Incorporating Life History Information Into Management Strategies For Reef Fishes: The Role of Reproductive Biology in the Conservation of Groupers in the Gulf of California

by Brad Erisman  

Goals
The main purpose of this project was to gain a better understanding of the life history and behavior patterns of groupers from the Gulf of California. The results were to be disseminated to stakeholders in Mexico (fisheries biologists, conservation groups, etc) to improve conservation and management strategies of groupers in the Gulf of California.

Cooperating Individuals / Organizations
Michele L. Buckhorn: University of California, Davis
Fernando Arcas: Grupo Ecologista Antares A.C. (GEA)
Jorge Torre: Comunidad y Biodiversidad A.C. (COBI)
Jorge Rosales-Casi n: Chairman of the Ecology Department at the Centro de Investigaci n Cient fica y de Educaci n Superi r de Ensenada (CICESE)

Summary of Results

Spawning patterns of M. rosacea.
Adult leopard groupers formed spawning aggregations of 150 - 700 individuals at specific sites near Loreto, and spawning occurred daily at these sites from late April to early June. Courtship occurred throughout the day, but spawning was restricted to the evening hours (1645-2020 h).  Adults spawned in groups of 6 - 100 fish, and pair-spawning was not observed. The group-spawning behavior of adults and the gonosomatic indices (GSI) of mature males (mean = 2.34%) indicated that sperm competition was intense. Male GSI decreased with body size, which indicated that small males invested more energy in gamete production and may have spawned more frequently than large males. 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 different from other groupers in that spawning aggregations persisted for extended periods, spawning was not synchronized with the lunar cycle, and adults aggregated during non-spawning periods.

Sexual development and sexuality of M. rosacea.
Data on the population structure, behavior patterns, and gonad morphology of leopard groupers indicate a gonochoric sexual pattern. The size distributions of adult males and adult females overlapped, and there was no difference in size with sex (unpaired t-test, p = 0.24). The size of first sexual maturity for females (210 mm SL) and males (220 mm SL) was also similar. No histological evidence of sexual transition from mature female to mature female was found, although many individuals passed through a bisexual juvenile phase prior to reaching sexual maturity as either male or female. Adults exhibited a group-spawning mating system, a behavior pattern observed only in gonochoric fishes. In groupers, sex and sex change is determined by social interactions. Protogyny is non-adaptive in group-spawning mating systems, and thus this likely contributed to gonochoric sexual pattern observed in M. rosacea. This is a remarkable finding, since this pattern has only been identified in one other species of grouper (Epinephelus striatus).  When placed in a phylogenetic context, protogynous hermaphroditism is the ancestral state for groupers, and it appears that gonochorism has evolved independently at least twice in two separate genera. 


Implications for Conservation and Management
The unusual sexual and spawning patterns of leopard groupers in the Gulf of California have several important conservation implications.  First, the extensive duration and site-specificity of spawning aggregations and the propensity of M. rosacea to form aggregations year-round increases the vulnerability of this species to practices of overfishing.  In fact, their tendency to aggregate throughout the year makes this species even more susceptible to overexploitation than other groupers, which only aggregate for brief periods to spawn. Policies and regulations that protect both spawning and non-spawning aggregations are needed for the effective management of leopard grouper fisheries in the Gulf of California. Potentially effective strategies include seasonal bans on fishing and trading during spawning, inclusion of spawning and feeding aggregation sites into no-take marine reserves, fishing quotas and gear restrictions for commercial fishers, and reduced daily catch limits for recreational fishers.

Second, the gonochoric sexual pattern of M. rosacea suggests that the population structure and reproductive output of populations are less impacted by size-based fisheries regulations.  Most groupers are protogynous fishes, which show a bimodal population structure consisting of small females and large males. For these fishes, traditional fishing methods (i.e. minimum size restrictions) select for the removal of large males, and this often results in sperm limitation, changes in operational sex ratios, decreased spawning activity, and eventual population declines.  Due to the unique sexual pattern of M. rosacea, standard fisheries catch regulations should not be detrimental to population growth, and setting a minimum size limit above the size of first maturity should be effective in reducing the effects of both growth overfishing and recruitment overfishing. 

Of course, any attempts to improve management of leopard grouper fisheries would require further research on their biology, continuous monitoring of populations and the fishery, and strict enforcement of regulations.

Future Plans
I hope to facilitate the incorporation of my research on M. rosacea into management of their fisheries by communicating these results to various stakeholders in Baja California.  I also plan to estimate other parameters that are important in fisheries management, such as the batch fecundity and spawning frequency of adults.  This information is needed to estimate annual reproductive output and spawning stock size, which in turn, are used by fisheries agencies to model populations and determine acceptable levels of harvest.

During this project, I collected a significant amount of preliminary data on the reproductive biology and behavior of several other groupers from the Gulf of California (i.e. Alphestes immaculatus, Epinephelus labriformis, and Cephalopholis panamensis).  Although more analyses are needed, it appears that these species are remarkably different in their sexuality, despite their sympatric distribution and close phylogenetic relationships. For example, A. immaculatus appears to protandrous, which is a form of sexual pattern previously undescribed for any species in the family Serranidae. Given the importance of reproductive parameters to fisheries management and the apparent diversity of reproductive patterns among these species, I hope to collect additional data on A. immaculatus, E. labriformis, and C. panamensis. 

This material is based upon work supported by the National Science Foundation under Grant No. 0333444.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.



 

UC Mexus
PADI Foundation
California Sea Grant
Maxwell Fenmore Foundation