Asunción Borrell

Geographical and temporal variation in levels of organochlorine contaminants in marine mammals

The interpretation of the spatial and temporal patterns of variation in organochlorine concentrations in marine mammal populations is complex because of the lack of wide-scale, long-term surveys. Therefore the results from several surveys must be combined and this causes undesired heterogeneity due to differences in the sampling and analytical techniques used and in the biological characteristics of the individuals sampled. Moreover, information is not homogeneously distributed in either space or in time. Most research is concentrated in western Europe, northern America and certain areas of Asia, while it is extremely limited or non-existent in Africa and most regions of the southern hemisphere. Marine mammals from the temperate fringe of the northern hemisphere, particularly fish-eating species which inhabit the mid-latitudes of Europe and North America, show the greatest organochlorine loads; noteworthy are the extremely high levels found in the Mediterranean Sea and certain locations on the western coasts of the United States. Concentrations in the tropical and equatorial fringe of the northern hemisphere and throughout the southern hemisphere are low or extremely low. The polar regions of both hemispheres showed the lowest concentrations of DDTs and PCBs, although levels of HCHs, chlordanes and HCB were moderate to high in the cold waters of the North Pacific. During recent decades, concentrations have tended to decrease in the regions where pollution was initially high but they have increased in regions located far from the pollution source as a consequence of atmospheric transport and redistribution. It is expected that the Arctic and, to a lesser extent, the Antarctic, will become major sinks for organochlorines in the future; this process may already be significant for some compounds such as HCB and HCHs. Effort should be devoted to both assessment of organochlorine trends in the now highly polluted populations of the temperate fringe of the northern hemisphere and to the implementation of long-term monitoring of marine mammal populations inhabiting polar regions.

Patterns of Lipid Content and Stratification in the Blubber of Fin Whales (Balaenoptera physalus)

The lipid content and layering structure of the blubber of 82 fin whales ( Balaenoptera physalus ) caught off Spain were studied in relation to individual biological attributes. The lipid content of the external blubber stratum is stable and shows no apparent variation with age, reproductive status, or day of capture in either sex. This indicates that this stratum does not play a significant role in the dynamics of fat storage in fin whales. The internal stratum, in contrast, is variable, clearly reflecting the nutritive reserves of individuals. The mid-stratum is a transition between the external and internal layers. Reproductive categories are discriminated best by the mean of the values of the three layers than by any of them used independently. For this reason, this mean is proposed as the best index of condition for fin whales. Reproductive status is the main factor determining variation in lipid content of blubber in females, but is meaningless in males. Ranking of blubber fatness for the reproductive categories is: pregnant females > males = immature females > resting females > lactating females. These dissimilarities are explained by the energetic, migrational, and physiological characteristics of the different population components. In males, lipid content of blubber decreased significantly with age, whereas in immature females it increased with age. In both sexes, lipid reserves accrued from early May until mid-August, but tended to decrease afterwards, following variations in food availability. The nutritive condition of lactating females improved during late lactation probably because of increasing food consumption and decreasing energetic demands of suckling young.

PCB pollution continues to impact populations of orcas and other dolphins in European waters

Organochlorine (OC) pesticides and the more persistent polychlorinated biphenyls (PCBs) have well-established dose-dependent toxicities to birds, fish and mammals in experimental studies, but the actual impact of OC pollutants on European marine top predators remains unknown. Here we show that several cetacean species have very high mean blubber PCB concentrations likely to cause population declines and suppress population recovery. In a large pan-European meta-analysis of stranded (n = 929) or biopsied (n = 152) cetaceans, three out of four species:- striped dolphins (SDs), bottlenose dolphins (BNDs) and killer whales (KWs) had mean PCB levels that markedly exceeded all known marine mammal PCB toxicity thresholds. Some locations (e.g. western Mediterranean Sea, south-west Iberian Peninsula) are global PCB “hotspots” for marine mammals. Blubber PCB concentrations initially declined following a mid-1980s EU ban, but have since stabilised in UK harbour porpoises and SDs in the western Mediterranean Sea. Some small or declining populations of BNDs and KWs in the NE Atlantic were associated with low recruitment, consistent with PCB-induced reproductive toxicity. Despite regulations and mitigation measures to reduce PCB pollution, their biomagnification in marine food webs continues to cause severe impacts among cetacean top predators in European seas.

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.

Age- and sex-related changes in organochlorine compound levels in fin whales (Balaenoptera physalus) from the eastern North Atlantic

Abstract Patterns of variation in organochlorine burdens with age and sex in cetaceans are poorly understood and differ between species. This paper presents the results of a survey on fin whales in this respect. Blubber from 166 individuals of known age and sex was analyzed for DDTs and PCBs. In young whales, pollutant burdens in specimens from the two sexes were indistinguishable but, from the onset of sexual maturity, concentrations of all organochlorines increased with age and body size in males and decreased in females. The relationships were not linear and in both cases tended to reach a plateau. The decrease observed in female blubber concentrations is attributed to reproductive transfer, mainly through lactation, and occurs throughout all the females life span, suggesting absence of reproductive senescence in this species. Relative abundance of degraded forms of pollutants increased with age in males and decreased in females. The tDDT/PCB ratio was negatively correlated with age in males and positively correlated in females. Different PCB congeners showed dissimilar trends. All these dissimilarities between sexes in the pattern of accumulation of the different forms of organochlorines are associated with differential activation of microsomal enzymes and with dissimilar transfer rates during reproduction in females. Because of these differences, pollutant burdens in males are characterized by higher levels of pollutants and by higher DDE/tDDT and tDDT/PCB ratios than those for females.

