Spawning and Movement Behavior of Migratory Coastal Cutthroat Trout on the Western Copper River Delta, Alaska

Abstract

We studied the movement patterns of migratory coastal cutthroat trout Oncorhynchus clarkii clarkii in the western Copper River delta, Alaska, near the northern extent of the subspecies' distribution. Life history information for coastal cutthroat trout is scarce within this region. Movement of coastal cutthroat trout was monitored from 1994 to 1996 with radiotelemetry and tag–recapture of fish at a two-way fishweir. Radio-tracking of 20 adults was conducted for a period ranging from 5 to 343 d. We observed anadromous and potamodromous migrations by fish that were morphologically indistinguishable and spanned a similar size range (mean fork length = 364 mm). Within these migratory groups, fish exhibited variation in movement patterns, including the timing of entry to spawning streams and postspawning movements. Anadromous and potamodromous fish entered study streams either during fall to overwinter and then spawn or during the spring just before spawning. Spawning was most concentrated in the upper portions of the study streams and occurred upstream to the highest available areas. Postspawning movements of potamodromous fish consisted of small-scale (<2 km) movement within the spawning stream or longer movements to larger rivers or lakes. Anadromous fish migrated to estuarine or marine habitat after spawning. Both anadromous and potamodromous fish moved to lentic freshwater habitat to overwinter. Our results provide empirical evidence for an array of life histories displayed by coastal cutthroat trout in south-central Alaska. We attribute the variety of movement patterns, at least in part, to the diverse assemblage of available habitat and seasonally abundant food resources provided by Pacific salmon Oncorhynchus spp. Future management should maintain the quality of and connectivity between reproductive, trophic, and refuge habitats distributed throughout the western Copper River delta.