Colonization, diversity, and seasonality of fishes at pelagic fish aggregating devices

The pelagic zone of the ocean can be a challenging environment in which to conduct

research and as a result we lack the robust baseline abundance and diversity data,

compared to what is available in more accessible coastal habitats, to be able to track

changes or stressors to the biota in this environment. Many large-scale fisheries

target pelagic fish, and much of the information available on these species is based

on fisheries-dependent data that may be biased towards hotspots and commercially

valuable fishes. Here, a long-term video and visual fish survey was conducted on two

subsurface moored fish aggregating devices (FADs) in the pelagic waters of the

central Bahamas to determine the feasibility of using moored pelagic FADs as tools

for collecting fish abundance and diversity data. A wide range of species was documented,

including large migratory fish that are the focus of commercial and recreational

fisheries, and smaller often overlooked species on which little abundance or

seasonality information exists. We found that FADs colonize quickly and reach a

peak stable (albeit seasonally cyclical) abundance and diversity within the first several

months after deployment. Species richness was higher in video surveys, but abundance

was higher in visual surveys, except for sharks. Our results highlight the need

to tailor survey methods to fit the context and study objective, and provide further

evidence for the importance of fisheries-independent data in monitoring pelagic

species.