EFFECTS OF MAT MORPHOLOGY ON LARGE SARGASSUM-ASSOCIATED FISHES - OBSERVATIONS FROM A REMOTELY OPERATED VEHICLE (ROV) AND FREE-FLOATING VIDEO CAMCORDERS

Vagile large juvenile and adult fishes are often under-represented in traditional sampling of Sargassum-associated fishes in the open ocean. We used underwater video recordings from free-floating camcorders and a remotely operated vehicle (ROV) to assess the relative abundance of large mobile fishes under large Sargassum mats (> 10 m diameter), und er dispersed clumps of Sargassum (<1 m diameter), and in open water wi thout Sargassum as a reference. In addition, we conducted dipnet sampl ing in each Sargassum treatment for a comparison to traditional method s. All samples were obtained in September 1992 along the western wall of the Gulf Stream off Cape Hatteras, North Carolina. A total of 31 fi sh taxa were identified from both video and dipnet collections. Only 8 taxa were identified in both video and dipnet collections, while 11 t axa were seen only in video and 10 were only found in dipnet collectio ns. Dipnet collections were dominated by juvenile balistids and other small, cryptic fishes, while the video observations were mainly of lar ger, rapidly-moving carangids. Fish diversity increased with the amoun t of continuous Sargassum habitat: four taxa were observed when no Sar gassum was present, 12 under clumps, and 19 under mats. Our results in dicated that mat morphology significantly affects the Sargassum-associ ated fishes, and that both video and traditional capture methods are c omplementary and should be used together to accurately census this com munity.