Site fidelity of slimy sculpin (Cottus cognatus): insights from stable carbon and nitrogen analysis M.A. Gray, R.A. Cunjak, and K.R. Munkittrick Abstract: Concerns regarding sentinel species for assessing environmental impacts include residency, abundance, and suitability for measuring responses, if effects are to be attributable to local conditions. Stable isotope analysis was used as a tool to investigate site fidelity of slimy sculpin (Cottus cognatus) to establish residency and exposure for the scul- pin. We predicted that sculpin collected from sites adjacent to agricultural activity would show higher δ 15 N values than those collected from sites in forested areas because of isotopic enrichment by fertilizers in the former. The predominant use of chemical fertilizer applications in the region, however, resulted in no specific enrichment of 15 N in sculpin col- lected in the agricultural region. However, there was an incremental enrichment in the fish muscle tissue of approxi- mately 5‰ in δ 13 C values in a downstream direction, irrespective of surrounding land use. As a result, the dual-isotope comparison was successful at demonstrating site-specific isotopic signatures across sites for 30 km of the river system. The site-specific signatures suggest that slimy sculpin are not moving considerable distances among sites and are incor- porating their isotopic signatures over a narrow spatial scale. The results support the use of the slimy sculpin as a sen- tinel species for investigating site-specific environmental impacts. Résumé : Les préoccupations associées à l’utilisation des espèces sentinelles pour l’évaluation des impacts environne- mentaux incluent leur résidence dans le milieu, leur abondance et leur aptitude pour la mesure des réactions, si l’on veut attribuer les effets aux conditions locales. Une analyse des isotopes stables nous a servi à évaluer la fidélité au site de chabots visqueux (Cottus cognatus) afin de déterminer la résidence et l’exposition de ce poisson. Nous avons prédit que des chabots récoltés dans des sites adjacents à des activités agricoles devraient avoir des valeurs de δ 15 N plus élevées que d’autres provenant de sites forestiers, à cause de l’enrichissement en isotopes provoqué par les en- grais. Cependant, l’utilisation généralisée d’engrais chimiques dans la région n’a pas causé d’enrichissement spécifique de 15 N chez les chabots récoltés dans la zone agricole. Il y a toutefois un enrichissement progressif de δ 13 C de l’ordre de 5 ‰ dans le tissu musculaire des poissons vers l’aval, quelle que soit l’utilisation des terres adjacentes. En consé- quence, la comparaison à l’aide des deux isotopes réussit à révéler des signatures isotopiques spécifiques pour des sites répartis sur 30 km du système hydrographique. Ces signatures spécifiques au site laissent croire que les chabots vis- queux ne se déplacent pas sur de grandes distances d’un site à l’autre et qu’ils obtiennent leurs signatures isotopiques sur une échelle spatiale restreinte. Ces résultats viennent appuyer le choix du chabot visqueux comme espèce sentinelle pour l’évaluation d’impacts environnementaux spécifiques à un site. [Traduit par la Rédaction] Gray et al. 1722 Introduction Aquatic environmental effects monitoring programs have generally favoured large-bodied fishes because of ease of collection, tissue size requirements for analysis, value placed on species because of public or commercial importance, and comparability to historical monitoring programs. Some of the limitations of larger-bodied fish species include their po- tential for movement over large distances and the challenges in determining the stressors associated with changes where there are multiple discharges that occur in relatively close proximity. Recently, there has been increasing attention given to less mobile, small-bodied fishes that may some- times be more appropriate as monitoring species (Gibbons et al. 1998; Fitzgerald et al. 1999; Tetreault et al. 2003). The Canadian Environmental Effects Monitoring program has seen a progressive increase in the use of smaller forage fish species in the fish surveys (Munkittrick et al. 2002). Many small-bodied fish species have smaller home ranges than tra- ditional monitoring species and so may help overcome some Can. J. Fish. Aquat. Sci. 61: 1717–1722 (2004) doi: 10.1139/F04-108 © 2004 NRC Canada 1717 Received 18 July 2003. Accepted 6 April 2004. Published on the NRC Research Press Web site at http://cjfas.nrc.ca on 16 November 2004. J17650 M.A. Gray. 1 Canadian Rivers Institute and Department of Biology, University of New Brunswick, Fredericton, NB E3B 6E1, Canada. R.A. Cunjak. Canada Research Chair in River Ecosystem Science, Canadian Rivers Institute and Department of Biology, University of New Brunswick, Fredericton, NB E3B 6E1, Canada. K.R. Munkittrick. Canada Research Chair in Ecosystem Health Assessment, Canadian Rivers Institute and Department of Biology, University of New Brunswick, Saint John, NB E2L 4L5, Canada. 1 Corresponding author (e-mail: r55me@unb.ca).