Effects of fish predation on density and size spectra of prey fish communities in lakes

Abstract

Brucet, Sandra. 2016. Effects of fish predation on density and size spectra of prey fish communities in lakes [in special issue: Size-based approaches in aquatic ecology and fisheries science: a symposium in honour of Rob Peters]. Canadian Journal of Fisheries and Aquatic Sciences, 73 (4). 506-518. 10.1139/cjfas-2015-0034 Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. Planktivorous and benthivorous fish have been documented to influence the density and size 32 structure of their prey communities in lakes. We hypothesized that piscivorous fish modify their prey 33 fish communities in the same way and sought to find evidence for such predation effects from a 34 comparison across 356 lakes located in nine European ecoregions. We categorized individual fish as 35 being either piscivore, non-piscivore or prey of piscivores, depending on species and individual size. 36We calculated piscivore, non-piscivore and piscivore prey densities, respectively, and fit linear 37 abundance size spectra (SS) on lake-specific piscivore, non-piscivore and piscivore prey size 38 distributions. Multiple linear regressions were calculated to quantify the effect of piscivore density 39 and SS slopes on non-piscivore and piscivore prey densities and SS slopes, by accounting for 40 potentially confounding factors arising from lake morphometry, productivity and local air 41 temperature. Piscivore density correlated positively with piscivore prey density, but was 42 uncorrelated to density of non-piscivores. Across a subset of 76 lakes for which SS slopes of 43 piscivores were statistically significant, SS slopes of piscivores were uncorrelated with SS slopes of 44 either non-piscivores or piscivore prey. However, densities of piscivores, non-piscivores or piscivore 45 prey were a significant negative predictor of SS slopes of the respective groups. Our analyses suggest 46 that direct predation effects by piscivorous fish on density and size structure of prey fish 47 communities are weak in European lakes, likely caused by low predator-prey size ratios and the 48 resulting size refuges for prey fish. In contrast, competition may substantially contribute to between-49 lake variability in fish density and size. 50 51

Structural equation models suggest that bottom‐up processes override top‐down processes in boreal pikeperch (Sander lucioperca) lakes

“…Negative relationships between piscivorous fishes and their prey have seldom been observed in earlier studies and often the significant relationships found have been positive, probably reflecting the importance of the environmental and bottom‐up effects (MacDougall et al., ; Mehner, ). Often, predatory effects of piscivorous fish on the prey fish communities have also not been found (Mehner et al., ). Our analyses made it possible to study the effects from bottom‐up and top‐down simultaneously, and we also found both positive and negative relationships between piscivorous and prey fishes, although also non‐significant effects were found.…”

“…However, there was only a marginal difference in pikeperch BPUE, when lakes managed with the former national 37 cm minimum size limit (128.5 g) were compared to lakes with a locally increased minimum size limit (189.9 g; Appendix S2). Size structure of predator populations could possibly be important for their ecological role (Mehner et al., ; Persson, Diehl, Johansson, Andersson, & Hamrin, ), but we focused on unstructured abundance indices of fish groups due to the better coverage of these data. Stocking might affect the biomass of the piscivores in the lakes, but the origin of the fish is likely to have only marginal impacts on their ecological role.…”

Size‐based interactions across trophic levels in food webs of shallow Mediterranean lakes

“…However, empirical research including simultaneous evaluation of individual size structures across interacting trophic levels and locations (Brose, Jonsson et al., ; García‐Comas et al., ) is limited, probably because equally well‐resolved size data comprising the entire food web are scarce (Woodward et al., ) and because the statistical fitting of the size distribution may be complicated by the appearance of nonlinear relationships (e.g. Mehner et al., ; Vidondo, Prairie, Blanco, & Duarte, ). As a result, the effects of size‐structured predation (i.e.…”

“…As a result, the effects of size‐structured predation (i.e. predation by individuals of different sizes) on the individual size structure of prey in natural food webs are poorly understood (Brose, Jonsson et al., ; García‐Comas et al., ; Mehner et al., ; Rudolf, ). Comparative examination of the size distribution in predator and prey communities may bring insight into the strength of the interactions between adjacent trophic levels (Brose, Jonsson et al., , ; Mehner et al., ; Trebilco, Baum, Salomon, & Dulvy, ) and into the biomass transfer through the food web (García‐Comas et al., ).…”

Size-based approaches to aquatic ecosystems and fisheries science: a symposium in honour of Rob Peters

“…The distinction between two broad trophic groups is also the focus of Mehner et al (2016), who compared prey fish and piscivorous fish in European lakes. They found no evidence that the prey size spectrum is affected by the piscivore spectrum; however, they did find a strong negative effect of prey fish density on the prey spectrum slope and a similar negative effect of predator fish density on the predator spectrum slope.…”