Abstract.-Population connectivity is a critical component in the life history dynamics of anadromous fishes and in the persistence of local populations. We used geochemical signatures in the otoliths of American shad Alosa sapidissima to determine natal origins and estimate rates of straying among river-specific populations along the U.S. Atlantic coast. Stable isotope (d 13 C, d 18 O and 87 Sr: 86 Sr) and elemental (Mg:Ca, Mn:Ca, Sr:Ca and Ba:Ca) signatures in otoliths of juvenile American shad from rivers from Georgia to New Hampshire varied significantly, allowing for an average of 91% cross-validated accuracy when classifying individual fish to their natal rivers. We also found significant interannual variability in the geochemical signatures from several rivers, due largely to differences in d 18 O values among years. We then used the ground-truthed geochemical signatures in the otoliths of juvenile American shad to identify the natal origins of spawning adults in the York River system in Virginia. Approximately 6% of the spawning adults collected in the York River were strays from other rivers. Of the remaining fish, 79% were spawned in the Mattaponi River and 21% in the Pamunkey River. The combined results of this and other recent studies suggest that although most American shad spawning in the York River were homing to their natal river, there was much less fidelity to individual tributaries. Small-scale straying could allow fish spawned in the Mattaponi River to subsidize spawning in the Pamunkey River, which has experienced persistent recruitment failure.

The Mattaponi River is part of the York River estuary in Chesapeake Bay. Our objective was to identify the organic matter (OM) sources fueling the lower food web in the tidal freshwater and oligohaline portions of the Mattaponi using the stable isotopes of carbon (C) and nitrogen (N). Over 3 years (2002)(2003)(2004), we measured zooplankton densities and C and N stable isotope ratios during the spring zooplankton bloom. The river was characterized by a May-June zooplankton bloom numerically dominated by the calanoid copepod Eurytemora affinis and cladocera Bosmina freyi. Cluster analysis of the stable isotope data identified four distinct signatures within the lower food web: freshwater riverine, brackish water, benthic, and terrestrial. The stable isotope signatures of pelagic zooplankton, including E. affinis and B. freyi, were consistent with reliance on a mix of autochthonous and allochthonous OM, including OM derived from vascular plants and humic-rich sediments, whereas macroinvertebrates consistently utilized allochthonous OM. Based on a dual-isotope mixing model, reliance on autochthonous OM by pelagic zooplankton ranged from 20% to 95% of production, declining exponentially with increasing river discharge. The results imply that discharge plays an important role in regulating the energy sources utilized by pelagic zooplankton in the upper estuary. We hypothesize that this is so because during high discharge, particulate organic C loading to the upper estuary increased and phytoplankton biomass decreased, thereby decreasing phytoplankton availability to the food web.

Tagging of American shad Alosa sapidissima may alter their migratory behavior, causing some tagged individuals to cease or delay the spawning run. In a tag recovery study designed to assess fishery impacts, this altered behavior would reduce the number of tagged fish available to the target fishery and would bias estimates of exploitation and fishing mortality rates. To investigate this possibility, we fitted 29 prespawning adults with acoustic tags and released the fish into the middle reaches of the York River, Virginia. Movements of individuals were remotely monitored at three hydrophone stations: (1) 7 river kilometers (rkm) downriver of the release site; (2) on the Mattaponi River, 48 rkm upriver of the release location; and (3) on the Pamunkey River, 56 rkm upriver of the release location. Almost half of the fish were apparently affected by capture, handling, and tagging, as they either abandoned their migration or delayed their upstream movements. The movements of some fish appeared to be unaffected by capture; these fish were not detected at the downriver station and were detected on the spawning grounds 2-5 d after release. Eighteen fish remained on the spawning grounds for 17-51 d (average ¼ 34.4 d) and were last detected at the downriver location, presumably during their seaward migration. Of the 26 tagged fish that migrated to either tributary after release, 15 originally selected spawning grounds on the Mattaponi River and 11 selected the Pamunkey River. One fish occupied both tributaries for several weeks each, suggesting possible spawning at both locations. We conclude that tagging protocols designed to measure the impacts of fishing on American shad should include telemetry to assess altered migratory behavior.

