An investigation into the effects of environmental variables on the early life history stages of fish, with special emphasis on the flatfish of the west of Ireland

Abstract

The temperate waters of the North-east Atlantic host a diverse marine ecosystem, and within that ecosystem fish are a valuable resource both in terms of ecosystem functioning and commercial exploitation. The West Coast of Ireland provides nurseries for the early life stages of many species of fish whose adult forms are found both inshore within estuaries and bays and offshore in shelf waters. This study sought to examine the relationship between some of those early-stage fish and their physical environment using field data and statistical modelling techniques. An analysis of the environmental determinants of the distribution of larval and early juvenile fish of various species within the confines of Galway Bay revealed that onshore winds are a key driver, providing a mechanism for transport and retention in the bay. Growth rates during the pelagic larval stage of plaice (Pleuronectes platessa) from the west of Ireland from one year were compared with samples from the eastern Irish Sea and the southern North Sea using otolith microstructure. Generalised additive mixed models (GAMMs) using cumulative degree day (CDD) as the main predictor of otolith growth brought to light differences in growth patterns between the areas, that may be related to spatial variation in hydrography, distance from spawning and settlement sites, and timing of spawning events. The duration of the pelagic larval phase was found to be negatively associated with water temperatures, consistent with previous studies of plaice. Similarly, growth during the larval stages of turbot (Psetta maxima) from sites in Kerry in the southwest and Galway in the west of Ireland was modelled using CDD within a GAMM framework. Minor but significant differences in growth were shown between the regions and the three years of the study period. Larval durations were negatively associated with higher temperatures though the relationship was not as pronounced as that in plaice. Settlement of turbot was modelled showing that tidal height, wind and rainfall were significant predictors of settlement events. These results show that larval fish on the west coast of Ireland and elsewhere respond to fluctuations in their physical environment over a range of scales.