Fisheries professionals charged with managing muskellunge Esox masquinongy frequently seek population information that requires the ability to identify cohorts as well as individuals; hence, reliable tagging methods are needed. Our approach was to simultaneously assess multiple marking techniques on different life stages of muskellunge over short and long time scales. We evaluated the short‐term detection of visible implant elastomer (VIE) and passive integrated transponder (PIT) tags in muskellunge fingerlings in experimental ponds. We compared survival (relative to that of control fish) and tag retention for two PIT tagging locations (the cheek and dorsal musculature) and one VIE location (the jaw). Overwinter survival did not differ between tagged and untagged fish (84–98%), but overwinter PIT tag retention was lower for the cheek (92%) than the dorsal musculature (100%). We also fin‐clipped and VIE‐tagged (jaw) 1,651 muskellunge fingerlings from 1997 to 2002 to evaluate long‐term tag retention in a broodstock lake. In addition, 125 adult muskellunge were captured and PIT‐tagged from 2003 to 2006. Muskellunge were sampled annually with trap nets and electrofishing during spring and fall. Only 2 VIE tags were detected in adults marked as fingerlings. The proportion of PIT‐tagged adults recaptured ranged from 52% to 84% during the sampling period. Our results indicate that both VIE and PIT tags are viable short‐term marks for muskellunge fingerlings, while PIT tags appear to be reliable long‐term tags when implanted in the dorsal musculature of adults.

Newly hatched walleye Sander vitreus (formerly Stizostedion vitreum) fry were treated by immersion in a solution of 700 mg of oxytetracycline hydrochloride (OTC)/L for 6 h to determine whether walleye fry could be marked at a younger age than previously described in the literature. The resulting marks varied in intensity but were observed on 100% of the fry inspected from groups that were treated at ages less than 24 h posthatch as well as those that were treated at ages less than 3 h posthatch. No false marks were observed on untreated controls in any of the treatment periods, and pond studies indicated no significant differences (P > 0.05) in either survival or growth between OTC‐treated fry and untreated controls. The results of this study demonstrate that walleye fry can be successfully marked immediately after hatching and that the entire annual production of walleye fry at a hatchery can be marked without additional fry‐holding facilities or significant disruption of routine hatchery operations.

New approaches are needed for sampling northern pike Esox lucius in the complex habitats they use as nursery areas. We evaluated the potential of Quatrefoil light traps to measure differences in density of larval and juvenile northern pike, and we monitored changes in capture probability as the fish grew in size and their swimming capabilities improved. In hatchery raceways, light traps were effective for collecting northern pike at densities that seemed most realistic relative to natural nursery habitat (4–20 fish/m2 surface area). Light‐trap catch rates differentiated among different densities in raceways, but efficiency decreased as density increased. Light traps effectively caught all sizes of fish, ranging from the stage when larvae first became active (12–13 mm total length [TL]) until the fish became too large to fit through the trap entrance (>66 mm TL). We also tried to apply the technique for sampling managed wetlands that simulated a more natural environment than the raceways. Light‐trap catches detected both increases and decreases that were attributed to different stocking rates used over 2 years in individual wetlands. Light‐trap catches showed patchy distribution of small northern pike and illustrated growth and differential survival of the fish among wetlands. Light trapping should be considered a potential tool for sampling both temporal and spatial variation in density and growth of larval and juvenile northern pike.

Osmotic induction of calcein was evaluated as a nonlethally detectable alternative to immersion in oxytetracycline for batch marking 42–58‐d old walleyes Sander vitreus. A preliminary laboratory study and five larger‐scale pond experiments were conducted to evaluate mark efficacy, mark retention, and tolerance to immersion in solutions of salt at 25 g/L or 50 g/L of water followed by immersion in a solution of calcein at 5 g/L of water. Walleyes became obviously stressed when immersed in the salt solutions, and mortalities immediately following the treatments ranged from 0% to 53%. All surviving walleyes possessed marks visible with a hand‐held detector. However, the intensity of marks decreased exponentially on walleyes held in ponds, and only walleyes treated by initial immersion in the salt solution of 50 g/L possessed detectable marks when harvested 17–19 weeks posttreatment. The brightest marks occurred on structures most protected from sunlight. Marks on pelvic scales removed at time of capture also remained visible via epifluorescent microscopy for at least 2 weeks when stored in a freezer. These results suggest that osmotic induction of calcein would be a suitable method of producing nonlethally detectable marks for short‐term stocking evaluations if techniques to reduce the stress induced by the marking process could be deployed. Received December 12, 2011; accepted May 1, 2012

Oxytetracycline (OTC) immersion treatments were evaluated at the Waterville State Fish Hatchery (Waterville, Minnesota) for producing fluorescent marks on larval Northern Pike Esox lucius otoliths. A pilot marking trial conducted with 7‐d‐posthatch (dph) larvae resulted in poor mark efficacy and prompted further investigation on the treatment of younger larvae and modification of the treatment by use of osmotic induction to promote better mark formation. Northern Pike treated within 24 h post‐hatch had significantly higher mark efficacies and marked otolith intensities than did Northern Pike treated at later life stages. Similar to the pilot marking trial, immersion of 7‐dph fry in OTC solution resulted in poor mark efficacy, in which only 38% of the inspected fry possessed visible marks and most of the marks that were visible appeared faint. Simple immersion of newly hatched fry in OTC solution resulted in 91% marking success, and 65% of the visible marks appeared either clear or intense. The poorer mark efficacy on 7‐dph fry suggests that differences in mark formation were more dependent on contemporaneous physiological processes than on otolith size. Osmotic induction prior to OTC immersion had a much weaker effect on mark intensity than did age‐class of treatment in the study. Received November 12, 2013; accepted March 30, 2014