We started our fishing trip as we might anywhere, looking for bait to catch swordfish and other large pelagics. But we weren’t off the Florida Keys, pitching sabiki rigs toward a navigation marker in 15 feet of water; rather, we were looking over the fresh catch at the morning fish market auction in Jeddah, Saudi Arabia.
With a half dozen bonito, two small narrowbarred mackerel, a ribbonfish, a few bags of large and small squids, two kilos of sardines and a loaf of fresh-baked fennel-seed bread, we were ready to start fishing.
This was not a vacation trip but rather a research fishing expedition with the express goal of outfitting swordfish and other large pelagic fish in the Red Sea with satellite tags to study their movement behavior. While Red Sea coral reefs were introduced to many people by Jacques Cousteau in the 1960s, the pelagic ecosystem here remains largely unstudied. With the exception of whale sharks and manta rays, no fish have been satellite tagged in the Red Sea – effectively making it the last frontier for pelagic predator research. Furthermore, unlike other regions of the world’s oceans where deeper water is markedly cooler than surface waters, the Red Sea, from about 650 feet down to its deepest point, nearly 10,000 feet, is only 21.5ºC (about 71ºF). Thus, the thermal constraints that typically limit the depth and distribution of pelagic fish may be minimal or non-existent, potentially changing their behavior from what has been documented elsewhere.
Our University of Washington team consists of Peter Gaube (principal oceanographer – Applied Physics Lab), Camrin Braun (assistant professor – School of Aquatic and Fishery Sciences), myself (postdoctoral scholar – Applied Physics Lab), and Tony DiGiulian (Saltwater Professional Consulting). Together, we aim to apply South Florida-style swordfishing tactics to catch our target species, archival-tag them, and release them back into the wild to record data and transmit that back to us via satellite.
On this first trip to Saudi Arabia, we fished offshore ridges and deep canyons between reef walls that extended all the way to the surface. While daytime deep dropping, we managed to catch one small swordfish that unfortunately was gut hooked and thus not a candidate for being tagged and released. However, we brought that swordfish to our collaborators at the Red Sea Research Center at the King Abdullah University of Science and Technology, who will use every unique tissue from the fish to sequence its genome – a process that provides us with the genetic architecture of the species. This information will be invaluable, as it will facilitate future genetic studies
While we weren’t able to tag a swordfish on this initial expedition, we did manage two scientific firsts on which we can build in the future. First, while fishing in about 2,000 feet of water, we caught a pelagic thresher shark and (to our knowledge) outfitted with a satellite tag the first individual of the species in scientific history, a male of about 90 pounds.
There are three species of thresher shark (genus Alopias): the common thresher (A. vulpinus) and bigeye thresher (A. superciliosus) occur in the Atlantic, Pacific, and Indian Oceans. On the other hand, the pelagic thresher (A. pelagicus) occurs only in the Pacific and Indian oceans. Common and bigeye threshers have been satellite tagged before but we believe our pelagic thresher to be the first of its species tagged. That tag will record depth and temperature for the next few months and then pop off to thresher, transmitting its data to us via satellite so that we can better understand the species’ vertical distribution.
Across the world’s oceans, thresher sharks and swordfish often occupy a similar niche in the food web, with both taking advantage of prey in deeper waters and exhibiting somewhat similar distributions. Thus, the data we receive from this first pelagic thresher shark will not only tell us about that species but is also likely to help us in targeting our future swordfishing efforts.
Second, we managed to also satellite-tag the first billfish ever in the Red Sea, a sailfish of 35 pounds or so that we caught while trolling skirted lures along the reef edge. This sailfish was outfitted with a different type of towed tag that transmits accurate location data to the satellite whenever the tag breaks the surface. In just under two weeks, that sailfish swam over 150 miles to the south where it was last detected offshore of Al Lith.
We will be returning to Saudi Arabia for another tagging expedition this April and now that we have a sense of where the fish are, we hope to deploy numerous tags on swordfish, sailfish, pelagic thresher sharks, and other top pelagic predators. If you are interested in learning more about this project, or would like to help support the tagging of swordfish around the world, visit gf.me/u/vusutu.
About the author: Dr. Martin “Martini” C. Arostegui is a postdoctoral scholar in the Air-Sea Interaction & Remote Sensing Department of the Applied Physics Laboratory at the University of Washington in Seattle. His research focuses on fish behavior, ecology, and fisheries management. He is also a representative of the International Game Fish Association, winner of the IGFA Lifetime Achievement Award, and has set over 200 IGFA world records.