Temperature and Maternal Age Effects on Burbot Reproduction

River regulation alters the thermal regime of many freshwater ecosystems, and impoundments are known to negatively impact the recruitment of fluvial Burbot Lota lota populations. Some conservation programs in North America and Eurasia have begun to incorporate stocking of hatchery Burbot to mitigate extirpation risks. Anthropogenic modification of river temperatures and population structure has unknown implications for Burbot reproduction. This study evaluated the effects of elevated water temperatures and different maternal ages on spawning and embryo development of hatchery Burbot. Juveniles stocked downstream of a hydroelectric dam were found to naturally mature in a warmer postdam regime. The river-adapted hatchery adults volitionally spawned in a broodstock facility at 2, 4, and 6 degrees C. The spawning period spanned 18 d at 2 degrees C but was shortened to 6-7 d at 4 degrees C and 6 degrees C. Survival of embryos to the eyed stage was 86.7, 47.9, and 0.1% at incubation temperatures of 2, 4, and 6 degrees C, respectively. Embryo deformity increased dramatically between 4 degrees C and 6 degrees C. Young (age-3) and old (age-7 and older) females spawned 4-12 d later than 5- and 6-year-old females. Age-3 females spawned smaller eggs, but no relationship was found between maternal age and embryo vital rates. It was concluded that juvenile stocking supplemented the abundance of reproductive adults in the highly altered ecosystem of the lower Kootenai River. Spawning temperatures above 4 degrees C potentially underlie Burbot recruitment bottlenecks in systems affected by impoundments, climate warming, or other barriers to coldwater spawning habitat. Contraction of the spawning period by warmer temperatures, a truncated population age structure, or both could synchronize spawning to coincide with suboptimal conditions for normal embryo development.