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About the Authors:
Marisa L. Trego
* E-mail: [email protected]
Affiliation: Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic & Atmospheric Administration, La Jolla, California, United States of America
Nicholas M. Kellar
Affiliation: Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic & Atmospheric Administration, La Jolla, California, United States of America
Kerri Danil
Affiliation: Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic & Atmospheric Administration, La Jolla, California, United States of America
Introduction
A new field is emerging that utilizes hormones in the blubber of wild cetaceans to study demography; pregnant females have been reliably identified by their blubber progesterone (P4) concentrations in several cetacean species. Determining the proportion of pregnant females in a free-ranging cetacean population can yield highly valuable information in the management of threatened stocks. With this tool we can estimate reproductive rates, project population growth, and compare reproduction with environmental or anthropogenic factors. However, to more broadly implement this method with field-collected samples it is necessary to know the level of variation of blubber P4 expected in pregnant animals of different species. Examining animals of known reproductive status among a suite of species can provide the necessary validation.
Previously, the reproductive endocrinology of small delphinids was predominately studied by quantifying serum progesterone levels in relation to female reproductive state. Correlations between serum progesterone concentration and reproductive status have been examined in fishery caught striped dolphins, Stenella coeruleoalba [1] and incidentally killed Dall’s porpoises, Phocoenoides dalli [2,3]. It is also a common practice with captive cetaceans to use serum to monitor hormone levels. For example, Sawyer-Steffan et al. [4] studied the presence of progesterone and estrogens in non-pregnant and pregnant captive Atlantic common bottlenose dolphin, Tursiops truncatus, in order to implement a successful captive breeding program. In addition, there is limited information on serum progesterone during estrus in Hawaiian spinner dolphins, Stenella longirostris, in captivity [5]. While this technique is effective when examining dead or captive dolphins, only one study has successfully measured serum progesterone in live wild cetaceans [6]. However, such sampling of wild animals is rare and not feasible for most populations. Also, repeat sampling over time is required to confirm pregnancies [4]. This constraint greatly reduces the utility of serum progesterone when monitoring reproduction...