By Terry Tillman
Curiosities abound in California’s marine environment, so much so that it’s difficult to pick just one example to showcase how peculiar and wonderfully diverse nature can be. None seems to top the list of life-style oddities quite like the California sheephead (Semicossyphus pulcher). This ocean denizen has long been a colorful actor in California’s marine landscape. Its large size, brightly contrasting coloration and fine flavored flesh, rivaling that of lobster, make it a much sought after table-fare. Recorded commercial harvests of sheephead in California date back to the late 1800’s, and historically high harvests were made throughout the 1900’s. Nowadays, commercial catches are more closely regulated, though sport harvest of sheephead often exceed that of the commercial catch, with trophy fish taken by both spear-fishing and hook-and-line.
So what’s so curious and odd about this popular fish?
Well, boys and girls, this fish is both a boy and a girl . . . or, I should say, both a girl and a boy. California sheephead are monandric protogynous hermaphrodites, which is a fancy way to say they change sex as part of their life cycle. Beginning as females, and on reaching a certain age and size …. whoosh, they turn into a male.
Our California sheephead populate waters off Monterey, California all the way to southern Baja California and the Gulf of California, in Mexico. They can reach a hefty 36.5 pounds (16.6 kilograms) and up to three feet (0.9 meters) in length, feeding mostly on invertebrates. Using their protruding canine-like teeth, and crushing pharyngeal plates (crushing tooth plates in the back of the mouth), they easily feast on hard shelled invertebrates like small filter feeders (barnacles, muscles, worms) as well as larger sea urchins.
The coloration of the sheephead varies with size, and of course, sex, though both sexes sport well defined white chin patches. While most females have uniformly pink coloration over their bodies, males develop a distinctive black and bright red banding pattern. As if uncomely protruding canine teeth weren’t bad enough, most males also develop a pronounced nuchal hump (enlarged forehead), furthering their comic appearance.
Sheephead have been reported in shallow sub-tidal waters out to depths of 280 feet (85 meters), though typically they are found in and around rocky reefs and kelp forests. Observations of sheephead around offshore oil platforms reveal a strong tendency for the fish to make daily vertical migrations from shallow water during the day to deeper water at night. They have a relatively small home range, and reveal a high degree of site fidelity (preference).
Because of its impressive size, adult male sheephead have few known natural predators. Since the late 1970s, Sheephead have been a consistent part of the recreational sport catch, although catch rates have decreased in recent decades. The decrease in sport-caught sheephead may be due to increased competition for fish from the commercial fishery in the 1980s, combined with a minimum size limit and reduced catch limits enacted in early 2000. Those regulations also included fishery closures in January and February. The current year, 2013, size limit is 12 inches total length (30.5 centimeters) and a daily bag limit of five Sheephead per day per person.
An excellent synopsis of unusual life history facts for California sheephead is provided by the Monterey Bay Aquarium Foundation, below:
During mating season (between July and September) male sheephead become territorial and defend their spawning territory. Dominant males lead the females in a circular pattern as they broadcast sperm and eggs, respectively. If a smaller male approaches, the male interrupts spawning activity to chase away the intruder. The females spawn between 36,000 and 296,000 eggs, which hatch into larvae. The young of the year sheephead don’t resemble adults; they’re a bright reddish orange with large black spots on their dorsal and upper tail fins and a white stripe running the length of their bodies.
All sheephead are born female. Most of them change to males following environmental clues we don’t fully understand. In 1990, Robert Cowen studied sheephead in four sites where the availability of food varied. In the area with the most food, females changed sex at about 13 years old and lived about 21 years. In the area with the least food, females changed sex at five to six years old and lived about nine years. At least in these two areas, the females changed sex about two-thirds of the way through their life spans. (1999-2013, Monterey Bay Aquarium Foundation, 886 Cannery Row, Monterey, CA 93940 Tel: 831.648.4800.)http://www.montereybayaquarium.org/animals/AnimalDetails.aspx?enc=n3f4wmcSJaNu4Cp/cHd0/Q==)
Within the marine ecosystem, the sheephead plays an important role by limiting sea urchin populations. Sea urchins graze on marine plants like kelp, and in the absence of population controls, can denude the sea floor of plant life. Should the kelp holdfast be gnawed away by urchin grazing, this can, in turn, disturb kelp canopy habitats. Recent studies indicate that urchin predation by sheephead have a significant effect in controlling urchin populations within certain habitats.
Like so many marine species in California, there are various threats to the California sheephead including: habitat loss, fishing pressure, reproductive success, and larval distribution and survival. More recent research, since 2004, shows considerable variability in sheephead populations in response to external environmental conditions and fishing pressures. In addition, there has likely been an overall decrease in the reproductive potential of California sheephead. These observations, coupled with the unusual life cycle of these fishes, suggest that conservation strategies may include dividing the sheephead management area into northern and southern zones, each with unique size limits, and possibly enforcing different size limits for males and females. Conservation strategies and protections for important ecological actors like the California sheephead will be critical to the preservation of the nearshore ecoregion and the kelp forest landscape.