ALBERT

Description: Temperature and ration level can differentially affect growth and life history characteristics of marine organisms. In this experiment we reared juvenile cuttlefish, Sepia elliptica, under two feeding regimes (satiation and half satiation) and two temperature regimes (25 and 30°C). This study examined differences in somatic growth, muscle tissue structure and composition as a function of temperature and food levels. We estimated body mass and the concentration of water, carbohydrate, protein and lipid in the mantle muscle tissue for each individual. Both high water temperature and high feeding rations increased growth rates. Temperature appeared to change the rates of muscle fibre generation and fibre growth similarly. In contrast, the ration level altered the relative rates of fibre production and fibre growth. The muscle tissue of individuals reared at 30°C had higher concentrations of carbohydrate and protein. In contrast, increasing ration levels only increased carbohydrate concentrations in the muscle tissue. The muscle tissue of reared juveniles had lower concentrations of carbohydrate and protein than wild individuals of similar size. In conclusion, water temperature and feeding levels both affect somatic growth, but the nature of the effect at the sub-organismal level differs.

Description: Three hundred and fifty individuals of 12 species of cephalopods which differed in their feeding habitats were sampled from the French Atlantic coast to the sub-Arctic region (Bay of Biscay, English Channel, west Irish coast and Faroe Islands) and analysed for their cadmium contents. Comparison of the Cd levels of the cephalopods showed that those from the sub-Arctic area contained very high Cd concentrations compared to those from lower latitudes such as along the French Atlantic coast. High Cd levels in cephalopods from the sub-Arctic zone correspond closely to the reported high Cd concentrations in the tissues of top vertebrate predators from the same area. Comparison of the weekly Cd intakes for the Faroe Island pilot whales with the `Provisional Tolerable Weekly Intake' for humans recommended by the World Health Organisation, showed that top vertebrate predators are often subjected to Cd doses far in excess of those recommended for humans. Our limited survey results suggest that cephalopods constitute an important source of Cd for cephalopod predators, and that this bioaccumulation effect is most evident at high latitudes.

Description: Large numbers of seabirds are killed each year within the Australian Fishing Zone (AFZ) by Japanese longline vessels targeting tuna. In recent years the estimated rate of seabird bycatch in the AFZ has been in the order of 0.15 birds/1000 hooks, translating to mortalities of 1000–3500 birds per year. These estimates are absolute minima because not all birds killed remain on hooks to be observed hauled aboard the vessels. The observed seabird catch rate varies annually, seasonally and spatially. Most birds are killed: (a) during the summer fishing season (October to March), even though most fishing effort occurs in winter; (b) when longlines are set during the day; (c) in the waters around southern Australia. Uncertainties in the observed catch rates prevent confident assessment of trends, but seabird catch rates do not appear to be showing a sustained decrease. The process of the incidental collection of seabird bycatch data (by observers whose priority is to fish sampling tasks) renders the seabird bycatch data inadequate for reliable assessment of trends in total numbers of birds killed over time. Sixteen seabird species of birds killed on longlines in the AFZ have been identified. These include black-browed (Diomedea melanophris), shy (D. cauta), grey-headed (D. chrysostoma), yellow-nosed (D. chlororhynchos) and wandering albatrosses (D. exulans), flesh-footed shearwaters (Puffinus carneipes) and white-chinned petrels (Procellaria aequinoctialis). Seventy-four per cent of birds killed were albatrosses and the species composition of the bycatch varied with seasons and areas. Most species of birds killed were characterised by unequal representation of sex and age cohorts, and these unequal representations were not consistent between fishing grounds or seasons.

Description: Some aspects of the biology and fishery of Octopus vulgaris caught by trawlers in the Balearic Sea (Western Mediterranean) are studied. The analysis of the size–frequency distribution followed the growth of specimens from January (6–7 cm ML) to August (11–12 cm ML). The sex ratio was estimated for each season and it was not significantly different from 1 : 1 in any of them. The stomach contents revealed that the octopus fed predominantly on crustaceans and fishes. Another octopus species, Eledone moschata, is present in this fishery but its catches were clearly lower than those of O. vulgaris. The analysis of the importance of these two species in relation to the rest of the commercial catch showed that octopuses represent between 20–40% of the total catch for trawlers. The highest catch rates (kg/h) were obtained in spring and at the beginning of summer. Time-series analysis of monthly catches from January 1981 to August 1996 showed two main oscillations. The lower one, with a periodicity of 12 months, reflects the annual biological cycle of the species; on the other hand, the higher one has a periodicity of 92 months, the time series available being too short to confirm the significance of this period.

Description: The cuttlefish Sepia pharaonis (maximum 250 mm mantle length, ML) and S. dollfusi (maximum 150 mm ML) are widely distributed in the Indo-Pacific from the Red Sea to Japan and Australia. They are the primary fishery in the Suez Canal and the most valuable commercial cephalopods in the northern Indian Ocean. However, their reproductive biology, essential for fishery management, is poorly known. Four maturity stages were described using morphology and histology. Based on the proportions of each maturity stage, as well as various maturity indices, spawning was found to take place from March to June for S. pharaonis and January to April for S. dollfusi. The size at maturity for S. pharaonis was 61 and 122 mm ML for males and females, respectively. In contrast, the size at maturity for S. dollfusi was similar in both the sexes (75 and 84 mm ML for males and females, respectively). Fecundity was estimated by counting the number of maturing and mature ova, which varied from 75 to 1525 for S. pharaonis and 30 to 273 for S. dollfusi. The monthly size-frequency distribution of ova provides evidence for the accuracy of the fecundity estimates. The data suggest that reproduction extends over ≈6–9 months; this probably represents the latter 1/2–2/3 of the life cycle, and may be typical for sepioid and teuthoid cephalopods.

