Lake Sturgeon Reproductive Structure in the Lower Niagara River

Evidence suggests that the lake sturgeon population in the lower Niagara River is recovering, driven by a small number of large cohorts from the mid-late 1990s. Due to the high relative abundance in this population, maturation of fish from these cohorts may disproportionately affect the spawning population’s sex ratio and age composition, which may have important population level consequences. We estimated sex ratio, maturation stages, and age structure of spring spawning aggregations of lake sturgeon in the lower Niagara River during 2012 and 2013 to assess the reproductive structure of this spawning population and to evaluate the relative importance of younger cohorts to the reproductive stock. Though the proportion of mature female and male lake sturgeon in the lower Niagara River appears similar to those of other healthy sturgeon populations, we have found little evidence of older spawning fish (aged 20+ years) as would be expected of well-established lake sturgeon populations. On the contrary, our results indicate that many mature fish appear to belong to relatively young cohorts (aged 12 – 18 years). Our results provide important baseline estimates of age and sex ratio of spawning fish in this population, which may be used to further investigate how demographic parameters such as mortality and recruitment may affect abundance and recovery status.