Fish in the Bay – Special Report, The Year of the Shark – 2022.

Schematic distribution of the 9-10 July shark catch: 20 Leopards + 2 Brown Smoothhounds.

Our block-buster shark year continues.  By the end of the August trawls, we had caught 95 Leopards and 6 Brown Smoothhounds since January.  The previous annual record of 58 leopards set in 2021 was already surpassed in June.

This is a combined shark report from the July and August trawls.

1. Luca Sartori’s Shark Report.

All were babies.  The 20 Leopard Sharks caught in July and the additional six from August almost all measured around 300 mm (one foot).  One exception was a small female at 155 mm from the July trawls. 

Two Leopards at Coy2, 9 July 2022.   Photo by Luca.

Lower South Bay is most likely the largest estuarine nursery for Leopard Sharks in the world. This is largely thanks to them having a strong supply of food. 

Leopard Mug Shot at Coy2.   Photo by Luca.

Leopard Sharks typically inhabit shallow coastal and estuarine waters from Oregon to Baja California according to the Monterey Bay Aquarium.  They grow to 2 meters in length and can live up to 20 years.      

Three Leopards and a Starry Flounder at Coy4 on 9 July.

Leopard Shark Diet.  Young Leopard Sharks eat a variety of bottom-dwelling creatures.  Polychaete Worms seem to be the favorite item in Lower South Bay.  Shrimp, crabs, isopods, clam siphons, and probably small gobies are also on the menu.

• The Monterey Bay Aquarium Leopard Shark page gives a good overview of Leopard Shark life history. https://www.montereybayaquarium.org/animals/animals-a-to-z/leopard-shark
• Hobbs et al (2015) “The most abundant organisms in the diets were multiple species of Polychaete worms, the majority of which were the Streblospio benedicti. Brachyuran crabs were the second most dominant taxa with the yellow shore crab, Hemigrapsus oregonensis, making up the majority of crabs. Fish taxa contributed to the diets with the longjaw mudsucker, Gillichthys mirabilis, being the dominant fish prey item by mass.”  https://www.southbayrestoration.org/sites/default/files/documents/011615_leopard_shark_chapter_final_report.pdf

Three more Leopards at Coy1, 7 Aug 2022.

Predators of Leopard Sharks.  The lack of predators makes Lower South Bay an excellent place for mama Leopard Sharks to deliver their young. The nearest predators are Seven-gill Sharks that anglers occasionally catch near Dumbarton Pier.  It seems that low and variable salinity keeps the Seven-gills away from Lower South Bay.

• Russo (2015) Russo found abundant evidence that Seven Gill Sharks and Caspian Terns were regularly eating newborn and young-of-year Leopard Sharks and Brown Smoothhounds.  He also reported at least one incident of a Great Blue Heron eating a young-of-year Leopard.  https://www.researchgate.net/profile/Ron-Russo/publication/282238231_Observations_of_predation_and_loss_among_leopard_sharks_and_brown_smoothhounds_in_San_Francisco_Bay_California/links/5a8db3fdaca272c56bc3fe6e/Observations-of-predation-and-loss-among-leopard-sharks-and-brown-smoothhounds-in-San-Francisco-Bay-California.pdf

Another Leopard Shark Mug Shot from Coy1 on 10 July.

Brown Smoothhound (top) and Leopard Shark (bottom) side-by-side comparison. LSB1, 9 July 2022. Photo by Luca

Leopard Sharks are highly gregarious, often schooling by age and gender.  They even hunt together with other species.

• Sea World Leopard Shark page. “Leopard Sharks are known to form large schools, occasionally aggregating with gray or brown smooth-hound sharks (Mustelus californicus and henlei) and piked dogfish (Squalus acanthias).”  https://seaworld.org/animals/facts/cartilaginous-fish/leopard-shark/ 
• Animals-net Leopard Shark page. “These sharks aren’t only social with each other; they are also known to interact and cooperate with other shark species. Scientists have seen groups of leopard sharks, dogfish, and smoothhounds sweep together through an area to flush out food.” https://animals.net/leopard-shark/ 

Leopard Shark and Brown Smoothhound.  Another side-by-side comparison. Coy2, 6 Aug 2022

Brown Smoothhound (aka Dogfish) are not as common in Lower South Bay.  We caught 2 Brown Smoothhounds in July and 4 more in August.  Smoothhounds are smaller than Leopard Sharks and live along the continental shelf.  They never grow above a meter in length.

Brown Smoothhound at LSB1, 9 July 2022.

Parasites.  While parasites are found on both types of sharks, it seems that Brown Smoothhounds are more vulnerable to them.  According to the Russo (2013) study done in the San Francisco Bay, only 40% of female Smoothhounds and 30% of males were free of parasites, while almost 70% of female leopard sharks and over 40% of males were free of parasites. 

Luca demonstrates several parasitic copepods infesting the Brown Smoothhound dorsal fin by pulling on their egg-string tails.

Four types of parasites typically infest these sharks.  Russo (2013) found that roughly half of the 362 Leopard Sharks he caught in SF Bay hosted parasites.  Four species of parasite were identified in this order of frequency: A. oblongus (27.3%), B. lobata (24.1%), P. bicolor (16.8%), E. coleoptratus (9.4%), and L. galei (3.6%).  Brown Smoothhound sharks were even more likely to host these parasites.  

• Russo (2013) https://www.researchgate.net/profile/Ron-Russo/publication/285131178_Observations_on_the_ectoparasites_of_elasmobranchs_in_San_Francisco_Bay_California/links/5a8db41fa6fdcc808c0f072f/Observations-on-the-ectoparasites-of-elasmobranchs-in-San-Francisco-Bay-California.pdf
• Also see Benz et al (2003) “Five pandarid (Copepoda) species, Dinemoura produeta, D. latifolia, Echthrogaleus coleoptratus, Pandarus bicolor, and Achtheinus oblongus, were collected from the external body surface of a [great] white shark, … taken from Morro Bay …”  https://www.researchgate.net/publication/29737809_Five_Species_of_Parasitic_Copepods_Siphonostomatoida_Pandaridae_from_the_Body_Surface_of_a_White_Shark_Captured_in_Morro_Bay_California
• Wikipedia page for A. oblongus (translated from Hungarian). https://hu.wikipedia.org/wiki/Achtheinus_oblongus

Luca shows another copepod parasite picked off of a Brown Smoothhound at Coy2, 6 Aug 2022

2. Additional shark notes by Jim.

Two Leopard Sharks at UCoy2 on July 10^th.

Upstream sharks.  The two sharks shown here were at UCoy2 which is probably their upstream limit. Salinity at this station was between 17 and 20 ppt.  Drought summer is probably helping keep upper Coyote Creek a bit more salty than usual.  We rarely catch Leopards this far upstream.

Same two Leopards from UCoy2 in July.  The faint slit-like mark between each shark’s pectoral fins is the natal scar. 

Leopard Sharks have “belly buttons!”  I learned from the Russo (2015) paper linked by Luca that Leopard Sharks can be identified as newborns by the presence of a small “natal scar” between the pectoral fins.  This scar will heal and fade away after about one year.

Leopard Shark and California Halibut at LSB1, 6 Aug 2022.