A Comparative Analysis of the Life History Traits of Sharks in the Order Hexanchiformes

Defense Date

10-2009

Document Type

Capstone

Degree Name

M.S. Coastal Zone Management

First Advisor

Brad Wetherbee

Second Advisor

Mahmood Shivji

Third Advisor

David Ebert

Abstract

The study of life history patterns is vital in understanding how organisms have evolved to fit in the natural world. This generally involves examining features that are both physiological and behavioral, and correlate to the dynamics of growth and reproduction throughout an organism’s life cycle. Chondrichthyan fishes are unique in the fact they have evolved a very different set of life history parameters from teleosts which has made them extremely vulnerable to over fishing. Determining both the general and species-specific life history patterns in elasmobranchs is a pivotal first step in understanding how their life history strategies will influence population growth or decline, but a limited amount of biological information is available on most species. Sharks in the order Hexanchiformes represent several interesting paradoxes among neoselechians. They are considered some the most ancient and widespread of sharks as well as top predators throughout much of their range, but still remain poorly understood in terms of their specific life history patterns. The overall effect of decreasing numbers of apex predators in marine systems, such as Hexanchids, is tremendously difficult to foresee but appears to be ecologically and economically significant, as well as long lasting. The status of many Hexanchid stocks remains data deficient, although worldwide fishing pressure remains prevalent. The particular life history traits of Hexanchiformes suggest they are highly K selected as a group and possess low ecological resilience, making them highly vulnerable to over-exploitation. By investigating the life history characteristics of cow and frilled sharks and incorporating the data into a Life History Matrix for Hexanchiformes any lack of critical life history information will be readily identifiable, allowing for greater insight when establishing regulations and policies aimed at conservation.

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