Striped marlin (Tetrapturus audax) support important commercial and recreational fisheries in the central and eastern Pacific and in the Indian Oceans. Although directly targeted in the past, nowadays most are taken as incidental catch in tuna longline fisheries. Pacific-wide landings currently average near 12,000 metric tons per year and represent about 86% of world landings. Recreational and commercial fishing for striped marlin began off southern California in the early 1900s using hand-held harpoons and rod-and-reel. The California State legislature banned the use of harpoons to take striped marlin in 1935 and further curtailed the sale and import of striped marlin in 1937 thus preserving the southern California fishery entirely for recreational anglers.
Generally, fish begin arriving in the coastal and insular waters off southern California in June and remain until at least October. The number of fish moving into the southern California bight during any particular year is associated with water temperatures. The colder water north of Point Conception usually limits their northward distribution although during El Nio years they commonly range north to about San Francisco. A 31 year-long angler survey indicates fairly low, but steady, catch rate of 0.10 fish per anger-fishing-day.
In Mexican waters, striped marlin are taken for local markets and export to other countries. These fisheries include both artisan, using hand-hauled gillnets and longlines, and larger driftnet vessels targeting swordfish and sharks. The water off the southern tip of the Baja California peninsula to Manzanillo, Mexico is an area of high striped marlin abundance, that support a large recreational fishery. The striped marlin catch rate is 0.65 per days-fishing. Estimated recreational catches of striped marlin off Los Cabos, BCS average 12,000 fish annually.
Interest in angler-based tagging and survey programs has intensified in recent years. A workshop held in 1999 at the Balboa Angling Club of Southern California was convened to develop a plan to expand and enhance research collaboration between California billfish anglers and scientists. The workshop (Pacific Federal Angler Affiliation for Billfish) produced a angler-based research program to improve striped marlin assessments by providing new information on abundance trends, stress of tagging, life history parameters, and for the collection tissue samples for DNA analysis.
The striped marlin (Family Istiophoridae) is a large, oceanic fish with a long, round bill, small teeth and tall dorsal fin which decreases in height ending just before the second dorsal fin. Striped marlin reach a maximum size of nearly 12 feet, weighing over 450 pounds. The International Gamefish Association all-tackle record is for a 494-pound fish caught near New Zealand in 1986. The species is widely distributed throughout most tropical and sub-tropical waters of the Pacific and Indian oceans. Fishery data indicate a horseshoe-shaped distribution across the central north- and central south Pacific with a continuous distribution along the west coast of the Central Americas. It is apparently more abundant in eastern and north central Pacific than elsewhere.
Movements tend to be diffusive as striped marlin do not to form dense schools but occur singularly or in small groups, usually segregated by size. Adult fish are found in the north- and south- central Pacific where spawning occurs. Spawning occurs in the central Pacific and off central Mexico. Sub-adult fish move east toward the coast of Mexico where they are found in high abundance around the tip of the Baja peninsula. Most striped marlin caught in the southern California sport fishery are three to six years old and weigh 120 to 200 pounds. Striped marlin are not reproductively active while off southern California.
Tag recapture data indicate movement from southern California to Baja California Sur, Mexico but show little or no movement in the reverse direction. Tag recapture data further reveal movement from off Mexico and southern California to near Hawaii, Peru, and the south Pacific near the Marquises Islands. Striped marlin are epipelagic, preferring water temperatures of 20° to 25°C during all stages of their life cycle. Acoustic telemetry studies indicate they spend 86% of their time in the surface layer above the thermocline.
Striped marlin are opportunistic feeders on epipelagic fishes including mackerel, sardine, anchovy, and will take invertebrates including squid and red crab when available. Off southern California, they are often seen feeding at the surface on these small coastal fish. Predation on adult marlin has not been documented but may occur from large pelagic sharks or toothed whales.
Stock structure in the Pacific is unclear. Current evidence indicates striped marlin are probably a single Pacific-wide stock although the possibility of separate North and South Pacific stocks does exist. Genetic data further indicates a great deal of population structuring in the Pacific which implies discrete spawning areas for fish from Hawaii, Australia and the eastern tropical Pacific. The Pacific striped marlin resource appears healthy regardless of whether a single Pacific-wide stock or two separate north and southern stocks are assumed. The relationship between catch and fishing effort in the high-seas longline fisheries show sustained catches over a wide range of fishing intensities, suggesting Pacific-wide catches are below a maximum sustainable yield of 24,000 metric tons. Catches are fairly stable at around 10,000 to 14,000 metric tons. Angler catch and effort surveys indicate CPUE off California and Mexico has changed little since 1985.
Striped marlin will soon be covered under new international management convention and a Federal Management Plan is currently being drafted for highly migratory species by the Pacific Fishery Management Council. These management groups provide a great opportunity for effective long-term management and conservation of striped marlin and other highly migratory species. However, stock assessments for striped marlin are badly outdated and in need of reexamination. New assessments should include current fishery statistics, a clear definition of geographical limits, better understanding of age, growth and reproductive status, better indices of abundance and the effectiveness of catch and release in the recreational fisheries.