Dive Dry with Dr. Bill

#483: Baitfish Bonanza

A few years ago I wrote a column I entitled "Carnage at Casino Point." I had been filming in the dive park when I encountered a small school of jack mackerel trapped between the inner esdge of the kelp forest and the Casino groyne (breakwater). Along shore the kelp bass had gathered, resting in the feather boa kelp, eyeing the baitfish and just smacking their lips. Then all Hades broke loose... the kelp bass started darting after the jack mackerel, slicing their sides and releasing a snowfall of silvery scales.

The kelp bass repeatedly attacked the baitfish and soon seagulls started plunging in from the sky trying to get at the fish. However, their plump little bodies only allowed them to break the surface by a few inches and their hunger was not satisfied that day. The bass seemed to take a cue from the birds and started leaping out of the water and coming down on top of the jack mackerel. It was Mother Nature at her finest... the Mutual Eating Society, real ecological interaction.

During an incredible episode of fantastic visibility recently, I dove the park and witnessed something that could have been titled as a sequel to "Carnage" ("Carnage Revisited?" Carnage II? Son of Carnage?). The cast of characters had changed a little. Diving in spectacular clarity and able to see for perhaps 80 ft in places, I noted the dive park was crowded with large schools of baitfish, mostly jack mackerel (Trachurus symmetricus) and Pacific sardine (Sardinops sagax), also known as the California pilchard.

Drifting through these schools was an awesome experience in and of itself. Who needs to pay thousands of dollars to dive the annual sardine runs in South Africa. I hypothesized that these baitfish had come in to feed on zooplankton that had appeared after the recent phytoplankton (plant plankton) bloom that reduced visibility to about 10 feet. It was absolutely stunning to watch these schools, especially the sardines, become polarized and flash like brilliant moving mirrors in the sea. I could just hover there in mid water and watch as they swam all around me.

Okay, so my readers probably aren't going to get all worked up over a bunch of silver fish munching away on microscopic plankton. I understand. However the ecological play that was unfolding in the dive park that day involved several higher order predators that were present to munch on the abundant baitfish. These included our regular players, the kelp bass (Paralabrax chlathratus) who were gobbling up individual fish plucked from the huge schools. Other players joined them. California sea lions (Zalophus californianus) dive bombed my dive buddy, Ruth Harris, and me... playing with us as a break to digest their "tummy fulls." Watching these graceful marine mammals cavort through the kelp forest was almost like watching a ballet (a professional one, not my little sister back wqhen we were young). However, I couldn't get it out of my mind that these same critters rip the fins off our young ocean sunfish (Mola mola) just for play.

All of a sudden the schools of baitfish would scatter, or bunch up into polarized schools suggesting a predator was close by. Some divers thought there might be a great white hanging around to cap off the food chain by munching a sea lion... or a diver (no, too metallic and not enough fat on our bones). After thousands of dives in the park, I was pretty comfortable that it was just a cormorant "flying" underwater chasing the baitfish, or the blacksmith (Chromis punctipinnis). My hunch was quickly verified as not one... not two... but three cormorants darted through the kelp forest in front of me chasing their prey. I now understood why fish school for safety... I was so confused having three possible subjects to film, I couldn't focus my camera on any one of them. One of the cormorants seemed confused as well, going after one fish and then doing an underwater 180 to head off in the other direc tion after a second one. Later I did manage to get some nice sequences of the birds as they swam past in hot pursuit.

Now this is the kind of ecology lesson that everyone should experience. I know it is what I tried to give my science students back in my teaching days at Toyon. This is what life is all about... munching (oh, and occasionally mating of course). These lessons are far more illustrative about biology than sitting in a lab dissecting a fish pickled in formaldehyde. And they are much more fun, too. To see a real food web in action is to see much of what ecosystems are all about. To paraphrase Carl Sagan and Hilary Clinton, it takes billions and billions of plankton to raise a school of baitfish... not to mention thousands and thousands of baitfish to nourish sea lions, kelp bass and cormorants. Or to give another example, you need lots of McDonalds french fries... er I mean tofu salads... to sustain yours truly! Oh, by the way, dear reader... yes, I know, I included much more than the usual count of those pesky Latin names you all love so much. Just decided I wanted to keep you on your toes.

© 2012 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. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). 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!

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Schools of jack mackerel (l) and Pacific sardine (r) in dive park; cormorant and California sea lion ready to munch.

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