Joseph G. Loesch and Douglas A. Dixon, The College of William and Mary, School of Marine Science, Gloucester Point, VA 23062-1346

Abstract. A juvenile index of abundance was developed for the alewife and the blueback herring in the Mattaponi and Pamunkey rivers, Virginia. The objectives were to: develop juvenile Alosa indexes sensitive to varying degrees of reproductive success; determine if the two species-specific indexes exhibited a common pattern of change in a river system; determine if index changes are common to both rivers; and determine if the index is related to nursery zone size. Sampling was conducted at night with a bow-mounted pushnet. The maximal CPUE for a series of weekly sampling was chosen as the index of abundance. Species indexes were strongly correlated within the Mattaponi and Pamunkey rivers (r = 0.89 and 0.85). Blueback herring and alewife indexes between rivers were also reasonably strong (r = 0.69 and 0.74). There was a strong correlation between the maximal CPUE and the seasonal CPUE (>0.90 for both species), but the CV for the maximal CPUE was always lower. The linear relationship of index values to nursery zone sizes was direct and significant (P>0.001), indicating no crowding effect. For the combined species data, the recruitment correlations for the Pamunkey and Mattaponi rivers were strong (0.78 and 0.87). When data were also combined for rivers, as in landings reports, the correlation between the maximal CPUE and year class recruitment was r = 0.86, indicating the index is determined after year-class strength is established.