Effects of size grading on growth, survival and cheliped injuries of signal crayfish (Pacifastacus leniusculus Dana) summerlings (age 0+)

Abstract

E¡ects of size grading and stocking density on growth and survival of 3.5-month-old signal cray¢sh (Pacifastacus leniusculus Dana) juveniles were investigated in a 3 Â 2 factorial design with size group (small, large and mixed) and stocking density (25 and 200 individuals m À 2 ) as factors for 90 days. Carapace length and wet weight growth of the juveniles were a¡ected by the presence or absence of other size groups, stocking density and animal size. All factors had statistically signi¢cant interactions, which make the interpretation of the results more complicated. The smaller cray¢sh grew faster in the absence of large animals and larger animals bene¢ted from the presence of smaller cospecies. Increasing density decreased the growth in length and weight. Survival (82^100%) was good in all groups. Subsequently, the within population dynamics was studied by selectively removing the largest individuals (selectively removing (SR) group). E¡ects on growth and survival of the remaining juveniles were evaluated on 6-monthold P. leniusculus juveniles reared in plastic tanks (100 juveniles m À 2 ) for 122 days. Size distribution manipulation was performed at days 34 and 70. Juveniles in SR group grew signi¢cantly faster in comparison with a control group (RR), from which juveniles were removed randomly. Also, the survival rate was signi¢cantly higher in the SR group than in the RR group. In conclusion, size grading of juvenile P. leniusculus either at the start of the experiment or repeatedly during the experiment increased growth performance of smaller animals in length and weight.

The effect of inter- and intra-specific competition on survival and growth rate of native juvenile noble crayfish Astacus astacus and alien spiny-cheek crayfish Orconectes limosus

“…The A. astacus in communal stock reached higher weight than those in single treatment at the beginning of rearing. Ahvenharju et al (2005) reported that larger individuals of Pacifastacus leniusculus benefited from the presence of smaller co-species. Higher mortality or inter-specific cannibalism showed O. limosus in comparison to A. astacus at this period.…”

“…The smaller crayfish grew faster in the absence of large animals. However, smaller juveniles had more injuries than larger individuals even when reared separately (Ahvenharju et al, 2005). Chelae form a substatial proportion of crayfish total biomass.…”

Competition and parasitism in the native White Clawed Crayfish Austropotamobius pallipes and the invasive Signal Crayfish Pacifastacus leniusculus in the UK

“…2) is interesting, and implies that A. pallipes may in fact be influencing the population structure of the invading species. The moulting of juvenile P. leniusculus is synchronized, resulting in reduced intraspecific cannibalism (referenced in Ahvenharju et al 2005). However, interspecific predation by the native A. pallipes (Gil-Sánchez and AlbaTercedor 2006) as well as other predators such as fish (Söderbäck 1992) may underpin the observed reduction in juvenile P. leniusculus in mixed populations.…”

Assessing the effect of size-grading for rearing young-of-the-year white-clawed crayfishAustropotamobius pallipes

“…Captive‐breeding for reintroduction is becoming a recognized conservation measure to try and halt population declines (Nightingale et al, ; Taugbøl & Peay, ). High survival rates can be achieved when raising young‐of‐the‐year A. pallipes ; however, even at low densities, there can be a large variation in size and health of crayfish juveniles within a single brood, even as early as 6‐months of age (Ahvenharju, Savolainen, Tulonen, & Ruohonen, ; J Nightingale pers. obs.…”