Clarifying Striped Marlin Stock Mixing Throughout the Pacific
Overview
Known for their acrobatic fighting abilities and stunning coloration, striped marlin are an ecologically and economically important billfish species found throughout the Pacific and Indian oceans. Frequently caught in longline fisheries targeting tunas and swordfish, several stocks of striped marlin have been found to be depleted across much of their range and international management bodies have highlighted the need for greater information on the biology of striped marlin in the Pacific to improve stock assessments and conservation initiatives for the species. The IGFA has stepped in to help provide this crucial data and ensure that healthy populations of striped marlin are around for future generations.
The Issue
Recent stock assessments for striped marlin in the western and central North Pacific and southwestern Pacific have highlighted uncertainty in the assessment results and continued overfishing and overfished status of striped marlin. With no indications of recovery despite decreasing fishing mortality estimates, assessment results highlight the need for improved information on striped marlin catches, age and growth, stock structure, and regional connectivity to support more effective management approaches.
The need for improved stock structure information was further supported by recent research by IGFA Conservation Programs Manager Jackson Martinez, who found that the central North Pacific may serve as a mixing ground for multiple stocks, or populations, of striped marlin throughout the year. Using state-of-the-art genetic approaches, his findings suggest that stock mixing in the central North Pacific, including areas fished by the Hawaii pelagic longline fleet, is not currently accounted for in stock assessments or management plans. This creates a mismatch between static management boundaries set by Regional Fisheries Management Organizations (RFMOs) and the best-available biological data. In addition, recent tagging data from the IGFA Great Marlin Race (IGMR) indicate that striped marlin make long-distance movements across the Pacific more frequently than previously thought, further highlighting the need for additional research to understand annual movement patterns and regional connectivity.
The Research
Based on the findings highlighted above and the need for improved data, the IGFA teamed up with Dr. Jan McDowell from the Virginia Institute of Marine Science to expand this genetic research throughout the full Pacific to investigate when and where stocks of striped marlin mix over time. This research will inform ongoing efforts by the Pacific RFMOs to improve the assessment and management of striped marlin, which are currently overfished throughout much of their range and are under a rebuilding plan in the western and central North Pacific.
To kick-start this study, we enlisted the help of recreational anglers fishing for striped marlin in various areas of the Pacific, including IGFA Trustees and Representatives, who are assisting with sampling efforts by collecting small fin clips from live striped marlin before release. We have also established sampling partnerships with scientific colleagues across the region who are collecting tissue samples from landed fish at local markets and sportfishing docks. Ongoing or planned sampling will occur over two years from Southern California to Peru, throughout the South and southwestern Pacific, New Zealand and Australia, and Taiwan.
The Goal
The primary goal of this study is to refine our understanding of when and where genetically distinct stocks of Pacific striped marlin mix, and how stock mixing varies with life stage and season. By working alongside Pacific RFMOs, the results of this study will contribute to improved assessment and conservation initiatives for striped marlin, ensuring the future of this iconic species for generations.
This study, especially the intensive sampling required to produce robust results, would not be possible without strong collaborations with the recreational fishing community. This is what the IGFA does best – advancing meaningful research on ecologically and economically important species while building and maintaining crucial partnerships with the angling community who make our work possible. Stay tuned for updates.