Despite
its importance in fisheries studies, there is insufficient
understanding on the effect of sampling error or bias on individual
growth and other stock indicators. We show the influence of sample
length distributions on parameter estimates, illustrating with an
example. For the brown swimming crab, we simulated length samples in
five configurations and estimated parameters of von Bertalanffy (k, L∞, t0), asymptotic weight (
W∞), weight-length relationship (a, b), growth performance (ϕ’) and
condition factor (Kn). Parameter estimates were compared with baseline
values using relative bias, standard error and root mean square error.
The results show that the accuracy and bias of parameter estimates
depend on the lengths sampled. For example, the bias and accuracy of L∞
and W∞
vary inversely with sampled length, whereas combining length segments yields smaller biases of k and t0 than those of
L∞
and W∞. In general, the accuracy of parameter estimates does not always
depend on sampling the entire length range, and errors are not the same
for all parameters. These results are useful to guide sampling when
resources are scarce. We discuss potential reasons for incomplete length
sample structure and offer recommendations to obtain best estimates for
parameters of interest. |