Dive Dry with Dr. Bill

064: Munching and Mating, Part I
Bat Rays Feeding

On a warm Sunday morning, I dropped down into my kelp forest cathedral to appreciate the beauty of nature. At a depth of about 50 ft. something caught my peripheral vision and I turned to look. Given the fantastic visibility recently, I was able to see a bat ray feeding about 60 ft. away. I slowly swam over to the ray and was able to get within three feet of it as it pounded the sandy bottom with its head to dislodge food. It took a brief look at me, decided I was harmless, and continued feeding.

As I've mentioned before, my icon marine biologist Ed "Doc" Ricketts and his close friend John Steinbeck were convinced that a good marine biologist had to be both hungry and libidinous to fully understand marine life. I've certainly been accused of both! Perhaps because of that, I've seemed very attuned to feeding and, er, um, ah... reproduction the past two weeks (some say my entire life).

I spent a fair bit of time watching this bat ray feed. It had just begun when I noticed it, so the clouds of sand it stirred up hadn't yet obscured my view. In fact, I had a fantastic vantage point. Unfortunately, my underwater video housing (which had finally been returned after six weeks in the shop) came back with a bad board for the second time and was still non-functional. I could only hover and watch the bat ray as it rammed its head (and mouth) into the sand and filtered it through its gills to feed on worms, clams and other marine delicacies buried there. Not my standard fare, but not unlike the foods offered by the street venders in Bangkok (not all Thai cooking is palatable in my opinion).

I returned topside to off-gas excess nitrogen from the dive (and indulge in the other important focus of marine biologists... just looking though!). After an hour, I decided to return to the same area in the Dive Park to see if the bat ray was still there. I quickly found him just beginning a new meal. I assumed it was a new meal since even I have trouble eating for more than an hour straight (well, if you don't count the time I set the "all-you-can-eat" prime rib record at Marmac's in Westminster, eating 13 prime ribs and several desserts courtesy of my friend and new employer, Chuck Liddell, one more than the old record set by a former L. A. Laker).

The bat ray kept pounding his head into the sand, digging a wider and larger hole. As it did, the sand poured out its gill slits and I assume it had a few scrumptious Chaetopterus tube worms or a tasty invertebrate bouillabaisse to munch on with its grinding teeth. As the hole deepened and the sand cloud developed, sheephead and other fish were attracted to the activity. They darted into the hole looking for tiny morsels the bat ray had declined. Soon there were several dozen fish taking advantage of the bat ray's disturbance, just as they do when divers with poor buoyancy control stir up the sandy bottom. Sheephead will also dig their own holes for food, but the feeding pits created by bat rays dwarf theirs. Besides, why waste energy when someone else will do the dirty work for you?

Like diver newbies in a beginning SCUBA class, the bat ray soon churned up enough sand to obscure visibility in the area and I moved on. The next day I returned to the Park to dive with my camera. By turning it on before I entered the water, I could record continuously on my dive but had no control over the camera functions. Within seconds of submerging, I could see a large cloud of sand in the same general area as the day before. I headed towards it and found a bat ray in the middle of the cloud, surrounded by more fish. Although quite obscured, I was able to take footage of the same bat ray feeding on that dive. After about 15 minutes the visibility was so bad, I left in search of clearer water. It reminded me of the time I was diving Long Point and came across a huge cloud of sand caused by a group of bat rays feeding there. It was so thick I never saw the bat rays themselves. When the bat ray feeds like this, it lifts its tail above the bottom so eventually only it is showing above the clouds.

On this weekend my interest in marine life munching was well satisfied. In the next episode I'll tell you how my interest in er, ah, um...mating was rewarded when I came across a male giant kelpfish guarding two females in his nest. Time for dinner... the other craving will have to wait at least a week (hopefully not too much longer).

© 2003 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.

Bat ray settling to bottom ready to feed; bat ray beginning to feed with tail in the "air;"
bat ray head obscured by cloud of sand; sheephead jealously inspected bat ray feeding pit.

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia