Synchronized hatch and its ecological significance in rainbow smelt Osmerus mordax in St. Mary's Bay, Newfoundland
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Date
2004-11Author
Bradbury, IR
Campana, SE
Bentzen, Paul
Snelgrove, PVR
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Show full item recordAbstract
Early life history stages in most marine animals are subject to high mortality through
predation, starvation, and dispersal. Accordingly, the potential exists for the selection of
behavioral mechanisms that reduce mortality. We examined the ecological significance of
synchronization in hatch and the initiation of larval drift in rainbow smelt, Osmerus mordax,
populations in St. Mary's Bay, Newfoundland. Larval abundances from six 24-h ring net
surveys (2-h intervals) in Colinet and Salmonier Rivers during 2002/2003 suggest synchronized hatch
following dusk (similar to2200 h). Monitoring of egg hatching in situ confirmed synchrony was at
hatch and not emergence. Larval abundance showed no relationship with temperature or flow rates, and
the consistency in hatch pattern suggested a light/dark cue. In experimental manipulations in which
eggs were exposed to light and dark conditions for 2-h periods, hatch percentages were up to five
times higher (p < 0.005) in dark treatments. We hypothesized that the linkage of hatch to low
light levels represents a mechanism to avoid elevated larval predation in daylight conditions. Egg
predation determined from predator gut content analysis suggested that extreme predation risk from
small (< 20 cm) salmonids peaked during the day, prior to dusk, and was lowest during night
(2200-0400 h). Microcosm experiments demonstrated that newly hatched larvae exposed to predators in
dark conditions did not change in number, but mortality averaged 60% in light conditions. Our
results suggest that predation pressure during the early life history of aquatic organisms might
play a strong role in the optimization of aquatic life histories.
Citation
Bradbury, IR, SE Campana, P. Bentzen, and PVR Snelgrove. 2004. "Synchronized hatch and its ecological significance in rainbow smelt Osmerus mordax in St.
Mary's Bay, Newfoundland." Limnology and Oceanography 49(6): 2310-2315. DOI:10.4319/lo.2004.49.6.2310