Dorsal Coloration as an Indicator of Different Life History Patterns for Striped Bass within a Single Watershed of Atlantic Canada

The striped bass Morone saxatilis spawning within a single river system are generally considered to be members of a single population unit. For some rivers in Canada, however, fishers have reported different‐colored groups of striped bass in the watershed during the prespawning and spawning seasons, which suggests the existence of population subgroups. We examined this “colormorph” phenomenon for a striped bass population in the Shubenacadie watershed of Nova Scotia, Canada. Spawning fish had three dorsal coloration patterns: green, which was indicative of fish from the ocean; black, which was indicative of fish that overwinter in a freshwater headwater lake; and mottled, which were fish of unknown origin. Body morphology appeared to be similar among the three groups. Although the age structures of the spawning populations revealed a wider range of age‐classes among greenbacked fish, the growth aspects (e.g., length, weight, and length at age) were similar. We estimated that during the prespawning period, one‐third of the population was actively foraging in the river; stomach contents suggested differences in diet among the morphs. Fatty acid analysis of gonadal material revealed significant differences between the green and black color types, indicating moderately long (months) separation and differences in feeding (i.e., ocean‐based versus freshwater‐based food webs). Otolith microchemistry analysis of strontium revealed that dorsal coloration at capture was indicative of long‐term habitat separation. Whether these two groups are reproductively isolated is unknown.