Diet and trophic niche overlap of native and nonnative fishes in the Gila River, USA: implications for native fish conservation

Abstract

Pilger TJ, Gido KB, Propst DL. Diet and trophic niche overlap of native and nonnative fishes in the Gila River, USA: implications for native fish conservation. Ecology of Freshwater Fish 2010: 19: 300–321. © 2010 John Wiley & Sons A/S Abstract – The upper Gila River basin is one of the few unimpounded drainage basins west of the Continental Divide, and as such is a stronghold for endemic fishes in the region. Nevertheless, multiple nonindigenous fishes potentially threaten the persistence of native fishes, and little is known of the trophic ecology of either native or nonnative fishes in this system. Gut contents and stable isotopes (13C and 15N) were used to identify trophic relationships, trophic niche overlap and evaluate potential interactions among native and nonnative fishes. Both native and nonnative fishes fed across multiple trophic levels. In general, adult native suckers had lower 15N signatures and consumed more algae and detritus than smaller native fish, including juvenile suckers. Adult nonnative smallmouth bass (Micropterus dolomieu), yellow bullhead (Ameiurus natalis) and two species of trout preyed on small‐bodied fishes and predaceous aquatic invertebrates leading to significantly higher trophic positions than small and large‐bodied native fishes. Thus, the presence of these nonnative fishes extended community food‐chain lengths by foraging at higher trophic levels. Although predation on juvenile native fishes might threaten persistence of native fishes, the high degree of omnivory suggests that impacts of nonnative predators may be lessened and dependent on environmental variability.

Factors associated with the success of native and nonnative species in an unfragmented arid-land riverscape

“…High productivity of nonnatives could lead to major competition with and predation on native fishes via high consumptive demand, although we would have predicted that total nonnative fish production rather than flathead catfish and common carp production should have been a more important correlate of success if this was the case. Ecological traits may also help explain the negative associations of flathead catfish with native fish production, as flathead catfish have been documented to be the most piscivorous fish species in the upper Gila River (Pilger et al 2010). The trophic ecology of flathead catfish (piscivore) and common carp (omnivore-detritivore) may also help explain their invasion success, as these trophic groups are predicted to be the most successful invaders in minimally altered systems (Moyle and Light 1996).…”

Does Feeding Behavior Facilitate Trophic Niche Partitioning in Two Sympatric Sucker Species from the American Southwest?

“…Gut-content studies support this hypothesized diet partitioning: Sonora suckers consume more invertebrate prey than desert suckers, both in terms of gut content volume (58% vs. 14%, respectively) and frequency of occurrence in guts (97% vs. 70%), whereas desert suckers consume more filamentous algae and diatoms than Sonora suckers by both volume (10% vs. 1.5%, respectively) and frequency (72% vs. 40%; Clarkson and Minckley 1988). Stable isotope analyses also indicate a higher proportion of animal tissue in the diet of Sonora suckers relative to desert suckers (Marks et al 2010;Pilger et al 2010), which provides further support for the hypothesis of trophic niche partitioning.…”

Introduced Flathead Catfish Consumptive Demand on Native Fishes of the Upper Gila River, New Mexico

“…Flathead Catfish typically have ontogenetic shifts in diet, where younger individuals (<100 mm) primarily consume invertebrate prey before becoming highly piscivorous (Etnier and Starnes 1993;Jackson 1999). Thus, lower elevation sites could have higher rates of consumption but native fish are affected through competition for invertebrate prey rather than fish predation (Pilger et al 2010). Lower elevation sites also have high densities of nonnative crayfish , possibly providing an alternative food source for Flathead Catfish.…”

“…The potential predatory impact of Flathead Catfish on native species in this system is unknown, despite there being a general negative association in biomass and production of Flathead Catfish and native species . Although its rarity makes it difficult to estimate population size, a few individual Flathead Catfish may have disproportionally large effects on native fishes because of the predators' ability to reach large sizes, travel large distances, and exhibit highly piscivorous feeding habits (Travnichek 2004;Vokoun and Rabeni 2005;Kwak et al 2006;Pilger et al 2010). Flathead Catfish in the upper Gila River vary in densities and size structures and are exposed to different water temperature regimes across an elevational gradient.…”