Date of Award


Degree Type


Degree Name

Master of Science




Biology (MS)

First Advisor/Chairperson

Dr. Jill B.K. Leonard


Large dams with upstream reservoirs can cause divergent selection in fish morphology; however, the effect of isolation from small dams without upstream reservoirs is largely unknown. This study investigated the effects of isolation on stream fish body morphology and the related effect of isolation time on morphological divergence by comparing fish associated with older barriers (waterfalls) to very new barriers (dams). These effects were investigated in five species from the southern Lake Superior basin. Geometric morphometric techniques were used to quantify differences in fish body shape based on species-specific landmarks. Significant intraspecific differences between stream populations and between above-barrier and below-barrier populations were found in three species. The majority of body shape variation was associated with deeper body depths (Salvelinus fontinalis and Rhinichthys atratulus) and position of pre-opercular spine and head length (Cottus bairdi). There was greater morphological divergence between Cottus bairdi separated by waterfalls than by dams. Nonparametric multiplicative regression identified the best environmental predictor for body shape as wetted width (Rhinichthys atratulus), stream velocity (Salvelinus fontinalis), or stream population (Cottus bairdi). These results suggest that for some species isolation by dams and waterfalls is associated with divergent intraspecific morphology.

Access Type

Open Access