Doctor of Philosophy (PhD)
Oceanography and Coastal Sciences
The cownose ray, Rhinoptera bonasus, is an elasmobranch commonly observed throughout the Gulf of Mexico. Cownose rays appear to be sensitive to water temperature. I performed laboratory experiments and collected field data to obtain basic life history information, and used the information to configure an individual-based bioenergetics model. The bioenergetics model was coupled to a matrix projection model, and the coupled models were used to predict how warmer and cooler water temperatures, compared to current conditions, would affect the growth and population dynamics of the cownose rays. The life history study determined weight at age, maturity by weight, and fecundity for cownose rays. Verified vertebral age estimates ranged from 0+ to 18+ years. Likelihood ratio tests indicated that a combined sexes Gompertz model best described the growth of cownose rays. A relationship between maturity and weight was estimated; annual fecundity was determined to be one pup. The laboratory experiments resulted in the estimation of standard oxygen consumption rate as a function of weight and temperature, and a Q10 value of 2.33. The bioenergetics model predicted that rays would have a slower growth rate and reach smaller average weights at age (9.6-16.8% smaller) if they inhabited 2oC warmer water than baseline (current) conditions, while individuals would grow faster and attain heavier weights at age (13.4-17.2% heavier) under a 2oC cooler scenario. Changes in growth rates under the warmer and cooler conditions also lead to changes in age-specific survivorship, maturity, and pup production, which I used as inputs to a matrix projection model. Faster growth of individuals under the cooler scenarios translated into an increased population growth rate (4.4-4.7%/year versus 2.7%/year under baseline), shorter generation time, and higher net reproductive rates, while slower growth under the warmer scenarios translated into slower population growth rate (0.05-1.2%/year), longer generation times, and lower net reproductive rates. Elasticity analysis indicated that population growth rate was most sensitive to adult survival. Reproductive values by age were highest for intermediate ages. The combination of coordinated laboratory experiments, field data collection, and coupled individual-based bioenergetics and matrix projection models provides a powerful approach for relating physiology to demographic responses.
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Neer, Julie Ann, "Aspects of the life history, ecophysiology, bioenergetics, and population dynamics of the cownose ray, Rhinoptera bonasus, in the northern Gulf of Mexico" (2005). LSU Doctoral Dissertations. 1992.
Bruce A. Thompson