Great Marlin Race tags shed light on Pacific blue marlin migratory patterns
The workhorse of the Great Marlin Race (GMR) is the pop-up archival satellite tag. These tags record information on temperature, depth and light until they detach from the fish at a pre-programmed date and transmit the data to researchers via Earth-orbiting satellites, meaning that data is recovered without having to recapture the fish.
Temperature and depth data provide valuable information about what part of the water column the fish use and the oceanographic structure of the water column. Light levels are used to estimate the location of the fish using techniques similar to earlier explorers.
The newest generation of pop-up archival satellite tags are much smaller and more sophisticated than the tags used during the first two years of the Great Marlin Race. Therefore, scientists are able to collect more data from longer tracks, which provide them with an insight into the overall migratory patterns of marlin that they did not previously have.
For example, scientists are more frequently observing that marlin tagged off the coast of Kona as part of the annual Hawaiian International Billfish Tournament (HIBT) are migrating great distances and are often ending up around French Polynesia.
These migrations may suggest that French Polynesia and Hawaii may be waypoints within the larger scale migratory patterns of Pacific blue marlin. Interestingly, some blue marlin tagged near Tahiti, French Polynesia appeared to migrate long distances in a northwesterly direction, which possibly could represent a new part of this migratory cycle.
They are also finding that not all marlin are making dramatic long distance migrations. In fact, some are relatively residential within a region and spend the full duration of the tag deployment in the general area where they were tagged, demonstrating that marlin exhibit a diversity of migratory behaviors.
For example, several blue marlin tagged off the coast of Kona spent the full 180 days of the tag deployment moving within the vicinity of the main Hawaiian Islands.
A great benefit of the GMR is that it is a long-term program, wherein billfish are tagged in the same tournaments over multiple years. So as they continue to tag more marlin, it is their hope that over time, they can learn more about the diversity of their migratory patterns and the factors that influence them in an effort to eventually “close the loop” on the global migratory cycles of marlin. As ocean conditions continue to change, it is important to understand how the environment influences billfish distribution.
By exploring the link between the physical environment and the distribution of marlin, we can learn how and why their geographic and depth distribution changes seasonally, interannually and over longer time scales, such as over El Nino/La Nina cycles.
The information obtained from the GMR can play a vital role in the development of effective management strategies and can help ensure a positive future for these amazing sportfish.