Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


John A. Musick


In lower Chesapeake Bay, the spawning season of the bay anchovy Anchoa mitchilli in 1988 was from early May to mid-September. Spawning was temporally synchronized and lasted for about 1.5 h each night. Spawning frequency per individual was every 4 d in early June and 1.3-1.9 d in other months. Batch fecundity was a linear function of fork length and body weight; regression slopes on 6 July and 4 August were significantly higher than those on 6 June and 31 August. Estimated mean total spawnings per female in 1988 was 54. Total egg production for a fish of average size was 45,110, which is equivalent to 346% of body biomass energy. Age determination based on lagenar otoliths showed that some fish spawned when as young as 2.5-3 months. Transport of the adult bay anchovy in darkness was studied in laboratory and field experiments. In a hydraulic flume, 99% of all fish were transported to the end of the flume in darkness at a current speed of 30 cm s&\sp{lcub}-1{rcub}&. In field experiments, fish marked with neutral red dye and released in a creek at flood tide were recaptured 5.1 km upstream 4 h after release at night, and were recaptured within 200 m of the release site 3 h after release in daylight. This nocturnal transport phenomenon may help in understanding behavior and distribution of pelagic estuarine fishes. The standardized CPUE data show long-term population fluctuations on the order of ten fold. The bay anchovy population also has extensive seasonal variations. A Fourier analysis removed the seasonal (short-term) variation from the long-term data series. An autoregressive analysis of the residual series indicated that it contained a significant first-order autoregressive process component (r&\sp2& = 0.26, P &\le& 0.0066), which was interpreted as a spawner-recruit relationship. Cross-correlation analysis indicated that bay anchovy population abundance was positively correlated with winter water temperature (r = 0.663, P &\le& 0.0001) and river flow (r = 0.376, P &\le& 0.027), but negatively correlated with the abundances of white perch (r = &-&0.437, P &\le& 0.011), and the squared function of residual wind speed (r = &-&0.377, P &\le& 0.026). A multiple regression model indicated that temperature, white perch abundance and wind made significant contributions (accounting for 78% of the variation) to the model.



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