The Survival Estimates In Non-Equilibrium situations (SEINE) model calculates mortality rates from changes in
the mean lengths.The model is a variant
of the Beverton and Holt (1956, 1957) annual mortality estimator which has
received widespread use due to limited data requirements but has also been
criticized due to the required assumption of equilibrium conditions (i.e. the
mortality rate has been constant for enough time so that the observed mean
length reflects the current mortality rate).Gedamke and Hoenig (2006) developed the SEINE
model for application in non-equilibrium conditions and to allow the mortality
rate to change at one or more points in time.
Given von Bertalanffy parameters, the length at full
vulnerability, and a series of annual observations of mean length over time,
the model estimates mortality rates and the years in which they changed. A grid
search over possible years of change is used to evaluate the likelihood surface
and provide starting values for the final estimation.Additional changes in mortality can be added
to the model and the improvement of model fit in relation to the additional
parameters can be evaluated through AIC values.
The model was developed for the assessment of goosefish (monkfish;
Lophius americanus) where sample
sizes for each year were quite low and the mean size was highly variable from
year to year.It has since been used in
similar data-poor situations including the assessment of the northeast skate
complex and mutton snapper in Puerto Rico.
The calculation engine was built using AD Model Builder by
Alan Seaver (currently at the NMFSNortheastFisheriesScienceCenter)
and Dr. Todd Gedamke (currently at the NMFSSoutheastFisheriesScienceCenter).
Beverton, R. J. H., and S. J. Holt. 1956. A review of
methods for estimating mortality rates in fish populations, with special
reference to sources of bias in catch sampling. Rapports et Proce`s-verbaux des
Re´unions, Conseil International pour l’Exploration de la Mer 140:67–83.
Beverton, R. J. H., and S. J. Holt. 1957. On the dynamics of
exploited fish populations. Fishery Investigations Series II, Marine Fisheries,
Great Britain Ministry of Agriculture, Fisheries and Food 19.
Gedamke, T., and J. M. Hoenig. 2006. Estimating mortality
from mean length data in nonequilibrium situations, with application to the
assessment of goosefish. Transactions of the American Fisheries Society
135:476–487.
