67 by November.
  • Good News: 12 Longfin Smelt were caught. These are our first winter arrivals.

Do not be alarmed.  Fish numbers typically decline with late autumn cooling weather, usually sometime after September.  This November’s total fish count at 703 is still better than November counts in 2018 and 2019: 454 and 148 respectively. 


Bay-side stations trawling results.


Upstream of Railroad Bridge.

Cold Snap!  The abrupt turn-over in fish populations was probably triggered by the California cold snap between 6 and 8 November.  Water temperatures dropped about 7 degrees: from 20 to 21 degrees in October to 13 to 14 in November.  (There was almost no rain, so salinity remained high at most stations.) 

Suddenly, Lower South San Francisco Bay went from balmy summer … to winter wonderland – from a fish perspective.  As summertime Anchovies and Silversides fled the area, about a dozen each spawning-ready Staghorn Sculpin and Longfin Smelt showed up.

News reports California cold snap on 6 November:


1. Summertime Fishes have Fled.

Fewer Silversides.  Silversides caught at Dmp1, 15 Nov 2020.

Silverside Population Crash made up most of this “Late-Fall Fish Decline.”  They are nonnative, and we don’t like them! 

Unfortunately, many probably survived.  Silversides can survive much colder weather.  It is likely that most of them simply fled further upstream.)


Northern Anchovy adult stragglers, 14-15 November 2020.  Blue = high salinity!

Sadly, the 2020 summer Anchovy Spawn ended abruptly.  The 12 Anchovies caught in November consisted of only a few bright blue adults and a handful of juveniles of varying ages.  We presume that the rest of the adult spawners migrated back out to sea. 


Northern Anchovy new recruits of 2020.

Northern Anchovy babies.  Some hatchlings from this summer are showing up!


2. Wintertime Fishes & Ducks.

Four Longfin Smelt from station A21-1

Longfin Smelt.  Longfins finally returned to upstream marshes with falling temperatures.   So far, we have only seen 12.  Longfins need cool temperatures and low salinity for successful spawning.  Lack of rain and high salinity will be a huge problem if it persists.  We need rain.


Staghorn Sculpins with young Palaemon Shrimp, Alv2, 14 Nov 2020.

Staghorn Sculpin. The 2020 Staghorn count is 567 so far which compares well with previous years.  Albeit, this year’s count missed a peak-Staghorn month of April due to COVID shutdown. 

Staghorns are always present, but big adults like these show up in early winter.  Around January, we should start seeing babies.  Then a big surge of baby Staghorns should show up near March or April if all goes well. 


Bufflehead Ducks at Coy4.

Lower South Bay is a bird refuge – particularly for wintertime ducks.  This is a southern terminus for many ducks that migrate along the great pacific flyway.  They started arriving a few months ago, but numbers increased in November.

A flotilla of Buffleheads stations itself off Calaveras Pont, near Station Coy4, each year.  Scaup and Surf Scoters tend to congregate further out in the Bay.  These diving ducks are voracious eaters of worms, snails, and clams.


Scaup and Surf Scoters at LSB1 & LSB2.


Green-winged Teal flying over east side of Pond A19.

Many dabbling ducks on the east side of Pond A19 on Sunday.  In addition to Green-winged Teal, we spotted lots of Shovelers, Gadwalls, and Coots foraging for bugs amongst the Pond’s tall reeds.  Dabbling ducks rest and feed in shallow brackish-to-fresh water ponds.  They are shy birds.  Hunters shoot at them.


Duck hunters with dog partially concealed on west side of Pond A19, 15 November.

Fewer ducks on the Pond’s west side.  Danger was not apparent to the naked eye, but telephotography identified the issue.  A trio of Sunday hunters was concealed in the cordgrass.  We heard a few shotgun blasts as we trawled the pond.  The ducks heard it too. 

… From the human perspective, it was a beautiful Sunday morning.  Just us, three hunters, a dog, and many crouching ducks in a big restored pond. 


3. Gobies, Gobies, Gobies.

A tray of mixed Gobies: Shokihaze, Shimofuri, & Yellowfin.

Catches of all four major categories of Gobies increased in November: Yellowfins, Shokihazes, Shimo/Chameleons, and Arrow/Cheekspots combined comprised over 550 of the 700+ fishes caught.  


Yellowfin Gobies.  Until the last decade, Yellowfins were overwhelmingly our most numerous Goby at least back to the 1980s.  They are still in the lead, but the lead is shrinking.  Goby numbers continue to suggest that Yellowfins may be gradually losing out to competition with Shokihazes and Shimo/Chameleons. 


Shokihaze Gobies at Coy4.

Shokihaze Gobies have been our second most common gobies since 2015.  Trawl catches typically increase a bit in winter.     


Arrow Gobies & Cheekspot Gobies.  124 Arrow/Cheekspots were counted in November.  Good News: This is the record catch since 2014.  And, 2020 already stands as our record year with 294 caught so far! 

However, these tiny fish can always be easily misidentified as baby Yellowfin Gobies or “Unidentified Larval” or simply slip through the net altogether, so the significance of these Arrow/Cheekspot record catches is uncertain.


