The bottlenose dolphin community of Doubtful Sound features a large proportion of long-lasting associations

More than 12 studies of different bottlenose dolphin populations, spanning from tropical to cold temperate waters, have shown that the species typically lives in societies in which relationships among individuals are predominantly fluid. In all cases dolphins lived in small groups characterised by fluid and dynamic interactions and some degree of dispersal from the natal group by both sexes. We describe a small, closed population of bottlenose dolphins living at the southern extreme of the species' range. Individuals live in large, mixed-sex groups in which no permanent emigration/immigration has been observed over the past 7 years. All members within the community are relatively closely associated (average half-weight index>0.4). Both male–male and female–female networks of preferred associates are present, as are long-lasting associations across sexes. The community structure is temporally stable, compared to other bottlenose dolphin populations, and constant companionship seems to be prevalent in the temporal association pattern. Such high degrees of stability are unprecedented in studies of bottlenose dolphins and may be related to the ecological constraints of Doubtful Sound. Fjords are low-productivity systems in which survival may easily require a greater level of co-operation, and hence group stability. These conditions are also present in other cetacean populations forming stable groups. We therefore hypothesise that ecological constraints are important factors shaping social interactions within cetacean societies.Communicated by D. Watts     

k-ε Predictions of the initial mixing of desalination discharges

Predictions from a k-ε model are compared with recently acquired experimental data from inclined negatively buoyant discharges. The k-ε model is part of a standard computational fluid dynamics package (CFX). Two approaches are taken when implementing the model. One involves using an essentially standard form of the model to predict flow behaviour. The other approach involves calibrating the model, through adjustment of the turbulent Schmidt number in the tracer transport equation, to achieve reasonable predictions for positively buoyant vertical discharges and then applying it to inclined negatively buoyant discharges. While the calibrated approach improves the predictions of some bulk parameters (notably the tracer spread and dilution) when compared to predictions from the standard model, the overall effect on the quality of the predictions is small. Comparisons with experimental data indicate that predictions from both the standard and calibrated simulations compare favourably with trajectory data, but integrated dilution predictions at the centreline maximum height are conservative (mean-integrated concentrations are over-predicted). The standard and calibrated k-ε predictions confirm the importance of buoyant instabilities on the lower (inner) side of the flow, the effects of which are clearly evident in the mean concentration profiles. However, these simulations have a tendency to overestimate the influence of stabilizing density gradients on the upper (outer) side of the flow and are unable to effectively predict the cross-sectional distribution of a tracer. In contrast to a previous study, the above comparisons indicate that predictions of bulk parameters from such models can be poor and indeed are no better than those obtained from relatively simple analytical solutions.     

A farewell to Dr Thomas Knacker (* 29.04.1951 – ? 30.10.2011): scientific contributions and personal memories

Background

The bioaccumulation potential of chemical substances is commonly determined in flow-through fish tests according to the Organization for Economic Cooperation and Development (OECD) technical guideline (TG) 305, aiming at the determination of bioconcentration factors (BCF). Investigations on aquatic organisms have shown a significant positive correlation between the accumulation of a chemical and the lipid content of organisms. Residue levels can thus differ between individuals, species, and size groups depending on their lipid content. BCF values can be normalized by lipid content; however, this requires the use of appropriate extraction techniques to ensure the complete extraction of total lipids from fish/tissue samples. The OECD TG 305 is currently under revision. A literature review was carried out to select preferred methods which shall be included in the updated OECD TG 305 along with a sampling schedule for lipid measurement in fish.

Results

An overview and appraisal of a broad range of lipid extraction methods is presented. Extraction procedures applied in bioaccumulation studies described in the literature and procedures currently used for such studies by governmental, academic, and industrial labs are surveyed. Possible impacts of unsuitable extraction techniques on lipid normalized BCF results were assessed. Default values for BCF normalization commonly used in bioaccumulation studies are described. The effect of differences in residue distribution over different organs and/or lipids on the normalization of BCF values is discussed.

Conclusions

A broad range of procedures for lipid extraction are available. However, only the use of suitable extraction techniques guarantees the complete extraction of total lipids from fish samples in bioaccumulation studies which is required to ensure the correct lipid normalization of BCF values. Preferred methods for inclusion in the updated OECD 305 test guideline as well as a standard schedule for lipid measurements are suggested.     

Detection of technetium-99 in Ascophyllum nodosum from around the Welsh coast

The presence of the radionuclide ⁹⁹Tc in the marine environment is of concern to environmental scientists because of its conservative nature and high concentration factor in commercially valuable species. The brown seaweed Ascophyllum nodosum (Linnaeus) Le Jolis was used to biomonitor the spatial distribution of ⁹⁹Tc around the Welsh coast, an area relatively unstudied with respect to this isotope. Over the course of a year an inverse relationship was observed between the ⁹⁹Tc concentration in A. nodosum samples and approximate straight-line distance from Sellafield. These data show that detectable levels of a Sellafield derived radionuclide are reaching the Welsh coast despite the overall northward movement of the Sellafield plume.     

Mortality factors, helminth burden, and contaminant residues in white-tailed sea eagles (Haliaeetus albicilla) from Finland

Eleven white-tailed sea eagles (WSEs) (Haliaeetus albicilla) collected in Finland between 1994 and 2001 were examined for their causes of death, including analyses of ubiquitous environmental contaminants and parasites. Four WSEs died due to electrocution. Two were lead poisoned and another had fragments of a lead bullet in its gizzard. An 11-year-old female drowned entangled in fishing gear, but also had mercury levels in its liver and kidneys known for detrimental physiological effects. One WSE was evidently killed by an intraspecific conflict, which was also assumed to be with another bird. The mortality factors of two WSEs could not be clarified, but one had a lead level of 4.604 microg g(-1) in its liver, indicating high lead exposure at a clinically relevant concentration. All organ levels of chlorinated pesticides, polychlorinated biphenyls, and cadmium were moderate and not harmful for birds of prey. Seven helminth species, but no ectoparasites or coccidians, were found in 8 of 10 WSEs investigated for parasites. The highest prevalence of 40% was found for the liver fluke Metorchis billis, but no severe parasitosis was diagnosed for the eagles. The two acanthocephalan species Corynosoma semerme and Polymorphus meyeri are both new records for WSEs.