Barbara Block: Atlantic Bluefin Tuna: A Novel Multistock Spatial Model for Assessing Population Biomass(Pew Marine Fellow, 1997)

Atlantic bluefin tuna (Thunnus thynnus) is considered to be overfished, but the status of its populations has been debated, partly because of uncertainties regarding the effects of mixing on fishing grounds, according to an article published in PLoS ONE on 9 December 2011 by Barbara Block, Prothro Professor of Marine Science at Stanford University, and colleagues. Block and her associates  formulated a new seasonally and spatially explicit fisheries model that is fitted to conventional and electronic tag data, historic catch-at-age reconstructions, and otolith microchemistry stock-composition data to improve the capacity to assess past, current, and future population sizes of Atlantic bluefin tuna. They applied the model to estimate spatial and temporal mixing of the eastern (Mediterranean) and western (Gulf of Mexico) populations, and to reconstruct abundances from 1950 to 2008.

They showed that western and eastern populations have been reduced to 17 percent and 33 percent, respectively, of 1950 spawning stock biomass levels. Assuming that future catches are zero, western and eastern populations are predicted to recover to levels at maximum sustainable yield by 2025 and 2015, respectively. If fishing were to continue in the eastern Atlantic at the unregulated levels of 2007, both stocks would continue to decline. The authors conclude that since populations mix on North Atlantic foraging grounds, successful rebuilding policies will benefit from trans-Atlantic cooperation.

Read the article, Atlantic Bluefin Tuna: A Novel Multistock Spatial Model for Assessing Population Biomass, on the PLoS One website.