Population Structure of River Herring in Albemarle Sound, North Carolina: A Two-Method Approach

Identifying the stock structure of fish is a crucial component in fisheries management. Fisheries scientists use various methods to separate distinct population units of exploited species. We examined the population structure of juvenile and adult Alewife Alosa pseudoharengus and Blueback Herring Alosa aestivalis in the Albemarle Sound, North Carolina using geometric morphometric and otolith shape analyses. Samples from various tributaries of the Albemarle Sound and a small sample of fish from the Metedeconk River in New Jersey were examined for differences in body and otolith shape. We used tps-Dig2 software to digitize 10 discrete morphometric landmarks on images of River Herring samples, and used SHAPE 1.3 software to trace outlines of corresponding otoliths.  Principle Component Analysis (PCA) of body and otolith shape variables indicated shape differences at the state and tributary level. Discriminant Analysis (DA) classified samples to tributary of capture with varying success (25-100%). Otolith shape, when separated by sex and age, contributed more successful classification (DA) than body shape. These results suggest that River Herring possibly form distinct population units within the Albemarle Sound.  This information is important to consider when forming Fisheries Management Plans for this imperiled resource.