Wildlife may be exposed to mercury (Hg) and methylmercury (MeHg) from a variety of environmental sources, including mine tailings, industrial effluent, agricultural drainwater, impoundments, and atmospheric deposition from electric power generation. Terrestrial and aquatic wildlife may be at risk from exposure to waterborne Hg and MeHg. The transformation of inorganic Hg by anaerobic sediment microorganisms in the water column produces MeHg, which bioaccumulates at successive trophic levels in the food chain. If high trophic level feeders, such as piscivorous birds and mammals, ingest sufficient MeHg in prey and drinking water, Hg toxicoses, including damage to nervous, excretory and reproductive systems, result. Currently accepted no observed adverse effect levels (NOAELs) for waterborne Hg in wildlife have been developed from the piscivorous model in which most dietary Hg is in the methyl form. Such model are not applicable to omnivores, insectivores, and other potentially affected groups, and have not incorpotated data from other important matrices, such as eggs and muscle. The purpose of this paper is to present a comprehensive review of the Hg literature as it relates to effects on wildlife, including previously understudied groups. We present a critique of the current state of knowledge about effects of Hg on wildlife as an aid to identifying missing information and to planning research needed for conducting a complete assessment of Hg risks to wildlife. This review summarizes the toxicity of Hg to birds and mammals, the mechanisms of Hg toxicity, the measurement of Hg in biota, and interpretation of residue data.

Effects of mercury on wildlife: A comprehensive review

1Some effects of fisheries on the associated biological systems are reviewed and management options and their inherent risks are considered.
2In addition to the effects on target species, other sensitive groups impacted by fishing are considered including marine mammals, turtles, sea birds, elasmobranchs and some invertebrates with low reproductive rates.
3Other impacts discussed include the destruction of benthic habitat, the provision of unnatural sources of food and the generation of debris.
4Management options are considered including the designation of marine protected areas, risk aversion, and the burden of proof.
5A balanced consideration of the risks and consequences of ‚Type 1’ and ‚Type II’ errors is advocated.

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Environmental effects of marine fishing

James G. Wiener, David P. Krabbenhoft, Gary H. Heinz, and Anton M. ScheuhammerCONTENTS16.1 Introduction 409
16.2 Evolution of the Environmental Mercury Problem 410
16.3 Global-Scale Environmental Cycling and Fate 413
16.4 Mercury Speciation and Environmental Concentrations 415

Ecotoxicology of Mercury

Many studies have shown that seabirds are sensitive to changes in food supply, and therefore have potential as monitors of fish stocks. For most seabird species breeding parameters suitable for biomonitoring have yet to be measured over a wide range of prey densities. However, it is clear that responses vary among species and care must be taken when interpreting seabird data as a proxy for fish abundance. For many years seabirds have also been used as monitors of pollution, especially oil pollution. Beached bird surveys provide important evidence of geographical and temporal patterns, and, for example, show consistent declines in oil release into the southern North Sea over the last 15 years. Analysis of oil on birds can now permit fingerprinting of sources, allowing prosecution of polluters. As predators high in marine food webs, seabirds also have potential as monitors of pollutants that accumulate at trophic levels. Recent work on mercury in seabirds has permitted an analysis of spatial patterns and of the rates of increase in mercury contamination of ecosystems over the last 150 years, since mercury concentrations in feathers of museum specimens can be used to assess contamination in the birds when they were alive. Surprisingly, pelagic seabirds show higher increases than most coastal ones, and increases have been greatest in seabirds feeding on mesopelagic prey. This seems to relate to patterns of methylation of mercury in low-oxygen, deeper water. Accurate measurement of long-term trends in mercury contamination depend on the assumption that seabird diet composition has not changed. This can be assessed by analysis of stable isotopes of N and C from the same feathers used for mercury measurement, a technique that also permits the monitoring of trophic status over time or between regions. While high mercury contamination of seabirds in the southern North Sea is unsurprising, we cannot yet explain certain unexpected results, such as high levels in seabirds from north Iceland compared with those from south Iceland or Scotland.

