Joseph Powers’ lecture focused on the population status of Bluefin tuna, and began by introducing how fish populations are measured.  Biomass is the major indicator of fish population status.  The level of biomass termed ‘Maximum Sustainable Yield’ (MSY) is used by fishery managers to get a sense of the maximum harvest that can be taken at regular intervals without completely debilitating the fish source through overfishing.  If the biomass level is above the biomass level at MSY, then the effects of ecological non-linearities on population are generally not considered.  A complicating factor, however, is that determining a baseline population from which to begin measuring decline can be difficult since measurements of a particular stock are not usually taken before fishing occurs for the first time. 

Bluefin tuna exist throughout the Atlantic Ocean and Mediterranean Sea.  They have been caught since antiquity using progressively larger-scale equipment.  Data from traps laid during the last 200-300 years indicate mean catches of approximately 20,000 tons per year, whereas data from the present estimates mean catches at 50,000 tons per year.  However, many uncertainties exist in the process of catch estimation.  These include inaccurate reporting of either current or past data, and variations in which stage of growth or harvesting the measurements were taken. 

Many uncertainties also exist regarding the movement of tuna between the East and West Atlantic stocks.  These are hypothesized to be divided by a longitudinal line in the middle of the ocean, but it is unclear what patterns determine fish movement across this line.  Evidence currently supports the idea that the tuna ‘home in’ to a particular location in order to spawn, and the Gulf of Mexico is widely considered to be one such spawning area.  Because historical ‘hot spots’ of Bluefin tuna such as that which formerly existed off of the Brazilian coast have experienced steep population declines in the past, many people consider maintenance of the stock in the Gulf of Mexico to be of vital importance.  The manner in which to preserve this breeding ground is contested, though, and involves many large-scale factors.  Some NGOs think that halting long line fishing is a good solution, whereas others advocate focusing on ranching or ocean zoning.  It is difficult to predict the future of Bluefin tuna populations, but it is clear that for producers and consumers around the world, this fish and the management of its stocks are crucial.