Migratory patterns of Pacific blue marlin
The 2014 Hawaiian International Billfish Tournament (HIBT) Great Marlin Race (GMR) in Kona, Hawaii, added another valuable dataset to the growing body of knowledge we have about Pacific blue marlin.
Scientists have been able to sustain annual studies of Pacific blue marlin from a single location for six consecutive years, which is allowing them to gain new insights into the migratory patterns of these animals and the environmental factors that shape them.
The first scientific manuscript describing these patterns has been submitted for publication. The submitted manuscript revealed that low oxygen and low temperature each affect the vertical and horizontal movements of
Pacific blue marlin, and the combined effects, both low oxygen and low temperature, are even greater than either factor by itself.
This was the first study of its kind, and it would not have been possible without the long-term commitment to research made by the HIBT and the ongoing generosity of the anglers, captains and crews who have supported these efforts year after year.
During the first year of the Great Marlin Race at the HIBT in 2009, and in most years since, tagged marlin tended to travel to the southeast. In fact, many swam all the way to the southern hemisphere to the vicinity of the Marquesas Islands in French Polynesia.
However, in 2010, none of the tagged marlin crossed the equator. In fact, they almost all traveled more east-southeast towards Central America and the Galapagos Islands. In order to understand why this may have occurred, they reviewed sea surface temperature data from that period of time.
What they noticed was that there was a tongue of cold water extending westward from South America along the equator, which appeared to have created a barrier to southward migration.
Interestingly, the migration patterns of marlin tagged in the 2014 HIBT International Great Marlin Race were similar to the patterns observed in 2010, which led scientists to wonder whether a similar La Nina-like, cold water tongue had occurred across the eastern equatorial Pacific. However, no such structure was observed during the time that would have been relevant (September to October, 2014).
Another observation scientists made from the 2014 HIBT IGMR tracks was that several of the marlin made extensive forays north of the Hawaiian Islands.
In the past, scientists have occasionally observed individual marlin that swam north for a short time, but last year, three of the four fish for which tracks were developed spent at least some time north of Hawaii, and two of those three marlin went far to the north, passing the 27-degree north parallel, where they spent several weeks before traveling south-southeast.
This unusual pattern may be a response to the unusually warm water throughout the Central Pacific in the fall and winter of 2014. With an even warmer Pacific basin developed in 2015, and peaking in late summer/early fall, it will be very interesting to see whether marlin tagged in the 2015 HIBT IGMR will exhibit similar migratory behaviors.
As the Pacific Ocean grows warmer and El Nino/La Nina cycles potentially become stronger and more common, there is a possibility that the distribution of Pacific blue marlin could shift – with more usable habitat available in the northern hemisphere, and less need to migrate south across the equator to remain in the warmer waters they prefer.
It’s also possible that more pronounced cold water equatorial flows during La Nina years could create a barrier to southward trans-equatorial movement, which could lead to a break in marlin populations in the northern and southern hemispheres, and therefore a concurrent ceasing of gene flow between these populations.