ALBERT

Description: Mean intracellular pH (pHi) and PCO2 (PiCO2) have been analysed based on pH and total CO2 measurements in tissue homogenates. Tissues were sampled from undisturbed worms (Sipunculus nudus), squid (Illex illecebrosus), trout (Salmo gairdneri), toads (Bufo marinus), and rats. Homogenate metabolism was inhibited by the addition of potassium fluoride and nitrilotriacetic acid (NTA). Model calculations revealed that the influence of dilution, medium buffers, and contamination by extracellular fluids was negligible. In white muscle tissue the resulting pHi values were virtually the same as found in studies using DMO (dimethyloxazolidinedione). If large fractions of mitochondria were present (e.g. in heart muscle), DMO derived pHi values were considerably higher, probably representing overestimates. Homogenate derived pHi values are concluded to represent the effective mean pHi by taking into account pH gradients, and the volumes and buffering of cellular compartments. High time resolution and small variability make this method especially useful to assess rapid changes in pHi, e.g. in exercising animals.

Description: The growth of “Growing Sealife”™ plastic squid was tested against the principles of the von Bertalanffy growth theory. The von Bertalanffy growth curve fits the data well on visual inspection, although the Schnute curve actually provides a statistically superior fit. If the von Bertalanffy growth curve provides a reasonable fit to data, this is frequently interpreted as evidence for anabolic and catabolic changes. The results of this paper for plastic squid are intended to provide a warning that such an interpretation does not necessarily follow.

Description: Methodology for assessing squid fisheries is presented focusing on the estimation of exploitation rate, stock size and the fishing power of the vessels. The assessment is designed to provide input into management decisions for effort limited fisheries. The fishery for Illex argentinus around the Falkland Islands is used as an example for the methods. The development of a management policy for this fishery is described more fully in a related paper. The methods are based on modifications to standard Leslie-Delury analysis. Various regression methods are utilized depending on the number of fleets for which detailed data are available. The statistical procedures also yield estimates of the standard errors of the estimates for evaluating the assessment advice.

Description: The biology of exploited cephalopod stocks is reviewed. Individual growth rates are high, slowing drastically or becoming erratic at sexual maturity. Growth estimates depend on aquarium studies and population modal analysis. In some cases, ring markings in the statolith appear to be age-related, but at present there is no generally applicable method of age determination. Sexes are separate and fertilization is normally by direct mating. Rapid maturation is followed by a single spawning season and, with few exceptions, an early death. Methods for estimation of fecundity are poorly developed. Annual recruitment to the population is essential and depends critically on each year's breeding success and the survival of eggs and hatchlings. Many cephalopod species have a planktonic stage of variable duration but no specialized larval stages. Cephalopods are carnivorous animals with very high gross growth efficiency. They are also consumed in large quantities by higher trophic levels leading to suggestions that cephalopods are potentially capable of supporting significantly increased levels of exploitation. The difficulties of modelling these populations are recognized

Description: The organization of the chitin-proteoglycan in Loligo vulgaris pen was examined ultrastructurally and related to the molecular order indicated by X-ray diffraction. There is a centrosymmetric striated repeat of 22 nm in the system which is based upon dark and light bands of unequal width. The banding is orientated perpendicular to the direction of the major molecular axis of the chitin fibres. The chitin molecules are laid down in sheets with a mutual, though irregular, twist to produce a laminated ‘plywood’ material.

Description: A deep Seismic reflection profile collected by DEKORP and BELCORP in the western Rhenish Massif was supplemented by wide-angle measurements. Signals from a vibrator source were successfully recorded to a distance of 60 km. A passive recording array was operated that recorded all shots along the profile. The wide-angle and near-vertical data were used to construct a velocity model for the profile. Most of the wide-angle reflections coincide with strong near-vertical reflections or bands of high reflectivity. The North Variscan Deformation Front, seen as a prominent shallow reflection on many profiles in this region, separates an upper crust with rather nigh velocities from a layer with lower velocities underneath. At a depth of 20–22 km a thin (2–3 km thick) layer of high velocities is found. The Moho is not reflective either in the near-vertical or in the wide-angle data, suggesting the presence of a thick crust-mantle transition zone.

Description: Brain pathways controlling the chromatophores of the squidLolliguncula brevis are described using cobalt iontophoresis. The results show several input and output pathways of the anterior and posterior chromatophore and lateral basal lobes. These connections allow coordination and modification of the chromatophore motor program throughout the motor pathway. Unlike other cephalopod species, there seems to be no direct input from the optic lobes to the lateral basal lobes inL. brevis. This species displays only a few simple patterns; therefore the underlying neural pathways for chromatophore control may be different from those of other cephalopods with more extensive patterning repertoires.

Description: The ventilatory system of cephalopods has evolved so that the animals minimise the energetic cost of either oxygen extraction or jet propulsion. Optimal design for jet propulsion requires a large stroke volume moving water through the system with minimal acceleration, so the oxygen-carrying capacity of the ventilatory stream is always greatly in excess of requirements. Oxygen uptake in a jet-propelled animal must be independent of the volume of the jet to avoid locking locomotion to oxygen uptake. Any such link is incompatible with the repayment of an oxygen debt after exercise, with added oxygen demand during digestion, and with regulation of uptake under hypoxic conditions. Cephalopods evolved for efficient jet propulsion must be able to alter the rate of oxygen extraction from the ventilatory stream. Squids and Nautilus do this; oxygen extraction is normally low, in the range 5–10% during jet-propelled cruising at subcritical speeds, but can rise to as much as 25% in acute hypoxia or at rest after exhausting exercise. Other cephalopods, such as Octopus, minimise the cost of oxygen extraction by propelling a minimal volume of water through the gills, extracting 35–50% (exceptionally 75%) of the available oxygen. This leaves little scope for a further increase in extraction, and any added demand is met by increasing the ventilation stroke volume. A consequence is that jet propulsion becomes extravagant; octopuses show much greater jet pressures than squid when they choose to swim. The two alternative specialisations are linked to life-style and cut across systematic boundaries.