Scythe Butterflyfish Not A ‘Tropical’ Species

I enjoyed Ken Kurtis’ recent article on Crane Point at the Empire Landing Quarry. This area of Catalina is one of my favorite local dive sites.

As Ken mentioned, one of the highlights of this site is the scythe butterflyfish. They’ve been seen in Catalina waters for decades, and as Ken said, most likely dispersed from their usual tropical distribution during an early El Niño. Unlike many tropical fish that enter our waters during such events, the scythe butterflyfish is not really a warm water species. In its normal range, it is a deep water species found from about 120 to depths of 500 feet or more. The water at these depths is colder than one would consider “tropical.” This is one reason why the scythe butterflyfish has easily adapted to our cooler surface waters, and can live at shallower depths where we divers can encounter them.

Often a species may enter “colder,” northern waters and survive, but not reproduce. I’ve been pleased to find and film several juveniles in the two-inch range at this dive site. Although they could represent larvae dispersed by another El Niño or other warm water event, I’m hopeful that their presence means that these butterflyfish are reproducing in our waters. In this case it would be a natural range extension… perhaps indicative of what is to come as our kelp forests give way to coral reefs due to global climate change (written tongue-in-cheek).

Dr. Bill Bushing

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