White-Clawed Crayfish in Muddy Habitats: Monitoring the Population in the River Ivel, Bedfordshire, Uk

Abstract

White-clawed crayfish Austropotamobius pallipes are usually associated with stony substrates, tree roots, or refuges in submerged banks. The River Ivel has the last known population of white-clawed crayfish in Bedfordshire. Prior to 2005, much of the bed comprised uniform silt, plus leaf-litter. Stands of reedmace Typha latifolia and other emergent vegetation were localised in less shaded areas. Initial survey results suggested a population at low abundance. A low-cost monitoring strategy was started in 2001 and continued three times a year to 2005, using engineering bricks, which offer artificial refuges. Crayfish are counted when bricks are lifted periodically. De-silting of c. 430 m river was carried out in February 2005, to improve habitat and to maintain the flood capacity in the channel upstream of a mill weir. Additional bricks were deployed a few weeks in advance of de-silting, then bricks and crayfish were lifted prior to dredging and were returned the next day. Starting upstream, soft, wet mud was dredged out, placed on the bank and searched manually for crayfish. Banks, tree roots and shallow margins were left undisturbed. In all, 4,142 crayfish were found in dredgings from a 430 m length of the mid channel. Crayfish were strongly associated with emergent vegetation, but many were present below the surface of the silt. Crayfish released in the dredged channel immediately burrowed into the silt retained on the channel margins. Monitoring after dredging showed no change in abundance in the main area with in-bank refuges and lots of bricks, but there was an increase in occupancy of bricks in an area where most crayfish had been in emergent vegetation.Key-words: white-clawed crayfish, habitat, mud, mitigation, monitoring. Les écrevisses étaient fortement associées à la végétation émergente, mais beaucoup étaient présentes aussi sous la surface du limon. Les écrevisses relâchées dans le cours d'eau dragué se sont aussitôt ré-enfouies dans le limon déposé sur les bords du cours d'eau. Le suivi réalisé après le dragage n'a pas mis en évidence de modification d'abondance dans le secteur principal avec les refuges en berge et beaucoup de briques, mais il a en revanche permis de constater une augmentation de l'occupation des briques dans un secteur où la plupart des écrevisses étaient précédemment dans la végétation émergente. ÉCREVISSES À PATTES BLANCHES DANS LES HABITATS

State of the ART: Using artificial refuge traps to control invasive crayfish in southern California streams

“…These data suggest that ARTs with larger diameters catch more crayfish and have a higher variance in the sizes of crayfish removed. These findings agree with research on white-clawed crayfish (Austropotamobius pallipes Lereboullet, 1858) in the United Kingdom (Peay et al 2006), which demonstrated the positive relationship between opening size in breezeblocks (concrete blocks with pre-constructed holes that provide the same overall function as ARTs in this study) and crayfish size. Specifically, they found that ARTs with 30-mm openings caught more crayfish and crayfish of a wider range of size classes when compared with ARTs with 10-and 15-mm openings.…”

“…With regards to bycatch of non-target organisms, ARTs can generally be deployed in areas with sensitive species, such as salmonid young of year or juvenile amphibians, because they do not have a trapping mechanism that prevents non-target species from escaping (De Palma-Dow et al 2020). On the other hand, in locations where native and non-native crayfish are sympatric, ARTs may be useful for monitoring native populations (e.g., Peay et al 2006) while removing invasive populations (e.g., Green et al 2018).…”

“…To address concerns of sampling bias and bycatch, some studies have explored the use of artificial refuge traps (ART) as a supplementary conservation and management tool. ARTs are typically constructed of either natural (Warren et al 2009, Kusabs et al 2018 or artificial materials (Peay et al 2006, Green et al 2018, O'Connor et al 2018) that replicate the form and function of crayfish burrows by providing refuge from predation during sensitive periods in their life history (Barbaresi et al 2004). ARTs typically reduce (if not completely eliminate) impacts to native aquatic species by including opening holes on one end where bycatch can escape.…”

Horizontal transmission of Thelohania contejeani in the endangered white-clawed (Austropotamobius pallipes) and the invasive signal crayfish (Pacifastacus leniusculus)

“…Cannibalism is common in crayfish, with larger adults and juveniles preying on smaller individuals (Abrahamsson, 1966; Mason, 1977), providing opportunities for ingestion of infected tissue. Crayfish use refuges in close proximity to each other as well as coming into contact when foraging and mating (Peay, 2002), providing opportunities for spore transmission via the water. This study also provides the first evidence for direct transmission of T. contejeani from infected white-clawed crayfish to the invasive signal crayfish, both by consumption of infected tissue and through exposure to contaminated water.…”