Ludo Holsbeek

Marine mammals from northeast atlantic: relationship between their trophic status as determined by δ13C and δ15N measurements and their trace metal concentrations

The relationship between trophic position through delta13C and delta15N and trace metal concentrations (Zn, Cd, Cu and Hg) was investigated in the tissues of six marine mammal species from the Northeast Atlantic: striped dolphin Stenella coeruleoalba, common dolphin, Delphinus delphis, Atlantic white-sided dolphin Lagenorhynchus acutus, harbour porpoise Phocoena phocoena, white beaked-dolphin Lagenorhynchus albirostris, grey seal Halichoerus grypus stranded on French Channel and Irish coasts. White-beaked dolphins, harbour porpoises, white-sided dolphins, common and striped dolphins display the same relative and decreasing trophic position, as measured by delta15N values, along both the Irish and French channel coasts, reflecting conservative trophic habits between these two places. Hepatic and renal Cd concentrations were significantly correlated to muscle delta13C and delta15N values while Hg, Zn and Cu did not. These results suggest that Cd accumulation is partly linked to the diet while other factors such as age or body condition might explain Hg, Zn or Cu variability in marine mammals. Combined stable isotope and trace metal analyses appear to be useful tools for the study of marine mammal ecology.

Total and Methylmercury in Sardines Sardinella aurita and Sardina pilchardus from Tunisia

Abstract This paper reports concentrations of total mercury and methylmercury in muscle, liver and gonads of two sardines ( Sardinella aurita, n= 184 and Sardina pilchardus, n= 87) from three coastal areas off Tunisia. Mercury concentration in muscle and liver showed significant positive correlation with fish length (i.e. with age). The relative methylmercury concentration was high and constant in muscle (>85% MeHg), and was decreasing with age in liver (from 50% to 20%), which might reflect the existence of a slow demethylation process. From the geographic point of view, Hg concentration was similar in the northern and eastern areas (0.32 μg g −1 dw in muscle for Sardinella aurita, 0.41 for Sardina pilchardus ) , but significantly lower in the southern zone (0.19 and 0.26, respectively, median values). Mercury concentration in the Tunisian sardines was twice to four times lower than in the northern Mediterranean Sea.

Heavy metals in dolphins stranded on the French Atlantic coast.

Heavy metal concentrations (total and organic Hg, Ti, Cr, Cu, Zn, Cd and Pb) were determined in the muscle, liver and kidney of 36 dolphins stranded on the French Atlantic coast between 1977 and 1990: 29 common dolphins Delphinus delphis, five bottlenose dolphins Tursiops truncatus and two striped dolphins Stenella coeruleoalba. Total Hg concentration in the liver increased with age, while relative methylmercury concentration decreased, reflecting the existence of a slow demethylation process. To a lower extent, a similar pattern was observed in the kidney and muscle. No age-related increase was found for other heavy metals, although the highest levels for Cd and Cr were always found in adults. No difference in contamination could be detected between the 1977-1980 and 1984-1990 periods.

Mercury in human hair and relation to fish consumption in Bangladesh

Human scalp hair mercury concentrations were determined in 219 hair samples from male individuals from different regions of Bangladesh. Total hair mercury concentrations were very low with a mean value of 0.44 +/- 0.19 micrograms Hg/g (range 0.02-0.95) for a moderately elevated fish consumption averaging 2.1 kg/month (range 1.4-2.6). A highly significant positive correlation (r = 0.88, P < 0.001) was found between fish consumption and hair mercury concentration. Neither age, region nor occupation had any influence on the hair mercury content. Our results in agreement with literature values, are described by equation (X = 183Y + 0.16) linking calculated daily methylmercury intake (X, mg) and hair total mercury level (Y, micrograms/g). Low concentrations in hair were linked to extremely low levels of daily mercury intake, the determining factor being remarkably low mercury levels in Bangladesh fish.

Mercury contamination of the harbour porpoise Phocoena phocoena and other cetaceans from the North Sea and the kattegat

Total Hg levels were determined in 17 harbour porpoises Phocoena phocoena collected in the North Sea and the Kattegat (muscle, liver and kidney), as well as in a sperm whale Physeter macrocephalus, a common dolphin Delphinus delphis and two bottle-nose dolphins Tursiops truncatus collected in Belgium. Juvenile porpoises (total body length less than 140 cm) were characterized by total Hg concentrations increasing with length (t.i. with age) with median values of 3.1 μg g−1 dw in muscle, 6.2 in liver and 5.7 in kidney, and liver to muscle resp. liver to kidney ratios varying between 1 and 2. In adults, liver concentrations were higher (up to 500 μg g−1 dw) with liver to muscle and to kidney ratios up to 20. Median McHg concentrations in 5 of the porpoises were 4.0 μg g−1 dw in muscle and 6.9 in liver. These values did not increase as strongly with length (t.i. with age, at least for juveniles) as total Hg did; as a consequence, the relative McHg levels decreased from 100% in juveniles to 2 or 3 % in the liver of adults. Such results seem to reflect the existence of a slow mineralization phenomenon and storage of inorganic Hg, mainly in the liver.

