Distribution, seasonal occurrence, recruitment and growth of juvenile commercial flatfish species on the west coast of Ireland

Abstract

The population dynamics of juvenile flatfish were investigated on the west coast of Ireland. Firstly, beach seining was carried out to assess spatial and temporal variations in flatfish assemblages, on sandy beach nursery grounds, in two regions, on the west coast of Ireland, Galway Bay (2002 to 2003) and Dingle Co. Kerry (2000 to 2003). In both locations 0+ plaice generally were numerically dominant in the catches. This is consistent with flatfish assemblages in European waters. There was a significant difference between beaches in the species composition and plaice densities in Galway Bay, while no annual differences could be discerned. Secondly, a push-net survey was carried out in Galway Bay from 2002 to 2003, to determine the settlement, seasonal occurrence, growth and mortality of 0+ plaice. Settlement occurred in late April in 2002, and in late March of 2003. Higher peak densities were recorded in 2003. Growth rates were similar to a predicted growth model obtained at optimal feeding conditions. Daily mortality rates were within that recorded elsewhere in European waters. Experimental push-netting showed that depth does not influence the catches of 0+ plaice in shallow water. Sampling at night produced significantly higher densities of 0+ plaice. Thirdly, otolith microstructure was used to determine hatching dates, larval period, settlement dates and growth of 0+ plaice in Galway Bay in 2003. Hatching time ranged from late January to late March. The larval period for fish ranged from 28 to 43 d, the lowest recorded in Europe. This was consistent with sea temperature, where higher temperatures have lower larval periods. Settlement period was longer than that determined by sampling, ranging from early to mid March to late April. Three cohorts of settlement were noted, which corresponded to pulses in hatching. Observed growth was similar to predicted growth and a strong inverse relationship was noted between growth and density.