Plaice egg mortality: can we determine survivorship?

The daily mortality rate of cohorts of plaice eggs in the Irish Sea is estimated throughout the spawning season in 1995 and 2000, using general additive models of egg production. Daily mortality (z) was found to vary between 0.15 and 0.29. Mortality rates declined through the season in 1995 but not in 2000. There were significant differences in the mortality rates of individual cohorts of eggs. The suitability of an exponential decay model to describe daily mortality is discussed. The mortality rates conform to previously described relationships between fish eggs and temperature. The estimates of mortality rate were found to be robust to imprecision in egg ageing, but ageing imprecision led to a bias in the estimation of survivorship of eggs from spawning to hatch. The bias will vary with mortality rate.