Fishing mortality (F) is defined by The Study Group on Unaccounted Mortality in Fisheries (ICES, 1995) as "'The sum of all fishing induced mortalities opccuring directly as a result of catch or indirectly as a result of contact with or avoidance of the fishing gear'"
They give the equation:
F = Fc + Fb + Fd + Fe + Fo + Fg + Fa + Fh, where
Fc == landed catch
Fb == illeagal, misreported, unreported
Fd == discard mortality: mortality from discards
Fe == escape mortality: mortality of fish that escape capture but still die
Fo == drop out mortality: fish that are caught in the net but are killed and fall out of the net before being brought aboard
Fa == avoidance mortality: death rate associated with the stress that fishing causes fish (i.e. avoiding the net)
Fg == ghost fishing mortality: fish that die in "ghost gear"--gear that is lost at sea
Fh == habitat degradation mortality
The most important of these are:
Fb, Fd, Fe, and Fg
Illegal, Unreported, and Unregulated fishing (IUU):
- IUU is a major source of uncertainty in stock assessments (they cite Bray 2000; Evans 2000; Ices, 1994, 2000, and 2004)
- Most information available is anecdotal
- Most estimates are fishery-specific
- FAO estimates that IUU kills about 8 million TONNES per year
- Mostly Tuna and deep sea species
- "Constitutes a doubling of catch in the last 20 years" (they cite Schmidt 2004)