Environ Biol Fish (2007) 79:49–60 DOI 10.1007/s10641-007-9187-8 SPECIAL ISSUE CROSSMAN Using movements and diet analyses to assess effects of introduced muskellunge (Esox masquinongy) on Atlantic salmon (Salmo salar) in the Saint John River, New Brunswick R. Allen Curry Æ Chad A. Doherty Æ Timothy D. Jardine Æ Steven L. Currie Received: 15 September 2005 / Accepted: 10 December 2006 / Published online: 26 January 2007 Ó Springer Science+Business Media B.V. 2007 Abstract The muskellunge was introduced in ment typical of areas farther upstream. Isotope the Saint John River system from stockings in a mixing models could not accurately determine the headwater lake in the 1970s. They have migrated proportion of Atlantic salmon smolts that may down the system as far as the river’s first dam, have been consumed by muskellunge, but anad- Mactaquac Hydroelectric Facility, at Fredericton romous salmon had £7% probabilities of being in and appear to have established several reproduc- the diet. A bioenergetics model suggested £5% of ing populations along the river. This exotic the annual food intake by muskellunge occurs invader represents a potential threat to the during the smolt out-migration period. For the severely depleted Atlantic salmon stocks in the Saint John River, the impacts of growing numbers river. We radio-tracked muskellunge over a 2- of muskellunge are multi-faceted creating a com- year period in the middle reaches. Home ranges plex management challenge. Muskellunge appear extended to ~100 km in both riverine and lacus- to minimally increase predation risk for Atlantic trine areas, including 78% of individuals trans- salmon smolts while their increasing numbers are located upstream of the dam making their way creating a growing recreational fishery and back through the dam successfully. Downstream potential threat to the native fish community of the dam, home ranges were <25 km. No and ecosystem. spawning areas were detected. An isotope anal- yses of diet indicated that the large sub-adults and Keywords Radio and acoustic tracking Á adults had established the greatest proportion of Stable isotopes Á Modeling diets their biomass in a more 15N depleted environ- Introduction R. A. Curry (&) Á C. A. Doherty Á T. D. Jardine Canadian Rivers Institute, New Brunswick Introduction of non-native species can result in Cooperative Fish and Wildlife Research Unit and significant changes in ecosystem structure and Stable Isotopes in Nature Laboratory, Biology Department, University of New Brunswick, E3C 6E1 functions if the introduced species becomes per- Fredericton, NB, Canada vasive, displacing and eliminating native species. e-mail: [email protected] There are many examples of introduced species becoming invasive in aquatic ecosystems. The S. L. Currie New Brunswick Department of Natural Resources, Great Lakes of North America have experienced Region 3, E3E IG3 Islandview, NB, Canada some dramatic changes in structure and function 123 50 Environ Biol Fish (2007) 79:49–60 of their ecosystems from introductions of sea The species’ impact on the river ecosystem is lamprey, Petromyzon marinus, zebra mussels, unknown. The river once supported a large Dreissena polymorpha, and round gobies, Neogo- population of wild Atlantic salmon, Salmo salar, bious melanostomas, as described for Lake Mich- but numbers have declined to <3,000 returning igan (Madenjian et al. 2002). We are learning that adults and the population is on the verge of being effects can begin at any trophic level and then declared endangered (Jones et al. 2004). With so permeate through the entire food web of the few salmon in the river, any threat to their ecosystem. survival has raised concerns by angler organiza- Introductions of large, predatory fish such as tions and agencies responsible for managing the Esox spp. can significantly impact resident fish salmon fishery. These groups consider muskel- communities (e.g., He and Kitchell 1990; Wynne lunge to be significant predators of salmon, 1995). Introductions of large predators such as especially out-migrating smolts and small salmon muskellunge, Esox maquinongy, are generally or grilse returning after one sea winter (Canadian perceived to create dramatic alterations of eco- Department of Fisheries and Oceans—DFO and systems because their impacts typically occur in Saint John River Management Advisory Com- the realm of recreational fisheries, i.e., where mission, personal communication). There is only humans are directly affected. For example, small- one report of Esox spp. feeding on out-migrating mouth bass, Micropterus dolomieui, introductions salmonids in reservoirs (Jepsen et al. 1998). DFO into northeastern North American waters have presently destroys all muskellunge captured in been correlated with changes in lake trout, their fish traps at all dams along the river. Salvelinus namaycush, population structure The continued expansion of muskellunge in the (VanderZanden et al. 1999). The invasion of sea SJR system is a dilemma for fisheries managers. lampreys into lakes Erie, Huron, Michigan, and No Esox spp. is native to the system (the smaller Superior are strongly correlated with the declines chain pickerel, Esox niger, was introduced in the in both recreational and commercial fisheries for 1800s) and therefore the muskellunge represents lake trout (e.g., Krueger et al. 1995). But intro- a large, exotic predator with the potential to alter ductions are not always negative. Species such as the ecosystem (Townsend 2003). In upstream muskellunge, smallmouth and striped bass, Mo- areas, the ecosystem functions being influenced rone saxatilis, and Pacific salmon, Oncorhynchus by muskellunge are unknown, but populations are spp., are highly prized and can support socially growing in the river and in several lakes where and economically acceptable recreational fisher- annual surveys capture age 0+ and 1+ muskel- ies after their introduction whether introduced lunge (E. LeBlanc, New Brunswick Department through planned management decisions or ille- of Natural Resources, personal communication). gally (Neal et al. 1999; Simonson and Hewett Muskellunge diet, as reviewed by Scott and 1999; Tanner and Tody 2002). Crossman (1973), typically consists of three main The introduction of muskellunge into a head- forage fish: yellow perch, Perca flavescens, brown water lake of the Saint John River (SJR; Fig. 1) bullhead, Amerius nebulosus, and sucker species, was an unintended expansion of a planned man- Catostomus spp., all of which occur in abundance agement introduction in the province of Quebec in the SJR (Curry and Munkittrick 2005). Across (Stocek et al. 1999). The species is now present the muskellunge range, they coexist with many throughout approximately 500 km of mainstem salmonid species, but significantly different hab- and tributary rivers and lakes upstream of Fred- itats most probably restricts interspecific interac- ericton, NB. Increasing numbers of individuals tions. In the SJR, there is a greater potential for are being captured in the first fish passage system contact between muskellunge and Atlantic sal- on the river (Mactaquac Hydroelectric Facility, mon because of the salmon’s upstream and 20 km upstream of Fredericton; see Fig. 2) and by downstream migrations through cool- to warm- anglers in the head pond stretching 100 km water runs, pools, and reservoirs that are not upstream from there (see for example, http:// holding habitats for salmon, but where muskel- www.muskiesnb.ca). lunge reside. How much contact occurs and 123 Environ Biol Fish (2007) 79:49–60 51 concentrated and potentially stressed in this area where they have either fallen over the dam or passed through the turbines (there is no fishway), and Atlantic salmon grilse moving upstream are held-up below the dam. Muskellunge predation on Atlantic salmon is potentially greatest in this area. Study area background The SJR is >650 km in length with portions of its >55,000 km2 drainage in Maine, Quebec and New Brunswick (Fig. 1). The fish community consists of >35 species with the greatest diversity down- stream of the Mactacquac Dam (Curry and Fig. 1 The Saint John River and landmarks related to Munkittrick 2005). Muskellunge were stocked as muskellunge movements in the middle reach from fingerlings multiple times during the 1970s in Lac Florenceville to Fredericton, NB Frontiere, Quebec (a planned management deci- sion). Muskellunge were first recorded in the 60 system in Maine during the mid-1980s followed by confirmation of the species at the Mactaquac 45 Dam in New Brunswick in 1988 (Stocek et al. s r e 1999). Populations supporting recreational fisher- b m u 30 ies are established in Glazier and Baker lakes, n l a t and the recreational fishery is rapidly expanding o T at Woodstock (Fig. 1) at the head of the Macta- 15 quac Dam’s head pond. The area used by muskellunge in this study 0 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 stretched from Fredericton upstream to Hartland, 8 8 9 9 9 9 9 9 9 9 9 9 0 0 0 0 9 9 9 9 9 9 9 9 9 9 9 9 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 NB (Fig. 1). Fredericton is ~25 km downstream Fig. 2 Total numbers of muskellunge captured annually in of the Mactaquac Dam where the river is ~1km the fish trap at the base of the Mactaquac Dam in the Saint wide and up to 3 m deep. From 5 to 15 km John River downstream of the dam there is a series of large islands creating multiple channels across a 1 km wide channel, but there is only one principle flow whether muskellunge exploit the opportunity to channel along the west bank of the river (1–3 m predate Atlantic salmon grilse or smolts is deep). The dam has deep water in its immediate unknown. spillway (~3 m) inhabited by many fishes and Our long-term goal is to determine the impact where a fish trap at the base of the dam is located of muskellunge on the SJR ecosystem.