ALBERT

Description: The free surface version of the GFDL model is used to study inflow and outflow through the Danish Straits, which connect the Baltic with the North Sea. Three problems are addressed: (i) the piling up of inflowing water in the Arkona basin; (ii) the transport ratios between Belt and Sound; (iii) the dominance of hydraulic or geostrophic control. Model results show that a cyclonic eddy (dome) is formed by the inflowing saline water that prevents this water from passing rapidly into the Bornholm basin. This eddy is enforced with increasing inflow due to a sea level difference between Kattegat and western Baltic. If density gradients along the straits are weak and the flow is dominantly driven by sea level differences between Kattegat and Baltic, the well-known ratio of 70% : 30% for the transports through Belt and Sound are confirmed. Strong density gradients can change this ratio considerably, especially in the outflow case, when the light water of the Baltic flows against the heavier water of the Kattegat. Under variable wind conditions, no fixed ratio is found. The flow in the Straits is geostrophically controlled; however, the strong baroclinic density field does not allow us to derive the transport simply from sea level inclination.

Description: For the purpose of this study, 5 311 post recruit of Illex coindetii were collected from the fishery of the Galician shelf, with sizes ranging from 32 to 379 mm dorsal mantle length (ML). Samples were taken monthly from November, 1991 to October, 1992. Sexual maturation, spawning season and population structure of Illex coindetii were analyzed. The spawning season extended throughout the year reaching a peak in July-August, with size at first maturity in males, 128 mm ML and in females, 184 mm ML. Males mature at a smaller size and attain lower size (279 mm ML) than females (379 mm ML). The sex ratio of the whole population sampled was slightly biased towards males, nevertheless monthly variations observed and the ratio obtained (1.09 : 1) does not suggest that there is spatial segregation by sexes in the fishing ground. From the total sample, 185 males and 281 females, covering the whole range of ML's, were randolmy separated out to calculate maturation indices. A correlation between the subjective scales and the values of these indices was established in both sexes. The nidamental gland length proved to be a reliable parameter for distinguishing between stages of maturity in females. The fecundity of the species varied between 3 500 and 285 000 oocytes, (the most frequent range being from 30 000 and 200 000 oocystes) in the ovary and the oviducts. The principal axis in the oviduct contained 2 331 ± 912 eggs. The number of spermatophores in the spermatophoric sac varied between 81 and 1 555, and it was observed that the number and the length of the spermatophores tended to increase with size of the males. Illex coindetii may be considered as an intermittent spawner.

Description: Most cephalopods are voracious and very mobile predators with highly developed sense organs that rival the equivalent vertebrate sense organs in complexity. A brief description is given of cephalopod predation and the sense organs that are directly, or indirectly, involved: (i) the vertebrate‐like lens eyes with their complex extraocular eye muscle system; (ii) the epidermal head and arm lines which are analogous to the lateral lines of fishes and aquatic amphibians; (iii) the vestibular analogue statocysts with receptor systems for linear (gravity) and angular accelerations; (iv) the proprioceptive neck receptor organ which controls head‐to‐body positions; (v) the sucker and muscle mechanoreceptors; and (vi) the contact and distance chemoreceptors. In addition, the possibility of hearing is discussed.

Description: Parasites were collected from 1,200 short-finned squid (Illex coindetii, Todaropsis eblanae) caught as by-catch in a multispecies trawling fishery in the northwest Spanish Atlantic waters in 1992-1993. Parasites found included six species of helmiths, three tetraphyllidean cestodes (Phyllobothrium sp., Pelichnibothrium speciosum, Dinobothrium sp.), two trypanorhyllidean cestodes (Nybelinia yamagutii, Nybelinia lingualis), and one ascarioid nematode (Anisakis simplex B). Two of these parasites (Phyllobothrium sp., A. simplex B) which could be recognised as component species, were used in analyses of host-parasite relationships. Levels of infection varied significantly with host size or stage of maturation for both squid species. Regional variation in infection level seems attributable to geopgraphical variation in variability of prey, discreteness and movements of host populations and to size or age-related changes in the prey selection of their host. Parasite evidences suggest that both ommastrephid squids are sympatric species sharing similar econiches, and serve as diet for large top predators (selachians and marine mammals) of Northeast Atlantic. Parasites may also be useful as an indirect indicator of the migratory habits of the squid.

Description: This study shows that calcium carbonate plays an important role as a cementing agent of various marine sediments. The measured vane shear strength of marine soil samples is shown to vary with depth and is strongly correlated with the calcium carbonate content. The results show that an increase in calcium carbonate of 1% causes an increase in shear strength of about 10 kPa. Moreover, under accumulating self‐weight, consolidation is found to be enhanced by calcium carbonate. It was also found that both the cementation and condensation due to calcium carbonate are the major factors accounting for the strength development of marine sediments, beside consolidation. These effects are often greater than those due to grain size effects.