MEPS 181:53-59 (1999)  -  doi:10.3354/meps181053

Non-random mortality of Baltic cod larvae inferred from otolith hatch-check sizes

Peter Grønkjær*, Michael Schytte

Institute of Biological Sciences, Dept. of Marine Ecology, University of Aarhus, Finlandsgade 14, DK-8200 Aarhus N, Denmark
*Present address: Dept. of Biology, BioSciences Complex, Queen's University, Kingston K7L 3N6, Canada. E-mail:

ABSTRACT: Recent evidence suggests that otolith size at hatch may reflect maternal (e.g. egg size and quality) or intrinsic (bioenergetic) factors influencing growth and survival of larval fish. In this field study, the hatch-check sizes of 133 Baltic cod larvae were examined with regard to larval age, vertical distribution and instantaneous protein growth rates. Larvae with small hatch-checks died around Day 12 to 13, whereas larvae surviving past Day 20 all had hatch-checks close to or larger than the overall mean. Furthermore, there were significant differences between hatch-check sizes of larvae residing at hatching depth (>45 m, mean hatch check size = 261 µm2) and larvae that had migrated towards more optimal feeding depths (<=45 m, mean = 301 µm2). There was a weak, but significant, positive correlation between hatch-checks sizes and instantaneous protein growth rates inferred from RNA/DNA-ratios of 37 larvae. This correlation improved when we excluded yolk-sac larvae. The differences in otolith hatch-check sizes between larval groups could not be attributed to differences in the environment during egg development. Thus, maternal or intrinsic factors controlling otolith size at hatch may influence the survival of Baltic cod larvae.

KEY WORDS: Baltic cod · Otolith hatch-check size · Vertical migration · Growth · Survival

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