Discrimination of stable isotopes in fin whale tissues and application to diet assessment in cetaceans

RATIONALE In stable isotope research, the use of accurate, species-specific diet-tissue discrimination factors (i.e., Δ(13)C and Δ(15)N) is central to the estimation of trophic position relative to primary consumers and to the identification of the dietary sources of an individual. Previous research suggested that the diet of fin whales from the waters off northwestern Spain is overwhelmingly based on krill, thus permitting reliable calculation of discrimination values in this wild population. METHODS After confirming that the stable isotope ratios (δ(13)C and δ(15)N values) in muscle from 65 aged fin whales remained constant through age classes (4-65 years), the signatures were determined in muscle, bone protein, skin, liver, kidney, baleen plates and brain, as well as food (krill), from a subset of individuals to calculate discrimination factors. Signatures were determined by means of elemental analysis isotope ratio mass spectrometry (EA-IRMS) using a ThermoFinnigan Flash 1112. RESULTS The isotopic values remained constant regardless of age. The mean Δ(15)N values between krill and whale tissues ranged from 2.04 in bone protein to 4.27‰ in brain, and those of Δ(13)C ranged from 1.28 in skin to 3.11‰ in bone protein. This variation was consistent with that found in other groups of mammals, and is attributed to variation in tissue composition and physiology. CONCLUSIONS Because discrimination factors are relatively constant between taxonomically close species, the results here obtained may be reliably extrapolated to other cetaceans to improve dietary reconstructions. The skin discrimination factors are of particular relevance to monitoring diet through biopsies or other non-destructive sampling methods. The large difference in bone protein discrimination factors from those of other tissues should be taken into consideration when bone collagen is used to determine trophic level or to assess diet in paleodietary isotopic reconstructions.

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.

Evaluation of toxicity and sex-related variation of PCB levels in Mediterranean striped dolphins affected by an epizootic

Individual PCB congener concentrations, including non-ortho chloro substituted, were determined in 30 striped dolphins (Stenella coeruleoalba) affected by the 1990-92 Mediterranean epizootic to investigate their toxic potential. PCB congener concentrations in these dolphins were among the highest ever found in comparable studies on marine mammals. Concentrations in males and females were significantly different because of pollutant transfer to offspring by females. Thus, PCB concentrations and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalents (TEQ) in males were approximately double those in females. Non-ortho, mono-ortho and di-ortho coplanar congeners accounted for approximately one third of the overall toxicity assessed through toxic equivalent factors (TEFs), as defined by Ahlborg et al. (1994). Di-ortho congener 170 and non-ortho congener 126 were the major contributors to TEQ (33% and 30% respectively).

Organochlorine compounds in common dolphins (Delphinus delphis) from the Atlantic and Mediterranean waters of Spain.

Blubber of free-ranging common dolphins (Delphinus delphis) from the northwestern coast of Spain (Atlantic), sampled in 1984 and 1996, and of common dolphins entangled in fishing nets in the southwestern Mediterranean, sampled during 1992 1994, was analysed for organochlorine pollutants. In the Atlantic, concentration of all pollutants was significantly higher in males than in females. The overall tPCB/tDDT ratio in this area was 3.35, which indicates a predominance of industrial inputs over those associated with agriculture. Individuals sampled in 1996 showed significantly lower DDT concentrations but a higher ppDDE/tDDT ratio than those sampled in 1984, which reflects the aging of the environmental load. In the same period, tPCB concentration remained constant and, as a consequence, the tPCB/tDDT ratio more than doubled. In the Mediterranean, the reduced sample size of adult individuals precluded proper statistical investigation of sex-related variation. The overall tPCB/tDDT ratio was 1.12, suggesting a higher contribution of pollutants of agricultural origin. Individuals had significantly higher levels of all DDT forms and a higher ppDDE/tDDT ratio than their counterparts from the Atlantic, but similar PCB concentrations. However, the relative frequency of the different congeners in relation to the total PCB load was different in the two areas. This indicates that the two populations do not mix, at least in the short- or medium-term. Organochlorine levels in both areas are at the mid to low end of the range of concentrations detected in other common dolphin populations and in that of other Delphinidae species from the same region. Although the impact of the organochlorine concentrations on the common dolphin populations surveyed cannot be assessed, it is considered unlikely that they have played a significant role in the decline that the species has suffered in recent decades in the western Mediterranean.

Variations in DDE percentage correlated with total DDT burden in the blubber of fin and sei whales

Abstract Total DDT burden and DDE percentage (DDE/DDT+TDE+DDE) in the blubber of fin and sei whales are highly correlated. Total DDT concentration may be an important source of variation for the DDE percentage detected in different individuals of the same population. Such a positive correlation is explained by the intensification of the dehydrochlorinative and differential excretive functions at higher pollutant levels. In the past, variations in the DDE percentage have been attributed to differences in the chronology of DDT input into the ecosystem and assumed to be indicators of population discreteness or changes in the pattern of DDT exposure of a given population. However, changes in the DDE percentage as related to total DDT burden may be important within the observed normal ranges of variation of total DDT residue levels caused by age and sex composition of the population. Therefore, the DDE percentage may be reliably used only when full control of the life history parameters of the sample is achieved and when strict homogeneity among the samples to be compared has been proved.