Recruitment in flatfish, with special emphasis on North Atlantic species: Progress made by the Flatfish Symposia

Abstract

In summarizing the main results on recruitment that emerged from the series of Flatfish Symposia, two aspects were distinguished: mean level and interannual variability. Recruitment to a stock appears to be related to the quantity of juvenile nursery habitats, suggesting that either larval supply or the carrying capacity of the nurseries is the limiting factor. However, available information on growth of 0-group flatfish suggests that the carrying capacity of nursery areas is never reached. Variability in year-class strength is generated during the pelagic egg and larval stage, probably by variations in the hydrodynamic circulation and in the mortality rates of eggs and larvae. Density-dependent processes seem to occur only during the juvenile stages, particularly in respect of growth. However, no impact on recruitment variability has been found. Density-dependent mortality during the phase shortly after settlement dampens the interannual recruitment variability. There is no evidence of densitydependent effects in the adult phase at present, but these may have been important at lower levels of exploitation. The importance of the factors determining recruitment vary not only among species, but also over the species' range. It is suggested that damping processes can only occur in the demersal stage, implying that variability in year-class strength can only decrease in fish species with a demersal stage. If true, ultimate variability in recruitment in fish species will be related to the relative duration of the pelagic and demersal stages. 2000 International Council for the Exploration of the Sea

Effect of an invasive mollusc, American slipper limpet Crepidula fornicata, on habitat suitability for juvenile common sole Solea solea in the Bay of Biscay

“…Survival and growth of early fish stages are maximised in these highly productive habitats (Miller et al 1984(Miller et al , 1988 and natural shallow areas can serve as nurseries for a variety of species that are widely distributed on the continental shelf (Lenanton & Potter 1987), in particular flatfishes (Van der Veer et al 2000, Riou et al 2001. The available area and the quality of coastal nursery habitats have a considerable influence on recruitment levels (Rijnsdorp et al 1992, Gibson 1994 and damage to these habitats may slow or prevent population recoveries (Hall 1998, Hill & Caswell 2001.…”

Scientific knowledge of biological processes potentially useful in fish stock predictions

“…By meta-analysis, Rijnsdorp et al (1992) found a positive relationship between average recruitment success and spatial extension of the nursery grounds for sole, which holds also for different plaice populations around the North Sea ( Van der Veer et al, 2000). Similar to flatfish, density dependent mortality has been detected in walleye pollock during the transition between the larval and the juvenile phase (Bailey et al, 1996).…”

“…Density dependent mortality has been identified in different flatfish species during the phase shortly after settlement, dampening the inter-annual variability in recruitment, but not explaining a significant part of the variability ( Van der Veer et al, 2000).…”

“…Brander and Houghton, 1982), have been explained by related changes in predation: Van der Veer and Bergman (1987) suggest a release from predation by crustaceans in the nursery area due to avoidance of these areas by the predator at low temperature. In general, density dependent predation on juveniles has been identified as a factor controlling recruitment success or dampening its variability (Van der Veer et al, 2000); in both ways it may have a significant influence on the population dynamics of most fish stocks and thus needs to be considered in recruitment predictions.…”

Shifts in nursery habitat utilization by 0-group plaice in the western Dutch Wadden Sea

“…Such habitats are generally highly productive, providing abundant food resources as well as protection to early juveniles against predators, features which allow fish to optimize the trade-off between growth and survival (Bergman et al, 1988;Beck et al, 2001;Gibson et al, 2002). Both the capacity and quality of the nursery (Gibson, 1994;Iles & Beverton, 2000;Rijnsdorp et al, 1992;van der Veer et al, 1994van der Veer et al, , 2000 and its connectivity with the adult habitat (Beck et al, 2001;Gillanders et al, 2003) are considered to influence annual recruitment levels to adult stocks in offshore waters. The residency of juvenile fish in nursery areas is speciesdependent and can range from several weeks to multiple years (Cabral & Costa, 1999;Martinho et al, 2007;Laurel et al, 2009), and the longer the permanence, the stronger the potential influence of habitat (biotic and abiotic) factors on growth and cohort survival (see review by Gibson, 1994).…”