The Hawaiian monk seal (HMS) is one of the world's most critically endangered species with the wild population at approximately 1200 animals and declining at a rate of 4% per year.1 Due to the small wild population and limited number of animals housed in public display facilities, little is known about the unique biochemical nature of the HMS when compared to other pinniped species and how the these values may change over the lifetime of the animal. The lifespan of a HMS is 25–30 years.2 This presentation will review the biochemical findings from 4 seals (ages 26–33 years) that lived long term at public display facilities and were being managed for diseases of old age compared to 2 free-ranging seals (ages 1 and 27 years) that were brought in for rehabilitation due to illness or injury.
The seals in this report include four males (ages 27–33 years) and two females (ages 1 and 26 years). Four of the geriatric HMS (3 males and 1 female) were housed in two public display facilities. Each showed similar abnormal indices on blood samples independent of clinical presentation, history and treatment protocols. These changes were not documented in samples obtained from two free-ranging seals that were brought in for rehabilitation, but died as a result of their conditions.
All four display seals exhibited moderate to severe hypernatremia (167–191 mEq/L) and hyperchloremia (123–158 mEq/L) without significant increases in the serum creatinine levels (1.2–1.7 mg/dL) up to one month prior to death. This electrolyte trend progressively worsened in two of the seals despite attempts at treatment. Based on the clinical picture and response to treatment protocols, the underlying etiology appeared to be a nephrogenic diabetes insipidus, although consumption of sea water could not be ruled out.2 Urine osmolality and electrolytes were not tested in any of these cases, so a definitive conclusion could not be reached. Three of the four animals had abnormal renal findings on histopathology.
The three males also displayed profoundly elevated serum levels of blood urea nitrogen (BUN) with stable creatinine values. The BUN:Creatinine (B:C) ratios ranged from 81:1 to 100:1. In humans, these findings have been associated with heart failure.3 Concurrent with the increase in the B:C ratio, an electrocardiogram of one seal also documented recurrent premature ventricular contractions. Changes consistent with heart failure were noted in two of the three males on histopathology.
The electrolyte and B:C ratio abnormalities may not have been noted in the free-ranging seals due to the acute progression of their diseases, whereas the clinical conditions in the exhibit animals were being managed by veterinary staff for months to years. The changes noted in these cases did not prove to be reversible, although different treatment protocols may yield a different outcome. Further study is warranted to document the true underlying etiologies. Perhaps identification of these conditions in future cases may provide a useful tool as a prognostic indicator as we consider life-extending treatments and quality-of-life issues for our geriatric patients.
The authors would like to thank the animal trainers and staff at Sea Life Park Hawaii, Waikiki Aquarium and the NMFS Hawaiian Monk Seal Research Program for their hard work and dedication to the animals under our care.
* Presenting author
1. Carretta JV, Oleson E, Weller DW, Lang AR, Forney KA, Baker J, Hanson B, Martien K, Muto MM, Lowry MS, Barlow J, Lynch D, Carswell L, Brownell Jr. RL, Mattila DK, Hill MC. U.S. Pacific marine mammal stock assessments: 2012. U.S. Dept. of Commerce, NOAA technical memorandum NOAA-TM-NMFS-SWFSC-504, 2013:378 p.
2. Endangered species in the Pacific Islands. [Internet]. [Updated 2012 Sep 20]. Pacific Islands Fish and Wildlife Office, US Fish and Wildlife Service; [Cited 2014 Jan 30]. Available from: www.fws.gov/pacificislands/fauna/himonkseal.html.
3. Kugler JP, Hustead T. Hyponatremia and hypernatremia in the elderly. Am Fam Physician. 2000;61(12):3623–3630.
4. Schrier RW. Blood urea nitrogen and serum creatinine: not married in heart failure. Circ Heart Fail. 2008;1:2–5.