Marlin species, in general, have very little commercial value and are most often taken as bycatch in fisheries targeting other species. That is not the case, however, for striped marlin (Tetrapturus audax) where directed longline fisheries developed in the early 1960s to satisfy a demand for Japanese fish sausage; today, striped marlin are harvested for the sashimi and frozen filet markets while also forming the basis of important recreational fisheries in the United States (California and Hawaii), Mexico, Ecuador, New Zealand, East Africa, and Australia. The combined impact of both commercial and recreational fisheries raises striped marlin above all other billfishes in economic value and are thus the most studied of the group. Striped marlin are found in more temperate waters than other billfishes with a strong preference for waters 68-77 °F. Plotting longline catches on a map illustrates a horseshoe-shaped striped marlin distribution that is continuous along the continents of the eastern Pacific with two branches stretching west, across the Pacific, primarily between 20°–30° above and below the equator . Despite numerous conventional tagging studies and DNA analyses of striped marlin samples from throughout the Pacific, scientists have no idea how much mixing there is between regions of high striped marlin abundance. This type of information is fundamental for our understanding of striped marlin stock structure and is necessary for appropriate fisheries models and management practices to be used to insure the health of this important resource.
Conventional tagging programs can provide insight into movement patterns and to this end over 12,000 tags have been placed on striped marlin. The overall return rate of these tags has been < 1% with over 90% of recoveries occurring in < 1 yr. With a record distance of 6713 km in 141 d, conventional tagging has demonstrated that striped marlin are capable of traversing long distances over short time intervals. However, anecdotal information from the northeastern Pacific appears to support some level of regional site fidelity and seasonal movement. For example, striped marlin tagged off southern California have been recovered off southern Baja California, Mexico; fish tagged off Mexico have been recaptured in California and one California tagged marlin was recaptured off California a year later (Squire, 1987). The inconsistent and conflicting results regarding the migration patterns and stock structure of striped marlin underscores the need for further work in this area. The advent of electronic tagging technology presented an opportunity to collect new fishery independent data to address the spatial movement patterns throughout the Pacific.
The Offield Center for Billfish Studies placed over 250 popup satellite tags on striped marlin throughout the Pacific in an attempt to learn more about this important species movement patterns and stock structure. Although tag shedding has proven to be quite a problem for marlin tagged with popup tags, we were able to striped marlin movement data for periods up to 9 months. All of our tagging results failed to demonstrate any movement of striped marlin across the Pacific or across the equator, in either direction (not taking into account fish tagged on the equator).
The popup tagging data alone does not allow us to confidently make any conclusions regarding striped marlin stock structure, but the popup data along with conventional tagging and DNA analyses make it very likely that local populations of striped marlin exist in different parts of the Pacific with only a limited amount of movement between these local populations.
The next step for the Offield Center for Billfish Studies with respect to striped marlin, is to initiate the world’s first archival tagging study. Archival tags must be surgically inserted so each fish must be brought onboard the research vessel and carefully handled so that it can be released in good condition. Packy Offield’s crew on the Kelsey Lee have perfected these handling procedures and are set to begin this work in the fall of 2008. The only way to retrieve data from an archival tag is to wait from someone to recapture the fish in the future and hope they return the tag. If you’re fishing for striped marlin in the Pacific and you see a strange tag sticking out of the belly of a striped marlin, or see a separate brightly colored tag near the dorsal fin that announces a reward for the fish, be sure to keep the fish, recover the tag from the belly cavity and contact us for a $500 reward!
The Marine Conservation Science Institute gratefully acknowledges the support of the Offield Family Foundation.