Why the Atlantic cod (Gadus morhua) stock off eastern Nova Scotia has not recovered

An age-structured population dynamics model, incorporating interactions bet ween Atlantic cod (Gadus morhua), the fishery, and the grey seal (Halichoer us grypus) population, was applied to the cod stock off eastern Nova Scotia (Northwest Atlantic Fisheries Organization Divisions 4Vs and 4W, commonly abbreviated to 4VsW), a stock that has dramatically declined since the late 1980s. Mortality was modeled as having three components: fishing mortality (F), seal predation (M-p), and all other sources of natural mortality (M). Specifically, M was assumed to be distinct for immature cod (ages 1-4; M-i ) and mature cod (age 5 and older; M-m), and respective annual variations w ere estimated. Parameters estimated also included recruitment (cod abundanc e at age 1; R), F, and M-p. Based on our estimates of F, M-p, and M, it is unlikely that the collapse of the 4VsW cod stock can be attributed to a sud den increase in M; fishing appears to have been the primary cause for the s tock's decline. However, after the moratorium on commercial fishing in 1993 , increasing M-p and M-m and low R may have contributed to the failure of t he 4VsW cod stock to recover.