Dive Dry with Dr. Bill

#237: Thornback Ray... A Day of Firsts!

For those who ask why I continue to dive Catalina waters week after week, year after year, decade after decade, century after century (well, it does seem like it some times... especially with another birthday just passed), I offer this column as an answer. Last Saturday was a day of firsts, four of them to be exact. The first first (ha!), an interview with yours truly, which had been taped at the Long Beach SCUBA Show, was broadcast on Scuba Radio that day. Now if I were a tennis player or a golfer instead of a SCUBA diver, I'd never be featured on Scuba Radio! Of course I couldn't listen to the broadcast because instead of diving in cyberspace, I was diving at Sea Fan Grotto, Dynamite Shack and Goat Harbor.

Second was the big first (if that makes sense). I was diving Sea Fan Grotto and descended to a maximum depth of 150 feet before turning around and heading upslope. I had been looking for mating nudibranchs (remember, the beautiful shell-less snails), and wasn't disappointed. When I reached about 120 feet, I saw what I thought was a round stingray resting out in the open on the sandy bottom. I slowly approached it with my new high definition video camera running. As the image in the small viewfinder became larger and clearer, I realized I was seeing the first thornback ray I've ever seen!

Now thornback rays are fairly common in the shallow waters of the southern California mainland, usually in less than 25 feet over sand or mud bottoms. My friends there see and film them frequently. In fact I am planning a trip to dive San Diego with dive buddies Missy and Heather and one of my goals is to film this species. The field guides say that thornbacks are found from northern California (where they are rare) down into Baja.

However, I have no recollection of ever seeing one in our island waters over the past 38 years. Certainly Catalina falls into that geographic range, so I wonder why this is the case... and why I saw this one so deep. Fish expert Dr. Milton Love does state they can be found down to 450 feet. These relatives of the sharks and rays generally bury into the soft bottom, but I see plenty of rays and related species that also do that... even with my aging eyesight!

Thornbacks are also known commonly as banjo "sharks." Given my lack of musical talent, perhaps that has something to do with my not seeing them before. They are not stingrays, but are members of the guitarfish family which includes our more common shovelnose guitarfish. Thornbacks have a round, flat head region and a long tail. There are two dorsal fins on the relatively thick tail which helps separate them from many other rays. However, the best diagnostic feature for identifying them are the three rows of hooked spines on the back and tail.

These rays can reach three feet in length, but this one was less than two feet. According to Dr. Love, very little is known about this species. They feed on worms, crabs, shrimps and clams found in or on the soft substrate. In turn they may be eaten by marine mammals such as the elephant seal, and possibly even the sea lion since they are known to eat small sharks. Apparently they do not possess a stinger and are considered to be not dangerous... unless you are a potential food item like a crab!

The third first of the day occurred at Dynamite Shack. I had finished my dive and was standing on the deck of the King Neptune talking to other divers when one of them pointed towards shore. We watched as a mule deer calmly walked down the hill to the water's edge and stepped in until it was submerged up to its neck. The deer proceeded to swim around as if it was simply enjoying a day at the beach. My assumption is that it was swimming to drown all the ticks and other parasites attacking its body. I did ask if mule deer were "in season" for spearfishers. Now, I do believe I may have seen this before... but it was probably during the 60's and since I was there, I really can't remember!

The fourth and final first of the day occurred at our last dive site, Goat Harbor. I descended to 150+ feet again looking for mating nudibranchs. I did see a sea lion checking out the King Neptune's anchor, but that wasn't a first. About 10 feet deeper I had a lovely vision of a beautiful Asian mermaid whose swimming skills certainly exceeded that of the sea lion... not to mention mine! She beckoned me deeper, but I'm too much of an "old salt" to fall for that. As I slowly ascended into shallower water, the lovely dark-haired lady faded from sight. Sigh, I guess I was just narc'ed! That "ultimate dive buddy" still eludes me... maybe this will be my year.

© 2007 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass" or "Common Fish and Invertebrates of the Sea of Cortez" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

Thornback ray head region, tail showing dorsal fins and rows of hooked spines;
thornback ray swimming, rear view of body.

This document maintained by Dr. Bill Bushing.
Material and images © 2007 Star Thrower Educational Multimedia