Abstract
Sex, age and sexual maturation are key biological parameters for aspects of life history and are fundamental information for assessing demographic changes and the reproductive viability and performance of natural populations under exploitation pressures or in response to environmental influences. Much of the information available on the reproductive condition, length at sexual maturity and sex determinations of endangered species has been derived from direct examination of the gonads in dead animals, either intentionally or incidentally caught, or from stranded individuals. However, morphological data, when used alone, do not provide accurate demographic information in sexually monomorphic marine vertebrate species (e.g. sharks, sea turtles, seabirds and cetaceans). Hormone determination is an accurate and non-destructive method that provides indirect information about sex, reproductive condition and sexual maturity of free-ranging individuals. Correlations between sex steroid concentrations and biochemical parameters, gonadal development and state, reproductive behaviour and secondary external features have been already demonstrated in many species. Different non-lethal approaches (e.g. surgical and mark-recapture procedures), with intrinsic advantages and disadvantages when applied on free-ranging organisms, have been proposed to asses sex, growth and reproductive condition. Hormone determination from blood samples will generate valuable additional demographic information needed for stock assessment and biological conservation.
Highlights
Much of the information available on the reproductive condition, length at sexual maturity and sex determinations of endangered species has been derived from direct examination of the gonads in dead animals, either intentionally or incidentally caught, or from stranded individuals
Hormone determination from blood samples will generate valuable additional demographic information needed for stock assessment and biological conservation
We briefly review the more invasive techniques and procedures that have generated demographic data and population parameters in marine vertebrates, those focused on establishing sex and reproductive status
Summary
Non-invasive, external indicators Inaccuracy in population structure estimates and sexual maturation Discriminant functions: Requires molecular approaches to validate discriminant functions (seabirds) Depends on: Age class Time of birth Habitat condition (wild/captive) Geographical region Visual examination: Error in interpretations when used alone Lack of external criteria for both sexes (sharks) Lack of correlation between presence of secondary sexual characteristics and size/age (sea turtles) Population differences Contradictory when compared with sex steroid levels and laparoscopic results Requires further evaluation and validation for determination of sexual maturation
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