Fish in the Bay – September 2024. Upstream Invasions.

A belated September report …

The overall raw fish count increased, but this was not good news.  Almost 50% of our September fishes, over 600 individuals, were Inland/Mississippi Silversides – the non-native egg-eating demon!

Exopalaemon Shrimp and Striped Bass, the other ecologically problematic non-natives, were also present – as described below.

Silversides and Exopalaemon shrimp were caught in upstream waters – Coy1 or farther upstream – typical for these highly invasive species.

We also caught three tires and varied debris – more on that below as well.

The summer Anchovy spawn continued.  But, Anchovy numbers were still low.

• Egg checks continued to indicate high female-to-male sex ratios at almost all stations.
• Females appear to preferentially crowd upstream. Is this for food?  Or to maximize brood survival?
• Why do male Anchovies generally loiter far downstream?

1. Upstream Invaders.

Silverside count = 610. Silversides are a major threat to restoration goals.  This non-native fish was introduced at Clear Lakes California in 1967 for mosquito control.  That story ended very badly:  https://californiawaterblog.com/2023/03/19/the-rapid-invasion-of-mississippi-silverside-in-california/#:~:text=The%20silverside%20was%20brought%20to,Lake%20gnat%20(Chaoborus%20astictopus).

• Silversides are small egg-eating fish. In addition to occasionally consuming mosquito larvae, they also consume massive quantities of eggs and larvae of other (native) fish species.
• Demon Silversides compromise our Anchovy and Longfin Smelt spawns.

Exopalaemon shrimp count = 1,025.  We wonder about the long-term impacts from this recently introduced fresh-water shrimp.

• Exopal shrimp are attractive and highly edible.
• They compete with native Crangon shrimp to some degree.

Photographic evidence: 5 of 6 Stripers in September were caught near the SJ-SC RWF facility discharge point.

Striped Bass count = 6.  Striped Bass grow very large in California’s SF Bay–Delta system. (Little ones are shown here.) Stripers are prized game fish!

Dr. Livingston Stone introduced this fish to California in 1879 in hopes that it could some day help feed the world.  Striped Bass planted in West Coast estuaries supported commercial fisheries within just a few decades.  https://www.laketexomafishingguides.com/fishing-articles/history-of-the-striped-bass/

Big bullies.  Smaller marsh fishes must flee or be eaten when Stripers show up.

2. One Shark; Six Senses.

Leopard Shark count = 1.  This was our third Leopard Shark for 2024 (two baby sharks were caught in June).  Lower than average salinity over most of 2024 plus low productivity must have repelled Leopards from LSB this year.

Long “claspers” = Boy Shark.  Claspers in sharks and rays are fins modified to deliver sperm. Only boys have them. They are not true separate sexual organs, but they essentially function similar to a penis in other vertebrates.

Shark teeth.  Leopard Sharks are strong but not aggressive. We handle them so often that we tend to forget they have a mouthful of tiny teeth.  Judging from the sharpness, a bite would probably hurt a lot if this shark felt inclined.

Ampullae of Lorenzini.  Leopard Shark snouts are peppered with tiny black dots.  Each dot is an electrical sensor.  Most sharks and rays have a sixth sense ability to “feel” electrical fields. They use this to seek and find tiny organisms hiding in the mud and sand. Moreover, electroreception appears to be a basal (ancestral) feature of early invertebrates.

• Even a shark’s electrical “sixth sense” may be tuned to attack (2018) – NIH-funded study illustrates how evolution may shape the senses. https://www.nih.gov/news-events/news-releases/even-sharks-electrical-sixth-sense-may-be-tuned-attack
• The Shark’s Electric Sense. Scientific American (2007) https://faculty.bennington.edu/~sherman/the%20ocean%20project/shark’s%20electric%20sense.pdf
  “The story begins in 1678, when Italian anatomist Stefano  Lorenzini described pores that speckled the forward part of the head of sharks and rays …  Astonishingly, Murray [in the 1960s] determined that the organs could respond to fields as weak as one millionth of a volt applied across a centimeter of seawater. This effect is equivalent to the intensity of the voltage gradient that would be produced in the sea by connecting up a 1.5-volt AA battery with one pole dipped in the Long Island Sound and the other pole in the waters off Jacksonville, Fla. Theoretically, a shark swimming between these points could easily tell when the battery was switched on or off. … No other tissue, organ or animal exhibits such extreme sensitivity to electricity.

• King et al (2018) Electroreception in early vertebrates … https://onlinelibrary.wiley.com/doi/10.1111/pala.12346
  “Electroreception, the ability to detect electric fields, is the most recently discovered of the major sensory modalities. Lissmann (1951) and Lissmann & Machin (1958) discovered that African knifefish (Gymnarchus) could detect perturbations in electrical fields produced by their electric organs, allowing them to navigate their environment. …  Passive electroreception was subsequently discovered in a broad range of vertebrates including basal actinopterygians (ray-finned fish), sarcopterygians (lobe-finned fish), amphibians, chimaeras (relatives of sharks and rays) and the jawless lampreys …”

3. Polychaete side-note.

Polychaete count: 2. (one nereid Polychaete + one scale worm). 

