Date Awarded

2002

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

John A. Musick

Abstract

Age and growth rates for salmon sharks (Lamna ditropis) in the eastern North Pacific (ENP) were estimated from seasonally formed bands in the vertebrae, and compared to previously published life history parameters for this species from the western North Pacific (WNP). Results of this study show that salmon sharks in the ENP achieve their maximum length at a faster rate, reach sexual maturity at an earlier age and achieve a greater weight-at-length than those in the WNP. Additionally, this dissertation shows that adult salmon sharks maintain a specific body temperature independent of changes in ambient temperature through a combination of physical and physiological means, and essentially function as homeotherms. Due to uncertainty in previous life history parameter estimates for sand tiger sharks (Carcharias taurus) in the western North Atlantic, age and growth rates were re-estimated using a larger sample size and captive individuals injected with oxytetracycline (OTC), a fluorescent skeletal marker. The results support a hypothesis that this species forms one pair of growth bands annually in the vertebral centra, whereas previous growth rate estimates were based on the formation of two bands per year. as such, the growth rate of this species is considerably slower than previously predicted and the population more susceptible to fishing mortality. Demographic analyses were conducted for salmon sharks in the ENP and WNP, and for sand tiger sharks (based on new life history parameter estimates) with uncertainty in vital rates incorporated via Monte Carlo simulations. Density-dependent compensation was included in models where fishing mortality was imposed by increasing sub-adult survivorship from output values generated by a previously published "Intrinsic Rebound Potential" model. The results indicate that both species are extremely vulnerable to fishing mortality and that no fishery should be implemented for sand tiger sharks or salmon sharks in the WNP. Salmon sharks in the ENP were the only population examined that indicated the potential to tolerate any fishing mortality. A comparison of growth completion rates and other life history parameters of ectothermic and endothermic sharks did not indicate that endothermic sharks achieve their maximum length at a faster rate than ectothermic sharks.

DOI

https://dx.doi.org/doi:10.25773/v5-a16a-xp68

Rights

© The Author

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