Seabirds as monitors of the marine environment

By-Catch: Problems and Solutions

No significant between sex differences were detected in Hg concentrations in primary feathers, pectoral muscle, brain, liver, and kidney tissues of fall migrating juvenile and second-year Bonaparte's gulls (Larus Philadelphia) collected in the Quoddy region. Adults showed sexual differences only in the first 5 primary feathers, and in muscle, kidney and brain. Differences in Hg concentrations among age groups were reflected in the primary feathers and body tissues, but as the molt progressed, Hg concentrations decreased as they converged toward a minimum asymptotic Hg level for each tissue. This suggests that the body burden of Hg was reduced through its redistribution from the body tissues into the growing feathers. Mercury concentrations in premolt head feathers (pre-egg-laying) did not vary significantly between adult females and males, whereas Hg concentrations in postmolt feathers (post-egg-laying) were significantly lower in females, suggesting that egg-laying was also a route for Hg elimination. After the completion of the molt, the new feathers contained most of the body burden of Hg (93.0% in adults).

Mercury levels in Bonaparte's gulls (Larus Philadelphia) during autumn molt in the Quoddy region, New Brunswick, Canada

The diving behaviour of seven free-ranging harbour porpoises (Phocoena phocoena) was examined using time–depth recorders. In total, 8167 individual dives were recorded over 254 h. The longest perio...

Diving behaviour of harbour porpoises, Phocoena phocoena

A bioenergetics-based budget which predicts net total Hg loss during the period of autumn moult was calculated for adult Bonaparte's Gulls in the southwestern Bay of Fundy, Canada. Daily food consumption and, hence, ingestion of Hg measured in prey samples, was calculated from estimated energy requirements during the period of moult. The amount of Hg eliminated was estimated from analyses of Hg content in excreta and feathers. Elimination of Hg via the feathers accounted for 68% of the total loss from the body in females and 59% in males during the period of autumn moult. Actual loss from the body over time was estimated as the difference between measured maximum (premoult) and minimum (postmoult) body burden of total Hg. The measured net Hg loss from the body during the period of autumn moult was 23% lower than the predicted value for females and 49% higher than the predicted value for males. The negative and positive deviations of measured Hg losses from the predicted values for the separate sexes averaged out to within 6% of the predicted value when the sexes were pooled.

A mercury budget for the Bonaparte's gull during autumn moult

Changes in the growth and reproduction of harbour porpoises from the Bay of Fundy are described by comparing samples collected in 1969–73 and 1985–88. The most pronounced change was an increase in the length of calves, from 92.1 cm (SE 1.6) in 1969–73 to 108 cm (SE 1.3) in 1985–88. Females in 1985–88 attained sexual maturity at a significantly younger age (3.44 yr) and shorter length (143 cm) than females from the older sample (3.97 yr and 147 cm). These changes may be attributable to an increase in prey availability to individual porpoises. This presumed increase in prey availability may have resulted from a decrease in porpoise density caused by incidental mortality in commercial fisheries, a simultaneous increase in prey abundance, or a combination of these factors.

Changes in Growth and Reproduction of Harbour Porpoises, Phocoena phocoena, from the Bay of Fundy

Characteristics of right whale (Eubalaena glacialis) and fin whale (Balaenoptera physalus) habitat in the lower Bay of Fundy were identified by quantifying physical and biological habitat variables...

David E. Gaskin

Papers

Mercury levels in Bonaparte's gulls (Larus Philadelphia) during autumn molt in the Quoddy region, New Brunswick, Canada

Diving behaviour of harbour porpoises, Phocoena phocoena

A mercury budget for the Bonaparte's gull during autumn moult

Changes in Growth and Reproduction of Harbour Porpoises, Phocoena phocoena, from the Bay of Fundy

Environmental characteristics of North Atlantic right and fin whale habitat in the lower Bay of Fundy, Canada