Description: The feeding ecology of Greenland halibut (Reinhardtius hippoglossoides) on the deep slope of the northeast Newfoundland continental shelf was investigated based on stomach analysis. Stomach samples were collected from the spring 1992 Canadian bottom trawl fishery at depths of 1000–1250 m. The squid, Gonatus spp., predominated in the diet, representing the first known instance of reliance of Greenland halibut upon this bathypelagic squid as prey in Canadian waters. A change from predation primarily upon pelagic prey, reported in earlier studies, may be related to annual variability in abundance and distribution of both Greenland halibut and its principal pelagic fish prey species, capelin (Mallotus villosus). Seasonal effects may account for the absence of epipelagic, juvenile Gonatus spp. from the diet. There was a linear size relationship in observed predation which may reflect a common size-related depth distribution pattern between predator and prey or, more likely, prey selectivity. At larger sizes, Greenland halibut switched from Gonatus spp. to groundfish as its principal prey. The importance of Gonatus spp. in the deep continental slope trophic web is reviewed.

Description: A small-scale trap fishery for many benthic species is carried out along the coastal shelves of the Canary Islands (Central-East Atlantic) by small boats (7.5 to 12.4 m in length). The target species of the fishery are seabreams (Sparidae), but substantial numbers of octopus (Octopus vulgaris) are also landed. In this paper, we report fishing data for octopus landed at the port of Mogán (Southwest of Gran Canaria) from 1989 to 1996. The landing of O. vulgaris increased steadily from 1989 to 1994, from 7 t to 25 t. However, in 1995, the catch fell to the level of 1989 (7 t), and in 1996 was only 6 t, the lowest figure for the decade. The CPUE shows two seasonal peaks of maximal abundance, one in April–May and the other in September–November, both coinciding with reproductive periods, while the lowest figure is in summer (July–August). We describe the fishing methods and the seasonal variations of the catch records and fishing effort in relation to years and market strategies.

Description: The sedimentary structure preserved within the seabed of Eckernförde Bay was investigated together with the oceanographic processes influencing that structure. A series of four cruises were undertaken during winter to summer conditions. An instrumented tetrapod was deployed to monitor boundary-layer processes controlling sediment transport. Coring devices recovered sediment to examine the benthic biological community, to measure rates of sedimentological processes, and to document sedimentary structure. During fair-weather conditions, the dominant mechanism for supplying sediment to Eckern-förde Bay is import from the Baltic Sea associated with internal waves. Earlier work has documented the erosion of shallow deposits during storms and the transport of this material to deeper sites in the Bay. Bottom shear stresses exerted in the Central Basin during all conditions are below critical stresses, which makes the Bay an excellent sediment trap. Sediment from both distant and local origins is reworked in the Central Basin of Eckernförde Bay by a pioneering community of benthic organisms, which is maintained by seasonal hypoxia/anoxia. The population is characterized by few species, small body sizes, young ages, and limited depth of mixing (∼1 cm). However, the community effectively pelletizes most of the sediment reaching the seabed. The very restricted thickness for the surface mixed layer (∼1 cm) and the substantial sediment accumulation rates (mean of 0.39 cm yr-1 for the Central Basin) give sediment a short exposure to modern oceanographic processes before being buried. These conditions allow for partial preservation of sediment deposited as storm layers, thus forming laminations of unpelletized sediment. These laminations separate thick beds of pelletized sediment deposited during fair weather or as thin storm layers (i.e., 〈1 cm thick). In general, the oceanographic processes in Eckernförde Bay allow for preservation of a high-resolution record of environmental processes. For example, changes recorded for the past half century indicate that slower sediment accumulation rates previously characterized some portions of the study area.

Description: Methane gas bubbles, generated by biochemical processes, are ubiquitous in the organic-rich, muddy sediments of coastal waters and shallow adjacent seas. Seismic surveys have provided considerable information on the spatial distribution of these gassy sediments. The basic biogeochemical processes responsible for methane generation and consumption are well known and models of acoustic and mechanical behavior of gassy sediments have been developed and tested under laboratory conditions. In spite of the considerable past effort, methane bubble distribution and concentration and the resultant sediment behavior have remained unpredictable prior to the studies described herein. This special issue of Continental Shelf Research describes the results of joint US/German led experiments designed to physically characterize and model the effects of benthic boundary layer processes on seafloor structure, properties, and behavior in the gassy sediments of Eckernforde Bay, Baltic Sea. Spatial and temporal distribution of the acoustic turbidity horizon, methane concentration, and the volume, size, shape, and distribution of bubbles are described for the first time. A kinetic model of the complex biochemical interactions of bacterial methane production and consumption, advective and diffusive transport processes, organic supply, and sedimentation rates has successfully been used to predict methane and sulfate concentration profiles, rates of biogeochemical reactions, and gas volumes. The spatial distribution and strength of acoustic turbidity is accurately predicted by these biochemical models, whereas the seasonal migration of the acoustic turbidity horizon correlates with changes in sediment temperature and is modeled using methane solubility. Short-term ebullition of methane from the sediment surface correlates with rapid change in bottom pressure or an increase in hydraulic flow from subbottom aquifers. Fine-scale characterization of bubble volume, shape, and size distribution coupled with concomitant in situ measurement of sound speed, attenuation, and scattering strength has allowed validation of frequency dependent acoustic scattering and propagation models. Eckernforde Bay is without doubt the most studied and well-understood area of gassy sediments and as such provides a 'natural laboratory' for future studies.