Performance of baited underwater video for estimating abundance of spiny lobsters

Abstract

Baited underwater video (BUV) is increasingly been used to sample fish species but lobsters are potentially good candidates for sampling with BUV as they are attracted to bait due to their scavenging habits. We built a cost effective BUV system to sample Palinurus elephas, a Mediterranean deep-water lobster. Camera deployments were performed at the Columbretes Islands MPA. We compared the standard method of estimating abundance with BUV, by recording the maximum number (Nmax) of individuals at any one point on the tape, with the estimated true number of lobsters having attended the bait (Ntot). We found it possible to use images of unique body patterns for identifying individuals over time. The highest Nmax - 6 lobsters in the field of view - was lower than the total number of lobsters estimated by identifying individuals in all three recordings - total of 7 to 11 individual lobsters. This highlights the extent of underestimation of abundance derived from Nmax estimates (Mean Nmax = 4 as opposed to Ntot= 8.6 by tracking individuals). Measurement of lobster size was trouble free with the coefficient of variation of all measurements being low. However, all measurements were biassed due to calibration problems related to lobster height above the bait bag. Taking into account the relatively low cost of the units, coupled with the ability of this system to work to depths impractical for visual surveys, we propose that this non-intrusive method will be useful for sampling deep water lobsters