Observations of a Black Grouper (Mycteroperca bonaci) Spawning Aggregation in Bermuda

Abstract

Diving observations at a black grouper (Mycteroperca bonaci) spawning aggregation site on Bermuda’s reef platform revealed many similarities to observations of this species obtained at multi-species spawning aggregation sites in Belize. In addition to similarities in body sizes, color patterns and some behavior, the principal spawning period in the days after the full moon was also similar. Although spawning was not observed in this study, there was ample indirect evidence of spawning at the site, i.e. courtship behavior by males, females with distended abdomens, and color changes. The formation of temporary spawning territories by males and courtship behavior within these territories is described and illustrated. Taken together, these data appear to indicate that the behavior of black grouper at spawning aggregations is consistent across a broad latitudinal range from Belize in the south to the northern limit of the species’ range in Bermuda. IntroductIon Relatively few studies have been published on the biology of black grouper (Mycteroperca bonaci), and most of these studies have concentrated on the reproductive biology of this protogynous hermaphroditic species (Crabtree and Bullock 1998, Garcia–Cagide et al. 2001, Brule et al. 2003, Teixeira et al. 2004). Spawning seasonality of black grouper at spawning aggregation sites in Cuba has been described by Claro and Lindeman (2003). Although the black grouper is recognized as a transient aggregation spawner (Domeier and Colin 1997), only a small number of studies have described the behavior of this species at fish spawning aggregation sites (FSAS) with the majority of the research being conducted in Belize (Heyman and Kjerve 2008, Paz and Sedberry 2008). One study in Florida (Eklund et al. 2000) examined an aggregation site in relation to a Marine Protected Area (MPA) boundary but provided less behavioral information as spawning was not observed. Whaylen et al. (2004) reported seeing small groups of black grouper with distended abdomens during observations at a primary Nassau grouper (Epinephelus striatus) spawning aggregation site in Little Cayman but spawning was not observed. Black grouper have been an important species to the Bermuda fishery for decades but suffered a significant decline in landings from the mid–1970s along with many other grouper species (Luckhurst 1996). Although it was known that black grouper aggregated to spawn, the location of spawning sites was apparently not well known in the local fishing industry. In contrast, red hind (Epinephelus guttatus) spawning aggregation sites were well–known and heavily fished, which prompted early management action to seasonally protect these sites (Luckhurst 1998, Luckhurst and Trott 2009). In the summer of 2003, the location of a spawning aggregation site for black grouper was revealed by fishermen and this lead to research to define the dynamics of the aggregation. It was determined that the black grouper site was relatively close to an existing red hind site which was seasonally closed to all fishing. Anecdotal evidence indicated that the black grouper site was being heavily fished and that the bag limit of one fish per boat per day was being routinely exceeded. As enforcement of the bag limit was problematic due to the large number of landing sites, it was decided to incorporate the black grouper site into a redefined and enlarged seasonally protected area (Fisheries Protected Areas Order 2004) which included the original red hind spawning aggregation site (Luckhurst, pers. obs.). Only after the site was seasonally closed to fishing was it possible to conduct an intensive research program to study the aggregation and learn more about its dynamics without interaction with fishermen at the site. The data presented here are the first to be derived from this ongoing study. MAterIAls And Methods A week before diving observations began, 2 mooring buoys were placed about 40 m apart near the presumed center of the spawning aggregation site at a depth of about 30 m. This was done to avoid anchoring on the site which could have disturbed the aggregated fish and also increased the efficiency of boat operations. There were 2 dive boats on the site for 3 days of the project with a single boat on the remaining 2 days. Diving observations commenced on the day of the full moon in June 2005 and continued for 6 consecutive days. No diving was possible on the fifth day due to rough sea conditions at the site. Teams of divers from each boat (2–4 divers per team) recorded their observations on waterproof paper on slates and all of the daily observations made during the study were collated and used for the present analysis. Divers surveyed the area widely and made estimate counts of the number of fish within their view and also estimated fish sizes. In addition, divers made notes on behavior and color patterns. After each dive, team members discussed