Dive Dry with Dr. Bill

070: Rock Wrasse

Wrasses are a very interesting group of fish. They are especially significant and often very beautiful in subtropical and tropical waters like those of the "Sea of Cortez" where I am currently diving. Members of this family in Catalina waters include the sheephead and senorita which I've written about previously, and the rock wrasse, today's featured fish. The wrasse family exhibits some interesting phenomena including sexual dimorphism (= two forms) where males and females have different appearance, and the ability to switch gender. Hmmm... sounds a bit like our own species!

Rock wrasse have cigar-shaped bodies and pointed teeth that project forward from the mouth. The young fish are a greenish color, but gradually turn orange-brown as they age. When mature, green colors appear again in the mix and they turn yellowish on the belly. It is reported that females may also develop a series of faint bars on their sides, but I have also seen them occasionally on males. These differences in coloration with age occasionally are enough to make one question whether they are members of the same species. Males also have a thick dark blue bar (which appears black) just behind their pectoral fin.

To make matters even more complex, about 5% of rock wrasse change gender as they age, just like their relatives the sheephead. The female turns into a male. Seems to me that in our own species, more males turn into females... but I have never done (or plan to do) any scientific research in that area!

Rock wrasse are found from Pt. Conception to Guadalupe Island and into the Sea of Cortez and are most common from the Los Angeles region south. I have yet to see them off Baja, but they are quite common here in the Dive Park. Although observed at depths in excess of 130 feet, they are most often found above 50 feet.

The rock wrasse reaches lengths of 15 inches and may live almost as many years. They become sexually mature when they are two years old at at 5-6" in length. Spawning takes place during the summer months and peaks in July. The eggs and larvae drift in the plankton for a while before settling in shallow water in the fall. During El Nino events, when the seasonal northward current along the coast may be stronger, larvae may be carried further north. Although I often see young juvenile sheephead and senorita in the fall, I have never knowingly seen a young rock wrasse. Apparently they are usually found in very shallow water where I do not dive.

Dr. Milton Love (Probably More Than You Want to Know About the Fishes of the Pacific Coast) writes that the rock wrasse is a diurnal species. Like most of us, it is active during the day but seeks shelter at night in algae on the bottom. Here they sleep in relative protection. Love reports that some may actually bury themselves in the sand at night with only the head exposed.

Although it is reported that they are bottom feeders, I often see them in the Dive Park feeding in the upper layers of the kelp canopy. There they will tear off portions of the kelp blades, usually in areas covered by bryozoa and other invertebrates. They also feed on snails, crabs and other invertebrates on the bottom. Their pointed, tweezer-like snouts and teeth make them well-adapted for picking invertebrates off seaweed and rocks.

I have noticed an interesting feeding behavior here in Catalina waters. They often follow new divers as they kick up the sand and stir up the bottom sediments (due to poor buoyancy control and hyperactive fin kicks), or when they kick the kelp fronds. Many of them may be seen in the diver's "wake" looking for invertebrates exposed on the bottom or in the kelp. When new divers aren't available, they will also wait on the edges as sheephead dig in the sand for food, or rubberlip seaperch suck up food from the bottom. I've even seen them check the "feeding pits" left when bat rays search for food.

It has been reported that rock wrasse only "occasionally" clean other fish, and that statement was based on observations of a single individual doing so. In our waters I have found that cleaning behavior is much more common than previously thought. I frequently observe them cleaning groups of halfmoon near the bottom and even higher in the water column. In fact you can often see several different groups of halfmoon near the sandy bottom trying to solicit cleaning from these wrasses. As additional evidence of this feeding mode, I have also photographed them cleaning garibaldi, opaleye, sheephead and kelp bass. Recently I observed their "sister" species, the senorita, cleaning them.

The fact that cleaning behavior is so common place here in Catalina waters illustrates an important fact about ecological science. When species are studied primarily in disturbed mainland (or island) habitats where ecological structure and conditions have changed, normal behaviors may not be displayed. Since Catalina's Dive Park has been a marine reserve for 40 years, it may reflect behaviors that would be normal in relatively undisturbed habitats. This is another example of the need for relatively pristine areas including marine reserves to better understand the ecological structure and function of a healthy habitat or species. We cannot properly manage our oceans without such knowledge.

© 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.

Rock wrasse male showing dark bar behind gill; orange female with stripes;
rock wrasse male cleaning garibaldi; rock wrasse female cleaning halfmoon

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