Health and heavy metals evaluation of two caribou herds of northern Alaska in response to a mortality event

Updated 2001-04-18

We compared animals from a caribou (Rangifer tarandus) mortality event in the area of Point Hope and Chariot (Cape Thompson), Alaska (USA) in 1995 to hunter-killed caribou from reference sites (Barrow, Red Dog Mine, and Teshekpuk Lake, Alaska). Gross and histologic endpoints, and element levels (As, Cd, Cu, Pb, Zn, Fe) were evaluated. Starvation/malnutrition were major factors leading to death or severe weakness as very little or no fat (very low body condition scores) and serous atrophy of fat (marrow cavity and histologically) were more prevalent in caribou associated with the mortality event as compared to reference sites animals. Accumulation of hepatic hemosiderin in Kuppfer cells was noted as an indicator of cachexia. Levels of lead in feces and liver, copper the rumen contents, and arsenic in muscle were higher in caribou harvested near Red Dog Mine and might be expected in the mineral rich area, but were not at a level of concern for toxicoses. Kidney levels of cadmium were significantly increased with increasing age, and presents a potential concern for human consumers, and is an expected finding. We concluded that heavy metals played no role in the mortality event and that caribou starved. Further investigation of regional minerals differences is required to understand the sources and transport mechanisms to explain these findings and to properly address mining activity impacts. Mortality events on the north slope of Alaska are not uncommon and likely involve starvation as described here, but in most cases are not investigated, even though recent industrial activities have heightened concern.

This is not a National Implementation Plan (NIP) project

Time frame

Project time span
1994 -
Data collection
1994 - 1996
Data processing
not specified
Data reporting
not specified

Contact information

Contact person
Todd M. O'Hara
Dept. of Wildlife Management North Slope Borough PO Box 69 Barrow, Alaska 99723 USA
1 907 852 0350
1 907 852 0351

Parameters and Media

Parameter groups measured/observed/modelled
Heavy metals
Other metals/elements
Media sampled/studied/modelled
Terrestrial mammals
Additional information or further specification of types of data / information collected, species / tissues / organs sampled, etc.

Species sampled: Caribou (Rangifer tarandus) Sampling sights in Alaska: Anaktuvuk Pass, Point Hope, Barrow, Cape Thompson, Teshekpuk Lake, Red Dog Mine Tissue/Media sampled: liver, kidney, muscle, rumen contents Elements analyzed: arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn), iron (Fe) additional information collected: age (cementum annuli); body condition scores; histology


Regions studied
Alaska, North Slope

Data availability

Are data archived or planned to be archived at an AMAP Thematic Data Centre?
Data centres
Terrestrial TDC
References to key publications (or planned publications) and data reports
Samples/specimens archived in specimen banks?

Methods & Procedures

Procedures and methodology used for, e.g., sampling and sample storage, sample pretreatment, extraction and analysis, including which laboratories are involved, references to methods employed, etc.

