Dive Dry with Dr. Bill

#338: Sheephead in the Skies

For decades you've been walking a well-worn path around Avalon, let's say between your home and the post office. Although you've passed by a certain building each day, all of a sudden you notice that there is a tile embedded in it that gives some of the history of the building. It's been there all this time... but you just noticed it. Today, for some reason, your perception shifted or you weren't thinking about the bills you'd find in your mail box (everything good these days comes by e-mail... if you don't count the spam).

Well, last weekend was one of those experiences for me. I've done well over 1,000 dives in our dive park... not to mention more than a thousand elsewhere along Catalina's coast. I was diving to capture more footage for the three cable TV episodes on giant kelp that I'm producing this spring. For that reason I spent most of my time up in the canopy filming the kelp blades and growth regions in the upper water column. When diving, I usually stay very close to the bottom, since I am quite sure a great white won't surprise me by popping up out of the sand or rock. I'm a marine biologist, I just know these things.

Since I stayed very shallow, no more than about 40-50 feet, for two of the dives, I had very long "bottom" times of 75 minutes each. The warm water, no colder than 65 degrees, made even a long dive very pleasant. That gave me plenty of time to really explore the blades in the kelp canopy, looking for tiny organisms that might add "color" to my episode on the incredible critters that use kelp for habitat or food. Video has nowhere near the resolution an underwater still camera has, so it can't capture them in good detail. Besides, I think it's well past time I get a prescription dive mask since my own vision is not exactly "high resolution" either these days. I still keep thinking I see a mermaid... and I'm not deep enough for narcosis!

I saw a number of critters too small for me to capture on tape, and others too small for me to even identify, so I switched to filming the "big boys." Fish such as the opaleye and halfmoon (or Catalina blue "perch"), both members of the sea chub family, are known to feed directly on kelp blades. I could see their bite marks on several of the young, juicy ones (but only a few on the aged, encrusted ones). Other fish are known to bite the kelp blades to ingest the small invertebrates that grow on them. Among these species are the common kelp bass, señorita, kelp rockfish and kelp surfperch all of which I've filmed a number of times in the past.

However, this weekend I noticed something I don't remember ever noticing before. In the past when I've cruised the canopy in the kelp forest, I've seen sheephead (even one of the four "Oscars" that frequent the dive park) making their presence known. However last weekend they weren't just cruising, they were "munching." I saw and filmed at least a half a dozen sheephead, all at about the age where they might turn from females to males, ramming their heads into the kelp fronds near the stem-like stipes. Most of the time I see the females digging holes in the sand to look for worms, clams or other infauna beneath the substrate. Most of the larger males are picking snails, rock scallops and other delicacies off the rocky reefs.. or bits of sea urchins when bad divers break them open (grrr).

When I see something new, I immediately try to interpret it in terms of the "ecological play" in the kelp forest (or whatever habitat I might be diving in at the time). What did the behavior mean for the rest of the kelp community? My first guess (we scientists call them an hypothesis) was that these sheephead were feeding on the snails that frequent the upper kelp. I often see top snails of the genus Tegula up there munching on juicy kelp blade salad. Some of the sheephead were of sufficient size to take the larger Norris' top or kelp snail. These snails live a life like Sisyphus, constantly crawling at a snail's pace up the stipes into the kelp canopy, getting brushed off and falling back to the bottom, then starting the cycle all over again. At least they get plenty of aerobic exercise. I looked closer to try to detect what the sheephead were feeding on, and verify my hypotenuse (er, hypothesis... I got a little confused there).

Yes, there were indeed top snails of both species that could be spotted on the kelp. Yes, the sheephead seemed to grab at them with their mouths, then take them in and crush the hard shells with their powerful jaws. Occasionally I would even observe a "shower of shell debris" falling from the canopy, indicating another snail had been crushed by a sheephead. Now, I don't know where you stand on escargot, but the last time I ate them (at The Drake Hotel in Chicago courtesy of Packy's mother), they were quite tasty. Warning: if I invite you up to have some top snails in butter, you might want to decline since my culinary skills are not up to that standard!

The next day I went out, ready to film more footage of the sheephead feeding in the canopy. Wouldn't you know it, I didn't see a single one up in the "skies" of the kelp forest! They were all bottom feeding. Hmmm... maybe they just fed in the canopy the previous day to throw me off guard. There will be no diving for Dr. Bill this coming weekend... at least not with cold water and a wetsuit. I will be over in Long Beach at the annual SCUBA Show spending time with about 12,000 similar-minded amphibians like myself. I'll have to report on whether I see a mermaid or not! Place your bets now!

© 2009 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 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!

Sheephead male (Oscar #1 of 4) as seen from a snail's eye view, sheephead female digging in the sand;
a lovely orange-bodied kelp snail, and a sheephead plunging headfirst
towards a snail in the kelp canopy.

This document maintained by Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia