Winter severity affects migration and contaminant accumulation in northern Great Lakes Herring Gulls

Herring Gull band returns were analyzed from 1962 to 1995. Winter severity was found to affect the winter distribution of Herring Gulls banded as flightless chicks on colonies in northern Lake Huron and northern Lake Michigan. The effects of winter severity were most pronounced in adults, followed by immatures. Little response was observed in juveniles. In adults, the proportion of band returns from southerly locations increased in response to increased winter severity. In general, concentrations of organochlorine contaminants in Herring Gull eggs collected annually from northern Great Lakes colonies increased with winter severity. However, the significance of the relationship between winter severity and organochlorine concentration was compound and colony specific. This probably reflected intercolony differences in winter migration patterns with concomitant differences in contaminant exposure during the overwintering period. With increased winter severity, gulls migrated to more contaminated southerly Great Lakes locations. After spending the winter in these areas the birds returned to their breeding colonies, transferring contaminants to their eggs. The degree to which Herring Gull eggs laid on colonies located in the northern Great Lakes reflect local contaminant bioavailability will be affected by winter severity and overwinter migration patterns

Comprehensive re-analysis of archived herring gull eggs reconstructs historical temporal trends in chlorinated hydrocarbon contamination in Lake Ontario and Green Bay, Lake Michigan, 1971-1982

Herring gull egg homogenates collected between 1971 and 1982 from a colony in central Lake Ontario (Scotch Bonnet Island) and from a colony in central Green Bay, Lake Michigan (Big Sister Island) were archived in the Canadian Wildlife Service Specimen Bank. Pooled samples (N = 10) were exhaustively analyzed in 1993 for a wide range of individual chlorinated hydrocarbon contaminant (CHC) compounds: DDT, mirex and chlordane compounds and metabolites, chlorobenzenes (CBzs), dieldrin, chlorostyrenes (CSs), hexachlorocyclohexanes (HCHs), polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), and 87 PCB congeners, including the TCDD-like non-ortho and mono-ortho congeners. PCBs and DDTs were the dominant residues in eggs from both Lake Ontario (31-242 mg kg-1 and 9-64 mg kg-1) and Green Bay (34-133 mg kg -1 and 14-91 mg kg-1). ΣPCBs declined by a factor of 4-5 and DDTs a factor of 4-7 at both colonies between 1971 and 1982. Lake Ontario eggs had significantly higher residues of 2,3,7,8-TCDD (0.2-2.0 μg kg-1), HCBz (0.1-4.7 mg kg-1), OCS (0.03-0.45 mg kg -1), three HpCSs (0.13-0.97 mg kg-1), mirex and mirex photodegradation products (2.1-9.2 mg kg-1) than Green Bay eggs. HCBz levels in Lake Ontario eggs declined a factor of 40, TCDD and chlorostyrenes a factor of 8-10, and mirex a factor of 4 between 1971-1978. Green Bay eggs had slightly higher levels of chlordane-related compounds, dieldrin and β-HCH than Lake Ontario eggs. There were no consistent or strong trends in residue levels of these pesticides, PCDDs (except TCDD) and PCDFs in either lake, indicating that rates of input and removal of these CHCs in the lakes were much closer in the early 1970s than was the case for the other compounds

The relevance of seabird ecology to great lakes management

Seabirds are an integral part of Great Lakes ecosystems. However, most species are of no economic importance to humans and, therefore, they receive little direct management attention. Because many species of seabirds on the Great Lakes rely on fish as their primary food, factors that alter fish availability will also affect seabird populations. This paper examines how management practices may indirectly affect Great Lakes seabirds leading to changes in population sizes, diet composition, and destruction of breeding habitat. Consideration of the impacts of management actions on non-target groups, such as seabirds, will require the application of an ecosystem approach to management. Although the ecosystem approach philosophy has been widely accepted from a theoretical perspective, little tangible evidence exists that it has been routinely applied

Stable nitrogen isotopes in waterfowl feathers reflect agricultural land use in western Canada

Stable nitrogen and carbon isotope analysis was performed on secondary feathers collected from flightless, mallard ducklings (Anas platyrhynchos) from 17 locations across western Canada. The δ15N values of mallard feathers ranged from +6.1 to +23.7‰(AIR). Mean δ15N feather values from the 17 locations were strongly correlated with the percentage of land under agricultural development. Higher δ15N values in waterfowl feathers collected from agricultural areas possibly reflected the entry of excess fertilizer nitrogen into local water bodies. However, other processes may have also been important. These results provide evidence that nitrogen isotope values in avian feathers may reflect long-term nitrogen additions to surface waters in agricultural areas and may also provide important clues in elucidating the origin of nonpoint source nitrogen inputs