Aerial searches for caribou carcasses were conducted 6-8 June 1995 in a Piper PA-18 airplane. The area searched extended from Cape Krusenstern to Cape Lisburne within approximately 32 km of the Chukchi Sea coast (10,300-11,600 km2). Searches were delayed until June when snow ablation was 90% complete. Searches were conducted approximately 500 ft above ground. In areas with topographic relief search lines followed drainages and ridge lines to maintain relatively constant elevation above ground and to provide the best view of tight valleys, river banks, etc. Transects spaced approximately 1.6-km (1 mi) apart were flown to ensure total coverage of flat areas; however, <20% of the total area was searched in this way. Residents of Kotzebue, Kivalina and Point Hope, Alaska (USA) were observers during these flights. Total mortality was estimated based on the proportion of the area searched and our perception of carcass sightability. Approximately 90% of the total area was searched: wind prevented the northern 10% of the area from being covered. However, persistent snowfields present in the area probably reduced the percentage of total area actually viewed to 75-80%. Our estimate of total mortality from the aerial searches was independently evaluated using radio marked caribou. At the time of the event, three radio marked caribou represented approximately 10,000 caribou given the total herd size, and number of radio marked caribou in the WAH (assuming collars were randomly distributed throughout herd). One of three radio marked caribou died that wintered in the area where this mortality event occurred. We were unable to directly evaluate sightability of carcasses; however, we felt sightability approached 100%. There are no trees in this area, shrubs are typically <2 m high and restricted to narrow riparian bands, vegetation is either absent or decumbent, and searches were conducted prior to the emergence of leaves. The five major study sites for examining and sampling caribou are highlighted in bold in Figure 1, the 1995 caribou mortality event occurred at Point Hope, Chariot, and the surrounding area. Caribou from near Red Dog Mine, Barrow and Teshekpuk Lake were healthy and were examined for reference. 1994 to 1996 sampling north slope, Alaska wide Animals found dead or euthanized by gunshot (Chariot and Point Hope, Alaska areas on Cape Thompson), and hunter-killed (Anaktuvuk Pass, Barrow, Point Hope, Teshekpuk Lake, and Red Dog Mine) were examined and sampled for this study. This sampling does introduce bias we cannot adequately address as the collection methods were different. Caution is warranted in comparing heavy metal levels as desiccation, tissue degradation, etc. may affect metal levels in found dead animals. The time of year, location, and number of caribou examined and/or sampled are listed in Table 1. Heavy metal analysis Frozen samples (-20 C) were sent in coolers by overnight express delivery to the Diagnostic Toxicology Laboratory, Mississippi State University, College of Veterinary Medicine (Starkville, Mississippi USA) where they were placed in a freezer (-80 C) upon arrival. Heavy metal analyses were conducted as in O’Hara et al. (1995). One gram portions of sample was weighed and digested as in O’Hara et al. (1995). Samples were then analyzed by Atomic Absorption (AA) Spectrophotometry (Perkin-Elmer 5000, Norwalk, Connecticut USA) with a graphite furnace (Perkin-Elmer HGA 500). Values were recorded as parts per million (ppm) wet weight (ww). Quality assurance and quality control were followed as in O’Hara et al. (1995). Aging Caribou were aged by counting cementum annuli of paired incisors when available, when not available the first premolar was submitted as in O’Hara et al. (1999). Teeth were submitted with species and season of death indicated; matched pairs were not identified until after teeth were aged. A birthday of June 1 is assumed for all animals. Of 45 matched pairs of caribou teeth 28 (62%) agreed, 12 (27%) disagreed by 1 year, four (9%) by 2 years, and one (2%) by 4 years. Based on anticipated cementum layer variability within an animal, and ager error these data indicate good age estimates. Body condition (BC) score Body condition scores were determined as outlined by Kistner et al. (1980), developed as a field technique for evaluating physical condition of deer and previously used for caribou (O’Hara et al., 1999). This technique is based on carcass fat at several sites (cardiac, omental, perirenal, and subcutaneous regions of the tail head and brisket) and on the mass of muscle. Scores were set as emaciated (0-10), poor (11-40), fair (41-70), good (71-80) and excellent (81-95). Obtaining a complete BC score was not always possible (i.e., time allowed for examination, scavenging). Six fat depot sites are given scores of 0 (no visible fat), 5 (slight quantities of fat), 10 (moderate fat), and 15 (heavy fat), and muscle mass is ranked as 0 (if carcass is "bony") or 5 (full). Mean scores should be calculated for sex and age-classes separately if possible. Our sample sizes are low for most sites for this to be done. Bone marrow fat evaluation is another useful technique that was used and is better suited for assessing very poor condition (Ransom 1965, Neiland 1970; Kistner et al., 1980). In emaciated animals serous atrophy occurs at these depot sites and was examined. Histology Tissue samples were collected as fresh as possible and placed in neutral buffered 10% formalin (VWR Scientific Products, Brisbane, California USA). Tissues were submitted for trimming and placement in paraffin blocks for thin sectioning and mounting on glass slides and stained with hematoxylin and eosin (H and E). Binuclear hepatocyte density was estimated by counting these specific cell types in 10 high power fields for each animal, the mean was calculated as the number of binuclear hepatocytes/high power field. Sarcocystis spp.-like structures were counted within a measured section of tissue (borders measured) and reported as number of cysts/cm2. The special stain, periodic acid-Schiff (PAS), for hemosiderin was used to characterize the pigment indicated by H and E staining. Statistics Comparisons of element levels between locations was done with Analysis of Variance (ANOVA) and Fisher's Least Significant Difference (LSD) using the Statistical Analysis System (SAS, Chapel Hill, North Carolina USA). Correlations, coefficients (slopes), probability of slope different from 0, and r2 were obtained from simple linear regression using SAS and Microsoft Excel for Windows 95 (7.0). Significant differences were concluded when P < 0.05.

QA/QC Information (what QA/QC procedures are implemented, laboratories involvment in QA/QC activities, model verification/validation routines, etc.)

see above

Additional Information

Is this a bi- AND multi-lateral project (i.e. a project involving cooperation between different countries)?
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