Heavy Metals, Organochlorines and Polycyclic Aromatic Hydrocarbons in Sperm Whales Stranded in the Southern North Sea During the 1994/1995 Winter

Seven male sperm whales stranded on the southern North Sea coast during the 1994/95 winter were analysed for stable pollutant concentrations in muscle, liver, kidney and blubber: heavy metals (total and organic Hg, Se, Zn, Pb, Ni, Cd, Fe, Cr, Cu and Ti), organochlorines (PCBs and pesticides) and polycyclic aromatic hydrocarbons (PAHs). High concentrations of Cd (up to 300 μg/g dw in kidney), Hg (up to 130 μg/g dw in liver) and PCBs (up to 5 μg/g dw in blubber) were detected, but not considered as the direct cause of mortality, while their possible indirect influence on the health status and/or behaviour of the North Atlantic sperm whale population is discussed.

Seabirds and marine mammals in the eastern Barents Sea: late summer at-sea distribution and calculated food intake

Abstract The at-sea distribution of seabirds and marine mammals in the eastern Barents Sea was determined using standardized transect counts during three cruises of RV“Dalnie Zelentsy” (Murmansk) in late summer 1991, 1992 and 1993. Totals of 32,268 seabirds, 485 pinnipeds, 25 cetaceans and 4 polar bears were counted during 554 half-hour counts. Numbers were converted into densities, total biomass and calculated daily food intake. Mean total food intake in kg fresh weight/km2.day was 3.1 for the entire zone and all years; fish eaters dominated the whole region, with an intake of 1.3 (mainly Brünnich’s guillemot, Uria lomvia, and harp seal, Phoca groenlandica), followed by zooplankton eaters (0.85, mainly fulmar, Fulmarus glacialis) and mixed zooplankton and fish feeders (0.75, mainly minke whale, Balaenoptera acutorostrata, and kittiwake, Rissa tridactyla). Year-to-year variations were of little importance, while geographic differences were obvious between Norwegian coastal, Atlantic and Barents Sea water masses, both quantitatively and qualitatively (relative importance of main diets). Within each zone, a strong geographic heterogeneity was noted, with high local concentrations at fronts between water masses and at ice edges.

Total and organic mercury in the starfish Ctenodiscus crispatus and the polychaete Maldanes sarsi from the Barents Sea

Total and organic mercury concentrations were measured in starfish (n = 116) and in polychaetes (n = 30) as a part of a broader ecotoxicological study of the Barents Sea. Total mercury concentration in starfish from the open sea was similar in both Arctic (0.2 μg/g dry wt.) and Atlantic (0.2 μg/g dry wt.) water masses but was higher in the samples from the coast of Novaya Zemlya (0.3 μg/g dry wt.). Though there was no difference in total mercury concentration between polychaete and starfish from the coast, there was a difference in speciation: the polychaetes had a higher percentage of methyl mercury (100%) compared to the starfish (3%). Total mercury concentration in these Barents Sea benthic invertebrates (0.25 μg/g dry wt.) was higher than in pelagic fish (0.07 μg/g dry wt.) but similar to demersal fish and particulate matter (0.25 μg/g dry wt.). They were all considered as close to pristine values.

Diurnal and Seasonal Variation in the Behaviour of Bottlenose Dolphins (Tursiops truncatus) in Bahía San Antonio, Patagonia, Argentina

Diurnal and seasonal patterns in the behaviour of a small population of bottlenose dolphins were assessed in Bahia San Antonio (BSA), Patagonia, Argentina, between 2006 and 2011. Results indicated that dolphins used the study area mainly to rest, travel, and forage, with a marked diurnal and seasonal pattern in their activity. During the early morning, most dolphin groups were resting, while towards the afternoon and evening, surface feeding and social activities peaked. During winter, social activities and surface feeding increased notably; during summer, diving behaviour reached its peak, presumably associated with a tail-out/peduncledive foraging strategy. The observed seasonal variation in foraging strategies is hypothesised to be related to the seasonal behavioural changes of prey species in the area that are linked to spawning. The variation in group size further appears to reflect the regulation of feeding competition while reconfirming the low predation risk within the study area. Results of this study indicate the behavioural and social flexibility of bottlenose dolphins in BSA and suggest a link to the seasonal variations in prey availability. Considering the general bottlenose dolphin population declines in Argentina presumably related to prey depletion, it could be argued that the temporal occurrence of spawning shoals and a general low presence of other top predators directly and indirectly make this a favourable area for this population. Additional information is required to more comprehensively address this hypothesis. The information presented herein serves as vital baseline data for future conservation management protocols.