John E. Olney

Geochemical Signatures in Otoliths Record Natal Origins of American Shad

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 (δ13C, δ18O and 87Sr:86Sr) 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 δ18O 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. Approxi...

Eggs and Early Larvae of the Bay Anchovy, Anchoa mitchilli, and the Weakfish, Cynoscion regalis, in Lower Chesapeake Bay with Notes on Associated Ichthyoplankton

The seasonal abundance and spatial distribution of eggs and early larvae of the bay anchovy,Anchoa mitchilli, and the weakfish,Cynoscion regalis, were determined from plankton collections taken during 1971–1976 in the lower Chesapeake Bay. Eggs and larvae of the bay anchovy,Anchoa mitchilli, dominated the ichthyoplankton, making up 96% of the total eggs and 88% of all larvae taken. A comparison of egg and larval densities from the lower Chesapeake Bay to existing data from other East Coast estuaries suggested that Chesapeake Bay is a major center of spawning activity for this species.Anchoa mitchilli spawning commenced in May when mean water column temperatures approached 17°C and abruptly ceased after August. Eggs and early larvae presented a continuous distribution throughout the study area during these months. Eggs and larvae of several sciaenid species, especiallyC. regalis, ranked second in numerical abundance. Larval weakfish were consistently taken in late summer of each sampling year but peak abundance and distribution was observed in August 1971. Sciaenid eggs exhibited a distinct polyhaline distribution with greatest concentrations observed at the Chesapeake Bay entrance or along the Bay eastern margin. Analysis of sciaenid egg morphometry and larval occurrence suggested spawning activity of at least four species. Additional important species represented by eggs and/or larvae in the lower Chesapeake Bay wereHypsoblennius hentzi, Gobiosoma ginsburgi, Trinectes maculatus, Symphurus plagiusa andParalichthys dentatus with the remaining species occurring infrequently.

Macroscale Assessment of American Shad Spawning and Nursery Habitat in the Mattaponi and Pamunkey Rivers, Virginia

Abstract Variation in habitat suitability can alter the growth and mortality of early life stages of fishes but is often difficult to measure, quantify, and apply to the entire system. We designed and tested habitat suitability index (HSI) models incorporating both proximate riverine parameters and surrounding landscape features as determinates of optimal spawning and nursery areas for American shad Alosa sapidissima. American shad eggs and larvae were collected in the Mattaponi and Pamunkey rivers, Virginia, during 1997–1999 as direct evidence of nursery habitat use and indirect evidence of spawning reaches. Hydrographic, physical habitat, shoreline, and land use features were examined for associations with the presence of eggs and larvae. Principal components analyses and logistic regressions indicated the importance of hydrographic parameters (current velocity, dissolved oxygen, and depth), physical habitat features (sediment type and woody debris), forested shoreline, and land use features to the pres...

Managing a Fishery under Moratorium: Assessment Opportunities for Virginia's Stocks of American Shad

Abstract Virginias river fisheries for American shad have been under moratorium since 1994. The moratorium is partial since the three stocks (in the James, York, and Rappahannock rivers) are harvested to an unknown degree in an offshore mixed-stock fishery. Current research efforts have three objectives: (1) to determine current status of the stocks relative to historical levels, (2) to determine appropriate target catch-rate levels for restoration, and (3) to develop new assessment tools so that a future moratorium can be avoided. Current status is being evaluated by monitoring catch rate of commercial fishers who are paid to fish with historical methods in historical locations; the contemporary catch rates are compared to those recorded in logbooks completed voluntarily by fishers prior to the closure. We propose to define restoration targets in terms of historic catch rates recorded in logbooks. This requires determination of relative catching power of historic (multifilament) and modern (monofilament...

Migratory Behavior of American Shad in the York River, Virginia, with Implications for Estimating In-River Exploitation from Tag Recovery Data

Abstract 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 ...

Testing the validity of Cating's (1953) method for age determination of American shad using scales

Abstract Catings 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 Catings 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, Catings method is not applicable to American shad in these Penns...

