A snapshot of a high density seahorse population in a tropical Rocky Reef

Abstract

Seahorses are fishes that suffer high trading pressure in the international market. Three species have been recorded in Brazil, Hippocampus reidi, Hippocampus erectus and Hippocampus patagonicus, already classified as threatened or data deficient. Guaíba Island is an ecologically relevant site due to its position between two bays in Rio de Janeiro state. The present study aimed to survey the seahorse population of Guaíba Island, verifying several population structure parameters. Eight diving sites were selected around the island. Only the longsnout seahorse H.reidi was recorded. The population showed the largest density ever recorded in the world for the species. Sex ratio was 1:1 and seahorses were reproductively active. We observed three juveniles. The mean length recorded was 8.9 ± 1.64 cm. The population structure was similar to others populations studied throughout the Brazilian coast.