Angling baits and invasive crayfish as important trophic subsidies for a large cyprinid fish

Abstract

Invasive species and anthropogenic sources of allochthonous trophic subsidies can have substantial eco-logical consequences for freshwater ecosystems, including modifying the diet of consumers and altering food web structure. Here, the diet of an omnivorous cyprinid fish, European barbel Barbus barbus, was assessed in relation to the presence of invasive signal crayfish Pacifastacus le-niusculus and pelletized fish-meal in four rivers in England. Pellets are often used in large quantities by river anglers and thus could provide an important trophic subsidy, not only to the fish but also indirectly via P. leniusculus. Carbon and nitrogen stable isotopes were used to estimate the proportion of diet assimilated from natural sources and from P. leniusculus and pellets by B. barbus of lengths between 420 and 800 mm. Pellets generally made a large contribution to the overall biomass of B. barbus (up to 59 % of population diet) and in the two rivers where they were present, P. leniusculus were also an important resource (up to 30 % of population diet). The proportion derived from macro-invertebrates (excluding P. leniuscu-lus) was substantially lower. Stable isotope mixing models further demonstrated considerable intraspecific variability in B. barbus diet within the rivers, with pellets comprising up to 79 % of the biomass of individual B. barbus in rivers where P. leniusculus was absent. Where present, P. le-niusculus effectively replaced and thus reduced the contribution of pellets to individual fish diet. Thus, isotopic evidence from three of the four rivers indicates that B. barbus populations are heavily reliant ([50 %) upon angler-introduced baits that act as an important allochtho-nous subsidy and will also prey upon invasive P. leniusculus where they are present.

Importance of Riparian Zone: Effects of Resource Availability at Land-water Interface

“…Moreover, we should conduct more research about newly emerged cross-system subsidies under changed environmental conditions (e.g. human-provided foods to predators, artificial light, and novel ecosystems), which are becoming more common and may have large impacts on aquatic and riparian ecosystems [143,[189][190][191], and think more about their effects on subsidy quality, quantity, and fluctuation intensity/frequency [10,36]. Also, we should not ignore the dark side of cross-ecosystem subsidies [117,152], which may also influence riparian biodiversity and ecosystem functioning through interactions of resource subsidy fluxes, consumer communities and their ecological feedbacks [192].…”

“…Moreover, if invasive species were prey for native species, they can become an important trophic subsidy for native predators. For instance, the invasive signal crayfish Pacifastacus leniusculus can contribute up to 30% of population diet of a native omnivorous cyprinid fish, European barbel Barbus barbus [143].…”

Importance of small fishes and invasive crayfish in otter Lutra lutra diet in an English chalk stream

“…However, angler catches indicate roach Rutilus rutilus, chub Squalius cephalus and barbel Barbus barbus are important target species (unpublished data), with minnow Phoxinus phoxinus numerically dominant. A recent study on the river assumed P. leniusculus were absent from the river (Basić et al, 2015).…”

Invasive crayfish impacts on native fish diet and growth vary with fish life stage

“…In rivers, signal crayfish may reduce the growth and abundance of small benthic fishes, through interspecific competition and predation (Guan and Wiles 1997;Light 2005), and out-compete fish for refugia (Griffiths et al 2004); yet other research has reported no effects of invasive crayfish on juvenile fish survival (Stenroth and Nyström 2003). However, there have been relatively few attempts to assess the specific impacts that signal crayfish may have on larger fish species of ecological and recreational importance (Reynolds 2011;Ruokonen et al 2012; but see Bašić et al 2015). Understanding the full-range of crayfish-fish interactions, and both the individual-and population-level consequences are essential if fish populations are to be managed successfully.…”