Dive Dry with Dr. Bill

028: Triggerfish

My diving in the Gulf of California has given me an opportunity to more closely observe a fish also found in our waters, the finescale triggerfish. This species and its relatives are not usually native to our temperate waters and kelp forests, but to the warmer waters of the Gulf of California south to Chile. They were first noted here during the extreme 1982-84 El Nino event when stronger currents from the south brought much warmer water into our region. Although these conditions were not good for our kelp and the species dependent on it, it sure was nice to dive in warm water off Descanso Beach! With predictions of a milder El Nino this year, it will be interesting to see if our local triggerfish population receives some new immigrants, either as adults or planktonic larvae and young.

The triggerfish have remained in our waters since then, and are occasionally seen from the glassbottom boats in Lover's Cove. I have observed them there briefly while diving, but they tend to be skittish and remain at a distance. Since our waters are much cooler than they are accustomed to, many have questioned whether they are able to reproduce off Catalina. I can't answer that question without a scientific study. It is possible these fish are long-lived, and new individuals may also have arrived during subsequent El Nino events. I'm just glad that humans can reproduce (or not as they choose) in any climate!

While diving SE Asia and the South Pacific, I familiarized myself with many other species of triggerfish. My favorites were the beautiful clown and Picasso triggerfish I followed frequently while snorkeling and diving the waters of Moorea, one of the Tahitian islands. Many other species were there as well. On my first dive in Moorea, I was fascinated by but not concerned about the nearly 100 sharks of four species that continuously circled my group. What really concerned me were the giant triggerfish in those waters. It was mating season and this species is well known for its aggressiveness in defending its nest.

If it were only the nest they defend, avoiding these large (up to 30") fish would be fairly easy. However, like many triggerfish, the giant defends not just the nest itself but a funnel-shaped territory originating at the nest and increasing in diameter upwards to the surface. Giant triggerfish will attack anything, including divers, that enter this territory. They are known to bite through swim fins and even take chunks out of a diver's legs. Fortunately I was able to prevent an attack by kicking my fins in their face when they approached (the recommended defense).

Although the finescale triggerfish also defends its nest in similar fashion but there appears to be no similar danger in Lover's Cove here. Perhaps it is because the waters are too cool to mate and form nests, and therefore there is nothing to defend. Possibly something is lacking in their diet here to produce the hormones that "trigger" aggressiveness. Here on Catalina I consider myself lucky just to get a glimpse of them. However in their Gulf of California home waters, these fish, although still skittish, were far easier to approach. I was able to get good video footage from both Isla Santa Catalina and "neighboring" Isla San Francisco using a slight telephoto lens. Most of the individuals there were often blotched with large dark spots on the side of their body. Ones I've seen in our waters tend to be more uniform, and there were a few like this intermingled with the others in Mexico.

Triggerfish are named because of the prominant first spine on their forward dorsal fin (see pictures). They propel themselves primarily with the secondary dorsal and anal fins, and are fairly distinctive if seen while swimming. Although found over sandy bottoms here and In Mexican waters, they seem to prefer rocky reefs where they can quickly escape into the crevices whenever the infamous Dr. Bill approaches with his video camera! I guess I need to pay them and get them to sign a model release for some tight portraits!

© 2003 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.

Image caption: Blunthead triggerfish (upper left) and finescale
triggerfish in the Gulf of California, Mexico

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia