Water Qual. Res. J. Canada, 2005 • Volume 40, No. 3, 288–298 Copyright © 2005, CAWQ 288 Site Fidelity of Mummichogs (Fundulus heteroclitus) in an Atlantic Canadian Estuary Marc A. Skinner, 1,2 * Simon C. Courtenay, 1,2 W. Roy Parker 3 and R. Allen Curry 1 1 Department of Biology and Canadian Rivers Institute, University of New Brunswick, Fredericton, New Brunswick E3B 6E1 2 Canadian Rivers Institute and Gulf Fisheries Centre, Fisheries and Oceans Canada, Moncton, New Brunswick E1C 9B6 3 Canadian Rivers Institute and Environment Canada, Fredericton, New Brunswick E3B 6Z3 The site fidelity of mummichogs (Fundulus heteroclitus) within the upper Miramichi River estuary, New Brunswick, Canada, was investigated to assess the value of using this fish as a sentinel species for monitoring effects of point source anthropogenic effluents such as pulp and paper mill effluent. During the ice-free season (May to November) of 2002, 4123 adult mummichogs (>30 mm TL) were captured, by beach seine and minnow trap, biweekly from four sites within the estu- ary. Fish were marked intramuscularly using Visible Implant Elastomer (Northwest Marine Technologies, Inc., Shaw Island, Wash., U.S.). Recaptures were made at the marking sites and elsewhere during this period and again during the ice-free sea- son of April to November 2003. A total of 639 (15.5% of those marked) mummichogs were recaptured with 617 (96.6%) found within 200 m of the point of initial release. Twenty-nine of the 617 were recaptured 2 or 3 times at sites of original marking. The remaining 22 recaptured fish moved distances ranging from 600 to 3600 m up- and downstream of initial marking sites. Eighty-two percent of recaptures were made within 12 weeks of the start of marking with the remainder recovered up to 72 weeks later. These findings are consistent with results from studies of mummichog movement in smaller water bodies and other parts of the species’ range. With regard to mobility, these results add to the growing body of litera- ture supporting the usefulness of mummichogs as a sentinel species in environmental monitoring programs for point-source impacts in Atlantic Canadian estuaries. Key words: mummichog, fish exposure, pulp and paper mills, Fundulus, mark-recapture, site fidelity * Corresponding author; ma.skinner@unb.ca Introduction Amendments made to the federal Pulp and Paper Effluent Regulations in 1992 require Canadian mills discharging effluent into aquatic receiving environments to conduct an Environmental Effects Monitoring (EEM) Program. This monitoring program was designed to be conducted in three-year cycles and was intended to assess the effective- ness of the amended effluent regulations in protecting fish, fish habitat and the use of fisheries resources (Courtenay et al. 2002). Following problems with catching sufficient fish that were reliably exposed to effluent during EEM Cycle 1 fish surveys (1993–1996), a Fish Survey Expert Working Group recommended the use of small-bodied sentinel species in Cycle 2 fish surveys (1997–2000) (Munkittrick et al. 1997). The mummichog (Fundulus heteroclitus) was suggested as a potential sentinel species for mills discharging into Atlantic coastal and estuarine waters (Courtenay and Couillard 1998). One of the main criterion for a sentinel species of point-source impacts is low mobility to ensure maximum exposure to a specific receiving environment (e.g., Gibbons et al. 1998a,b). For Canadian pulp and paper EEM fish surveys, fish found within effluent plumes having concen- trations equal to or greater than one percent, are consid- ered exposed (Environment Canada 1998). Such plumes in dynamic estuarine and coastal waters can be small, on the order of hundreds of metres, even for pulp mills discharg- ing large volumes of effluent. Several pulp and paper mills along the Atlantic coast of Canada selected the mummi- chog for monitoring based on its availability in the receiv- ing environment. The results of mark-recapture studies suggest low mobility in populations from the central part of the species range in the eastern United States. Lotrich (1975) reported a 36-m home range for mummichogs in a Delaware salt marsh tidal creek and Sweeney et al. (1998) found mummichogs in a New Jersey salt marsh tidal creek to move distances <650 m. Mummichogs were used successfully as a sentinel species for Cycle 2 fish surveys at three Atlantic Cana- dian pulp and paper mills in northern New Brunswick between 1997 and 2000 (Courtenay et al. 2002). How- ever, while sampling at mills discharging into the Miramichi and Restigouche river estuaries, consultants noted that mummichogs could only be captured immedi- ately preceding and after high tides (Jacques Whitford