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In summary, according to preliminary results, Arostegui and Carlisle believe that there’s likely some interplay between sea surface temperature and habitat compression that determines whether conditions are favorable for blue marlin. Over the four years of data analyzed, marlin were found to transit through and even inhabit areas of vertical habitat compression as long as sea surface temperatures were greater than 25°C. Marlin were also found to traverse areas that had sea surface temperatures below 25°C. However, blue marlin tended to avoid areas of upwelling/habitat compression that also had cool sea surface temperatures. Because blue marlin spend so much of their time in surface waters, Arostegui and Carlisle contend that the physical oceanographic conditions in the upper layer of the water column may affect blue marlin more than those at greater depths. As such areas of upwelling with associated shoaling of the thermocline/oxycline and sea surface temperatures less than 25°C may represent a physiological barrier for blue marlin migration in equatorial waters of the Pacific. This work by Martini Arostegui and Dr. Aaron Carlisle represents just the beginning of broader, more comprehensive analysis of IGMR tag data. Deploying PSATs on billfish in locations around the world allows us to assess population connectivity and habitat use. Multiyear deployments in events like the Hawaiian International Billfish Tournaments provide scientists with an incredible opportunity to investigate marlin behavior in response to different prevailing oceanographic conditions. None of this, however, could have been achieved without the tag sponsors, anglers, crews and other individuals that have supported the IGFA Great Marlin Race. Not only is the collective benevolence of these individuals making this research possible, but it is also sending a very powerful message to fisheries scientists and managers that we believe more needs to be done to understand and conserve these magnificent animals. Vertical Habitat Compression While habitat compression associated with La Niña conditions may be a factor that affects trans-equatorial movements of blue marlin in the Pacific, previous research has shown that blue marlin and other billfish species exist in other areas that exhibit habitat compression. In fact, habitat compression in some areas may be favorable for billfish because it also concentrates their preferred prey. Arostegui, M. 2014. The Influence of ENSO on Migrations and Vertical Movements of Blue Marlin (Makaira nigricans) in the Equatorial Pacific South of Hawaii. B.S. Honors Thesis, Stanford University, Stanford, 42 p. 68 BISBEE’S CONSERVATION JOURNAL Q1/Q2 • 2016


BCJ_Q1/2_2016
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