Life History Introduction l Strandings l Fishery Observer Program l Blubber Steroid Hormones l Frozen Tissue Archive
Gaining even basic knowledge about wild marine mammals is fraught with challenges. Step into the shoes of a field biologist for a moment. Imagine you are on the bow of a research ship, and just a few feet before you are a thousand spotted dolphins, zigging and zagging, leaping and diving. At any given moment, only a fraction of the school is visible from the surface. Each animal comes up just long enough to breathe, then disappears again. Now imagine trying to estimate how many dolphins are in that school, how many are young or old, male or female, pregnant or not pregnant. It seems next to impossible, doesn’t it?
To help us, we employ a darting technique that takes a small piece of skin and blubber called a biopsy. This technique lets us obtain up to fifty biopsies in a single day. Back in the lab, we analyze the levels of reproductive steroid hormones in the blubber using laboratory procedures developed here at SWFSC.
Elevated progesterone is a reliable indicator of pregnancy. Elevated estradiol indicates sexual maturity.
Elevated testosterone indicates sexual maturity.
We quantify these hormones in the blubber and use the information to determine how many animals in a population are sexually mature, pregnant, or both; this tells us about the health and status of that population.
• Taking a blubber sample is the most tenable way to gather life history information from wild cetaceans.
• Hormones persist in blubber much longer than they do in most other tissues.
Common Dolphins (Delphinus delphis)
Northern Right Whale Dolphins (Lissodelphis borealis)
Pacific White-sided Dolphins (Sagmatias obliquidens)
Humpback Whales (Megaptera novaeangliae)
Spotted Dolphins (Stenella attenuata)
Spinner Dolphins (Stenella longirostris)
Bowhead whales (Balaena mysticetus)
Our laboratory procedures have not only yielded valuable life history data, they have also given us insight into steroid blubber physiology. For example, we have learned where in the blubber to expect higher than average steroid content.
The Big Picture
In many dolphin and whale species, the answers to simple questions are poorly understood, such as:
how often do animals reproduce?
how many years between birth and sexual maturity?
what proportion of the population are young animals versus adults?
Quantifying the hormone levels in blubber can help us to answer these questions.
Knowing pregnancy rates and maturity status enables us to monitor the growth or decrease of those cetacean populations that have been affected by human activities. It also helps us to determine whether a depleted population is recovering, and how well.
Mansour, A. A. H., D. W. McKay, et al. (2002). "Determination of pregnancy status from blubber samples in minke whales (Balaenoptera acutorostrata)." Marine Mammal Science 18(1): 112-120.
Stoops, M. A., G. B. Anderson, et al. (1999). "Use of fecal steroid metabolites to estimate the pregnancy rate of a free-ranging herd of tule elk." Journal of Wildlife Management 63(2): 561-569.
Yoshioka, M., T. Okumura, et al. (1994). "A proposed technique for quantifying muscle progesterone content in minke whales (Balaenoptera acutorostrata)." Canadian Journal of Zoology 72(2): 368-370.