STEM Logo

Dive Dry with Dr. Bill

#442: Bat Ray "Season"

I've lived on the island and dived Catalina waters for 42 years now. Over that time even my dense mind has detected "seasons" in the underwater world. And yes, for those living in places remote from southern California, even the terrestrial environment here has seasons... wet and dry (although I think Mother Nature has gotten confused with the recent rains in May!).

As summer approaches, we are beginning to see the waters warm up and the warm water wussies from further south are beginning to re-enter our waters again. If we don't have a repeat of the unseasonably cool temperatures from last summer, we might even see a few marlin and broadbill appear. I started wearing my thin 3/2mm wetsuit nearly two months ago (hoping that the cold would help me burn off some of the bioprene I've acquired from sitting at a computer all winter).

Winter used to be the season of the best diving out here. Cool water temperatures and shorter daylength made plankton blooms much less frequent, and the water was at its clearest... except after a heavy rain that delivered sediment-laden run-off into our nearshore waters for a few days. The appearance of the Asian "devil weed," known scientifically as Sargassum horneri, has diminished the quality of diving during the winter... and is forcing me to consider spending the cooler months in warmer places like the Red Sea, the Philippines and South America. If it's good enough for marlin and broadbill to retreat to warmer waters, it's certainly good enough for me... assuming I can scrounge up enough of our devalued US dollars to pay my way there.

As daylength increases during spring, it triggers another "season" in our waters... plankton season. Yes, those tiny microscopic critters (especially given my eyesight) harvest the increased light energy from the Sun and convert it into biomass to feed all the other critters that depend on them for food... the baitfish that feed the yellowtail and bonita, as well as the filter feeders like scallops and mussels that feed sheephead. Visibility diminishes, often making this "season" a less-than-desirable one for diving.

We are currently transitioning between plankton "season" and what I consider one of the worst times of the year (if there really ARE bad times) for diving... bat ray "season." Now many divers thrill at the sight of bat rays hammering the soft bottom in their endless search for tube worms, clams and other "delicacies." People love to film their majestic beauty as they "fly" through the water column with grace. As for me, I detest the darned things. Masses of them gather in our shallow water and pound the heck out of sandy and silty bottoms, stirring up the sediments and greatly increasing the turbidity of the water. I've got pretty much all the video footage I need of them, so not much need to film more.

Amazingly enough, the good doctor (that's me) has actually been working for pay this season. What a concept! I've been monitoring the Sea Trek operation in Descanso Beach to help determine if a relatively small number of people walking on the sandy bottom with space aged helmets on their heads materially affect the turbidity of the water. As I suspected, and wrote the Coastal Commission about last year, the bat rays out there are creating far more of a disturbance. Their feeding was so intense two weeks ago that I couldn't even find a pair of the light sensors used to monitor the possible effects. Of course within a relatively short time, the sediments settled and the water became more transparent... just as it does when the many bathers shuffle out into the waters there. Sandy bottoms are highly disturbed habitats (and I'm not suggesting they are in need of a shrink).

Being the prophet (wish it was profit instead) of Munching and Mating, I can't neglect the other "M" word with respect to bat rays. In addition to munching on the sandy bottoms, these relatives of sharks engage in that other pleasurable activity during this time. I've been fortunate to have filmed them "in the act" several times, but not as fortunate as one diver in the dive park who witnessed a female give live birth. Now THAT I'd like to capture on video some day, even if it means sticking around here during bat ray "season."

© 2011 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

To return to the list of ALL of Dr. Bill's "Dive Dry" newspaper columns, click here.


Bat ray beginning to feed with sheephead waiting for the "scraps" and close up of another digging feeding pit with its head;
dust cloud obscuring all but the bat ray's tail and two bat rays "flying united" (so to speak).

This document maintained by Dr. Bill Bushing.
Material and images © 2011 Star Thrower Educational Multimedia