Peter J.H. Reijnders

Inter-species differences for polychlorinated biphenyls and polybrominated diphenyl ethers in marine top predators from the Southern north Sea: Part 1. Accumulation patterns in harbour seals and harbour porpoises

Harbour porpoises (Phocoena phocoena) and harbour seals (Phoca vitulina) are two representative top predator species of the North Sea ecosystem. The median values of sum of 21 polychlorinated biphenyl (PCB) congeners and sum of 10 polybrominated diphenyl ether (PBDE) congeners were 23.1 microg/g lipid weight (lw) and 0.33 microg/g lw in blubber of harbour seals (n=28) and 12.4 microg/g lw and 0.76 microg/g lw in blubber of harbour porpoises (n=35), respectively. For both species, the highest PCB concentrations were observed in adult males indicating bioaccumulation. On the contrary, the highest PBDE concentrations were measured in juveniles, likely due to better-developed metabolic capacities with age in adults. A higher contribution of lower chlorinated and non-persistent congeners, such as CB 52, CB 95, CB 101, and CB 149, together with higher contributions of other PBDE congeners than BDE 47, indicated that harbour porpoises are unable to metabolize these compounds. Harbour seals showed a higher ability to metabolize PCBs and PBDEs.

Individual-Based Model Framework to Assess Population Consequences of Polychlorinated Biphenyl Exposure in Bottlenose Dolphins

Marine mammals are susceptible to the effects of anthropogenic contaminants. Here we examine the effect of different polychlorinated biphenyl (PCB) accumulation scenarios on potential population growth rates using, as an example, data obtained for the population of bottlenose dolphins from Sarasota Bay, Florida. To achieve this goal, we developed an individual-based model framework that simulates the accumulation of PCBs in the population and modifies first-year calf survival based on maternal blubber PCB levels. In our example the current estimated annual PCB accumulation rate for the Sarasota Bay dolphin population might be depressing the potential population growth rate. However, our predictions are limited both by model naivety and parameter uncertainty. We emphasize the need for more data collection on the relationship between maternal blubber PCB levels and calf survivorship, the annual accumulation of PCBs in the blubber of females, and the transfer of PCBs to the calf through the placenta and during lactation. Such data require continued efforts directed toward long-term studies of known individuals in wild and semi-wild populations.

Harbour porpoises (Phocoena phocoena) and wind farms: a case study in the Dutch North Sea

The rapid increase in development of offshore wind energy in European waters has raised concern for the possible environmental impacts of wind farms. We studied whether harbour porpoise occurrence has been affected by the presence of the Dutch offshore wind farm Egmond aan Zee. This was done by studying acoustic activity of porpoises in the wind farm and in two reference areas using stationary acoustic monitoring (with T-PODs) prior to construction (baseline: June 2003 to June 2004) and during normal operation of the wind farm (operation: April 2007 to April 2009). The results show a strong seasonal pattern, with more activity recorded during winter months. There was also an overall increase in acoustic activity from baseline to operation, in line with a general increase in porpoise abundance in Dutch waters over the last decade. The acoustic activity was significantly higher inside the wind farm than in the reference areas, indicating that the occurrence of porpoises in this area increased as well. The reasons of this apparent preference for the wind farm area are not clear. Two possible causes are discussed: an increased food availability inside the wind farm (reef effect) and/or the absence of vessels in an otherwise heavily trafficked part of the North Sea (sheltering effect).

Population development of harbour seals Phoca vitulina in the Wadden Sea after the 1988 virus epizootic

Abstract The mortality as a result of the 1988 virus epizootic amongst harbour seals Phoca vitulina in the North and Baltic Seas is estimated at 60% in the entire Wadden Sea. In the years 1989–1994, a prosperous recovery of the population has been observed which is reflected in a high post-epizootic rate of increase. The average annual rate of increase for the entire area was 16%, highest in The Netherlands (average 21%) and lowest in Denmark (average 10%). This rate of increase is significantly higher than in the pre-epizootic period 1976–1987, when the population increased at a rate of around 9% per year. The difference is partly attributed to a considerably lower initial juvenile mortality after the epizootic. The present first-year mortality is statistically significantly lower than in the 1970s. It is about equal in all regions and estimated at approximately 40%, whereas it was approximately 65% in the 1970s. The post-epizootic reproductive rate in The Netherlands is significantly higher: 21% on average, against 13% before 1988; it is also higher in Niedersachsen (21 vs. 16%), but lower in Schleswig-Holstein (19 vs. 23%), while in Denmark it has not changed (both 17%). It is hypothesised that the improved reproductive rate in The Netherlands might be a result of selective mortality during the epidemic, which within the adult female segment would have predominantly affected those not reproducing. It is emphasised that though the population is recovering well, its size of almost 8800 animals in 1994 is still only one quarter of an estimated reference figure of 37 000 seals around 1900. How long the recovery will continue at its present rate depends on environmental conditions in the area, such as pollution, disturbance and food resources; nor can a recurrent flickering of the epidemic be excluded.

