OHI+ Tanzania_Technical Report_2018

Ocean Health Index – Tanzania 2018 42
for this particular approach. Thus, consistent with previous work (Halpern et al. 2012), countries are
rewarded for having wild stocks at the biomass that can sustainably deliver the maximum sustainable
yield, +/-5% to allow for measurement error, and are penalized for both over- or under-harvesting.
Missing status scores, SS, needed to be gapfilled for a large proportion of the catch (12/25 stocks).
Gapfilling was necessary because B/B MSY values could only be estimated for taxa identified to the species
level. Furthermore, B/B MSY values for some species were not able to be estimated due to model nonconvergence
or too few years of catch data. Missing status scores were gapfilled using the median status
scores of the stocks sharing a region and year, the median value was then adjusted using a taxonomic
reporting penalty (see Table 12 below). For catch not reported to the species level, a penalty was applied
for increasingly coarser taxonomic reporting, as this is considered a sign of minimal monitoring and
management. The penalty is based on the ISSCAAP convention for taxon codes
(http://www.fao.org/fishery/collection/asfis/en), which defines 6 levels of taxonomic aggregation, from
6 (species) to 1 (order or higher). When g