Sx. Cadrin et Ds. Vaughan, RETROSPECTIVE ANALYSIS OF VIRTUAL POPULATION ESTIMATES FOR ATLANTIC MENHADEN STOCK ASSESSMENT, Fishery bulletin, 95(3), 1997, pp. 445-455
Historical and retrospective comparisons of Atlantic menhaden virtual
population analyses (VPA) from 1955 to 1995 revealed substantial incon
sistency in estimates of management variables in the last year of stoc
k assessments. Estimates of management variables from several historic
al stock assessments were generally consistent throughout most of the
time series. In the last two years, however, historical estimates have
deviated from revised estimates. Relative performance of alternative
ad hoc methods for estimating fully recruited fishing mortality (F) in
terminal years showed that all methods were imprecise, but convention
al catch-curve estimates were unbiased and had the least retrospective
inconsistency. Retrospective differences in terminal estimates of age
-1 F by separable VPA ranged widely for eight alternative settings but
were clearly minimized by using seven years of catch data. The genera
l magnitude of retrospective difference was +/- 1.2 billion recruits (
46% relative difference), +/-9,000 metric tons of spawning stock bioma
ss (33% relative difference), and +/-4.7 percent maximum spawning pote
ntial (106% relative difference). Retrospective differences in recruit
ment, spawning stock biomass, and spawning potential were positively s
kewed but not biased, indicating that the frequency of positive and ne
gative inconsistencies are equal but that the positive differences are
much greater in magnitude. The skewed distribution of retrospective i
nconsistency should be considered for managing the Atlantic menhaden f
ishery.