Reef fish assemblages: a re-evaluation using enclosed rotenone stations

Abstract

The reef fish assemblage at Orpheus Island, Great Barrier Reef, was examined using visual censuses and the ichthyocide rotenone. Small 3.5 m 2 quantitative rotenone samples, using a fine-mesh net to enclose the site, were compared with visual-point censuses (prior to the placement of the net), random-point censuses and strip censuses. Furthermore, the fishes collected inside and outside the net were examined to determine the relative efficiency of enclosed versus open rotenone samples. Rotenone samples comprised 128 species in 28 families. Of these, only 49% of the species overlapped between the enclosed (inside net) and open (outside net) samples. Only 17.7% of the species in the enclosed rotenone sample were seen prior to collection. Rotenone samples reveal that visual censuses underestimated the abundance of small taxa. Overall, rotenone samples increased the estimated number of species by 40.4% and the total fish abundance by 50.1% (75.3% for fishes < 50 mm). Biomass increased by less than 1.0%. However, through relatively high energetic demands, high turnover rates and their role as potential prey, small fish taxa may play a greater role in reef processes than previously assumed. The limits of visual censusing techniques are highlighted, emphasising the value of small, enclosed, intensive rotenone samples for providing reliable quantitative samples of small taxa.

Comparative analysis of tidepool fish species composition on tropical coastal rocky reefs at State of Ceará, Brazil

“…ACKERMAN & BELLWOOD (2000) observed that a significant proportion of the total number and biomass of fishes on the reef were not accounted for by visual census. Nevertheless, non-destructive techniques should be recommended whenever reef ecosystem conservation is at stake, due to their little environmental interference and the possibility of fish observation in their natural habitat .…”

The paradox of inverted biomass pyramids in kelp forest fish communities

“…Before model fitting, we narrowed the size fraction used for analysis to the range of body sizes that can be surveyed effectively with underwater visual transects. Small fishes (&15 cm) are subject to poor detectability in visual surveys [30], hence we used the corresponding mass of 32 g as the lower size cut-off for inclusion in analyses (additional detail provided in [8]). Only three fish larger than 2048 g were observed across all surveys, hence we excluded them and set this mass as our upper cut-off.…”

An assessment of sampling biases across studies of diel activity patterns in marine ray-finned fishes (Actinopterygii)

“…While over half of the overrepresented families include reef fishes, such as butterflyfishes (Chaetodontidae), wrasses (Labridae), surgeonfishes (Acanthuridae), triggerfishes (Balistidae), and squirrelfishes (Holocentridae), more cryptic reef taxa, such as blennies and gobies, are highly underrepresented (Table 1). As blennies and gobies are among the most species-rich clades of reef fishes (Eschmeyer and Fricke 2015) with speciation rates that rival those of African rift lake cichlids ), this bias is not the result of rarity, but rather corresponds with another known bias: under-sampling small cryptic species during the collection of visual survey data (DeMartini and Roberts 1982, Ackerman and Bellwood 2000, Schmitt et al 2002. This detection bias extends beyond blennies and gobies in our results.…”