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Dive Dry with Dr. Bill

#611: "Butterflies... But Not in My Tummy

Over the past few months I've been writing frequently about the changes observed in our local kelp forests (or at least what's left of them) during this unusual warm water episode. Over the decades I've lived here on Catalina, I've witnessed a number of warm water episodes, with most of them connected to El Niño events. I think scientists are still not certain if this qualifies as one, but whatever we call it the unusually warm water has had a startling effect on our local marine communities.

The warm water and hurricane surges have brought visitors to our shores from "south of the border." Of course marine life really doesn't respect the artificial political boundaries we Homo sapiens establish. The Pacific is all one big ocean to them and the only boundaries they respect are the ones imposed by environmental factors such as water temperature or food resources. Some of the ones I've written about previously are the finescale triggerfish, the slender mola, the Guadalupe cardinalfish and the virtual clouds of Solmaris jellyfish.

Today's subject is yet another species that appeared in our waters during past episodes, the scythe butterflyfish (Prognathodes falcifer). When it first arrived it was known as Chaetodon falcifer, but those fish specialists who live in labs must have found a difference in their fin counts, parasites or something to rename them... or perhaps it had to do with the more accurate approach of molecular genetics (DNA). I doubt the fish were even conscious of this name change and probably still swim about calling each other Tom, Marsha, Dick and Jane. On further research it looks like Prognathodes was the name originally given to them back in 1862 and scientists reverted back to the first name.

It is often a shock to divers who experience these fish for the first time in our waters. They look as if one is diving over a beautiful tropical reef rather than in our cooler waters. The body is yellow in color with dark markings. A black "scythe" runs from below the eyes on the ventral surface to the forward spines of the dorsal (upper) fin and then down to below the base of the caudal or tail fin. The soft dorsal and anal fins are black but edged in white. There is also a black stripe from the mouth "through" the eye and up to the forward part of the dorsal fin.

Their long, pointed snouts identify them as "pickers" when it comes to munching. However, I wouldn't call them "picky" eaters since they feed on seaweed and small invertebrates. The mouth is small and it is interesting to watch these and other butterflyfish species pick at the reef... although perhaps not as exciting as watching a good basketball game for most people. We marine biologists are a strange lot, aren't we?

These fish are often rather localized in distribution around Catalina. Most of the ones I've seen were at the Empire Landing or East End Quarries among the big boulders there. There have been other sightings at sites like Farnsworth Bank and below Mount Torquemada (or as I have long referred to it, "Pregnant Sleeping Indian Woman"). Their primary distribution is from Baja California into the Gulf of California (aka Sea of Cortez) through central America and down to the Galapagos.

Many people assume that because they are found "south of the border," that they prefer warm water. Actually this fish poses an interesting ecological example. Down south they actually frequent water as deep as 900 feet where it is much cooler than anything I'd consider "tropical." When they reach our cooler waters, they are found at much shallower depths. In the past I usually observed them at 30-50 ft below the surface. However, during this warm water episode they are being seen down to nearly 100 ft at the quarries.

According to Dr. Love (not me but Milton up at UCSB), scythe butterflyfish are said to reach a maximum length of about seven inches although Paul Humann's field guide indicates their average length is about 3-4 inches. In past years I have filmed young butterflyfish at the Empire Landing Quarry. I have hoped this means they are reproducing here since given their depth range our waters are probably warm enough for them to not only survive but to reproduce as well. However, it is also possible that the youngsters appeared as larvae swept up north from Mexico by currents. In that case their continued presence in our waters may be a result of periodic replacement during such periods rather than local reproduction.

© 2014 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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Baby scythe butterflyfish at Empire Landing in the upper left and adults.

This document maintained by Dr. Bill Bushing.
Material and images © 2014 Star Thrower Educational Multimedia