Using Length-Frequency Analysis to Identify Spatial and Temporal Variation in Cohort Occurrences

Differences in a streams physiochemical conditions largely influence which species are likely to be present, but examining variation in the spatial and temporal distribution and occurrences of age specific cohorts are less well known. Fish communities were sampled in August and November over a 8-14 year period at six sites across two stream networks to evaluate the feasibility of identifying early cohorts of two prairie stream fishes, central stoneroller (Campostoma anolmalum) and southern redbelly dace (Chrosomus erythrogaster), using length-frequency analysis. Early cohorts (age-0 or age-1) were successfully identified for both species across all sites and sampling events when the species was present, but sites varied in age-specific probability of occurrences. For stonerollers, some sites had high occurrences (0.85) for both age classes, some sites had higher (>0.20) occurrences of age-0 fish than age-1 fish, some sites had higher (>0.35) occurrences of age-1 fish than age-0 fish, and one site had a large (0.5) decrease in occurrence of age-1 fish between months. Probability of occurrences for dace was less variable than stonerollers, with all sites having high (>0.85) occurrences of age-1 fish in each sampling event and increasing occurrences in age-0 fish from August to November.