Predation by Northern Pikeminnow and Tiger Muskellunge on Juvenile Salmonids in a High‐Head Reservoir: Implications for Anadromous Fish Reintroductions

Abstract

The feasibility of reintroducing anadromous salmonids into reservoirs above high‐head dams is affected by the suitability of the reservoir habitat for rearing and the interactions of the resident fish with introduced fish. We evaluated the predation risk to anadromous salmonids considered for reintroduction in Merwin Reservoir on the North Fork Lewis River in Washington State for two reservoir use‐scenarios: year‐round rearing and smolt migration. We characterized the role of the primary predators, Northern Pikeminnow Ptychocheilus oregonensis and tiger muskellunge (Northern Pike Esox lucius × Muskellunge E. masquinongy), by using stable isotopes and stomach content analysis, quantified seasonal, per capita predation using bioenergetics modeling, and evaluated the size and age structures of the populations. We then combined these inputs to estimate predation rates of size‐structured population units. Northern Pikeminnow of FL ≥ 300 mm were highly cannibalistic and exhibited modest, seasonal, per capita predation on salmonids, but they were disproportionately much less abundant than smaller, less piscivorous, conspecifics. The annual predation on kokanee Oncorhynchus nerka (in biomass) by a size‐structured unit of 1,000 Northern Pikeminnow having a FL ≥ 300 mm was analogous to 16,000–40,000 age‐0 spring Chinook Salmon O. tshawytscha rearing year‐round, or 400–1,000 age‐1 smolts migrating April–June. The per capita consumption of salmonids by Northern Pikeminnow having a FL ≥ 200 mm was relatively low, due in large part to spatial segregation during the summer and the skewed size distribution of the predator population. Tiger muskellunge fed heavily on Northern Pikeminnow, other nonsalmonids, and minimally on salmonids. In addition to cannibalism within the Northern Pikeminnow population, predation by tiger muskellunge likely contributed to the low recruitment of larger (more piscivorous) Northern Pikeminnow, thereby decreasing the risk of predation to salmonids. This study highlights the importance of evaluating trophic interactions within reservoirs slated for reintroduction with anadromous salmonids, as they can be functional migration corridors and may offer profitable juvenile‐rearing habitats despite hosting abundant predator populations.Received September 3, 2015; accepted December 7, 2015 Published online April 19, 2016

Hatchery‐reared endangered Colorado pikeminnow (Ptychocheilus lucius) undergo a gradual transition to piscivory after introduction to the wild

“…All of these sources of information suggest that a rapid diet switch to piscivory should occur during the juvenile stages investigated here. As a related example, diet and isotopic studies of the closely related Ptychocheilus oregonensis J. Richardson, 1836 (Northern pikeminnow) clearly demonstrated a rapid switch to piscivory at similar ages as the Colorado pikeminnow in the present study (McIntyre, Beauchamp, Mazur, & Overman, ; Sorel et al, ). Although data on the trophic ecology of Colorado pikeminnow are limited, and several uncertainties about the implications of the results remain, the nearly 25% reliance on invertebrate prey of fish of TL >250 mm could potentially signal an impediment to the re‐establishment of Colorado pikeminnow in the San Juan River.…”

Effects of Turbidity on Prey Selection and Foraging Rate of Hatchery‐Reared Juvenile Tiger Muskellunge

“…; Sorel et al. ). Numerous studies have evaluated variables that may affect the survival of tiger muskellunge, including the use of artificial (pellet) versus natural (fish) diets administered prior to stocking (Gillen et al.…”

“…; Sorel et al. ). The purpose of this study was to test the effects of turbidity at four levels (Secchi depths of >84 [tap water], 53, 26, and 18 cm) on prey selectivity and foraging return of juvenile tiger muskellunge by using three different prey species (Goldfish Carassius auratus [a surrogate for Common Carp Cyprinus carpio ], Gizzard Shad Dorosoma cepedianum , and Green Sunfish Lepomis cyanellus ) that are commonly found in southern U.S. reservoirs.…”

“…Tiger muskellunge (Northern Pike × Muskellunge) are stocked into aquatic systems throughout North America (Crossman 1986;Wahl et al 2012) to control overabundant or undesirable fish species (Lepak et al 2014;Koenig et al 2015;Sorel et al 2016) or to create sport fisheries (Wahl et al 2012;Sorel et al 2016). Numerous studies have evaluated variables that may affect the survival of tiger muskellunge, including the use of artificial (pellet) versus natural (fish) diets administered prior to stocking (Gillen et al 1981); predation Wahl and Stein 1989); and predator acclimation (Wahl et al 2012).…”

Predicting the contributions of novel marine prey resources from angling and anadromy to the diet of a freshwater apex predator

“…However, anadromous fishes can also play an important role in the transfer of MDN to freshwaters via their direct consumption by freshwater apex predators (Guillerault, Bouletreau, Iribar, Valentini, & Santoul, 2017;MacAvoy, Macko, McIninch, & Garman, 2000). Where the upstream migration of anadromous fishes is impeded by blockages such as weirs and dams (Clavero, Blanco-Garrido, & Prenda, 2004;Ovidio & Philippart, 2002), their downstream aggregations potentially provide important foraging opportunities for piscivorous fauna (Sorel et al, 2016).…”