Fisheries in the Pacific

Overview of tuna fisheries, stock status and management framework…
• SB/SB F = 0 , the current amount of spawning biomass (or adult tuna quantity) (SB) compared
to the estimated amount of adult fish that would be present within the stock if it had not
been fished (SB F = 0 ). 23
These indices are used to draw a plot which provides a visual display of the estimated
status of the four tuna stocks relative to reference points (fig. 12).
Figure 12: The modified Kobe plot (“Majuro plot”) identifying the status
of the stocks according to reference points on fishing mortality (F/Fmsy)
and spawning biomass (SB/SBF0)
The plot describes the 2012 stock status for skipjack (Rice et al. 2014), bigeye (Harley et al. 2014) and yellowfin
(Davies et al. 2014) and the 2010 stock status for South Pacific albacore (SP Albacore) (Hoyle et al. 2012). Stocks
located in the white area are estimated healthy, overfishing is occurring for stocks in the orange area (catches
are too high for sustainability) and stocks in the red area are overfished (the level of the spawning biomass is
too low to sustain the stock). Many stock assessment runs are performed for each stock, using different combinations
of input parameters (e.g., different estimates of growth rate, rates at which fish die due to natural
causes, etc.). These lead to slightly different estimates of current stock status. Hence the stock assessment run
selected as the ‘reference case’ for management advice is shown as the main ‘point’ (plain circle), and the range
of estimated status from key uncertainty runs with these different input parameters are shown as lines radiating
out from that point.
stock is occurring, meaning that the rate at which fish are being caught is not sustainable in the long term.
23. Within the WCPFC, a limit reference point of 20%SB F=0 has been adopted for key tuna stocks as it
is considered a level below which the health of tuna stocks will be affected. It means that when the current
adult biomass represents less than 20% of the amount that would theoretically have been present if no
fishing had occurred, the stock is considered overfished, meaning that the level of the stock is too low.
At present, the Commission has not adopted target reference points. However, at the time of writing
(May 2015), discussions on options for SB/SB F=0 target reference points for skipjack within the range
of 40-60% of unfished spawning biomass were ongoing.
41