Age, Growth, and Timing of Spawning of an Endangered Minnow, the Oregon Chub (Oregonichthys crameri), in the Willamette Basin, Oregon

Abstract

The Oregon chub Oregonichthys crameri is an endangered floodplain minnow en- demic to the Willamette River drainage in western Oregon. We determined age and growth of Oregon chub at 3 locations and the timing of spawning at 2 locations. We found that Oregon chub live much longer than previously thought (up to 9 y) and that most of the fish older than 5 y were females. We found strong relationships between somatic growth and otolith (lapillus) growth within populations and considerable variation among populations. Mature fish were primarily-2 y old, and all fish >40 mm long had gonads that were developing or mature. Oregon chub spawned from mid-May through early August with peak activity in July. Juveniles that hatched prior to mid-June were not found in October, suggesting reduced survival of early hatched fish.