The Age
Structured Assessment Program (ASAP) is
an age-structured model that uses forward computations assuming
separability of fishing mortality into year and age components to
estimate population sizes given observed catches, catch-at-age, and
indices of abundance. Discards can be treated explicitly. The
separability assumption is relaxed by allowing for fleet-specific
computations and by allowing the selectivity at age to change smoothly
over time or in blocks of years. The software can also allow the
catchability associated with each abundance index to vary smoothly with
time. The problem’s dimensions (number of ages, years, fleets
and abundance indices) are defined at input and limited by hardware
only. The input is arranged assuming data is available for most years,
but missing years are allowed. The model currently does not allow use
of length data nor indices of survival rates. Diagnostics include index
fits, residuals in catch and catch-at-age, and effective sample size
calculations. Weights are input for different components of the
objective function and allow for relatively simple age-structured
production model type models up to fully parameterized models.
The calculation engine was built using AD Model Builder by
Drs. Christopher M. Legault (currently at the NMFS Northeast Fisheries
Science Center) and Victor R. Restrepo (currently at the NMFS
Southeast Fisheries
Science Center).
ASAP has been used as an assessment tool
for red grouper (SEFSC), yellowtail flounder (NEFSC), Pacific sardine
(SWFSC), Pacific mackerel (SWFSC), Greenland halibut (ICES), Norther
Gulf of St. Lawrence cod (DFO), Gulf of Maine cod (NEFSC), Florida
lobster (FFWCC), and fluke (NEFSC).
