Fish in the Bay – June 2022, Supplemental Report, Fishes & Other Critters.

By Luca Sartori, California State Maritime Academy Class of 2025.   https://www.csum.edu/

Editor’s note: Luca is spending his summer internship developing a close personal relationship with our Lower South Bay fishes and bugs.  This is his supplement to the June Fish in the Bay report.

Three Leopards at Coy3.

Leopard Sharks: We caught 15 leopard sharks in June. Most were small juveniles (around 250 mm), but we did catch a larger one (550 mm). They are safe here because there are no animals that prey on young sharks in Lower South Bay, and there are plenty of worms and shrimp for them to feed on.

More Sharks from station Coy4.

Most sharks were likely around 3 months old when we caught them. As they grow older, they move to more saline and deeper waters.

While the June count is a sharp decrease from the fifty we caught last month, the drop-off is to be expected.  As they grow and get stronger, they are more likely to evade the trawl net. 

Large male Bat Ray at Coy3

Bat Rays: 14 were caught. Most were adults with a few smaller babies caught as well.

One adult had its stinger cut off. Fishermen will often cut the tail to prevent Rays from stinging while unhooking them. While a Bat Ray can survive without its stinger, it won’t be able to defend itself as well against bigger predators like Seven-gill Sharks.  Cutting off the tail is like removing a finger from a person! 

Shiner Surfperch at Alv-3.

Shiner Surfperch: We counted only one Shiner Surfperch in our entire trawl. The lonely specimen was found at Alv-3 and was pretty young. Surfperches declined significantly in this area in recent decades.  We think this is simply due to more competition from other species since Surfperches still seem to be doing quite well everywhere else.

American Shad at Dmp1.  Salinity was 13.6 ppt.

American Shad: We caught a Few American Shad, such as these caught in Dump Slough. Per our previous post, we can tell that they are in lower salinity water due to their brownish-golden backs. 

While all the loose scales might concern you, this is simply one of their survival mechanisms that allow them to escape from predators.  They shed scales similar to how lizards may break off their tails upon capture.  Loose shiny scales provide camouflage and confuse predators. 

Striped Bass: We caught one striped bass upstream in Art 1 and found a dead one at Art 3. Striped Bass are not very tolerant of higher temperatures, so that’s likely what killed it. While striped bass are non-native, some native fish, like Longfin Smelt and White Sturgeon, can also suffer from heat stress.  

Palaemon shrimp at coy-4

Palaemon Shrimp. Invasive Palaemons are again the top shrimp. 

Crangon Shrimp declined massively from over 10,000 caught in May to only 844 in June. In just one month, Crangon went from making up over two-thirds of the shrimp population to less than a fifth of our shrimp catch. A similar decline happened in 2021.  The cause is still unknown.

Calaveras Point seals exhibiting “Vigilance Behavior.”

Harbor Seals have been doing their usual routine and are entering their molting season. We counted a total of 19 seals.  However, the total population is likely much greater because the seals tend to hunt during high tide. We estimate the population at roughly 50, which makes it a decently sized colony for this area.  The larger Mowry Slough population is the main Lower South Bay colony which has over 160 seals and has been reported to produce up to 100 pups in a given year.

• Lyman Fancher (1979) provides history and a census of the Mowry Slough and Calaveras seal populations in the early 1970s. https://scholarworks.calstate.edu/downloads/dz010v85z 
• The National Park Service has links to a library of San Francisco Bay pinniped monitoring reports at this link. https://www.nps.gov/im/sfan/pinnipeds.htm#51006A011DD8B71B0B657952A3568009 

Another view of the Calaveras Point seals at our closest approach.

The seals are alert in these photos.  This is to be expected as we are in one of the larger boats that pass by.  We keep as much of a distance as we can, and we did not see any seals flush.

• Fox (2008) studied harbor seal behavior at nearby Bair Island Refuge. https://scholarworks.sjsu.edu/cgi/viewcontent.cgi?article=4587&context=etd_theses 

Bald Eagle.  During our Saturday trawls, we spotted a bald eagle hunting in the marsh.   I quickly snapped a photo before it flew far away. This is likely one of the adult eagles that live at Curtner Elementary school in Milpitas.  It could even be the same one we photographed at Sandy Wool lake in the nearby hills a few days later.

Luca Sartori