Do trophic subsidies affect the outcome of introductions of a non‐native freshwater fish?

Abstract

SUMMARY1. Understanding how environmental variables and human disturbances influence the outcomes of introductions of non-native freshwater fish is integral to their risk management. This can be complex in freshwater ecosystems that receive subsidies that increase food availability, as these may influence the outcome of introductions through promoting the survival, reproduction and establishment of the introduced propagules through increasing their access to food resources. 2. We determined how natural and/or artificial trophic subsidies affected the reproduction and establishment of the introduced topmouth gudgeon (Pseudorasbora parva) in replicated pond mesocosms. The mesocosms all started with eight mature fish and were run for 100 days during their reproductive season. The subsidies consisted of natural terrestrial prey and/or fishmeal pellets (a common trophic subsidy that can be significant in systems that are used as sport fisheries or for aquaculture). 3. After 100 days, fish in the natural subsidy ponds showed minimal growth and very low reproductive output. Analysis of d C and d 15N indicated that their progeny, 0+ fish produced in the ponds, exploited the terrestrial prey. By contrast, in ponds where pellets were added, mineral nutrient availability and primary production were significantly increased, and the mature fish fed mainly on the aquatic resources. The increased productivity of the ponds significantly increased fish growth and fitness, resulting in high numbers of 0+ individuals that did feed on the pellets. 4. Thus, subsidies that can increase both primary production and food resources (such as pelletised fishmeal) can significantly influence the ability of colonists to establish a population rapidly. Management efforts to minimise the risk of introductions should thus consider the role of these types of allochthonous subsidies.

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

“…Estimates of isotopic turnover rates are important for understanding how, for example, ontogenetic dietary shifts affect stable isotope data (e.g. Buchheister & Latour, 2010;Hertz et al, 2015), and for incorporating into the design of manipulative field studies and mesocosm experiments where the duration of the study could be confounded if they are not of sufficient length for isotopic equilibrium to be reached (Jackson et al, 2013;Tran et al, 2015). Consumer tissues tend to be considered at equilibrium with their diet after 4-5 halflives (Hobson & Clark, 1992).…”

Stable isotope discrimination factors of omnivorous fishes: influence of tissue type, temperature, diet composition and formulated feeds

“…However, these formulated feeds are increasingly present as strong trophic subsidies in many European freshwaters, primarily through their use as baits by anglers in both lentic and lotic habitats (Jackson et al, 2013;Bašić et al, 2015;Gutmann-Roberts et al, 2017), but also from aquaculture (e.g. Grey et al, 2004).…”

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“…Subsequent mesocosm and pond experiments have suggested that the extreme abundance of P. parva in the invaded pond of Britton et al (2010) was likely to have resulted from high angling activities resulting in their baits providing strong trophic subsidies (Jackson, Allen, Pegg & Britton, 2013). These subsidies appear to significantly increase the growth and survival of young-of-the-year P. parva, enabling them to overcome the biotic resistance imposed from other cyprinid fishes .…”