abstract

Hematologic and biochemical reference values for free-ranging pinniped populations provide important baseline information with which to evaluate population health and disease, and also to evaluate the condition of individual animals that strand and are admitted to rehabilitation centers. Northern fur seal (Callorhinus ursinus) rookeries include those on the Pribilof and Bogoslof islands in the Bering Sea, as well as smaller breeding populations on San Miguel Island and the Farallon Islands, California. Small numbers of Northern fur seals strand annually along the California coast, with pups usually stranding in the fall and winter and juveniles and adults sporadically throughout the year.

Hematologic reference values have been published for adult males from St. Paul Island, Alaska but not for other ages or sexes.^1,2 Blood collected from Northern fur seal pups in the Pribilof Islands (PI, n=188) between 1995 and 2000, from San Miguel Island (SMI) in July (n=34) and September 2007 (n=25), and from stranded pups admitted to The Marine Mammal Center (TMMC) in 2006 (n=18) and 2007 (n=5) were used to establish hematologic (Table 1) and serum biochemistry (Table 2) reference intervals. Manual hematologic analyses were performed for blood collected from PI pups, and included PCV and manual WBC and differential counts. No serum biochemistry analyses were performed. For blood samples collected from all SMI and TMMC pups, complete automated hematologic analyses were performed, with the exception of differential cell counts, which were performed manually. Sufficient serum was available for complete automated biochemical analyses for all TMMC pups, but only for 20 SMI pups from the July 2007 samples.

Exact birth dates were known for PI pups, so accurate age determinations were possible. Birth dates were not known for SMI or TMMC pups, and were standardized to June 30 of each year for age estimation. Pups admitted to TMMC were older than those sampled either from PI or SMI, and estimated ages ranged from five months to 11.5 months of age. Creation of separate reference intervals based on age was possible for PI pups as shown in Table 1, but because of smaller sample sizes was not possible for pups from SMI or TMMC.

For each measured analyte, Wilcoxon rank sum tests (aka Mann-Whitney U tests) were used to compare values and assess for differences between results from different sites. Significant differences are indicated in each table. Most differences found are attributable either directly to age (with very young pups from PI, and older pups from TMMC), or the likely prevalence of known pathogens such as hookworm.^3,4 Comparisons of the hematologic data between the SMI samples in July and September 2007 (not presented in the table due to space constraints) show significant differences suggestive of recovery from hookworm infection, for example decreased total WBCs, decreased neutrophils, decreased band neutrophils, decreased eosinophils, and increased platelets in September. Other significant changes also suggest some degree of enduring anemia in September as compared to July, such as decreases in total RBCs, hematocrit, hemoglobin, MCH, MCHC, and increased RDW. Similar comparisons were not possible for the PI pups because of the small number of samples from three month old animals, the age at which hookworm infections are typically cleared. Pups in rehabilitation at TMMC had changes suggesting biliary stasis (elevated GGT) and muscle damage (elevated CK, not statistically significant), which are consistent with malnutrition, the most common cause of admission.

These reference intervals provide useful information for assessing the health status of wild northern fur seal pups, as well as those admitted to rehabilitation centers. The intervals will continue to be refined and reanalyzed as more samples are collected.

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acknowledgements

The authors thank Carlos Rios for laboratory analysis of samples from The Marine Mammal Center and San Miguel Island.

References

1.  Hunter L, Madin SH. 1976. Clinical blood values of the Northern fur seal, Callorhinus ursinus. J Wildlife Diseases 12:526-530.

2.  Hunter L, Madin SH. 1978. Clinical blood values of the Northern fur seal, Callorhinus ursinus. II. Comparison of fresh versus stored frozen serum. J Wildlife Diseases 14:116-119.

3.  Lyons ET, Melin SR, DeLong RL, Orr AJ, Gulland FM, Tolliver SC. 2001. Current prevalence of adult Uncinaria spp. in northern fur seal (Callorhinus ursinus) and California sea lion (Zaolphus californianus) pups on San Miguel Island, California, with notes on the biology of these hookworms. Veterinary Parasitology 97(4):309-318.

4.  Olsen OW, Lyons ET. Life cycle of Uncinaria lucasi Stiles, 1901 (Nematoda: Ancylostomatidae) of fur seals, Callorhinus ursinus Linn., on the Pribilof Islands, Alaska. 1965. J Parasitology 51(5):689-700.