Fish reproductive phenology shifts with increasing temperature and year.

Temperate fishes often spawn in response to environmental cues, such as temperature, thereby facilitating larval emergence concurrent with suitable biotic and abiotic conditions, such as plankton blooms. Climatic changes may alter the reproductive phenology of spring- and autumn-spawning freshwater fish populations. Such effects may depend on the sensitivity of reproductive phenology to ambient temperatures. We applied a meta-analysis approach to test whether annual temperature and year affected fish reproductive phenology. Based on preliminary tests in walleye () and Lake Constance whitefish (), we hypothesized that increasing temperature would promote earlier spring-spawning and later autumn-spawning. We found spawning was significantly earlier in the spring and later in the autumn. We found that migration of autumn-spawning species occurred earlier with warmer temperatures, implying that with increasing temperatures, migrating autumn-spawning species will increase residence time in tributaries. We also found that spring-spawning fishes reproduced earlier in more recent years, while we observed no significant effect in autumn-spawners. Spring- and autumn-spawning fishes displayed interannual variation in spawning dates (mean range of 34.4 and 27.0 days over 33.9 years, respectively), with spring-spawning fishes displaying a significantly broader range in spawning dates.