The hip-chain transect method for underwater visual census (UVC)

The hip-chain transect method for underwater visual census (UVC),Grant Leeworthy,Tim Skewes

The hip-chain transect method for underwater visual census (UVC)  
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Underwater visual census (UVC) benthic surveys are typically done by laying out rope or lines on the sea bottom. A diver then follows and count species of interest. Such rope transects are slow to deploy and retrieve, limiting the number of transects that can be completed and, therefore, the precision of the survey. Most benthic species have a patchy dis- tribution, meaning that a high number of sites must be surveyed. Several methods for carrying out UVC surveys without using transect lines have been developed in order to increase the efficiency of sampling. Timed swims (Hart 2006), manta-tows (Moran and De'ath 1992) and flow meters (Conand pers comm . 2007) are very efficient methods, however, all are subject to some uncertainty with regard to transect dimen- sions, especially transect length. The hip-chain transect method, which uses a thread-release measuring device, has the advan- tage of providing an accurate measure of transect length, while also being very efficient because it eliminates the need to lay and retrieve a transect line. The diver lays the transect line as he swims, using a biodegradable cotton thread, with the dis- tance from the point of origin measured as the thread is released. This has the added advantage of allowing access by divers into areas that boats can- not access, due to draught restraints or the pres- ence of navigational hazards. Using the hip-chain method dramatically increases the number of samples that can be completed dur- ing limited (and often expensive) field programmes; this in turn can increase the precision, accuracy and extent of marine surveys. The hip-chain method is an improvement on existing technology and will allow for greater accuracy and a broader focus for future marine survey-based studies.
Published in 2007.
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