Growth in length and in body depth in young‐of‐the‐year perch with different predation risk

Abstract

Body shape of young-of-the-year (YOY) perch Perca fluviatilis, and number and size of potential predators (perch and pike Esox lucius) were compared across five lakes in northern Sweden. Body depth and dorsal fin ray length of YOY perch differed between lakes, with high relative body depth and long dorsal fin rays found in the lakes where the number of large piscivores was the highest. The most slender fish were found in the lake where the perch population had the smallest individuals and pike occurred in very low numbers. The average body mass in YOY perch from the two lakes with highest and lowest body depth, respectively, were the same, which indicates a difference between lakes in the relation between growth in length and in depth. Both body depth and fin ray length were correlated with predation risk by pike. Fin ray length was also correlated with number of piscivorous perch. Selection for different body shapes can be caused by different biotic and abiotic factors, singly or in combination, and the results from this study indicates that predation risk is one of these factors affecting body depth and fin ray length in perch.

Risk-taking behaviour in foraging young-of-the-year perch varies with population size structure

“…However, earlier surveys, made in 1993 (by the Department of Environment, City of Umea˚), 1996 (Steven Chong 1997, unpublished honour's thesis, Queen's University, Ontario, Canada, all lakes except Fisksjo¨n), and 1998 (Erik Heibo and Carin Magnhagen, unpublished data), show similar size distributions of perch in the four lakes as in 1999 and 2000. Also, differences between the lakes in the size distribution of young-of-the-year perch caught in late summer was similar in 2004 as in 1999 and 2000 (Magnhagen and Heibo 2004). The population structures in these lakes thus seem quite stable and I assume here that the relative differences in size distribution between the lakes in 2004 were similar to that found in previous years.…”

“…Seven preylength classes were used in the model (10-70 mm), corresponding with perch sizes shortly after hatching and up to the maximum size obtained at the time of the behaviour study. Individual cannibalistic attack rates (per day) for all perch caught in the 1999-2000 surveys (N = 4136, Magnhagen and Heibo 2004) were calculated according to their body length. Individual attack rates (A) were calculated according to: where c = cannibal body length, and v = victim body length.…”

Ecomorphological dimorphism of juvenile Trachurus japonicus in Wakasa Bay, Japan

“…An alternative explanation for the deep BD of the compressed morph is predator fish avoidance (e.g. Brönmark and Miner 1992; Magnhagen and Heibo 2004), but we could not detect significant dimorphic differences in DFH (Table 1), which was shown by Magnhagen and Heibo (2004) to correlate with predation risk.…”

Environmental correlates of population variables of perch (Perca fluviatilis) in boreal lakes

“…Back calculation of growth was expressed in terms of weight, to avoid variation due to differences in condition factor and body shape. A predator like pike may induce increased body height in prey species like perch (Magnhagen and Heibo 2004). Analysis of variance, with ln(opercular bone) as the dependent variable, and ln(fish weight) and Lake (categorical) as predictors, showed significant effects of both fish weight and lake (Two-way ANOVA F 24,942 =19088.0, p<0.0001 and F 24,942 =12.75, p<0.0001, respectively).…”