Cooperative Fish and Wildlife Research Units Program: Vermont
Education, Research and Technical Assistance for Managing Our Natural Resources

Timing of hatch in fish populations can be critical for first-year survival and, therefore, year-class strength and subsequent species interactions. We compared hatch timing, growth rates and subsequent mortality of age-0 Rainbow Smelt Osmerus mordax and Alewife Alosa pseudoharengus, two common open-water fish of northern North America. In our study site, Lake Champlain, Rainbow Smelt hatched almost a month earlier than Alewife (hatching began on 26 May for Rainbow Smelt and 20 June for Alewife). Abundance in the sampling area was highest in July for age-0 Rainbow Smelt and August for age-0 Alewife. Later-hatching individuals of both species grew faster than those hatching earlier (0.6 mm/d vs. 0.4 for Rainbow Smelt; 0.7 mm/d vs. 0.6 for Alewife). Mean mortality rate for age-0 Rainbow Smelt was 3.4%/d and for age-0 Alewife was 5.5%/d during the first 45 days of life. Alewife mortality rates did not differ with hatch timing but daily mortality rates of Rainbow Smelt were highest for earlier-hatching fish. Cannibalism is likely the primary mortality source for age-0 Rainbow Smelt in this lake. Therefore, hatching earlier may not be advantageous as the overlap of adult and age-0 Rainbow Smelt is highest earlier in the season. However, Alewife, first documented in Lake Champlain in 2003, may increase the mortality of age-0 Rainbow Smelt in the summer, which should favor selection for earlier hatching.