Dive Dry with Dr. Bill

#155: Butterfly (Fish) are Free

Water temperatures off Catalina have been pretty warm recently. At times I've felt like I was almost in the tropics, especially with the great visibility (60-70') I experienced on a dive at Italian Gardens a while back. Thanks to Scuba Luv, I was able to do two dives recently at the Empire Landing Quarry dive site. I felt even more like I was in the tropics as butterflyfish swam around me on these dives. Yes, butterfly fish here in cool temperate waters. Specifically the scythe, or scythe-marked, butterflyfish which apparently established itself during an El Nino event decades ago.

I'm accustomed to seeing butterflyfish at the many tropical and subtropical dive sites I travel to during our harsh southern California winters (assuming I have the cold cash to do so... or, better yet, someone pays me to go!). Along with angelfish and other fish families, these beautiful fish are typical of coral reef habitats. However, they are not typical of the large boulder habitat afforded at both the Empire Landing and East End quarries (the only two locations I've seen these fish). Yet they seem to be surviving, and even reproducing in our chilly waters. Maybe the cold forces the males and females to huddle closer together during mating season.

The scythe butterflyfish is a somewhat unusual member of its family. Most species are found in the relatively shallow waters of coral reef habitats. This one is a deep water species, usually found from 120 to over 500 foot depths in the warmer regions of its range. It is known from the Galapagos, Guadalupe Island, the Sea of Cortez and north to... Catalina! In our waters its distribution shifts markedly from that in its more southern, and warmer, locations. I find that I have my best luck with this species swimming at "exactly" 42 feet whether at the east or west quarry. It must be the magic number (although not enough there for me to play the lottery with).

This shift in vertical distribution is not unusual, and in fact occurs with some frequency in fish throughout their range. Fish that are found in shallow waters in their northern range may be found in deeper, cooler water in the southern part. It is there they find the temperature conditions most favorable to their physiology and reproduction. This species frequents the cooler waters at depth in its southern range, but moves closer to the surface where the water is warmer off our island. Here, in the warmer shallow waters, it finds the best temperature for it to function and mate. As for mating, I'm glad we can adjust the temperature of our own environment just by adding a few blankets! It allows our species to reproduce throughout the year and anywhere from the Arctic to the Tropics (or at least practice... not that I'd know about that)!

And reproduce these fish appear to be doing. While diving the quarry, I noticed several pairs of butterflyfish feeding in the rocks. Although I didn't see any courtship or actual mating, these fish did appear to be paired off. Butterflyfish in the tropics have been said to pair up for life ("until death do us part"), although scientists now question the "forever" part. Suffice it to say their relationships are longer than the "hooking up" that appears to be popular with some these days (both fish and humans). I saw at least eight individuals in different locations on my first dive. On a later dive at this quarry, I did notice courtship behavior (and, sigh, it made me quite jealous!).

Members of ScubaBoard that I know have reported these fish at nearby Sea Fan Grotto and even at Cape Cortes on the backside of the island near the mouth of Cat Harbor. Since I have no reason to doubt either of these sightings, it appears the fish are reproducing and spreading out since butterflyfish tend to be a little territorial. Perhaps they are establishing this cooler water location in advance of serious global warming in their southern range!

Although these fish are reported as 3-4" long, they may reach lengths of six inches which is closer to the size I observed. They are yellow with a distinct scythe shaped black mark on each side. Most butterflyfish I have seen elsewhere are yellow and black, but like their namesakes they do come in a wider variety of colors in tropical seas. The dorsal fin of the scythe butterflyfish extends to the top of the head, making this fish look like it has a spike hairdo. Perhaps it, like some of our youth, prefers punk rock. I'll stick to classic rock and folk music myself... still a child of the 60's.

The long snouts on butterflyfish are like forceps and allow them to pick invertebrates like snails and crustaceans off the rocks with ease. I was able to observe and film some of this feeding behavior on these dives. I've heard reports from other divers that they will also pick invertebrates off the blades of kelp in our waters. In the tropics they are well-known as cleaners, picking parasites off other fish. I have not observed this behavior in our waters... perhaps because the "odd" looking butterflyfish are not like the other cleaners our local fish are accustomed to (senorita, rock wrasse, etc.). Maybe it is the spike hairdo that scares the others off.

© 2005 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. Buy my "Munching and Mating in the Macrocystis" DVD so you can take Dr. Bill home with you... we'll both be glad you did!

Images of the scythe butterflyfish at the Empire Landing Quarry dive site.

This document maintained by Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia