  The recovery of many groundfish stocks throughout the Northwest Atlantic has
been impeded by elevated natural (i.e., non-fishing) mortality (M) among
older/larger individuals. The causes of elevated mortality are not well known,
though predation by rapidly growing grey seal herds and unreported fishing are
thought to be possible drivers of mortality for Atlantic Cod (Gadus morhua) on
the Western Scotian Shelf and in the Bay of Fundy (known as "4X5Y cod") and in
nearby ecosystems. We developed a statistical catch-at-age model for 4X5Y cod
that accounted for both grey seal predation and estimated bycatch/discards to
evaluate the degree to which either of these factors may influence cod
mortality. The model was fit over a range of predation and discarding scenarios
to account for uncertainties and a lack of data for these processes. We found
that most cod M remained unaccounted for unless cod comprised a large
proportion (>0.45) of the grey seal diet by weight. If the reported bycatch
estimates are taken as accurate, then the magnitude of cod discards from
non-directed fisheries was minor, though these estimates are highly uncertain.
