Habitat use by crayfish in stream pools: influence of predators, depth and body size

Abstract

SUMMARY Crayfish in headwater streams are subjected to predation from two sources: (a) fish; and (b) terrestrial predators including wading birds and mammals. Field observations of the mortality of tethered crayfish of two size classes were used to examined how predation risks imposed by the two types of predators varied with water depth and crayfish size. We also examined the depth distribution of large and small crayfish in stream pools with and without predatory fish. Predatory fish, mostly green sunfish, Lepomis cyctuellus, and creek chub, Semotilus atromaculatus, rapidly consumed tethered small crayfish (body length = 25–30 mm) in deep areas (0.4–0.7 m), but not in shallow areas (0.05–0.15 m) of stream pools. Tethered large crayfish (body length = 50–75 mm) suffered little mortality from fish at either depth. Terrestrial predators such as racoons, Procyou lotor, and herons, Butorides and Ardea, caused little crayfish mortality in deep areas, but rapidly consumed both small and large crayfish exposed in shallow areas. A comparison of habitat use by crayfish in pools with and without fish suggests that small, but not large, crayfish shift their distributions to shallow water in the presence of fish. In pools without fish, the distribution of small crayfish was independent of depth, whereas large crayfish occupied deep water.

Chytrid fungus Batrachochytrium dendrobatidis has nonamphibian hosts and releases chemicals that cause pathology in the absence of infection

“…The abundance and distribution of alternative hosts might also help explain geographic variation in the distribution and rates of spread of B. dendrobatidis. For example, both crayfish and B. dendrobatidis-related amphibian declines are more common in stream than pond systems (38,39). Additionally, crayfish infection with B. dendrobatidis might explain how crawfish frogs (Lithobates areolatus) obtained B. dendrobatidis infections while overwintering in crayfish burrows (40).…”

Habitat Preference of Different Size Classes of Austropotamobius Pallipes in an Irish River

“…Observations on the impact of predators on crayfish survival and growth suggest that juvenile crayfish, which are vulnerable to predatory fish, will inhabit shallow water where they are less susceptible to such predation (ENGLUND, 1999;ENGLUND and KRUPA, 2000). Adults will prefer deeper waters to escape terrestrial predators, such as otters and minks, which represent a greater danger to a large crayfish.…”

Crayfish Use of Trash Versus Natural Cover in Incised, Sand-Bed Streams

“…Several plausible explanations exist. First, as noted above, juvenile crayfishes in many systems prefer stream margins, particularly in the presence of fishes or large crayfishes (Rabeni 1985;Englund and Krupa 2000), and juveniles constituted the majority of my catches. Second, tree roots appeared to be a preferred cover type for juveniles, and root mats occurred only along stream banks; however, crayfishes also were more abundant in constructed habitat bundles placed near banks than mid-channel in a nearby stream (Warren et al 2009), suggesting that the result was not due solely to the presence of tree roots.…”