The multi-species Philippine tuna purse seine fishery targets three tuna species: skipjack (Katsuwonus pelamis), yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus). These are highly migratory pelagic fishes that grow to different maximum lengths and weights. At present there is no mesh size regulation specific to the fishery in the Philippines although tuna purse seines generally use 8.9cm (3.5 in) mesh size in the bunt of the net. An empirical analysis was conducted to compare the catches of purse seine nets with two different mesh sizes in the top portion of the bunt: 8.9cm and 12.7cm. Field measurements of the morphometric characteristics of the three species were used to develop functional relationships between length, weight, body width, as well as operculum, pre-dorsal and maximum girths. An analysis of the selectivity characteristics of a purse seine was completed based upon the individual species' observed morphometric relationships and theoretical mesh retention characteristics of the net. Using these data along with the life history characteristics of the three target species, single species and multi-species Yield per recruit (YPR) and Spawning Stock Biomass per Recruit (SSBPR) models were developed. The results of the catch comparison analysis indicate statistical differences in the catch compositions of the two nets by weight, but there were no material differences from a fishery management perspective. The multi-species YPR is maximized with the 20.3cm 98.0in) mesh opening. However there is no yeild for skipjack with this mesh opening as indicated by the single species analysis. At low fishing effort levels of up to 100 vessel-months, the multi-species yeilds for mesh openings 8.9cm, 12.7cm, 15.2cm, 17.8cm, and 20.3cm are about the same. Assuming that the relative abundance of the three tuna target species remains constant in time and in all fishing areas, a management strategy to increase the yield from the fishery would be to adopt a slowly increasing bunt mesh opening, starting with the 8.9cm then slowly increasing the mesh opening up to 20.3cm over many years.