Characterizing the trophic niches of stocked and resident cyprinid fishes: consistency in partitioning over time, space and body sizes

Abstract

Hatchery‐reared fish are commonly stocked into freshwaters to enhance recreational angling. As these fishes are often of high trophic position and attain relatively large sizes, they potentially interact with functionally similar resident fishes and modify food‐web structure. Hatchery‐reared barbel Barbus barbus are frequently stocked to enhance riverine cyprinid fish communities in Europe; these fish can survive for over 20 years and exceed 8 kg. Here, their trophic consequences for resident fish communities were tested using cohabitation studies, mainly involving chub Squalius cephalus, a similarly large‐bodied, omnivorous and long‐lived species. These studies were completed over three spatial scales: pond mesocosms, two streams and three lowland rivers, and used stable isotope analysis. Experiments in mesocosms over 100 days revealed rapid formation of dietary specializations and discrete trophic niches in juvenile B. barbus and S. cephalus. This niche partitioning between the species was also apparent in the streams over 2 years. In the lowland rivers, where fish were mature individuals within established populations, this pattern was also generally apparent in fishes of much larger body sizes. Thus, the stocking of these hatchery‐reared fish only incurred minor consequences for the trophic ecology of resident fish, with strong patterns of trophic niche partitioning and diet specialization. Application of these results to decision‐making frameworks should enable managers to make objective decisions on whether cyprinid fish should be stocked into lowland rivers according to ecological risk.

Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

“…When scales from larger, wild fish are used then it is recommended that only material collected the edge of the scale is used as it represents the most recent growth (cf. Bašić & Britton, 2016;Gutmann Roberts et al, 2017).…”

“…Barbus barbus is also an important riverine species in many European rivers (Britton & Pegg, 2011), being a benthic foraging species that often specialises in feeding on baits introduced by anglers (Gutmann Roberts et al, 2017). They are also invasive in a number of European rivers, with concern over the interactions of their populations with indigenous fishes (Bašić et al, 2016). Consequently, knowledge on their nitrogen stable isotope turnover rate has importance for ecological studies on their trophic position and impacts, with many of these studies likely to be reliant on the non-destructive sampling of scales and fin tissue due to the value of their populations to recreational angling (Britton & Pegg, 2011).…”

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“…A summary of the spatial scale of some experimental approaches that can be used to predict the impact of invasive freshwater fishes. The spatial scales of the experimental systems (as volume or area) are provided as examples to highlight differences between the approaches, rather than representing definitive size limits Invasive Barbus barbus versus native Squalius cephalus Bašić and Britton (2016) then, for example, increase the number of treatments by using different combinations of fish numbers, adding other fishes, using different food rations or food items, increasing environmental complexity, and/ or manipulating water temperature and day length.…”

“…Bašić and Britton, 2016;Britton et al, 2017;Copp et al, 2017;Gutmann Roberts, Bašić, Amat Trigo & Britton, 2017). In the case of sympatric P. parva, C. carpio and L. gibbosus, this trophic niche partitioning was also coincident with constricted niche sizes compared with the species in allopatry, indicating more specialised diets in sympatry and thus some consistency with the niche variation hypothesis Copp et al, 2017).…”

Spatial variability in the growth of invasive European barbel Barbus barbus in the River Severn basin, revealed using anglers as citizen scientists

“…More recent applications include non-lethal tissue sampling for genetics (Williams et al, 2015;Guindon et al, 2015) and stable isotope analysis (Basić et al, 2015;Basić and Britton, 2016). Given the frequent difficulty of obtaining ecological information on B. barbus in large rivers using regular sampling methodologies such as electric fishing (Britton et al, 2013), then the use of angling within data collection approaches could provide considerable benefit.…”