Contributions to the early life histories of alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis): Rearing, identification, ageing, and ecology

• Main Author: Sismour, Edward Norbert
• Format: Others
• Language: English
• Published: W&M ScholarWorks 1994
• Subjects: Ecology and Evolutionary Biology
• Online Access: https://scholarworks.wm.edu/etd/1539616856; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=2423&context=etd

Early life histories of alewife (Alosa pseudoharengus) and blueback herring (A. aestivalis), collectively known as river herring, are poorly documented for Chesapeake Bay populations. Improved knowledge of these early life histories potentially will aid fisheries, habitat and resource management. Investigations were conducted following two lines. First, alewife and blueback herring larvae reared from eggs were used to investigate methods for species identification and to validate the otolith increment method for age determination. Blueback herring larvae hatched from naturally-spawned eggs were reared to age 24 d. Alewife and blueback herring larvae hatched from artificially-spawned eggs were reared to age 32 d and age 37 d. Alewife larvae exhibited paired melanophores laterally along the notochord starting at about 15 mm SL, contracted xanthophores dorsally on the head, and lacked xanthochrome at the caudal fin base. Blueback herring exhibited one or two melanophores dorsally on the notochord starting at about 11 mm SL, relatively large xanthophores dorsally on the head, and xanthochrome at the caudal fin base. Other pigment variation was found. Estimated deposition of otolith increments was 1.16 and 0.90 increment d&\sp{lcub}-1{rcub}& for blueback herring larvae and 0.90 increment d&\sp{lcub}-1{rcub}& for alewife larvae. Increment enumeration was affected by otolith microstructure appearance, but estimated deposition did not differ statistically from one increment d&\sp{lcub}-1{rcub}&. Second, larval river herring distributions, abundances, growth rates, and hatch dates in the Pamunkey River tidal freshwater reach were analyzed. Distributions and abundances of zooplankton prey for river herring larvae were also analyzed. High abundances in two tidal creeks suggested that larvae occur in these areas from about late April to about mid-May. Larval river herring growth, pooled across seasons, was faster in the tidal creeks, 0.46 mm d&\sp{lcub}-1{rcub}&, than the mainstem river, 0.34 mm d&\sp{lcub}-1{rcub}&. Faster growth in the tidal creeks may increase survival by reducing the larval stage duration. Older larvae, pooled across habitats, grew faster than younger larvae, 0.59 mm d&\sp{lcub}-1{rcub}& and 0.35 mm d&\sp{lcub}-1{rcub}&. Larvae with relatively earlier hatch dates were associated primarily with the mainstem river while larvae with relatively later hatch dates were associated primarily with the tidal creeks. Zooplankton abundances were higher in the tidal creeks than the mainstem river.