|Juvenile whitetail damselfish; Photo by Dan Gotshall|
By Reef Check California Director, Dr. Jan Freiwald
In October, a fish species never-before recorded in California waters was observed off Catalina Island. Ken Kurtis, a diver from the Los Angeles area, was shooting some underwater photos in the shallow waters off Catalina when he noticed a fish that did not quite belong. What he saw was a small blue damselfish (same family as the garibaldi - Pomacentridae), with a patch of greenish-yellow extending from its head onto the forward part of its dorsal fin and a translucent white tail. He took video of the fish and reported it to other divers at one of Reef Check’s partner organizations, the Long Beach Aquarium of the Pacific. The individual was quickly identified as a juvenile whitetail damselfish (Stegastes leucorus) by several experts.
The first to identify this fish as a whitetail damselfish was Dr. Bill Bushing. To further investigate Ken’s first observation of this species in California he went diving, located the individual and captured more video. Dr. Giacomo Bernardi, a Molecular Ecologist at UC Santa Cruz who has collected genetic samples of this and its two closely related sister species from their native range, and has studied their population distributions extensively, states that the three species form the whitetail damselfish species complex that partition between islands. They are interesting because they demonstrate a pattern of speciation (i.e. evolution of new species) first discovered by Darwin in the Galapagos, but rarely found in fishes. Stegastes beebei (named after William Beebe, the author of World's End, his narrative of an epic trip to Galapagos) is found in the Galapagos Islands and adjacent areas, Stegastes baldwini is restricted to Clipperton Island, a small island due south of Baja California, and then this species Stegastes leucorus, that is found at the Revillagigedo Islands, mainland Mexico, Guadalupe Island, and now Catalina!
According to Bernardi, the closest location that this individual could have come from would be Guadalupe Island off the coast of Baja California – a 300 mile journey through the open ocean. Reef fish, such as this damselfish, go through a larval phase after they hatch, during which the tiny organisms swim in the open ocean before returning to settle on a near-shore reef. The whitetail damselfish typically spends about 20 days as pelagic larvae in the open ocean before it needs to find a reef to grow up on. Once it settles onto a reef, a whitetail major may grow to lengths of about 14 centimeters and live up to 19 years. Dr. Bernardi may try to collect a (non-lethal) genetic sample of this individual. He would then compare this to his database of genetic samples from the fish’s native range to positively identify where the individual came from. In any case, this fish had to have travelled a great distance, and it is unlikely that only one individual would make this long and unusual journey. Although this is the first known recording of a whitetail damselfish in California waters, we may be seeing more of them around Catalina in the future.
This find demonstrates how the presence of well-trained divers who are familiar with the local species can lead to new discoveries, and how they help keep an eye on our local marine environments and the ways they continuously change. This has been a great find Ken!
|Adult whitetail damselfish; Photo by Dan Gotshall||Screen grab from video showing juvenile whitetail damselfish behind a juvenile garibaldi (Ken Kurtis)||
Photo of Catalina's juvenile whitetail damselfish taken by Dr. Bill Bushing