Contaminant Burdens in Scaup


Dr. Scott Petrie, Long Point Waterfowl Excutive Director
Dr. Shannon Badzinski, Long Point Waterfowl Scientist

Long Point Waterfowl initiated its scaup research program in 1999 in response to declining continental scaup populations and the fact that little was known about the staging or wintering ecology of Lesser or Greater Scaup using the lower Great Lakes region. The continental scaup population began declining in the mid-1980s which corresponded with the period in which the number of staging and wintering scaup using in the lower Great Lakes increased substantially, presumably in response to the expansion and proliferation of Zebra and Quagga mussels (hereafter Dreissenid mussels). At Long Point, we have found that both Lesser and Greater scaup consistently include zebra mussels in their diets. Further, waterfowl days (an index of waterfowl use of an area) for scaup at Long Point rapidly increased from 58,000 in 1987, prior to the zebra mussel colonization of Long Point, to over 5 million in 1999.

Several hypotheses were formulated by waterfowl experts to explain the long-term population decline and its apparent lack of recovery. This is when Long Point Waterfowl began to investigate the zebra mussel’s new role in the Lesser Scaup’s diet. The zebra mussel is a non-native bivalve that was introduced to Lake St. Clair in 1986, probably through the dumping of ship ballast water. In the absence of natural predators and with limited competition, zebra mussels rapidly increased in numbers and expanded their range throughout the Great Lakes. Studies have since reported densities in excess of 200,000 individuals per square metre in some portions of Lake Erie and Lake St Clair. Meanwhile, native bivalves, which averaged 10 individuals per square metre prior to zebra mussel colonization, have been almost completely displaced by this highly competitive species. Consequently, zebra mussels now dominate the benthic community and they have substantially increased the bivalve availability to staging waterfowl.

This may be problematic, because zebra mussels are filter feeders and they accumulate sediment and contaminants [eg. polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs)] into their tissue more readily than native bivalves. These contaminants can then be passed up the food chain to the waterfowl that consume them. For instance, when fed contaminated zebra mussels, the closely related Tufted Duck has been shown to lay fewer and smaller eggs, with reduced hatchability and increased organochlorine levels. Smaller ducklings were also produced, and adult female mortality increased. Therefore, the consumption of large quantities of zebra mussels on the lower Great Lakes may be contributing to the continental scaup decline. The number of juveniles as well as adult female Lesser Scaup have declined in the United States duck hunt, suggesting that adult female survival and/or reproductive rates have declined.

In response to this concern, Long Point Waterfowl collected scaup from hunters on lakes Ontario, Erie and St. Clair during fall 1999 and spring 2000.

These birds were analysed for :

1) types and levels of contaminants and heavy metals within liver, kidney and muscle tissue
2) body condition (levels of fat, protein and calcium)
3) dietary intake

Zebra mussels themselves were also be analysed for contaminants and heavy metals. After careful analysis, Long Point Waterfowl documented that Scaup using the Canadian and US sides of the lower Great Lakes consistently consumed Dreissenid mussels and acquired liver selenium concentrations high enough to cause reproductive impairment in captive Mallards. In the mid-2000s, Long Point Waterfowl initiated a long-term satellite telemetry project to obtain more information on migration of scaup from the lower Great Lakes, specifically to determine how much time during spring female Lesser Scaup had available to depurate selenium prior to egg-laying. Hypothetical calculations based on departure selenium burdens in lower Great Lakes females, time spent in migration between the lower Great Lakes and presumed breeding locales and published data on nest initiation times corroborated contaminant burden studies on the breeding grounds that selenium in most birds was below levels associated with reproductive problems. Similarly, a collaborative study Long Point Waterfowl undertook with researchers from Simon Fraser University and the US Geological Survey Alaska Science Center provided more evidence that selenium likely was not a major factor affecting female Greater Scaup body condition, breeding propensity, or egg/young development after arrival at a major breeding area at the Yukon-Kuskokwim Delta, Alaska.

Much of Long Point Waterfowl’s student- based research during the mid to late 2000s focused on what effects elevated selenium burdens have on health and survival of staging and wintering Lesser and Greater Scaup. Lindsay Ware’s M.Sc. research showed that nearly all Greater Scaup wintering at Hamilton Harbor, Lake Ontario had elevated liver selenium levels, but those burdens did not seem to cause individuals to have reduced body condition nor exhibit signs of oxidative stress or visual indicators showing impoverished health. Caroline Brady’s M.Sc. research was designed to determine overall health, body condition, and survival of scaup that hypothetically arrive in fall and spend the fall, winter and spring on the lower Great Lakes. Caroline’s captive study showed that even individuals that were fed selenium at concentrations much higher than typically available in foods from the lower Great Lakes had acquired very high liver selenium burdens and had high survival rates that were similar to birds in control (background selenium in food) and intermediate (selenium normal for lower Great Lakes scaup foods) selenium dosage groups. Somatic fat reserves were lower in high dosage birds after 10 weeks of selenium exposure (analogous to a fall-staging period on the lower Great Lakes), but similar to control and intermediate birds after 23 weeks (end of winter period) exposure. Indices of oxidative stress and immune responses and other visual measures of overall health also were not negatively affected by increased selenium burdens. Based on Long Point Waterfowl’s research (and that done by others to date), it seems that selenium, at least by itself, likely is not a major or widespread factor affecting population dynamics of Lesser or Greater Scaup.

Long Point Waterfowl’s scaup research initiative has provided a wealth of information with respect to the contaminants hypothesis and in amassing evidence against selenium as a major contributing factor to the scaup problem in North America. Long Point Waterfowl’s scaup satellite telemetry project remains active and will provide novel information about migration pathways and macrohabitat use of birds that typically use the lower Great Lakes during migration. Data from the 46 scaup implanted with satellite transmitters during springs 2005-2008, along with 10 additional birds implanted at Lake Erie in spring 2010, will also be used to evaluate timing of May Waterfowl Breeding Population and Habitat Surveys with respect to scaup migration in a collaborative study with Dr. Al Afton of the US Geological Survey and Louisiana State University.

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