California sheephead

The California sheephead is a carnivorous, epibenthic reef fish, foraging mostly in the daytime in sand-rock reef habitats.[11] Its feeding territories are very productive and allow individuals to occupy small, permanent, economically defendable home ranges.[14] As a large temperate wrasse, it is a predator of sea urchins and other benthic invertebrates and play a critical role in also regulating prey populations in kelp forests.[15] Since it feeds heavily on urchins, it is consequently an important species for indirectly regulating kelp growth in southern California's coastal waters.[11] However, it exhibits flexibility in prey selection if its main food source is not readily available at a particular time.[13] 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.[15] 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.[16] They forage both in groups and alone, and larger fish tend to shift towards more heavily armored prey.[10][16]

As a reef fish, signals about the sheephead's predation risk often comes from the presence of damage-released chemical cues produced by injured prey animals.[17] These clues are only released when the skin is ruptured, and act as a reliable indicator of the presence of an actively foraging predator.[17] 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.[17] When a sheephead is captured by a predator, and damage-released chemical cues are discharged, the information is available for both conspecifics and heterospecifics to use.[17]

California sheephead showing teeth in kelp bed habitat

The behavior of California sheephead is shaped by the daily cycle of light, twilight, and dark.[16] Diurnal fishes, like the sheephead, make a round trip between their refuges and foraging areas twice a day, and additional daily trips may be made by breeding fishes to spawning sites.[14] This elaborate diel timing of movements is driven by the need to forage or mate while minimizing predation.[14] Patterns in the movement of California sheephead are mediated by fish sex and size; for example, large males will exhibit higher site fidelity than females.[12][13] However, males also show wider ambits than females, and the size of their ambits changes seasonally.[13] During spawning season, males show a daily increase in their ambits during a period of potential spawning, and also make daily journeys offshore into deeper water.[13] Females (which would be expected to move more frequently among male territories) do not expand their ambits significantly during this same period.[13] 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.[13] 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.[16]

Male and female California sheephead have overlapping home ranges; although they are not usually considered a territorial species, male sheephead can exhibit territorial behavior.[10] Male sheephead are increasingly territorial throughout the day during periods of spawning activity.[10] Since spawning activity occurs around sunset, it may be that they only have differences in space use for short periods on various days during the spawning season, thus male territoriality only occurs in this same timespan.[10]

California sheephead populations vary in their reproductive potential and reproductive capacity, and these differences are correlated with the natural sea surface temperature gradient.[18] 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.[15][18] Population densities and sex ratios of hermaphroditic fishes are also intimately linked to ecological factors and human activities.[18] 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.[18] 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.[18] Sheephead are also haremic spawners, meaning each male defends a group of females with which he breeds.[12]

California sheephead can transition from a reproductively functional female to a functional male during the course of a lifespan in response to social factors.[11] 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.[18] The transitional phase takes between two weeks and several months, and steroid hormone concentrations are thought to be related to sex change due to the total degradation of the ovaries and the appearance of testes.[11] The exact timing of the sexual morphogenesis is suppressed by aggressive interactions with dominant males and triggered by the removal of alpha males.[19] There is a period of reproductive inactivity during gonadal remodeling, and the sex change in this species is unidirectional.[11] In later stages of the transition, fish possibly are functionally male, but maintain an intersexual gonadal appearance.[11]

California sheephead at fish market

The California sheephead is considered a vulnerable species because of its high fishing rates off of the coast of Southern California.[5] Usually most of the fish caught are the largest males, causing a shortage in males in the population and the subsequent morphogenesis of the largest females to males.[1] This, in turn, creates a deficiency in the number of eggs produced and weakens the population in a particular fishing area.[19] Male numbers seem typically low which also could result in sperm limitation for the species, with further male reduction, resulting in reduced reproductive output: males are readily targeted in the recreational spear fishery.[1] Commercial and recreational fishing pressure has increased (there is also an artisanal sector), and this has caused catches to decline over the last decade.[1] To control the catches of sheephead and prevent overfishing, the California Department of Fish and Game in 2001 established regulations that restrict the catch size of sheephead and the areas where these fish may be caught.[8]

Size restrictions on sheephead were fairly minimal before 1999 for both the recreational and commercial fisheries. But, in 1999, the California Department of Fish and Wildlife set the minimum catch size for the commercial fishery to 12 in or 30 cm (total length) and followed with the same size limit for the recreational fishery in 2001.[1] To further decrease commercial harvest, the minimum commercial harvest size was increased to 13 in 2001 and the 10-fish recreational bag limit was reduced to five.[1]