Life history traits of adult broad whitefish and humpback whitefish

Abstract

Broad whitefish Coregonus nasus and humpback whitefish C. pidschian are important to the regional subsistence economy of the Kuskokwim River watershed, Alaska, where they and other whitefish constitute greater than half of the nonsalmon fish harvests. Harvest occurs year-round from lakes, ponds, and the mainstem by subsistence fishermen and through a limited number of commercial permits. Little is known about the life history (e.g., migration patterns) of these species, and subsistence fishers have raised concerns about declining body size and abundance. Project objectives were to 1) characterize annual movement patterns of mature broad whitefish and humpback whitefish, 2) verify suspected spawning locations and locate new spawning locations for broad whitefish and humpback whitefish, 3) describe overwintering locations for broad whitefish and humpback whitefish, 4) characterize age and length at maturity for broad whitefish and humpback whitefish, and 5) characterize the habitat of at least one humpback whitefish spawning area. During 2006-2009, we implanted radiotransmitters in 135 mature broad whitefish and 83 humpback whitefish and tracked movements in the Kuskokwim River drainage. We identified two mainstem spawning areas used by broad whitefish and three tributary spawning areas and one mainstem spawning area used by humpback whitefish. Broad whitefish continued to move into spawning areas under the ice and spawned in late October or early November. Humpback whitefish spawned in early October before the river froze over. Individuals of each species migrated as far as 800 river kilometers to spawning areas. Both species migrated downstream after spawning, overwintered in the mainstem Kuskokwim River, and exhibited fidelity to oxbow and tundra lake feeding areas in the summer. Consecutive year spawning was exhibited by individuals of both species and occurred more frequently in males than females for broad whitefish. The median age (5 y) of broad whitefish captured for radiotagging was younger than ages observed in samples collected from other broad whitefish populations in Alaska and Canada. Only mature humpback whitefish in spawning condition were found during October in suspected spawning areas in the Holitna and Swift rivers.