386-403 Helander.p65

© Royal Swedish Academy of Sciences 2002 Ambio Vol. 31 No. 5, August 2002 http://www.ambio.kva.se INTRODUCTION In this paper, white-tailed sea eagle (Haliaeetus albicilla) and sea eagle are used synonymously. The white-tailed sea eagle population on the Swedish coast of the Baltic Sea has been under strong influence of environmental pollution for decades. Consistent breeding failures over several years among a few well-studied pairs on the Swedish coast were reported in the early 1960s by Olsson (1) and other ornithologists, leading to the start of a nationwide survey in 1964 of the breeding population and its reproductive success. The surveys revealed a strongly reduced reproductive ability and a declining population (2). Retrospective studies of the Swedish Baltic population have demonstrated a significant decline in brood size, starting already in the first half of the 1950s, and a reduction in productivity in the second half of the 1950s and early 1960s to below half of the background level (3). A further decline in productivity to below 25% of the background level occurred during the 1970s (3, 4). Similar poor breeding results were reported for the 1970s also from the Estonian and Finnish coasts of the Baltic (5, 6), indicating a common cause related to the Baltic ecosystem. The alarming drop in the reproductive ability of the sea eagles in the Baltic region shows a strong resemblance to the situation reported for some bald eagle Haliaeetus leucocephalus populations in North America (e.g. 7–12). Colborn (13) suggested a fledgling ratio (mean number of fledglings per successful territory to the mean number of fledglings per active territory) of > 2 as an indicator of exposure to organochlorine chemicals affecting the productivity in the bald eagle. The fledging ratio of the Swedish sea eagle population on the Baltic coast 1965–1984 was in the range 3.4– 5.0, thus indicating a significant exposure to chemicals during that period. Studies on the reproductive ability of individual white-tailed sea eagle females on the Swedish Baltic coast, in relation to the contamination with organochlorine and mercury residues in their eggs, indicated that 2,2-bis(4-chlorophenyl)-1,1-dichloroethene (DDE) had the strongest negative influence on their reproductive capacity (14, 15). Following the ban of DDT use in the countries surrounding the Baltic Sea in the early 1970s, the levels of DDT and its metabolites have decreased significantly in Baltic biota (16, 17). Studies by Koivusaari et al. (18) indicated an increase in productivity on the northern Finnish Baltic coast already in 1974–1978, coinciding with a significant decrease of DDE but no change in the levels of polychlorinated biphenyls (PCB) and mercury in a small sample of sea eagle eggs from that region. In the Swedish population on the central and southern Baltic coast, residue levels in sea eagle eggs also declined, but the average productivity remained at low level throughout the 1970s. As the DDE levels in eagle eggs decreased further during the 1980s and 90s, a substantial improvement in reproductive ability was observed in this population (4, 19). However, in spite of comparatively low levels of DDE in their eggs, some females on the Swedish coast still reproduced very poorly (4). This could be the result of a direct influence from chemical compounds other than DDE in the eggs, or from a remaining effect on the female of a previous exposure to DDE or some other anthropogenic compounds. Studies on the white-tailed sea eagle and its close relative, the bald eagle, have indicated a stronger negative correlation to productivity for DDE than for any other analyzed compound (9, 14, 15, 20–22). A close correlation between the residue levels of DDE and PCB in the samples, however, made it impossible to exclude adverse effects also from the PCBs. The need for research on the effects of specific PCB congeners to clarify their role on reproduction in relation to that of DDE has been emphasized (13). Polychlorinated dibenzo-p-dioxins and furans (PCDD/F) and especially 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are embryo-toxic. The same type of effect is also expressed by specific PCB congeners with one or no chlorine in the ortho-positions (coplanar PCBs). In the Great Lakes of North America, reproduction problems among several bird species have been linked to TCDD-like toxicity (23, 24). A symptom-complex has been described (25) where one of the symptoms is malformation of the avian bills. Such abnormalities have also been observed in nestling bald eagles (26, 27) and white-tailed sea eagles (28). This indicates that the eagles might also suffer from reproduction problems due to substances that express TCDD-like toxicity. In fact, it has been claimed that depressed reproduction in the 1990s among bald eagles on the Great Lakes shoreline and sea eagles on the Finnish Baltic coast was mainly due to the effects of coplanar PCBs (29–31). In this paper, we investigate the role of DDE, PCB, coplanar PCBs and eggshell parameters for the reproductive ability in 3 sub-populations of white-tailed sea eagles in Sweden. To facilitate proper selection of samples, the representativeness of the sampled dead eggs is studied. We also investigate the changes in the PCB-pattern in sampled eggs between time periods. The study is based on eggs collected 1965– Report