Pollution and Marine Mammals

Publisher Summary Awareness of the threat of environmental contaminants to marine mammals is widespread. A high concentration of certain compounds in the tissues of these animals has been associated with organ anomalies, impaired reproduction, and immune function. This has prompted alertness about the impact of pollution and stimulated research into the relationship between observed effects and pollutants. The main reasons for the lack of proof of the impact of pollution on marine mammals are the difficulty or impossibility of experimenting in laboratory conditions with these animals, and the frequent occurrence of confounding factors that hamper the establishment of cause–effect relationships. The concept of pollution incorporates many different substances to which marine mammals are exposed and might adversely affect their health. These include chemical compounds, oil-pollution-derived substances, marine debris, sewage-related pathogens, excessive amounts of nutrients causing environmental changes, and radionuclides. Pollution is only one of the many environmental factors that influence the health status of marine mammals. Natural environmental variations such as redistribution of planktonic organisms may bring changes in distribution, abundance, or recruitment of the species that constitute the food of marine mammals. Habitat may be disturbed by a wide range of human activities, including recreation, construction works, and many others. Some persistent chemicals are bioaccumulative and their concentrations in living organisms undergo a progressive amplification through food chains, a process called biomagnification. The impact of pollution on marine mammals can occur throughout the entire chain from exposure, uptake, and metabolism to excretion. Concentration in prey is a determining factor.

Recruitment in the harbour seal (Phoca vitulina) population in the Dutch Wadden Sea

Abstract During 1974 to 1978 population dynamics of the harbour seal population in the Dutch Wadden Sea have been studied. Frequent aerial surveys provided data upon the size of the population. During boat trips information about the age composition was obtained by measuring track widths. These data have been used in a simulation model to calculate the birth rate and the initial juvenile mortality. It was found (1.) that the initial juvenile mortality in the Dutch population is higher than that in Schleswig Holstein; (2.) that pup production in the Dutch population is low compared to the population in Schleswig Holstein if the ratio adult females to males in the Dutch population is supposed to be equal to that in Schleswig Holstein, or that mortality amongst adult females in the Dutch population is higher than in Schleswig Holstein; (3.) that the number of subadults in the Dutch population is relatively high compared to a stable population (Schleswig Holstein) and that apparently immigration from elsewhere occurs; (4.) that the reproductive rate was higher or the juvenile mortality lower during 1974 to 1978 than in the preceding decennium.

Status of grey seals along mainland Europe from the Southwestern Baltic to France

An air bag inflator (10) includes inflation fluid stored in a chamber (18). The inflator (10) includes a combustible sheet member (100) which comprises an oxidizable substrate, such as a polytetrafluoroethylene film, and a layer of a fuel material, such as magnesium, on the substrate. The combustible sheet member (100) is disposed in a perforated tube (90) in the chamber (18). The combustible sheet member (100), when ignited by an igniter (70), emits combustion products through openings (98) in the perforated tube (90) to warm and increase the pressure of the inflation fluid in the chamber (18). The inflation fluid includes 5% to 20% oxygen to support the combustion of the combustible sheet member (100).

On the extinction of the Southern Dutch harbour seal population

Abstract The harbour seal population in the southern part of the Netherlands, the Delta area, has decreased sharply since about 1953. Causes for the observed decrease, such as hunting pressure, habitat limitation through construction works, disturbance and water pollution, are discussed. As in the Wadden Sea, where the seal population has been studied more intensively, the initial sharpest decrease was caused by overhunting, probably followed by the impact of pollution. Construction works have had a secondary effect, as by the time these began, numbers were already very much reduced.

Earlier pupping in harbour seals, Phoca vitulina

The annual reproductive cycle of most seal species is characterized by a tight synchrony of births. Typically, timing of birth shows little inter-annual variation. Here, however we show that harbour seals Phoca vitulina from the Wadden Sea (southeast North Sea) have shortened their yearly cycle, moving parturition to earlier dates since the early 1970s. Between 1974 and 2009, the birth date of harbour seals shifted on average by −0.71 d yr−1, three and a half weeks (25 days) earlier, in the Dutch part of the Wadden Sea. Pup counts available for other parts of the Wadden Sea were analysed, showing a similar shift. To elucidate potential mechanism(s) for this shift in pupping phenology, possible changes in population demography, changes in maternal life-history traits and variations in environmental conditions were examined. It was deduced that the most likely mechanism was a shortening of embryonic diapause. We hypothesize that this could have been facilitated by an improved forage base, e.g. increase of small fishes, attributable to overfishing of large predator fishes and size-selective fisheries.

The Influence of Topographic and Dynamic Cyclic Variables on the Distribution of Small Cetaceans in a Shallow Coastal System

The influence of topographic and temporal variables on cetacean distribution at a fine-scale is still poorly understood. To study the spatial and temporal distribution of harbour porpoise Phocoena phocoena and the poorly known Risso’s dolphin Grampus griseus we carried out land-based observations from Bardsey Island (Wales, UK) in summer (2001–2007). Using Kernel analysis and Generalized Additive Models it was shown that porpoises and Risso’s appeared to be linked to topographic and dynamic cyclic variables with both species using different core areas (dolphins to the West and porpoises to the East off Bardsey). Depth, slope and aspect and a low variation in current speed (for Risso’s) were important in explaining the patchy distributions for both species. The prime temporal conditions in these shallow coastal systems were related to the tidal cycle (Low Water Slack and the flood phase), lunar cycle (a few days following the neap tidal phase), diel cycle (afternoons) and seasonal cycle (peaking in August) but differed between species on a temporary but predictable basis. The measure of tidal stratification was shown to be important. Coastal waters generally show a stronger stratification particularly during neap tides upon which the phytoplankton biomass at the surface rises reaching its maximum about 2–3 days after neap tide. It appeared that porpoises occurred in those areas where stratification is maximised and Risso’s preferred more mixed waters. This fine-scale study provided a temporal insight into spatial distribution of two species that single studies conducted over broader scales (tens or hundreds of kilometers) do not achieve. Understanding which topographic and cyclic variables drive the patchy distribution of porpoises and Risso’s in a Headland/Island system may form the initial basis for identifying potentially critical habitats for these species.