Consumption of fish and other prey items by Lake Erie waterbirds

Lake Erie provides valuable habitat for large populations of waterbirds that rely on fish and other aquatic biota for food. To better understand the relationship between waterbirds and their prey, it is important to quantify the role of waterbirds in the food web. Field observations of their population sizes and diet preferences were applied to a bioenergetics model to estimate consumption of fish and other items by waterbird species occupying the three basins of Lake Erie in the late 1990s. The total quantity of fishes consumed annually by resident and migrating birds on Lake Erie was 18,776 metric tons. Fish consumption by nesting and migrant waterbirds was greatest in the western basin of Lake Erie (14,784 metric tons/yr) followed by the eastern (2,078 metric tons/yr) and central (1,914 metric tons/yr) basins. Migrant populations of red-breasted mergansers consumed the most fish (6,612 metric tons/yr). These diving ducks consumed approximately 35% of the total amount of fish consumed by waterbirds on the lake. Nesting populations of double-crested cormorants (5,857 metric tons/yr), nesting populations of herring gulls (1,597 metric tons/yr), and migrant common mergansers (1,149 metric tons/yr), were the second, third, and fourth largest consumers of fish from Lake Erie, respectively. Waterbirds consume approximately four times more fish by weight than were harvested by Ontario's commercial fishery in 2000; however, in general, the species of fishes most often consumed by waterbirds are not of economic importance. However, there may be exceptions to this rule

To normalize or not to normalize? Fat is the question

Concentrations of lipophilic contaminants in biota are frequently corrected for variation in tissue lipid content. Usually, this correction is accomplished by dividing tissue contaminant concentration by lipid concentration to form lipid‐normalized data. This ratio‐based approach is satisfactory when contaminant concentration varies in direct proportion to lipid content. However, when such a relationship does not exist, erroneous conclusions may be reached. Recent research has emphasized the potential shortcomings of the use of ratio variables. We demonstrate the importance of considering these shortcomings when lipid‐normalizing data. Three examples are presented, and an alternative approach based upon the use of analysis of covariance (ANCOVA) is suggested. Copyrigh

Adjusting for temporal change in trophic position results in reduced rates of contaminant decline

The development of ecological tracers to track the flow of energy and nutrients through food webs has provided new insights into the factors that are important in regulating diet composition in wildlife. The Great Lakes Herring Gull Monitoring Program has provided information regarding temporal trends in levels of bioaccumulative contaminants since the early 1970s. In recent years, data from this program have also been generated to examine ecological changes in the Great Lakes. Because the contaminants that are evaluated as part of this program biomagnify, food is the primary determinant of contaminant concentrations in the eggs that are analyzed annually. Fluctuations in diet composition could affect the interpretation of temporal trends by affecting exposure to contaminants. Retrospective analyses involving ecological tracers, i.e., stable nitrogen isotopes and fatty acids, have shown temporal change in the diets of Great Lakes herring gulls at some monitoring colonies. These dietary differences have led to temporal variation in the trophic position of herring gulls. Given that higher trophic level organisms incur greater exposure to biomagnifying contaminants, it is necessary to adjust for these temporal changes in trophic position to get an accurate indication of how contaminant burdens are changing within the Great Lakes ecosystem. Here, we outline a method to adjust for temporal changes in indicator species trophic position and discuss how these adjustments affect the interpretation of contaminant temporal trend monitoring data

Colonial waterbirds nesting on Egg Island, Lake athabasca, 2009

In June 2009 a census was conducted of colonial waterbirds breeding on Egg Island in western Lake Athabasca. This island supports the largest breeding colony of Caspian Terns (Hydroprogne caspia) in Alberta. California Gulls (Larus californicus) and Herring Gulls (Larus argentatus) also nest on the island. One hundred and one Caspian Tern nests (=pairs) were counted during 2009. Since 1990, the number of terns nesting on the island appears stable. However, more frequent surveys of waterbird populations are recommended, particularly in light of growing industrial activity in this region

Assessing temporal trends in contaminants from long-term avian monitoring programs: The influence of sampling frequency

The effect of sampling frequency on the detection of statistically significant temporal trends in egg contaminant levels was examined using data from the Great Lakes Herring Gull Monitoring Program. Decreased identification of statistically significant trends was apparent in the sampling regimes where samples were collected less frequently. When statistically significant declines were observed, sampling at two and four year intervals resulted in the trend being identified later than with annual monitoring. The design of monitoring programs must balance costs and data quality. Programs should ensure that the data collected are adequate to address critical questions

Mercury in parasitic nematodes and trematodes and their double-crested cormorant hosts: Bioaccumulation in the face of sequestration by nematodes

Endoparasites can alter their host's heavy metal concentrations by sequestering metals in their own tissues. Contracaecum spp. (a nematode), but not Drepanocephalus spathans (a trematode), were bioaccumulating mercury to concentrations 1.5 times above cormorant hosts. Nematodes did not have significantly greater stable nitrogen isotope values (δ15N) than their hosts, which is contradictory to prey-predator trophic enrichment studies, but is in agreement with other endoparasite-host relationships. However, Contracaecum spp. δ-3C values were significantly greater than their hosts, which suggest that nematodes were consuming host tissues. Nematodes were accumulating and thus sequestering some of their cormorant hosts' body burden of methyl mercury; however, they were not dramatically reducing their hosts' accumulation of methyl mercury