Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


John A. Musick


The most commonly used equation to describe size at age in fishes is the von Bertalanffy equation (VBE), which assumes that growth rate is based on the balance of anabolic and catabolic processes: dW/dt = HW&\sp{lcub}\rm d{rcub}&-kW&\sp{lcub}\rm m{rcub}&. Anabolism, HW&\sp{lcub}\rm d{rcub}&, is considered proportional to gill surface area (A = rW&\sp{lcub}\rm d{rcub}&), and a "generalized" VBE (GVBE) has been previously determined: L&\sb{lcub}\rm t{rcub}& = L&\sb\infty&(1-exp(-KD(t-t&\sb{lcub}\rm O{rcub})))\sp{lcub}\rm 1/D{rcub}&, where D = b-bd and b is from W = qL&\sp{lcub}\rm b{rcub}&. The growth rate may be rewritten in terms of gill area, A, as dW/dt = kA/(A&\sb\infty&/W&\sb\infty\sp{lcub}\rm m{rcub}&)-kW&\sp{lcub}\rm m{rcub}&. Gill areas were examined for sandbar and tiger sharks. Values of the gill area coefficient, d, were fit to a modified Ford-Walford equation (OFW) and the gill area growth equation using length at age data for sandbar, tiger, dusky, blue, white, and shortfin mako sharks to calculate GVBE parameters. The adequacy of the GVBE is dependent on the data set. The OFW produced realistic results for seven data sets, but produced unrealistic L&\sb\infty& estimates for three other data sets. The gill area growth equation produced realistic results for five data sets, but not for two other data sets. A&\sb\infty&/W&\sb\infty& for the lamnid sharks are greater than for the carcharhinids, and within the carcharhinids, A&\sb\infty&/W&\sb\infty& for tiger, dusky and blue sharks are similar, but greater than for sandbar sharks. Growth in individual sandbar sharks was not correlated with individual gill areas. The results support the hypothesis that species- or population-specific dW/dt &\propto& A/W, and that decreasing A/W results in asymptotic growth. However, other factors may obscure the influence of individual variability in gill area on individual variability in growth rates.



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