Seasonal Habitat Use by Walleye in a Warmwater River System, as Determined by Radiotelemetry

Abstract

Thirty-one adult walleyes Stizostedion vitreum were implanted with radio transmitters and tracked in the main-stem Ceder River, Iowa, and two of its tributaries from September 1986 through July 1988. The objectives were to (1) identify specific habitat use by walleyes at various times of the year; (2) determine interstream movement patterns; and (3) identify walleye spawning sites. Fish with transmitters were located 363 times, and 92% of fish locations were within 9.7 km of a dam on the Ceder River. Walleyes preferred (P < 0.05) gravel-cobble substrates during autumn and were often in water 1.25–1.8 m deep. Overhead cover was not essential. When decreasing water temperature approached 5°C, most fish overwintered in pools 1.5–3.0 m deep. Activity of walleyes increased as spring water temperature rose to about 2.8°C, the approximate temperature at which most walleyes moved upstream. Actual spawning took place at about 11°C and occurred in a riffle (the tailwater of a dam) comprising large cobble and small boulders in a current of 1.41.5 m/s. Walleyes drifted downstream after spawning to pools 1.2–1.8 m deep and were sedentary for about 2 weeks. Several female walleyes died soon after the spawning season. During summer, walleyes preferred gravel–cobble substrates (P < 0.05), used a variety of depths, and were near current breaks and upstream edges of pools. When summer temperatures reached 30°C, some walleyes sought deep pools. Exploitation of walleyes within the first year of study would have been 54% if most fish had not been released by anglers. This study indicated that (1) adult walleyes preferred moderate current with cobble–gravel substrates most times of the year; (2) spawning occurred nearly exclusively in the tailwater of a dam; (3) walleyes were concentrated and spawned within a very short time span; (4) preferred walleye habitat is nearly nonexistent in many portions of the Ceder River system; and (5) impoundments accumulate sediment and thereby reduce walleye habitat upstream but protect habitat downstream.