Diver towed GPS increases both statistical power to estimate densities and functionality to observe behaviours of sparsely distributed spotted handfish (Brachionichthys hirsutus, Lacépède 1804)
Lynch, Tim; Green, Mark; Davies, Claire
2015-10-01
Journal Article
Biological Conservation
191
1
1
700-706
Spotted handfish are a critically endangered anglerfish. Monitoring of the species has in the past been been undertaken via underwater visual census parameterised with fixed length 100 m x 3m strip transects measured with reels lines. However, the sparse distribution and cryptic nature of handfish resulted in low statistical power to track populations through time. To achieve reasonable confidence of detecting change in local populations over time ~ 40 transects are required for density estimates, making the logistical and resourcing constraints of monitoring onerous. We trialled a new method at one study site with a known local population of fish, replacing reel transect of fixed length with variable length strip transects parameterised with a diver towed Global Positioning System (GPS) float. From 18 transects we determined a density of 24 (± 3.5) handfish per hectare, but a bootstrapping Monte Carlo simulation suggested little improvement in precision occurred after 6 transects. Modelling these results to previous estimates at the site indicated that our GPS float approach required many fewer transects and dives to determine 50% increases or decreases in fish densities. This improvement was partly due to the better sampling efficiency; with 3 times the average search area per transect but was also probably a result of longer transects being a better sampling solution for monitoring a sparse population. Our results returned a normal sample distribution of fish counts with few zeros and many multiple observations, which differed to the original approach which was heavily skewed towards zero observations per transect. However, at very low populations densities even this more robust solution will start to require many samples to detect change. Our GPS parameterized surveys also improved the functionality of observing fish behaviour as we could accurately plots fish allowing for detailed investigation of distributions across depths and in relation to size frequency. When fish were observed they were also bi-laterally digitally photographed to record their unique natural markings. By synchronisation the photographs timestamp with the GPS clock, we were able to geo-locate individual recaptures and post hoc analysis of limited results suggests net movements were limited. This new sampling approach makes monitoring logistically feasible for spotted handfish and may have applications for other sparsely distributed benthic species.
Elsevier
Animal Behaviour
EP151318
Journal article - Refereed
English
Lynch, Tim; Green, Mark; Davies, Claire. Diver towed GPS increases both statistical power to estimate densities and functionality to observe behaviours of sparsely distributed spotted handfish (Brachionichthys hirsutus, Lacépède 1804). Biological Conservation. 2015; 191(1 1):700-706. http://hdl.handle.net/102.100.100/91758?index=1
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