Life-history
To determine if fatty acid groups differed in size-at-age, length vs.
age was modeled using the Von Bertalanffy length-age model fit to length
at age-of-capture of individual fish (Quinn et al., 1999):
The length-age model describes length Lt at
age-of-capture t as a function of theoretical maximum length
(L∞ = mm), instantaneous rate at whichLt approaches L∞ (K= 1/year), theoretical age-at-zero length (t 0 =
years), and multiplicative error (ε ). Model parameters,L∞ , K , and t 0, and
associated standard errors were estimated using nonlinear regression.
Residual sums-of-squares were compared between a full model (separate
models for each group) to a reduced model (a single model for all
groups) in a likelihood-ratio test (Hosmer Jr et al., 2000). If the
likelihood-ratio test was significant (P <0.05), we concluded that growth differed among groups identified by
fatty acids. If the likelihood-ratio test was not significant (P> 0.05), we concluded that growth did not differ among
groups. The same test was repeated for each pair of groups, with and
without giant individuals (fork length ≥900 mm) included in each group,
to isolate the influence of this subset in our size-at-age comparison
due to the prevalence of giants in one of the groups (see Results).