Transport models for planktonic fish eggs and larvae often use temperature to drive growth because temperature data are readily available. This pragmatic approach can be criticised as too simplistic as it ignores additional factors, such as food availability and growth-rate-dependent mortality. We examined the extent to which temperature could explain the larval duration and growth variability in post-settlement plaice from the southern North Sea, Irish Sea and west of Ireland. Larval duration and individual growth were estimated from the otolith microstructure of juvenile plaice collected from nursery grounds in each region, and average sea surface temperatures were reconstructed for each region from satellite data. Hatch dates, larval duration and settlement dates all differed among the regions, reflecting the timing of spawning and the physical characteristics of each region. Models incorporating presumed temperature history and region explained 73% of variability in individual larval growth (as estimated from otolith microincrement widths), again demonstrating important differences among the regions. The results suggest that sea temperature can be used to drive growth models of plaice larvae, although allowance must then be made for interregional differences. However, larval duration can be estimated using a pan-regional model based on the average temperature experienced during the larval phase.
The ichthyoplankton of Galway Bay was sampled over the spring and summer of 2007 and 2008 to determine what environmental factors influenced the distribution of larval and early juvenile fish. A total of 549 fish representing 27 taxa were caught. Catches decreased throughout each sampling season, and were generally poor in 2007. Catches were numerically dominated by sprat (Sprattus sprattus), dab (Limanda limanda), sand eel (Hyperoplus immaculatus) and whiting (Merlangius merlangus). Environmental factors driving distribution of fish were modelled using a binomial generalized linear model. The strength and direction of wind in the five days preceding sampling was the only significant environmental factor. Sustained onshore winds increased the probability of encountering larval fish in the areas sampled. The rainfall, tidal state, tow depth and wind conditions during sampling were not significant. Among the parameters measured it appears that onshore winds sufficiently strong to overcome the residual circulation are the main physical driver for the distribution of larval fish in Galway Bay.
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