Underwater visual census (UVC) is the most common approach for estimating diversity, abundance and size of reef fishes in shallow and clear waters. Abundance estimation through UVC is particularly problematic in species occurring at low densities and/or highly aggregated because of their high variability at both spatial and temporal scales.

This study tested the efficiency of an UVC method based on diver towed GPS, the Tracked Roaming Transect (TRT), designed to maximize transect length with respect to diving time invested in monitoring and compared it to other methods (e.g. Conventional Strip Transects).

The obtained results show that the TRT was 74% more time and cost efficient that the CST and, for a given time, the use of TRT increased the precision of density estimates.

It is stated that the results of the study are relevant for the design of monitoring programs where the level of sampling effort would depend on a trade-off between the desired precision and logistic and material constraints. While highlighting that this method can be used for surveying other groups of marine animals (e.g. giant mussels, marine turtles or lobsters).

The authors, based on the results of the study, encourage the use of the TRT for improving density estimates of species occurring at low densities and/or highly aggregated, as well as for exploratory rapid-assessment surveys in which divers could gather spatial ecological and ecosystem information on large areas during UVC.

 

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0190990

Irigoyen AJ, Rojo I, Calò A, Trobbiani G, Sánchez-Carnero N, et al. (2018) The « Tracked Roaming Transect » and distance sampling methods increase the efficiency of underwater visual censuses. PLOS ONE 13(1): e019099