Modifying Surber sampling technique increases capture of freshwater crabs in African upland streams

Abstract

We compared 2 methods for sampling the freshwater crab Potamonautes odhneri (Colosi) in Kenyan streams: standard Surber sampling, in which a sample is taken over a period of several minutes; and rapid Surber sampling, in which the process is reduced to around 10 seconds. Rapid Surber sampling caught more crabs than standard Surber sampling, This suggests that the crab species investigated is normally able to evade capture if sampling is carried out at an unhurried pace, but that if precision is sacrificed for speed, then capture efficiency increases. The size of crabs caught using the 2 techniques was similar, and use of baited traps set in the same locations showed that Surber sampling methods were not capturing larger individuals. Like all methods available to sample large benthic crustaceans, rapid Surber sampling has its limitations, but this study demonstrates that it can be used as a method for rapid assessment of crab presence and for comparative determination of population density, to significantly greater effect than the standard method of Surber sampling.

Effects of litter diversity on decomposition and biological colonization of submerged litter in temperate and tropical streams

“…We collected 5 benthic samples at random locations in riffles and pools (total of 10 samples) with a dip net (300-μm mesh size), following Cheshire et al (2005) and Yule et al (2009), but with a shorter sam-pling time. We disturbed an area covering ∼30 × 50 cm vigorously for 10 s, so as to avoid escape of large macroinvertebrates (Magana et al 2012). We emptied all contents of the net into polythene bags, preserved them in 75% ethanol, and transported them to the laboratory for further processing.…”

“…occurred in some streams sampled by Dobson et al (2002), but many were not captured by the method they used. Later studies have revealed high density and biomass of crabs in Kenyan highland streams (Dobson et al 2007, Magana et al 2012). Most of the shredder taxa identified in our study are represented in temperate streams.…”

Range extension of Oziothelphusa mineriyaensis Bott, 1970 (Decapoda, Gecarcinucidae) in North Central Province, Sri Lanka

“…This study was as a part of a survey, conducted from 2012 to 2014, to document the current distribution and diversity of the freshwater fauna in 2 districts (Anuradhapura and Polonnaruwa) of the North Central Province. The specimens were hand collected (n = 8) using the Rapid Surber sample method (Magana et al 2012) and counts were taken using the visual encounter method (Patton 2010) in selected locations. All the collected specimens were preserved in 70% isopropyl, given voucher numbers, and deposited at the zoological laboratory, Faculty of Applied Sciences, Rajarata University of Sri Lanka (Table 1).…”

Freshwater crabs (Decapoda: Pseudothelphusidae) increase rates of leaf breakdown in a neotropical headwater stream

“…In some studies, freshwater crabs may have been excluded because of methodological reasons (Dobson, 2004;Magana et al, 2012;Masese et al, 2014). Exclusion of crabs from macroinvertebrate analyses, however, could lead to highly biased estimates of shredder biomass, and an underestimate of shredder effect on leaf breakdown because crabs have a much higher biomass than most insects (Aguiar, Neres-Lima, & Moulton, 2018;Camacho et al, 2009;Tonin, Hepp, Restello, & Gonçalves, 2014).…”

“…Freshwater crabs may have been overlooked in some studies because they can be challenging to collect using standard macroinvertebrate sampling methods due to their large size, high mobility, and nocturnal activity (Magana, Dobson, & Mathooko, 2012;Masese et al, 2014).…”