Background

Reproduction is one such life history trait that must be fully understood if successful management of these cartilaginous fish is to occur. Without information regarding when elasmobranchs mature and reproduce, population demography or stock assessments can never be adequately conducted. Unfortunately, existing information regarding sexual maturity and reproductive cycles in elasmobranchs is largely based on gross examination of morphological changes associated with reproductive organs and structures (i.e. testes in males and ovary weight in females). While this information has proven valuable in obtaining reproductive information, collecting pertinent data requires that specimens be sacrificed. This can be problematic, especially for species that have been classified as endangered or threatened.

Recently, circulating concentrations of plasma steroid hormones, such as 17-?-estradiol, progesterone, and testosterone, have been used with gross morphological changes to evaluate events associated with reproductive cycles and sexual maturity in a number of sharks, skates, and rays. The results from such studies indicate that morphological changes in reproductive tracts and gonadal steroid hormone biosynthesis are intimately linked in elasmobranch reproduction. That is, as the reproductive tracts become active, they begin to produce more hormones. While research suggests that plasma steroid hormone concentrations alone can provide the necessary information to gauge sexual maturity and reproductive cycle status of elasmobranchs by non-lethal means, drawing blood to obtain a plasma sample from large specimens is problematic. Thus, unless other non-lethal methods can be identified, management related information regarding reproductive biology for prohibited or large species will remain difficult if not impossible to obtain.

Aims and Objectives

This project seeks to develop the methodologies that will allow hormone concentrations in skeletal muscle tissue to be used as a reliable and noninvasive surrogate for the study of elasmobranch reproductive biology representing four different reproductive modes:

1. oviparous [Leucoraja erinacea];
2. placental viviparous [Rhizoprionodon terraenovae];
3. lecithotrophic aplacental viviparous [Squalus acanthias];
4. matrotrophic aplacental viviparous [Dasyatis Sabina].

These species were chosen for this study because they have robust populations within their given geographic ranges.