Dive Dry with Dr. Bill

#242: Butterflyfish Babies

I had a full weekend of diving on SCUBA Luv's King Neptune recently, which of course happens quite frequently. However, this was an especially interesting and rewarding weekend as I hope you will soon see. On Saturday we were diving Twin Rocks on our first dive. On my way back to the boat, I discovered a Tylodina fungina out in the open. These yellow snails with a thin brown hat that looks like a Chinese coolie's are a somewhat unusual find, especially ones large enough to film. I stopped to record some footage, and intentionally ran my tank low (to 300 psi) figuring I wouldn't need it on my surface swim back to the boat.

Boy was I wrong. I surfaced well up current from the boat and expected a nice drift back to it. I dive without a snorkel, so I had to turn on my back to kick since I had little air in my tank. The next thing I knew, I was swiftly rushing past the boat and ended up far behind it. A fast current had kicked up outside the kelp forest and I was blown way behind the boat before I could reach the current line. Of course I was not alone... all the divers were "swept away" as well. Divemasters Shelley and Devin were on the spot immediately to assist everyone, and put my heavy camera in the kayak so I'd have both hands free. As luck would have it, the current line snagged on the valve of my pony bottle and I couldn't free myself. Thanks to the ladies, I was extricated and began the long hand-over-hand pull back to the boat.

The next day Captain Tony looked for dive sites that would not involve strong currents. For one of our dives we ended up at the Empire Landing Quarry. I was thrilled since we rarely go there and I love to search for and film the scythe butterflyfish. I was in the water immediately and swam at my usual 40-50 feet to locate them, but saw only a few adults on the outbound leg and they were quite skittish. I got very little footage and was disappointed. There had been other dive boats at the site before us, and I wondered whether divers from those boats had caused these fish to be so wary. On my return, I stayed at about the 30 foot level... a bit shallower than I usually find these cooler water tropical fish.

Then I saw it... a miniature version of the adults only about two inches long. It was a baby scythe butterflyfish! I had never seen a baby, much less filmed one. This one seemed relatively unconcerned about my presence and the camera's lights. It flitted around in front of my lens, and didn't leave until three baby garibaldi teamed up to chase it away. It's times like that when I think we should reopen season on these pesky orange (and blue) intruders even though they are our state salt water fish. I moved on back towards the dive boat, and saw another one at the same depth. This one also let me film it for a while. Obviously these youngsters had not developed a healthy concern for what could have been a predator. After all, I'm hardly vegetarian!

Why did these sightings excite me? It confirmed my assumption that these fish were reproducing in our waters. Scythe butterflyfish are normally found further south in deeper, cool water. When a species disperses to a region outside its normal range, it may have difficulty surviving the change in conditions and food sources (or predators). Obviously a species entering a new area needs to find food it can munch on for individual survival. It must not encounter new predators it is not prepared to out-fox (er, out-fish).

Beyond mere survival of the individuals, the species must also be able to reproduce in the new region. Often the new conditions may be too cool (or too warm in reverse in a species dispersing south) for them to mature sexually and reproduce. Since we've seen the butterflyfish in our waters for several decades, I assumed they were reproducing. However, until this weekend I had never seen positive evidence in the form of very young butterflyfish. Now I have! I've also heard that snorkelers in Lover's Cove have seen young finescale triggerfish, another species which dispersed north into our waters decades ago presumably during El Nino events.

After the King Neptune returned, I was walking past Coyote Joe's , and was hailed by Chris and Sally Bartel (formerly of the Catalina Island Marine Institute, CIMI, and both avid divers). I mentioned what I had seen and they confirmed they had observed baby butterflyfish at several island locations as well. In view of this, I have to wonder whether their dispersal to and successful reproduction in our waters, establishing a northern expansion of their range, is a result in part of global warming. Studies at Stanford's Hopkins Marine Station in Pacific Grove (Monterey) have shown a shift towards more warm-water species and a reduction in cold water species there over the past century. My Harvard classmate Al Gore might be interested in this. Maybe I'll even make it into the sequel of "An Inconvenient Truth!"

© 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!

Two 2" baby butterflyfish pursuing Munching (much too early for Mating!) .

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