Step 4. Initial stock assessment
After conducting a PSA on target species, we assessed the status of individual fish targets, with a focus on the targets that were revealed as highly vulnerable to overfishing through the PSA: Goliath Grouper, Nassau grouper and Red Snapper. First, we used the method matrix to determine which methods were available for the current data streams. Several data-limited methods were then used to estimate stock status relative to unfished levels and the intensity of fishing mortality, including length based methods and the MPA density ratio.
Because NGOs and some fishermen had measured the lengths of individual fish in the catch, we were able to use length based methods to calculate fishing mortality (F) and to assess distribution of lengths from catch data. Specifically, we used the mean length (LBAR) and Froese sustainability indicators methods. The estimated fishing mortality was two to three times greater than natural mortality, an indication of high fishing pressure. Goliath grouper, Nassau grouper and red snapper appear to be overfished and are experiencing overfishing under a range of life history parameters. Ranges of life history parameters were tested due to uncertainty about the actual values of life history parameters in fishery; values were taken from the scientific literature, rather than measured in the field. Additionally, Nassau grouper, red snapper and the Goliath grouper are often caught under the length of maturity, suggesting the need for size or catch limits or size limits for these species.
Preliminary Assessment Results for three species:
Using a data set that is independent of the catch data, we estimated the relative density of each fish target in MPAs and fishing areas, over time. We calculated the MPA Density Ratio (MPA-DR, fished biomass:unfished biomass) for these three finfish species using the SCUBA visual census data. Results presented above are only for the most recent conditions for 2013 and the running average of density ratio from 2009-2013 to account for variability introduced by natural events like storms. We found that the MPA Density Ratio for both grouper species fell within the cautionary range of 0.2 to 0.6, suggesting that fishing pressure should be reduced. The snapper is approaching the cautionary range, with an MPA-DR estimate greater than 0.6, so harvest can continue but this target should be monitored carefully; it is being fished fairly hard, but is not depleted – yet.