Chameleon Gobies at LSB1; Shimofuri Goby from Dmp1

Chameleon Gobies & Shimofuri Gobies.  169 Shimo/Chameleons were caught in November – our second-highest monthly catch after December 2018.  But, at 325 for the year, 2020 also stands as our record year for this pair. 

Shimo/Chameleon Goby populations have increased steadily over the last several years. 


4. Bryozoan & Tarp – a hard bottom is good to find in LSB.

Encrusting Bryozoan collected from LSB1 on 14 November.

Encrusting Bryozoan.  For the third or fourth month in a row, we pulled up large chunks of Bryozoan reef at LSB1.  The Bryozoan itself is not new, we have seen it for years, but big coral-like formations seem to be a new thing.  Did high salinity make this Bryozoan explode in 2020?  Or did we simply not detect a gradual increase?  (Note: Bryozoa are supposed to be slow-growers – on the order of millimeters per year.

Rightly or wrongly, I have long felt that Lower South Bay needs more hard-bottom habitat.  Hopefully, Bryozoan reefs will help shelter tiny fish and anchor seaweeds and filter-feeding oysters.  The Bryozoan zooids themselves are filter-feeders that suck up excess nutrients.  If there is a downside to this, I have not found it yet.


Bryozoan closeup.  Each calcium carbonate cell contains a zooid:


Oyster Drills and Tunicates may impede Corbula Clams in the Deep Bay.  As mentioned in previous posts, we find few Corbula Clams beyond station Coy4.  Unlike most clam species, Corbula do not burrow deep into the mud. Instead, they lay exposed on the bottom.  As Corbula propagate into marine waters, they are subjected to marine creatures that immobilize them or eat them.  These are just two examples:

  • Atlantic Oyster Drills. As their name implies, Oyster Drills drill through oyster shells and eat oysters.  I don’t have direct proof that Oyster Drills eat Corbula, but Corbula shell is far weaker than an oyster shell.  (This may call for an experiment.)                         
  • Tunicates (sea squirts or sea grapes). These weird chordates anchor on any hard substrate that facilitates their sessile lifestyle. Again in November, we found many tunicates anchored on Corbula Clams at Coy4.  To some degree, each clam is immobilized, and colonies of filter-feeding tunicates stuck to their shells probably consume planktonic clam progeny as well.


Canvas tarp peppered with snail eggs at LSB1.

By chance, we picked up a stray piece of canvas tarp from the bottom at LSB1.  Not surprisingly, this stray piece of hard bottom was eagerly exploited as anchorage by at least four species:  two types of snail egg capsules, tunicates, and algal fragments.  


Lantern-shaped egg capsules on canvas tarp = Atlantic Oyster Drill eggs.


High Salinity.  For almost all of 2020, LSB remained a bit saltier than normal.  Some marine creatures, like Decorator Crabs, penetrated further south and persisted.  In November, the winter temperature drop facilitated the spread of Tunicates & Comb Jellies.  These critters typically show up around January. This winter, they arrived a few months early.


5. More Parasites on Sharks – and a Flounder.

Leopard Sharks.  Three sharks were netted at LSB1.  Two had copepod hitchhikers. 


“Sea Lice” are common on sharks in LSB, but they afflict other fish species as well.  Long-time readers may recall that we have plucked nasty bugs like these off of Northern Anchovies in the past.


Starry Flounder: new host – new parasite.  We discovered another copepod parasite on the underside of a Starry Flounder caught on Saturday.  Interestingly, the bug moved when we nudged it.  It was adhering to the flounder by suction and was able to scoot around the surface of the fish when disturbed.

Copepod parasites are very host-specific:  This louse looks very different from the shark varieties shown further above.  It is probably the Atlantic flatfish parasite, Lepeophtheirus pectoralis, or a close relative:


6. Tires & Bent Fish = Emerging Contaminants?

Tires in Alviso Slough!  Some may wonder: “Why do otter trawls catch so many tires?”  Answer: “There are a lot of tires at the bottom of these sloughs!”  Fishfinder screenshots show 13 tires we have not yet caught. 

In years past, people used old tires as fenders on piers and boat docks and such.  I suppose that is how most of these got here.  Tires provide good shelter for small bottom-dwelling fish and shrimp.  We always collect a fish and bug bonanza with every tire.

However, current tire pollution can impact salmonids.  A bunch of recent articles discuss toxic effects of chemical antioxidant 6PPD (N-phenyl-N’-(1,3-dimethylbutyl)-p-phenylenediamine) on salmonids in Puget Sound.

(Note:  Most chemicals in long-dormant tires on the Alviso Slough bottom probably leached out decades ago.  These forgotten ones simply remind us that millions of tires still mounted on vehicles are ground to dust on local roadways every day. Tire dust then sluices into storm drains, thence to the sloughs along with any 6PPD contaminants they may contain.) 


Scoliosis.  Every few to several months we catch a bent fish or two.  This November, we caught three in Alviso Slough: a Silverside, a Shokihaze, and a Shimofuri Goby. 

Some years ago, I read that this spinal deformity can be caused by high concentrations of Selenium, Mercury, or organochlorine pesticides.  Recent literature links fish scoliosis to additional factors:

Bent Fish could be a bad sign of disease or pollution.  Fortunately, we only see a few to several bent fish out of thousands caught each year.  But, we keep an eye on this.   


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