Potential Predation by Fish and Invertebrates on Early Life History Stages of Striped Bass in the Pamunkey River, Virginia

Abstract Field surveys in the Pamunkey River, Virginia, indicated that numerous fish and invertebrate predators varied in their spatiotemporal coincidence with eggs and larvae of striped bass Morone saxatilis on spawning grounds. In the laboratory, the cyclopoid copepod Acanthocyclops vernalis was observed to attack and kill striped bass larvae, In addition, juveniles or adults of satinfin shiner Notropis analostanus, spottail shiner N. hudsonius, tessellated darter Etheostoma olmstedi, white perch Morone americana, striped bass, bluegill Lepomis macrochirus, pumpkinseed Lepomis gibbosus, channel catfish Ictalurus punctatus, and white catfish I. catus ate yolk-sac larvae under laboratory conditions. Consumption of larvae by spottail shiners and satinfin shiners increased with increasing prey density to a maximum observed ingestion of 150 and 81 larvae per predator per hour, respectively. At prey concentrations simulating ambient Pamunkey River conditions (20–100 larvae/m3), consumption by both species ran...

Tracking Nursery Habitat Use in the York River Estuary, Virginia, by Young American Shad Using Stable Isotopes

Abstract We developed and applied a stable isotope turnover model to estimate how long age-0 American shad Alosa sapidissima reside within tidal freshwater and brackish-water habitats in the York River estuary, Virginia. The residence time was estimated by modeling the changing stable isotope ratio (either the carbon [δ13C] or sulfur [δ34S] stable isotope ratio) of an age-0 American shad as it migrates seaward from its present habitat to a new habitat and determining the minimum time required to acquire the isotopic signature of its new habitat. A sensitivity analysis of our turnover model indicates that the results are robust at relatively fast turnover rates, such as those experienced by young fish, but that at slow turnover rates the model can yield biologically meaningful differences with relatively small changes in variables. The average ± SE isotopic ratios for the dorsal muscle tissue of age-0 fish increased along the estuary, from −31.8 ± 0.3‰ for δ13C and −5.2 ± 0.7‰ for δ34S at the farthest upri...

Contribution of allochthonous carbon to American shad production in the Mattaponi River, Virginia, using stable isotopes

Our objective was to quantify the contribution of autochthonous, locally-produced phytoplankton, and allochthonous, terrestrial-derived organic matter (OM) to the production of young-of-year (YOY) American shad(Alosa sapidissima) using stable isotopes. We measured the carbon and nitrogen stable isotope composition of YOY American shad in the tidal fresh water of the Mattaponi River, a tributary in the York River estuary, during three consecutive years. The isotopic ratios of larval American shad varied among years, indicating a switch from reliance on a primarily autochthonous food web pathway during low and moderate discharge years (50–90%; 2002, 2004) to a primarily allochthonous pathway during a high discharge year (< 35% phytoplankton; 2003). Reliance on phytoplankton by larval fish declined exponentially with increasing Mattaponi River discharge. In 2003, juvenile production was also supported by allochthonous OM, though autochthonous phytoplankton accounted for an increasingly large fraction during June through August, up to 40–55%. We also found a long-term, positive relationship between the duration of above average flow during April through June in the Mattaponi River and a corresponding index of juvenile American shad abundance. The largest American shad cohort recorded since 1967 was observed in 2003, a high discharge year. The production of this cohort was largely supported by allochthonous OM. The results suggest an important link between river discharge, energy flow, and recruitment, wherein high discharge favors reliance on terrestrial carbon by YOY American shad, owing to changes in zooplankton diet, macroinvertebrate abundance, or both, and also favors high American shad abundance.

Pterygiophore-Interdigitation Patterns in Larvae of Four Morone Species

Abstract The diagnostic potential of dorsal and anal pterygiophore-interdigitation patterns was examined in larvae of striped bass Morone saxatilis, white bass M. chrysops, white perch M. americana, and yellow bass M. mississippiensis. The number and position of pterygiophores relative to interneural spaces 1–6 and 10–13 and to interhaemal spaces 12–15, as well as total number of dorsal and anal pterygiophores, are characters useful in delimiting larvae of these species. Interdigitation patterns useful in distinguishing yellow bass from white perch larvae were not found; however, these two species may not co-occur. Received November 12, 1983 Accepted May 9, 1983