Meeting Abstract
Although the field of nighttime ecology remains understudied, nocturnal surveys can play an integral part in assessing fish assemblages. While little is known about seahorse nocturnal behaviors, congregations were documented at night in an isolated saltwater lake in the Bahamas. Population surveys for seahorses and their potential predators, octopus and crabs, were conducted in Sweetings Pond, Eleuthera, Bahamas, at midnight and midday during March and August 2018, using belt transects organized perpendicular to the shoreline and increasing in depth. Nocturnal surveys reported densities (1.2 seahorses/m-2) significantly higher than those reported on the same transects during the day (0.2 ind/m-2) and in previous studies in Sweetings Pond (0.14 ind/m-2). Predator densities followed a similar pattern with higher densities observed during the night. Sex ratios were consistently male-biased, and the frequencies of fish in different reproductive categories were significantly influenced by time of day. Daytime populations were made up of 70% males, with a high frequency of pregnant males in March, whereas nocturnal populations saw an increase in number of females observed. Seasonal recruitment was detected for the first time in this population, with an increase in juveniles detected in the shallow ends of transects during nocturnal surveys in March. Seahorses were also perched significantly higher in the water column during the night regardless of reproductive category, depth, or season. Considering H. erectus is listed on the IUCN Red List as Vulnerable, the drastic increase in population size due to changes in detectability, changes in sex-ratios, and presence of juveniles during nocturnal surveys has crucial implications for understanding their ecology and conservation.
