Vertical distributions of 3 size groups of herring larvae Clupea harengus L. in isothermal and stratified waters off the north coast of Scotland were recorded by repetitive sampling, adjacent to dnfting markers, with an opening and closing high-speed plankton net. Concurrent measurements of light intensity at the sea surface, wind velocity and water column hydrography were related to the distributions of larvae by time series analysis. Results indicate that larvae in the size range 6 to 18 mm aggregated to form a layered distribution during the day but dispersed at night. However, the mean depth of the populahon was most strongly influenced by turbulence, especially wind-induced mixing. A predlchve model of larval vertical distribution has been derived.

An individual‐based modelling approach was developed to investigate the spatial and temporal patterns in the recruitment processes of North Sea haddock, Melanogrammus aeglefinus. The approach was based on the realization that the survivors to recruitment of an annual cohort are most probably not drawn at random from the initial population of eggs, but represent the fastest‐growing individuals. Individual growth rates reflect the unique exposure of each larva to the environment along its drift trajectory. In this context, the environment refers to a wide range of factors affecting growth such as food, turbulence and temperature. A combination of a model of egg production by the adult stock, a particle‐tracking scheme, and a model of larval growth and mortality rate was used to simulate the dispersal trajectories, and the survival of haddock larvae spawned at different times and locations on the continental shelf. The particle tracking was driven by flowfields from a climatological implementation of the Hamburg Shelf–Ocean Model (HAMSOM) for the North Sea and NE Atlantic. The system was able to resolve spatial and temporal patterns in the recruitment process and indicated that the surviving population of larvae was drawn from a restricted part of the spawning distribution. The results have the potential to guide the development of future conservation measures in fisheries management.

The large‐scale distribution of haddock (Melanogrammus aeglefinus) larvae in the northern North Sea was mapped in a grid survey carried out in late April 1996. A drifting buoy was deployed in the centre of one of the areas of concentration of larvae located off the east coast of the Shetland Isles, where intensive sampling was carried out for ≈ 10 days. Daily larval haddock growth variability, estimated from otolith microstructure analysis, was independent of the measured variability of the physical and biological environment of the larvae. The survey coincided with the onset of the spring plankton production bloom, and a likely explanation for the absence of environmental effects on larval growth was high food availability and larval feeding rates. Nevertheless, differences in growth were observed between cohorts, with larvae hatched later in the spring displaying higher growth at age than those hatched earlier. Particle‐tracking modelling suggested that differences in temperature history between cohorts, on their own or compounded by a potential interaction between temperature and the development of plankton production, may explain the higher growth rate of the larvae hatched later in the season.

Cenozoic calcareous oozes, chalks and limestones drilled during Leg 7 are mainly biomicrites. Foraminifera, and lesser amounts of radiolarians, are in an abundant matrix of nannofossils and broken foraminifers. The faint parallel lamination and diagenetic changes leading to induration are described and illustrated with photomicrographs.Sediments containing more than 70 per cent calcium carbonate dominate the sequences cored at Sites 62, 63 and 64. A few sections of cores from Site 65 contained about 15 to 40 per cent carbonate. At other Leg 7 sites, sediments generally contain less than 1 per cent carbonate.The carbonates are chalk oozes, chalks and limestones of pelagic origin. With the exception of a few rare foraminiferal turbidite beds in radiolarian ooze sections, the carbonates are dominantly microcrystalline calcite (Figures 1 and 2). The micrite is composed of whole and fragmented coccoliths, discoasters, small fragments of foraminiferal tests, and particles too fine to identify but probably the finest particles of broken nannofossils and foraminifers. Less abundant are whole tests and larger fragments of foraminifers which constitute from 0 to about 40 per cent of the samples in the smear slides and thin sections. Clay, glass shards and other volcanic debris, radiolarian tests, pyrite, and other components are present in varying amounts. These sediments can be classified as biomicrite, calcilutite, or nannofossil (nannoplankton) oozes and chalks.Primary sedimentary structures are common but usually indistinct. Where it can be discerned, bedding is parallel. It can be seen only at lithological boundaries, such as between ash-rich and ash-poor beds, and where textural variation within the carbonate reveal fine lamination. For instance, foraminifer-rich layers 0.5 to 3 millimeters apart can be seen in some thin sections (Figures 3 and 4) or on smoothed surfaces. The fabric of such sediments shows a preferred orientation of the long axes of whole and broken foraminifers that is parallel to the lamination ( Figure 5). These sediments are sparsely packed, that is to say, the sand-sized foraminiferal and radiolarian tests are mainly separated by the micrite matrix and only rarely touch one another (Figures 1, 2 and 5).Mottles are most evident in the younger parts of the carbonate sections, where they show by color contrast rather than by local textural changes. In the upper parts of the holes the oozes are greenish grays, pale purple and light grays, whereas at depth the chalks are whitish greens, white and very pale grays. The rocks of little chroma show few mottles, except for purplish ones, due to pyrite. However, the same rocks have portions where textural and fabric layering is evident adjacent to portions where it is not. The latter portions were probably burrowed, but do not show mottles because of the light color of the rocks.Some of the changes in the sediment with increasing depth in the holes apparently are due to changes in sedimentation with time, and some to diagenesis. The decrease in cl...

A patch of herring larvae Clupea harengus L. was located off Cape Wrath (north coast of Scotland) on 23 Aug 1985 and its movements tracked for 13 d. The trajectory was first eastwards to approximately 3"45'W and then northwards up the west side of the Orkney Isles. Hydrographic, current meter and drifting buoy measurements indicated that significant variation in the circulation regime of the inshore waters between Cape Wrath and the Orkney Isles occurred during the tracking period, and these were clearly reflected in the drift trajectory. Repeated sampling of a fixed line of stations over a 4 mo period from August to November indicated that larvae were retained in the inshore region off the north of Scotland but were rapidly dispersed from areas further offshore.