Nassau grouper (Epinephelus striatus) spawning aggregations: hydroacoustic surveys and geostatistical analysis

With the near extinction of many spawning aggregations of large grouper and snapper throughout the Caribbean, Gulf of Mexico, and tropical Atlantic, we need to provide baselinesfor their conservation. Thus, there is a critical need to develop techniques for rapidly assessing the remaining known(and unknown) aggregations. To this end we used mobile hydroacoustic surveys to estimate the density, spatial extent, and total abundance of a Nassau grouper spawning aggregation at Little Cayman Island, Cayman Islands, BWI.Hydroacoustic estimates of abundance, density, and spatial extent were similar on two sampling occasions. The locationand approximate spatial extent of the Nassau grouper spawning aggregation near the shelf-break was corroborated by diver visual observations. Hydroacoustic density estimates were, overall, three-times higher than the average density observed by divers; however, we note that in some instances diver-estimated densities in localizedareas were similar to hydroacoustic density estimates. The resolution of the hydroacoustic transects and geostatisticalinterpolation may have resulted in over-estimates in fish abundance, but still provided reasonable estimates of total spatial extent of the aggregation. Limitations in bottom time for scuba and visibility resulted in poor coverage of the entire Nassau grouper aggregation and low estimatesof abundance when compared to hydroacoustic estimates. Although the majority of fish in the aggregation werewell off bottom, fish that were sometimes in close proximity to the seafloor were not detected by the hydroacoustic survey. We conclude that diver observations offish spawning aggregations are critical to interpretations of hydroacoustic surveys, and that hydroacoustic surveys provide a more accurate estimate of overall fish abundance and spatial extent than diver observations. Thus, hydroacoustics is an emerging technology that, when coupledwith diver observations, provides a comprehensive survey method for monitoring spawning aggregations of fish.

Bibliographic Details

Main Authors:	Taylor, J. Christopher, Eggleston, David B., Rand, Peter S.
Format:	book_section biblioteca
Language:	English
Published:	NOAA 2006
Subjects:	Ecology, Management, Fisheries,
Online Access:	http://hdl.handle.net/1834/20288
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