Murkin et al. 1983

Murkin HR, Abbott PG, Kadlec JA. 1983. A comparison of activity traps and sweep nets for sampling nektonic invertebrates in wetlands. Freshwater Invertebrate Biology 2: 99-106.

These authors compared a specific activity trap design to a specific sweep net technique for sampling nektonic animals in small ponds in a wetland in Manitoba, in the context of evaluating incorporation of these techniques into long-term wetlands ecology monitoring programs. The activity trap consists of a 3.8 L glass bottle with a plast funnel inserted in the opening, held together with wire and elastic bands, and suspended in the water column from a stake driven at an angle into the sediment. The sweep net technique avoids benthic organisms and most benthic debris and vegetation by sweeping vertically upwards from resting flat on the substrate.

The fauna collected by the two methods was correlated when measured across variables of water temperature and water depth, suggesting that for at least total diversity, the two methods are collecting similar samples. Differences emerged when fish and predatory invertebrates were present in the traps, possibly attracted to the traps by the presence of prey species, including Hyalella azteca, which may have been subsequently consummed. Fish and other fast-moving animals were also rarely collected by the sweep nets. Activity traps appeared to select for the most mobile size- and age-classes of gastropods such as lymnaeids, which were absent from most sweep net samples.

The activity traps provide quantitative samples of only some taxa, primarily those that were classified as “herbivore-detritivores” in the absence of predators inside the traps. Predatory taxa were probably overrepresented in the traps, while some apparent prey taxa were underrepresented in traps when predators were present.

The activity traps provided several important advantages compared to sweep nets. There is reduced inter-operator variation, traps were easier to use among vegetation, they collected even fast-moving animals such as fish and large predatory invertebrates, and they integrated the nekton over 24 hours, unlike the time-of-day specific sweep nets.