Mutton Hamlet Photo credit: Octavio Aburto
Using Reproductive Parameters to Manage Grouper Fisheries in the Gulf of California
by: Brad Erisman
Project Goals
The primary goal of this project was to describe the reproductive patterns of three groupers from the Gulf of California: the leopard grouper (Mycteroperca rosacea), the mutton hamlet (Alphestes immaculatus) and the Panama graysby (Cephalopholis panamensis). This included investigations on sexual patterns, courtship and spawning behaviors, population structures, home range sizes, and temporal spawning patterns. The second goal was to communicate the results of this project and recent research on other groupers in the Gulf of California to pertinent fisheries agencies and conservation groups in Mexico.
Goals Achieved
A considerable amount of data on the courtship and spawning behavior, population structure, home range, sexuality and spawning periodicity were collected for all three species. Results from this project are currently included in two manuscripts that have been accepted for publication and two that are in preparation for publication. I will present my research findings to faculty and students of the Marine Ecology Department at Centro de Investigaci n Cient fica y de Educaci n Superior de Ensenada (CICESE) this spring and to Comunidad y Biodiversidad, A.C. (COBI) this summer. The purpose of this presentation is to facilitate the dissemination of this research to the scientific community and conservation groups in Baja California.
Summary of Results
Leopard grouper (M. rosacea): Adult leopard groupers formed large spawning aggregations (150 700 fish) at specific sites in Loreto, Mexico in April and May, and spawning occurred daily at these sites from late April through early June. Courtship occurred throughout the day, but spawning was restricted to the evening hours. Adults spawned in groups of 6 - 40 fish, and pair spawning was not observed. The site-specificity of leopard grouper spawning aggregations and diel spawning period were typical of most aggregating groupers, and the size and structure of these aggregations was similar to other species in the genus Mycteroperca. Leopard grouper behavior patterns were unusual in that spawning aggregations persisted for extended periods, spawning was not synchronized with the lunar cycle, and adults aggregated during non-spawning periods (year-round feeding aggregations). The extensive duration and site-specificity of spawning aggregations and the propensity of M. rosacea to form aggregations year-round increases the vulnerability of the species to overfishing. Policies and regulations that protect these aggregations are needed for the conservation and effective management of leopard grouper fisheries in the Gulf of California.
The sexual pattern and sexual development of the leopard grouper, Mycteroperca rosacea, were investigated from 483 specimens collected from the Gulf of California, Mexico. Histological, population, and behavioral data indicated a gonochoric sexual pattern. Some juveniles passed through an immature bisexual phase of gonadal development, but no evidence of post-maturational sex change was found. The size distribution and size at sexual maturity were similar for both males and females. In accordance with predictions of the size-advantage model, the gonochoric sexual pattern of M. rosacea is likely influenced by its group-spawning mating system.
Mutton hamlet (A. immaculatus): Adults are reproductively active from April through September, and courtship occurs in pairs during the evening hours. Behavioral observations and magnetic resonance imaging analyses (MRI) both suggest that adults are nocturnal, and this type of activity pattern has not been described in any other species of grouper. Males are smaller and younger than females, and sex ratios are male-biased. This suggests that mutton hamlets are protandrous hermaphrodites (male to female sex change). This is the first evidence of protandry in any grouper species in the world and has significant implications for both fisheries management and evolutionary biology. Traditional management strategies designed for most groupers and non-hermaphroditic fishes are likely to be detrimental to populations of mutton hamlets. Traditional size-based fisheries are predicted to selectively remove large females from populations. As a result, egg production will decline, sex ratios will shift, and populations will decline. Successful management must include policies that protect females from harvest and conserve population of breeding adults.
Panama graysby (C. panamensis): Many aspects of the reproductive biology of the graysby are s imilar to other grouper species. Histological, behavioral, and population data all indicate a protogynous sexual pattern, where individuals reproduce first as females and later change sex to reproduce as males. Males are larger and older than females, and sex ratios are female-biased. Males guard territories of 100-400 m2, and females occupy smaller territories within that of the males. Males control a harem of 2-6 females, and they spawn with these females in paired courtship during the evening hours. Spawning occurs from July to September and is non-lunar. Management strategies implemented for other protogynous groupers should be successful in the management of this species.
Although males are socially dominant and control a harem of females, they are much less colorful and less aggressive than females. Females compete violently during courtship, soliciting males and disrupting matings of other females. In fact, females cluster to form leks (= assemblages of individuals for the sole purpose of mating), where they will simultaneously display to a passing male in an attempt to solicit spawnings. This constitutes a new discovery of animal behavior, since leks are male-based by definition, and female leks have only been described in one other species, a butterfly. The culmination of these behaviors suggests that the graysby is sex-role reversed; a behavior pattern that is extremely rare among animals and even rarer in fishes (known only in two groups of fishes). More importantly, this represents the first example of sex-role reversal in the absence of parental care (adults are broadcasts spawners), and as a result, it significantly changes current theories on mechanisms driving sexual selection.
Accepted Publications
1) Erisman BE, Rosales-Casian JA, Hastings PA (2007) Evidence of gonochorism in a grouper, Mycteroperca rosacea, from the Gulf of California. Environmental Biology of Fishes In press.
2) Erisman BE, Buckhorn ML, Hastings PA (2007) Unusual spawning patterns in the leopard grouper, Mycteroperca rosacea, from the central Gulf of California, Mexico: implications for conservation and fisheries management. Marine Biology In press.
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