Ecology of bigmouth sleepers (Eleotridae: Gobiomorus dormitor) in a Puerto Rico reservoir

Abstract

The bigmouth sleeper Gobiomorus dormitor is an eleotrid species found in southern Florida and Texas, along the Atlantic coast of Central and South America, and the Caribbean Islands. This species is important in terms of recreational and consumptivefishing, and conservation. Bigmouth sleepers are harvested by anglers in parts of their range, while in Florida hydrological changes, habitat loss, and reduced waterquality have reduced the species' already small geographical distribution,necessitating conservation measures. There is a paucity of data regarding the biology of bigmouth sleepers, but accurate knowledge of this species' ecology and behavioris crucial to effective conservation and management plans. Although bigmouth sleeperstypically inhabit lotic habitats, they have been found in four reservoirs in PuertoRico. In Carite Reservoir, abundance and size data indicate that habitat is suitablehabitat for bigmouth sleepers, and the presence of a diversity of size classes ofsleepers suggests that either in-reservoir reproduction or significant recruitmentto the reservoir from an outside source is occurring. This research was initiated to evaluate the likelihood of each, and to learn more broadly about bigmouth sleeperecology. Population biology, diet, and reproduction of bigmouth sleepers in CariteReservoir were examined between 1999 and 2001. Many sizes of bigmouth sleepers werecollected during this study, ranging from 25 to 400 mm TL. The estimated totalpopulation size in 2000 and 2001 was 1,783 and 3,353 fish, respectively. Daily growthrate of tagged fish ranged from -0.08 to 0.10 mm/day, and was negatively correlatedwith length of fish at marking. Diet of small bigmouth sleepers (50 - 100 mm TL) mainlyconsisted of insects, whereas larger fish primarily preyed upon fish and freshwatercrabs. Sexual dimorphism of bigmouth sleepers was evident in the anatomy of theirurogenital papillae; these differences developed at sizes as small as 50 mm TL and persisted throughout the year. Reproduction was seasonal, with the highest gonadosomaticindicies occurring in May and June and the lowest in January and February. The smallestmature male observed was 159 mm TL, while the smallest mature female was 179 mm TL. Size frequency distributions of oocytes in female ovaries during the reproductiveseason typically fell into two size groups, a group of primary oocytes (< 0.20 mm)and one group of maturing oocytes (> 0.20 mm). The largest oocytes observed were 0.70mm from a 270-mm female. Fecundity was negatively correlated with date, suggesting batch spawning. Fecundity was relatively high (mean = 140,836) and was positively correlated with female body weight. Results of this research not only provide managersand conservationists a better understanding of bigmouth sleepers in Puerto Rico reservoirs, but also contribute to the knowledge of this species' ecology throughoutits range.