A PRELIMINARY INVESTIGATION OF THE YELLOWFIN TUNA (THUNNUS ALBACARES) POPULATION IN THE ATLANTIC OCEAN USING THE INTEGRATED STOCK ASSESSMENT MODEL, MULTIFAN-CL

SUMMARY The ICCAT tropical tuna working group proposed that a stock assessment of yellowfin tuna (Thunnus albacares) in the Atlantic Ocean should be attempted using the fully integrated stock assessment model MULTIFAN-CL. Two model variations were attempted. The base case model assumed a single recruitment event per year, with a variation model assuming a recruitment event every three months. Unfortunately, tagging data were not included in these models as several inconsistencies were found in the tagging database. The outputs from both the base case and quarterly recruitment models appear to be overly optimistic. For the base case model, current Biomass was estimated to be below B MSY , however current F was far below F MSY . For the quarterly recruitment model, both reference points were well within their estimated MSY values. These findings are inconsistent with the output of previous stock assessments on this species in the Atlantic region. The base case model estimated higher levels of both current as well as initial biomass than the quarterly recruitment model. This assessment should be viewed as part of an ongoing process, as the addition of tagging data may well result in a more realistic assessment of the yellowfin tuna stocks in the region.