Evaluation of visual encounter surveys of the noble crayfish, Astacus astacus, and the spiny-cheek crayfish, Orconectes limosus

Abstract

Several methods of sampling are commonly used to detect freshwater crayfish (Decapoda: Malacostraca). Many of them are laborious, time-consuming, and require dedicated equipment. The aims of this contribution are i) to compare visual encounter surveys and baited trap success in the detection of the noble crayfish, Astacus astacus (L.), which is endangered in Poland, and ii) to assess the time needed to detect the invasive spiny-cheek crayfish, Orconectes limosus (Raf.). The study is based on data collected between 2016–2018 in various habitats of Astacus astacus and Orconectes limosus in Poland. Visual encounter surveys are at least as effective in assessing the presence of A. astacus as the trapping method. The modal value for the detection time of O. limosus at all sites and all surveys was two minutes. Sample rarefaction showed that one survey covered 11.33 (SD = 0.43) of a maximum of 12 detections per survey. This suggests that, despite some limitations, visual detection might be an efficient method for determining crayfish presence/absence for a wide range of applications.

Alien Crayfish Species in the Deep Subalpine Lake Maggiore (NW-Italy), with a Focus on the Biometry and Habitat Preferences of the Spiny-Cheek Crayfish

“…From a methodological point of view, we support the efficiency of visual inspection for the detection of crayfish [25,60] to be used as a complementary tool of traps. By setting a standard time for preliminary inspection through visual survey, we were able to verify 75 sampling points for a total of 170 km of inspected shoreline in a reasonable time.…”

“…Moreover, only through inspections we were able to assess the occurrence of P. clarkii, as this species never felt into traps. Although the method is not without bias [25], visual encounter survey is an effective and inexpensive approach to screen for the presence of alien crayfish from large lakes.…”

“…We classified the type of substrate basing on their granulometry as sand/silt (particle size < 1 mm), pebbles (particle size range 2-256 mm), and boulders (particle size > 256 mm) [24]. We assessed the occurrence of alien crayfish by visual encounter surveys [25] in the sites visited for preliminary inspections. We standardize research efforts by setting visual assessment time at 20 min/site [25].…”

“…We assessed the occurrence of alien crayfish by visual encounter surveys [25] in the sites visited for preliminary inspections. We standardize research efforts by setting visual assessment time at 20 min/site [25]. In parallel, local fishermen were interviewed to gain anecdotal data on the distribution of the species.…”

New records of the invasive red swamp crayfishProcambarus clarkii(Girard, 1852) (Decapoda: Cambaridae) from Poland

“…In Dąbie Pond, two observations lasting at least 30 minutes were made on 21 July 2018 and 6 September 2018 as a part of F. limosus visual encounter survey (see Bonk et al, 2019).…”