Fish in the Bay – August 2024. Bat Ray Care & Feeding – in the Nursery.

Once again, fish totals were low in August.  We presume this is the lingering El Nino effect.  Hopefully, a flip to La Nina will soon rejuvenate the system.  

Warm temperatures continued to pound the upstream area.  Temperatures at half the upstream stations were above the iconic 25-degree centigrade upper heat stress limit for Striped Bass.  Big fishes, like Striped Bass, Sturgeon, and Leopard Shark retreat to cooler Bay waters when it warms up like this.    

Water temperatures at downstream stations were 3 to 4 degrees C cooler. Also, salinity was considerably higher.    — That’s where we found 59 Bat Rays!

This report focuses on the late season Bat Ray catch because we haven’t seen enough of them so far in 2024. 

1. What Bay Rays like to eat.

UC Davis biologists Gigi and Alex measured and gently released Big Mama Ray.  Alex minded her stinger while Gigi measured.

The first Bat Ray we caught in August was a big mama at station Alv3. 

• ‘Big Mamas’ are very important in every fish species.
  • Big mamas: New study confirms old, fat female fish are better left in the sea. https://oceana.org/blog/big-mamas-new-study-confirms-old-fat-female-fish-are-better-left-sea/  “… hefty females lay bigger, more nutrient-rich eggs than small females. Previous research has shown that hatchling survival increases with both egg size and nutrient content.”
  • Big Female Fish https://blogs.ifas.ufl.edu/charlotteco/2018/05/17/big-female-fish/ “There’s a term that scientists use called “Big old fat fecund female fish” or BOFFFF. BOFFFF is a hypothesis that has been tested on a wide variety of fish species, and the results have shown that for many species, older female fish reproduce more and produce better eggs and better offspring.”

Mama showed us what she was eating!  As we examined Big Mama in the tub, she spit up Crangon Shrimp and Goby chunks!  She may have spit out a Musculista mussel or two as well, but it was hard to tell.

• Mama Bat Ray’s breakfast! We sifted our fingers through both live and broken halves of shrimp and macerated gobies in the debris collected in the trays.
• Follow the carbon flow: Inside the stomach of one chomped-up goby, we could see a Crangon Shrimp!  This was a marsh version of a “Turducken.”  https://www.merriam-webster.com/dictionary/turducken  … In this case, we had a shrimp, inside a Goby, inside a Bat Ray.  

Conclusion:  Bat Rays eat Yellowfin Gobies, Shrimp, and probably even baby Halibut.

2. Bat Ray reproduction.

More than 50 baby Rays were caught just short distance away at stations Coy2, Coy3, and Coy4. 

• Mama Rays seek brackish bays and inlets to give live birth to between two to ten pups during the warmest months.

At least 6 Mama Rays delivered pups somewhere near stations Coy2 & Coy3 in July-early August.

3. Shrimp & other bugs = Bat Ray Food.

Bat Rays love shrimp!  In summer months, we catch most Bat Rays along “Shrimp Alley” in the main stem of lower Coyote Creek (stations Coy1, Coy2, Coy3, Coy4, and Alv3).

• Crangon Shrimp count = 6555.  Crangon Shrimp numbers jumped way up in August.  Rising salinity attracted large numbers of young Crangon to settle back into lower Coyote Creek and the downstream end of Guadalupe River/Alviso Slough.
• Palaemon Shrimp count = 2087. Non-native Palaemon are not doing as well this summer. (Hooray!)
• Exopalaemon Shrimp count = 146. Exopalaemon shrimp are pretty much restricted to the fresher upstream end of our trawling area.

Alternate Bat Ray food.  When shrimp are scarce, Rays will eat other benthic invertebrates.

Corbula Clam count = 553.  Nuisance Corbula numbers are up this year.  The previous three drought years appeared to hammer them.

Musculista Mussel count = 727.  This month’s number alone is bigger than all years prior to last year, 2023. 

• Musculista have thoroughly invaded lower Alviso Slough and LSB stations.
• In warmer months, we consistently now find plant, shell, and sediment detritus consolidated by Musculista byssal threads.
• Good News? Musculista shells are soft.  Bat Rays probably tear through Musculista beds.

Tunicate count = 33.  Literature says that Leopard & Nurse Sharks eat Tunicates. Bat Rays probably also eat them in a pinch.  

4. We also caught two Mud Balls in August.

Bat Rays love mud.  They suck up mud and sediment to extract fish, worms, clams, and other creatures.  We don’t fear the mud! 

5. Red tides kill Bat Rays & other fishes we like!

July & August are high danger months for potential H. akashiwo Fish-Killing Red-Tide blooms.  The single-celled organism is always present.  Longer days, warm temperatures, and high stratification contribute to H. akashiwo explosions. 

• We keep our eyes on the water. If an orange or dark brick-red fish-killing bloom is detected, we alert Water Board and other concerned agencies.

6. Communing with the Cosmos.

Marsh creatures are adapted to the tide cycle. Bat Rays, birds, and bugs time their feeding based on tide heights and currents.  

• Know where your Moon is. Tides drive currents, turbidity, and sedimentation in Lower South Bay (LSB).  New and full moons = spring tides.

Example: New Moon Moment on August 4th:  As we swirled our hands in the mud in Pond A21, our modern instruments alerted us that the Moon and Sun were exactly in conjunction. 

• We felt light-headed as combined gravitational pull lifted us upward.
• New Moon Moment happens once every month.

High tide in Pond A21 during New Moon Moment, 4 August 2024.