15 JUNE 1999
S.D. Leach, E.D. Houde-1999
Journal of Fish Biology, 54(4): 767-786 (from Current Contents)
Abstract:
Episodic increases in temperature of greater than or equal to 5 degrees C above 20 degrees C, over 48 h or declines in pH of 1.0 unit from pH 7.0 reduced survival of yolk-sac and feeding-stage larvae of American shad Alosa sapidissima. Over 16 days all measures of survival, growth, and production were more favourable at each higher temperature in the 15-25 degrees C range. More favourable responses were also obtained at the higher prey level (500 v. 50 Artemia nauplii/l) and at the higher pH (7.5 v. 6.5). Combinations of high temperature and high prey levels, at pH 7.5, led to highest larval production. Little growth or production occurred at 15 degrees C, regardless of pH or prey level. The effect of pH was strong with respect to survival, but weak with respect to growth. In attempts to restore American shad populations by larval stocking, release times and sites can be critical to optimize survival and eventual returns. Releases of larvae potentially will be most effective when made at temperatures >20 degrees C, pH > 7.0, and prey levels > 50/l. These conditions are most likely to occur in Maryland tributaries of Chesapeake Bay between mid-May and early June.
(S Carolina Dept Nat Resources, Dennis Wildlife Ctr, POB 190, 305 Black Oak Rd, Bonneau, SC 29431, USA, e-mail:
leach@cbl.umces.edu)