THE VERDICT ON STRIPED MARLIN: OVERFISHED!

"As Bad Off as White Marlin," Says One Official

The Pacific's striped marlin (Kajikia audax) and the Atlantic's white marlin (Tetrapturus albidus) have a lot in common. Too much, in fact. The two species are virtually identical genetically, according to DNA evidence, giving rise to the theory that they were once a single species, separated eons ago when primordial upheavals on earth divided the global sea into Atlantic and Pacific Oceans. But today, they've been reunited - on the distressingly long list of species endangered by global overfishing.

The plight of white marlin is familiar to all readers of the Marine Bulletin, especially since 2002 as this magnificent but disappearing billfish has flirted with listing under the Endangered Species Act. The numbers of all large ocean predators have declined by 90 percent in the last 50 years, claims a widely cited 2005 study (Ransom and Myers). The white marlin could stand as exhibit A, right alongside the even more famous but equally depleted Atlantic bluefin tuna. The numbers of white marlin, according to the International Commission for the Conservation of Atlantic Tunas, have been reduced to about 12 percent of what they were in the 1960s.

As recently as a year ago, the status of striped marlin was discomfortingly classified as "unknown." Because marlin and sailfish are a ubiquitous bycatch in Pacific longline fisheries, and longline effort has been increasing in recent years, it was widely suspected that Pacific billfish, too, might be overfished. But no formal stock assessment had ever been done. Until now. A 2007 assessment of striped marlin by the International Scientific Committee for Tuna and Tuna-Like Species of the North Pacific Ocean (ISC) confirms our worst fears; that, as one ISC official told NCMC, "the striped marlin is as bad off as the white."

A Deadly Recipe

The striped marlin is not as big as blue or black marlin, but it can grow up to 12 feet in length and weigh 450 pounds. Although it has the greatest distribution of any Pacific marlin, inhabiting temperate and tropical waters from the Indian Ocean to the edge of the North American continent, striped marlin are more abundant in the eastern and central parts of the Pacific. Striped marlin, like all billfish, are caught as bycatch in pelagic longline fisheries targeting swordfish and tunas. Foreign fishermen often land and sell them for local and global markets. In fact, the striped marlin is sometimes targeted by longliners because of its relatively high market value.

A deadly recipe of rapidly expanding longline fleets and a general lack of regulation in all but a few Pacific fisheries has taken its toll. An ISC Marlin Working Group studied the most up-to-date data on the striped marlin fisheries last year and concluded:

• Spawning biomass (the population of mature adults) has declined from around 40,000 metric tons in the early 1970s to about 5,000 tons in the early 2000s. Spawning biomass in 2003 was estimated to be 14-15 percent of the 1970 level.
  
  
• Recruitment (the strength of each new generation) has been in decline since the 1970s. Recently it's been about half the long-term average.
  
  
• Both spawning biomass and landings will continue to decline if the current fishing mortality rate is maintained.
  
  
• A 30-40 percent reduction in fishing effort is needed to bring fishing mortality down to a sustainable level.

The bottom line, then, is that striped marlin are severely over-exploited, with the number of spawning age fish reduced by 85 percent over the last several decades resulting in way below average reproduction. This decline will continue unless fishing mortality is significantly decreased; it must be cut by about a third just to halt the decline, by more if the population is to rebuild.

Close U.S. Markets to All Billfish

Billfish are magnificent creatures, large ocean predators at the top of the food chain. Wiping out the sea's keystone predators can weaken the entire food web and create cascading effects in pelagic communities, with dire consequences for the ecosystems as well as fisheries. Billfish support highly valuable and conservation-oriented recreational fisheries that release nearly every fish they catch to re-populate and keep the fishery healthy.

White marlin and the other Atlantic billfish have been banned from the U.S. seafood trade since 1989. California prohibited the sale of striped marlin decades ago. In 2004, the Pacific Fishery Management Council outlawed trade in Pacific striped marlin taken within its jurisdiction.

But outside the U.S., billfish are caught as bycatch in swordfish and tuna longline fisheries. These fisheries also have substantial interactions with sea turtles, seabirds and marine mammals, as well as sharks and other vulnerable species. Because of the commercial value of marlin (and to a lesser extent sailfish), foreign fishermen often land and sell billfish for commercial markets.

It will surprise many readers to learn that the U.S., despite its home-grown conservation ethic, is a major importer of billfish caught by foreign fishermen, fish that come mainly from the Pacific (legal) but also from the Atlantic (illegal). An open and flourishing U.S. market for foreign-caught billfish places additional pressure on unregulated Pacific stocks, while creating a black market for Atlantic-origin fish.

"The biggest contribution the U.S. can make to conserving Pacific billfish at this time," says NCMC president Ken Hinman, "is to close our markets to all marlin and sailfish, regardless of origin, while making it a priority to seek stronger international conservation agreements in the Pacific. This new information on the plight of striped marlin means we can no longer pretend we don't know what's happening."

NCMC Marine Bulletin -- Winter 2008

Read more on NCMC's campaign to Give Pacific Billfish a Break.