Interesting thought: Earthworms are like us!  Annelids (segmented worms) have long been recognized as an evolutionary midpoint between simple animals, like sponges, jellies, flatworms, and roundworms, to the complex chordate forms, like ourselves. 

• Science says that marine polychaetes are more closely related to ancient ancestral annelids with eyesight and all the extra body parts. Garden-variety earthworms are degenerate descendants that lack eyes, tentacles, and pseudopods,
• We are like earthworms of the chordate phylum! Like earthworms, we also lost fins, gills, and at least one sense on our evolutionary journey to a terrestrial lifestyle!
• Disturbing thought:  Polychaetes are very intelligent.  Earthworms are relatively dumb.

4. Platyhelminth – A New Lifeform for LSB.

Flatworm count = 1.  We found this worm hiding on an ancient oyster shell at station LSB1.  This was a first for us and a personal bucket-list lifer organism for me.  (I amateurishly studied freshwater planaria in the distant past. But, this was my first meeting with one of the marine types.)  What an interesting organism!

This “Platyhelminth” (Greek for “flat worm”) looks somewhat similar to the Pseudoceros genus: belonging to the family Pseudocerotidae.

• Pseudoceros canadensis https://www.inaturalist.org/guide_taxa/2111736 
• Pseudoceros mexicanus  (50mm) https://www.underwaterkwaj.com/ca/flatworm/Pseudoceros-mexicanus.htm 

General Info:  California Marine Flatworms.  https://cadivingnews.com/california-marine-flatworms/  “… The free-living flatworms are grouped into the Class Turbellaria.

There are about 4,500 different species of Turbellaria, and these are exceptionally simple animals. They are generally small, four one hundredths of an inch to one inch, but a few can grow to over one foot. Flatworms have no circulatory or respiratory system–they are small enough to exchange oxygen for carbon dioxide directly through their skin. They have a very primitive nervous system, consisting of a concentration of nerves towards their head. …

Flatworms are hermaphroditic–they have both male and female sex organs. However, they need a partner to reproduce, since they cannot fertilize themselves.” 

Flatworm Monster (video) – The video shows a much larger marine flatworm someone found in an aquarium. https://www.youtube.com/watch?v=o1m0EWnQr1U&t=65s   

5. Bat Rays.

Bat Ray count = 25.  All of these were young or baby Bat Rays. The September year-to-date count was 119.

Warm weather plus increasing salinity since June finally encouraged mama Bat Rays to deliver their broods in Shrimp Alley.

Baby girl Ray eating a shrimp at Coy3.

Bat Ray diet study #2.  At least one baby Ray at station Coy3 had a shrimp hanging out of her mouth.  We took an extra few seconds to confirm. 

• Yes! Baby Bat Rays eat shrimp!

Every rose has a thorn.

Bat Ray stingers are like fingernails – except they are much sharper and have backward-pointing serrations.  They often break off and get stuck in the net.  

Safety tip:  Always check the net for broken Bat Ray stingers.  Stingers remain hazardous even when detached from the animal.
Safety tip #2:  Plucking or pulling a stinger can permanently damage a Ray. Never do that!  (It’s like yanking off a fingernail!)  A hopelessly entangled stinger can easily be snapped-off using pliers without injuring the Ray.     

6. Harbor Seals.

Harbor seals in restored Pond A19.  Four Harbor Seals lounged on a mudflat at the entrance to Pond A19 as we motored in on September 8th.  These seals belong to the 30-to-40-member colony that resides about four miles downstream at the Calaveras Point rookery. 

Three of the four seals perched on the mudflat as we exited Pond A19.

Normally, we try to maintain a recommended 100-meter distance between us and seals so as not to disturb them.  In this case, that buffer distance was impossible given the width of the channel inside the pond.

The seals watched us warily as we passed.  We turned our heads, thought peaceful thoughts, and pretended to be uninterested in hopes that it would help calm them.  Ultimately, the seals dove for cover as we made our closest approach.  Their heads popped up periodically … they waited patiently … for us to sail far enough away. 

7. Marsh Junk.

Too much Junk!  For no apparent reason, we snagged a lot of junk in September: 3 tires, 2 logs, and a root ball were netted.  We also observed a giant wood piling floating near LSB1 and reported it as a navigation hazard to the local Coast Guard. With all this junk, we were only one tire short of completing something like a Flintstone’s mobile. 

We disposed of all junk items ashore with exception of two of the tires due to limitations of space and weight.    

Why so many tires? –Tires in the old days were often discarded in ad hoc landfills or repurposed as pier bumpers and boat fenders.  Nowadays, they lie buried along the bottom of Alviso Slough and portions of Coyote Creek.

We carry them back for disposal when we can. Tires are heavy and usually encrusted with small barnacles and slippery hydrozoans – one or two tires at a time is about all we can manage.