On the Recruitment of O-Group Plaice in the North Sea

Rocky shore monitoring around the Sullom Voe Oil Terminal in Shetland has produced a 20 yr dataset of population fluctuations for 40-plus species at 15 to 20 sites separated by distances up to 30 km. Synchrony in population changes was quantified by correlation among series of abundance categorised on quantitative scales. Two periods were analysed separately, pre-and post-1992, following changes in methods and extent of monitoring. Positive average correlations among sites were found for 10 out of 16 species pre-1992 and for 23 out of 26 post-1992, statistically significant for 4 and 8 species for the 2 periods, respectively. The intertidal barnacle Semibalanus balanoides showed most synchrony among sites for both periods, while dogwhelks Nucella lapillus and macroalgae (Fucus vesiculosus, F. serratus, Mastocarpus stellatus) had very low average correlations among sites. Littorina saxatilis was the only other species with significant positive correlation among sites in both periods. Corallinaceae, Verrucaria maura and V. mucosa, and Littorina neglecta were less synchronised pre-1992 than post-1992, while L. obtusata showed less synchrony post-1992. Differences in reproductive biology and ecology failed to explain patterns of synchrony among species. Species with planktonic larvae were no more likely to be synchronised than those without. There was a tendency for species living higher on the shore to be more synchronised post-1992, but species predominant on wave-exposed shores were no more synchronous than sheltered-shore species. The more synchronised species in this study need to be monitored at relatively few sites to detect change, whereas more sites may be needed for species in which change occurs on a local scale. Population synchrony also suggested usefulness of species as indicators of large-scale change: the barnacle S. balanoides is the best indicator among species in the study area.

Section: Discussionmentioning

confidence: 99%

Spatial synchrony of population changes in rocky shore communities in Shetland

Burrows¹,

Moore²,

James³

2002

“…Coherence between modelled growth rate under optimum food conditions and growth rate in the field estimated from changes in population mean length has been used as evidence that growth is not density-dependent in 0-group flatfish populations (Zijlstra & Witte 1985, Bergman et al 1988, van der Veer et al 1990. However, negative size-selective mortality will exaggerate growth rates estimated from changes in population mean length (Ottera 1992, van der Veer et al 1994.…”

Section: Size-selective Predationmentioning

confidence: 99%

Size-selective predation of 0-group flatfishes on a Scottish coastal nursery ground

Ellis¹,

Gibson²

1995

Fish predation on 0-group flatfish (plaice Pleuronectes platessa, dab Limanda limanda and flounder Pleuronectesflesus) populations on Tralee Beach. Scotland (56" 31' N, 5" 29' W) was studied by stomach content analysis during the summers of 1992 and 1993. I-group grey gurnard Eutrigla gurnardus, poor-cod Trisopterus minutus and whiting Merlanyius inerlangus and 0-group cod Gadus rnorhua were the major fish predators of the 0-group flatfishes. Flatfishes >45 mm total length appeared to have a refuge in size from predation by the fishes sampled. Predation by fishes was shown to be negatively size-selective, concentrated on the smaller size-classes of flatfishes. Smaller individuals were eaten by a greater taxonomic variety and a larger size range of predators than larger flatfishes. Smaller flatfishes'were therefore vulnerable to a larger number of predators. The size distributions of predators affected the pattern of predation because only the larger individuals ate flatfishes. It is therefore proposed that the degree of overlap in the size distributions of predators and prey determine the magnitude of predation. Growth rates and the timing of settlement in any one year will therefore have a considerable influence on predation, with the potential to result in a 'match or mismatch' of predator and prey size distributions.

“…Increased recruitment of plaice has been related to temperature, with good year-classes resulting from cold winters (Harding et al 1978, Zijlstra & Witte 1985. The causal mechanisms are not clear, although decreased predation during the early juvenile stage has been suggested as one of the factors (Bergman et al 1988).…”

Section: Implications For Recruitment Processesmentioning

confidence: 99%

“…The causal mechanisms are not clear, although decreased predation during the early juvenile stage has been suggested as one of the factors (Bergman et al 1988). Egg mortality has been shown to be positively related to temperature (Zijlstra & Witte 1985), which may be due to increased predation at high temperatures. It is not known whether a relationship exists between larval mortality and temperature.…”

Section: Implications For Recruitment Processesmentioning

confidence: 99%

Growth, otolith growth and RNA/DNA ratios of larval plaice Pleuronectes platessa in the North Sea 1987 to 1989

Hovenkamp¹,

Witte²

1991

Somatic growth, otolith growth and RNNDNA ratios of larval plaice were studied in the southern North Sea during the years 1987 to 1989. Somatic growth rates were strongly correlated with seawater temperature. Both otolith growth and RNAIDNA ratios were correlated with somatic growth. Age at metamorphosis declined with increasing temperature, but there was no relationshp between size at metamorphosis and temperature. Development seemed to be more related to temperature than to size. Large between-year differences were observed in the relationship between body size and otolith diameter. Otolith growth indces were used to compare back-calculated otolith growth between years or periods. In general growth was positively related to temperature, but early otolith growth was fastest at intermediate temperatures. It is proposed that the high temperature in 1989 had a negative effect on growth during the early larval stages, but a positive effect on the later stages.