Abundance Trends and Fisheries for Highly Migratory Species in the Pacific Ocean

We review abundance trends and fisheries for highly migratory tunas, billfishes, and sharks in the Pacific. Following World War II, Japanese longline fleets increased fishing effort and expanded across the Pacific. Substantial increases in catches of tunas and tuna-like species occurred from 1950 to 2000. Target species changed through time as deep-set longline effort replaced shallow-set effort. This led to greater catches of bigeye tuna which is currently experiencing overfishing and approaching an overfished condition. There have also been changes in fishing fleets through time and in particular, purse seine effort now accounts for the vast majority of skipjack and yellowfin tuna catches. Despite vast increases in fishing effort directed at tunas, many stocks are fully exploited and are not depleted. Pacific bluefin tuna is an exception and is experiencing overfishing and is overfished. Bycatches of billfishes and sharks have also led to diverse trends in abundance. Some billfish stocks, e.g. striped marlin, have been overfished while others, e.g. swordfish are abundant. In contrast, many shark stocks, e.g. oceanic whitetip shark, have declined in abundance due to low fecundity and limited resilience to harvest although blue shark may be an exception to this pattern.