Abstract

The importance of competition for food as a factor regulating survival, growth, and fecundity in populations of signal crayfish (Pacifastacus leniusculus) and Noble crayfish (Astacus astacus) was studied in ponds in the south of Sweden. From May to September 1993 a dense population of the signal crayfish was studied in eight earthen ponds (each with an area of 120 m²). Populations in four ponds were fed a pellet diet while crayfish in four ponds were kept as unfed controls. During summer 1995, we investigated growth and survival of noble crayfish in artificial outdoor ponds (each with an area of 50 m²). We had four treatments with age 2+ males, each replicated three times: unfed controls (10 crayfish/m²), crayfish fed the pellet diet (10 crayfish/m² and 20 crayfish/m²) and a treatment where crayfish were fed fish (10 crayfish/m²). Capture-recapture data showed that the growth of adult P. leniusculus males (marked in May and recaptured in August) receiving additional food (mean carapace increase 7.5 mm) was greater in comparison with unfed crayfish (mean carapace increase 3.8 mm). Daytime activity for unfed was significantly higher than for fed crayfish. The percentage of mature females in September differed between treatments. The mean percentage of mature females in ponds with fed crayfish (234 females investigated) was 82.4% of all females, whereas only 51.1% were mature among the unfed crayfish (21 0 females). Survival of unfed A. astacus was 75%, significantly lower than the survival of fed crayfish (96%). The weight increase of the surviving crayfish was lower for the unfed (28%) compared to fed crayfish (37%). Density did not effect survival or weight increase, i.e. there were no differences between the two treatments with crayfish that were fed the pellet diet.

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