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.
Identifer | oai:union.ndltd.org:wm.edu/oai:scholarworks.wm.edu:etd-2321 |
Date | 01 January 1991 |
Creators | Luo, Jiangang |
Publisher | W&M ScholarWorks |
Source Sets | William and Mary |
Language | English |
Detected Language | English |
Type | text |
Format | application/pdf |
Source | Dissertations, Theses, and Masters Projects |
Rights | © The Author |
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