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Experiments on the use of sea bird mitigation methods were conducted aboard Uruguayan pelagic longliners between 2010 and 2012. Experiments looked at the difference between setting bait at the sea surface and setting baits underwater. The researchers recorded the abundance of sea birds following the vessel and incidences of attacks on bait and mortality. When the bait was set underwater, there was a marked reduction in the number of seabirds following the vessel and attacks on bait. Mortality levels of birds caught on bait set 4 m below the surface were 87% lower than mortality levels for birds when bait was set at the surface. There were no bird mortalities when bait was set 10 m below the surface. The mortality level of birds when bait was set at the surface was 11.6 birds/1000 hooks. No differences in catch rates of target species (tuna) were observed when bait was set at the surface or below the surface.