Estimating the density and biomass of moray eels (Muraenidae) using a modified visual census method for hole-dwelling re
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Environmental Biology of Fishes (2005) 73: 415–426 DOI 10.1007/s10641-005-2228-2
Estimating the density and biomass of moray eels (Muraenidae) using a modified visual census method for hole-dwelling reef fauna Marianne Gilberta , Joseph B. Rasmussena,b & Donald L. Kramera a Department of Biology, McGill University, 1205 Avenue Docteur Penfield, Montreal, Quebec, H3A 1B1, Canada (e-mails: [email protected], [email protected]) b Department of Biological Sciences, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta, T1K 3M4, Canada Received 9 May 2004
Accepted 26 January 2005
Key words: activity periods, Barbados, Caribbean, piscivore, predatory reef fishes, UVC Synopsis We developed a modified visual census technique suitable for fairly sedentary, hole-dwelling species and used it to determine the diversity, density, biomass, and habitat use of morays at four sites including fringing, patch, and bank reefs in Barbados, West Indies. The method involved a careful search during two passages over transects by day and by night, noting size and position of morays seen, and using the number of new observations on the second passage to estimate the proportion of morays not seen. First passage counts were generally higher than numbers of morays recorded in previous visual censuses. These estimates were raised when we used the time period (day or night) with the highest average density visible for each species, added different individuals from the two passages, and corrected for individuals not seen. We saw more goldentail morays (Gymnothorax miliaris) during the day but more spotted (G. moringa), viper (Enchelycore nigricans), and chestnut (E. carychroa) morays at night. Counts of chain morays (Echidna catenata) did not differ significantly between night and day. Relative abundance and size of moray species varied among sites and to a lesser extent among habitat types within sites, but spotted morays were generally the most important in numbers and biomass. Mean estimated moray density and biomass were much higher than in most previous visual censuses, but similar to rotenone samples on other reefs and comparable to those of other families of predatory fishes. Our findings confirm that morays are abundant and potentially important predators that should be the focus of more attention in ecological studies of coral reefs.
Introduction Our knowledge of coral reef fish abundance, diversity and behaviour is based mainly on visual observations, and the difficulties of nocturnal observations may bias our understanding. For instance, the diurnal community includes many herbivores and omnivores as well as some carnivores, but the nocturnal community is dominated by predatory species (Helfman 1986). If such pre-
dators are not readily visible during the day, their impact may be underestimated. The moray eels (family Muraenidae) may be a particularly important example of an understudied group. Approximately 200 recognized species exist (Smith & Bo¨hlke 1990; Robins et al. 1991; Bo¨hlke & Chaplin 1993; Smith 1997; Bo¨hlk
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