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California Sheephead, Semicossyphus pulcher, are monandric protogynous hermaphrodites and are commercially and recreationally valuable labrids. They are a prominent species occupying the southern California rocky reef and kelp bed fish assemblage.  Both the ecology and life history patterns of California sheephead have been shown to vary with local environmental conditions. 
California sheephead are a carnivorous, epibenthic species of reef fish, foraging mostly in the daytime in sand-rock reef habitats. Their feeding territories are very productive, and allow individuals to occupy small, permanent, economically defendable home ranges. As a large temperate wrasse, they are predators on sea urchins and other benthic invertebrates and play a critical role in also regulating prey populations in kelp forests. Since they feed heavily on urchins, they are consequently an important species for also indirectly regulating kelp growth in southern California’s coastal waters.  However, they exhibit flexibility in prey selection if their main food source is not readily available at a particular time.  Populations with diets dominated by crabs and sea urchins, however, reach larger sizes and mature and change sex at larger sizes than populations that consume higher proportions of bivalves, barnacles, and bryozoans. Since they forage in the daytime and are considered a diurnal species, they may rely on anatomical characteristics which allow them to feed in exposed locations in broad daylight while overcoming the defenses evolved by their prey. They forage both in groups and alone, and larger fish tend to shift towards more heavily armored prey.  
As a reef fish, information on the sheephead’s predation risk often comes from the presence of damage-released chemical cues produced by injured prey animals. These clues are only released when the skin is ruptured, and act as a reliable indicator of the presence of an actively foraging predator. Chemical cues may be released not only with injury, but also when pathogens or parasites penetrate the skin; therefore, the reliability of the chemical cues as indicators of predation risk is decreased. When the sheephead is captured by a predator, and damage-released chemical cues are discharged, the information is available for both conspecifics and heterospecifics to utilize.
Reef fishes occupy home ranges that are at least one order of magnitude smaller than those occupied by birds, mammals, or lizards. The unique ecological conditions experienced by reef fishes may account for their small space requirements, and the productivity of their environment also contributes to this phenomenon. Home ranges in California sheephead vary greatly, and this variability can be attributed to differences in habitat shape (embayment versus contiguous coastline) and to natural habitat boundaries (deep, sandy expanses). They are found in rocky-reef areas 54% of the time, and within those areas, a greater percentage of daytime is found in high relief areas. Although their home ranges are thought of as particularly well defined, the size and fidelity may vary ontogenetically and seasonally and with habitat availability. Sheephead home ranges are relatively small, and the fish have a very high site attachment. They are considered mainly a rocky-reef and kelp-bed associated species, but they occasionally frequent sand habitats in foraging forays. Sheephead may select rocky areas with kelp most often due to the increased habitat complexity, which likely offers additional feeding opportunities and potential refuge from large predators.
The behavior of sheephead is shaped by the daily cycle of light, twilight, and dark. This elaborate diel timing of movements is driven by the need to forage or mate while minimizing predation. Diurnal fishes, like the sheephead, make a round trip between their refuges and foraging areas twice a day, and there may be additional daily trips by breeding fishes to spawning sites. Patterns in the movement of California sheephead are mediated by fish gender and size; for example, large males will exhibit higher site fidelity than females.   However, males also show wider ambits than females, and the size of their ambits changes seasonally. During spawning season, males show a daily increase in their ambits during a period of potential spawning, and also make daily peregrinations offshore into deeper water. Females (which would be expected to move more frequently among male territories) do not expand their ambits significantly during this same period. Each of the movements offshore by males is followed by a return to nearshore habitat prior to twilight, suggesting the occupation of a spawning territory at that time. At twilight, continuing to about 10 to 15 minutes after sunset, the degree of activity above the reef rapidly decreases and sheephead seek shelter for the night; this ‘quiet’ period is a time of major activity for larger reef predators.
Male and female California sheephead have overlapping home ranges, and although they are not usually considered a territorial species, male sheephead can exhibit territorial behavior. Male sheephead are increasingly territorial throughout the day during periods of spawning activity. Since spawning activity occurs around sunset, it may be that they only have differences in space utilizations for short periods on various days during the spawning season, and thus male territoriality only occurs in this same timespan.
California sheephead populations vary geographically in reproductive potential and reproductive capacity, and these differences are correlated with the natural sea surface temperature gradient. It is possible that fish in cooler waters may require less energy for growth and may be able to convert more energy into reproduction than fish at warmer sites.  Spatial and temporal changes in fishing pressure, coupled with environmental changes across populations over time, tend to affect the reproductive potential of each population of California sheephead. Sheephead are also haremic spawners, meaning that each male defends a group of females with whom he breeds.
California sheephead can transition from a reproductively functional female to a functional male during the course of a lifespan in response to social factors. Protogynous sex change typically follows the size-advantage model, where gonadal transformation occurs once the reproductive potential of an individual would be greater as a male than as a female. The transitional phase takes between 2-3 weeks to several months, and it is hypothesized that steroid hormone concentrations are related to sex change due to the total degradation of the ovaries and the appearance of testes. The exact timing of the sexual morphogenesis is suppressed by aggressive interactions with dominant males and triggered by the removal of alpha males. Because sportfishing removes territorial males, this causes a sex change in the oldest, largest females. As a result, the removal of large males has the effect of dramatically reducing the number of eggs produced, and hence the total reproductive output of a population. There is a period of reproductive inactivity during gonadal remodeling, and the sex change in this species is unidirectional. It is possible that in later stages of the transition, fish are functionally male but maintain an intersexual gonadal appearance. Spatially separate populations of California sheephead vary in their sex ratios (number of females to number of males), in size of individuals at sex change, and in the sex ratio threshold. Abundant resources may allow for higher population densities, increasing both encounter rate and sex ratio. Population densities and sex ratios of hermaphroditic fishes are also intimately linked to ecological factors and human activities.
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