Cating's method of using scales to age American shad (Alosa sapidissima) has been the standard for more than 50 years. However, the only validation of this method is for ages 4–6 in the Connecticut River. To test the method for these—and older—age classes in another river, we obtained scales from 52 known‐age fish from two Pennsylvania rivers and had 13 experienced biologists estimate ages using Cating's method. Each biologist read the scale impressions twice, and these readings were then assessed in terms of precision, accuracy, and bias. Percent agreement between estimates for the same scale set (precision) ranged from 50.0 to 76.5%. Percent agreement between estimated age and known age (accuracy) was highest for ages 3–6 (33.7–48.5%), markedly lower for age‐7 (12.1%), and lowest for age‐8 fish (3.9%). Ages of the youngest fish were often overestimated, and those of the oldest fish were typically underestimated (bias). Therefore, Cating's method is not applicable to American shad in these Pennsylvania rivers. In fact, this scale‐ageing method has never been validated across all ages for any American shad stock. Thus, we recommend against using age‐based techniques to assess stocks of American shad until further age‐validation studies have been completed.

We describe macro-and microscopic criteria to judge maturation stages of female American shad (Alosa sapidissima) collected in the York river, Virginia, USA. For comparison, we also examined ovaries of fishes collected in the Edisto river, South Carolina, and the Connecticut river, Massachusetts. The study augments a developing stock assessment program that is evaluating the use of index-removal and change-in-ratio estimators of exploitation rate and absolute abundance. Samples were obtained from traps at the York river mouth, staked gill nets in mid-reaches of the river, and drift gill nets on the spawning grounds (approximately 100 km from the river mouth). To judge maturation stages, we used the following macroscopic characters : ovary color, gross appearance of oocytes, degree of blood infusion, and value of the gonosomatic index (ovary weight divided by somatic weight). Stain reactions and presence or absence of cellular characteristics (nucleoli, nuclear migration, oil globules, yolk vesicles, atresia, and postovulatory follicles) were used as microscopic criteria. No differences in scoring of maturation stage were observed in comparisons of samples from different regions of the ovary. American shad in both semelparous (Edisto river) and iteroparous populations (York and Connecticut rivers) exhibit indeterminate fecundity and group-synchronous oocyte development. Unyolked, partially yolked and advanced yolked oocytes are observed in all maturity stages except spent females. There is histological evidence that an individual female spawns in batches over a period of days or weeks since both recently developed and older post-ovulatory follicles are observed simultaneously with advanced yolked oocytes. Most post-spawning females captured at the river mouth are only partially spent with ovaries that contain large numbers of advanced oocytes. A reproductive cycle for American shad in the York river is proposed. Successive or batch spawning in wild populations has important ecological implications since an individual can spread her gametes over a large spatio-temporal scale, thereby increasing the chances that progeny will encounter salubrious conditions. Key RnSUMnNous décrivons des critères macro et microscopiques pour juger des stades de maturité des aloses américaines femelles (Alosa sapidissima) captur¡es dans la rivière York, Virginia, USA. A titre de comparaison, nous examinons également des ovaires de poissons capturés dans la rivière Edisto, South Carolina, et dans la rivière Connecticut, Massachusetts. L'étude fait partie d'un programme en cours d'évaluation de stocks, qui utilise la méthode des changements de proportions et de la méthode des changements d'indices d'abondance par prélèvement pour estimer le taux d'exploitation et d'abondance absolue. Des échantillons ont été obtenus grâce à des trappes à l'embouchure de la rivière York, des filets fixes (à mi-parcours migratoire) et des filets dérivants sur les lieux de ponte (à environ 100 km de l'embouchure). Afin d'établir les stades de matu...