Remote surveillance:monitoring fish populations

Posted on June 1, 2016

Submerged vegetation provides freshwater animals with food, substrate and refuge opportunities. Although the structural complexity of aquatic vegetation can make it difficult for researchers to study the behaviour of resident species and measure the size of their populations, the advent of high-resolution, low-light video systems promises to alleviate these problems. Working in Florida, researchers carried out trials in experimental ponds (each 0.4 ha in area, with a maximum depth of 2.4 m), which were completely covered by surface-matted waterweed (Hydrilla verticillata). They stocked the ponds with different densities of sunfish and largemouth bass and lowered a wide-angle video camera to depths of 1.0-1.5 m to record fish images below the weed canopy. Fish were counted at 10–20 random points in each pond every two weeks between July and October, each count being the maximum number of fish visible on-screen at a given time. Fish showed no strong behavioural response to the camera’s presence. At the end of the sampling period the ponds were drained to estimate true population size. Analysis showed that fish counts were directly proportional to true fish abundance. As well as being a non-lethal method of assessing abundance and species diversity, underwater video analysis can also provide information on behavioural variables such as movement, foraging activity and co-occurrence.

Reference: Wilson, K.L. et al. 2015. Use of underwater video to assess freshwater fish
populations in dense submersed aquatic vegetation. Marine and Freshwater Research 66, 10–22.