Fishy Numbers for White Marlin Stocks

NEWS FEATURE NEWS FEATURE Fishy numbers for white marlin stocks Genetic tests show we have been mistaking a lookalike billfish for the prized white marlins—their stocks may be lower than we thought. Mark Schrope vague allusions to the fish that Lowe said Science Writer had a body “clothed with large scales of a peculiar shape and nature.” The defining reappearance came in 1974 (2). Richard In 1840, the English chaplain and amateur This case of mistaken identity is exacer- Robins, then at the University of Miami, naturalist Richard Thomas Lowe published bating an already contentious issue: How FL, had taken a trip the previous decade to a four-line description of a proposed new to properly manage what some believe is a Europe to collect fish samples. He soon re- species of fish. It was a billfish: a big, fast dangerously dwindling Atlantic white mar- alized that four of those were “of a species predatory fish with a prominent bill. The lin population, as scientists struggle to fig- whose presence had been unsuspected.” billfish group includes the storied marlins ure out the abundance of each species. Comparing their morphology to Lowe’s immortalized by Ernest Hemingway. Lowe was at least as passionate about initial description he decided they were the Lowe based his description on a single natural history as he was about ministering. same. specimen collected off the coast of Madeira, From 1826 to 1852, he had his own congre- The Atlantic is home to only a handful of Portugal, where he had a church. But that gation on Madeira, but he found plenty of billfish species, most easily identified by the specimen, and Lowe himself, would disap- time for his side passion, publishing mul- experts. Not so for the roundscale, it would pear in 1874, and the species was all but tiple papers on fish and the odd crustacean. turn out. Since Robins’s samples were col- forgotten. Lowe was also involved for years in a re- lected in the eastern Atlantic, US research- It would take precisely a century for ligious schism on the island and ultimately ers didn’t realize that these fish could be Tetrapturus georgii, also known as the retreated to England. But he returned to lurking in their own waters, and hence roundscale spearfish, to be officially redis- Madeira on occasion. In 1874, sailing from were unaware that many of the fish they covered, and decades more before genetic Liverpool to the island, the steamship Li- were calling the white marlin were actually tests would establish its uniqueness. Today, breria sank in the Bay of Biscay, and Lowe, roundscales, a near lookalike. thanks in large part to those tests, scientists his notebooks, and apparently his only T. know that many of the fish they once called georgii sample perished. Stark Genetic Differences white marlin are actually Lowe’s species. For a century, all that remained were During the 1990s, some of Robins’s colleagues in Miami began to wonder if the roundscale might also be found in the west- ern Atlantic. Dennis Lee, the head of the National Oceanic and Atmospheric Ad- ministration (NOAA)’s Southeast Fishery Observer Program (SFOP) in Miami, began talking of the possibility during observer training sessions, but there was little to go on. Robins had outlined some challeng- ingly subtle defining characteristics that included, relative to white marlins, a larger distance between the anus and the anal fins, in addition to rounded scales and fins. Within a few years, the Miami researchers had candidate samples. Elsewhere, other researchers also began considering the possibility of a new species of billfish. But convincing the larger community proved difficult. “We would have discussions with Image courtesy of Guy Harvey. other billfish researchers and they would White marlin. shrug and say, ‘That’s pretty interesting’ www.pnas.org/cgi/doi/10.1073/pnas.1302602110 PNAS | March 12, 2013 | vol. 110 | no. 11 | 4151–4153 Downloaded by guest on September 24, 2021 and turn around,” says Lawrence Beer- kircher, the current head of SFOP. “I don’t think they really believed it.” It wasn’t until 2006 that the situation became indisputably clear. Beerkircher had sought the help of his former advisor, fish genetics specialist Mahmood Shivji, at Nova Southeastern University’s Guy Har- vey Research Institute, Dania Beach, FL. Shivji had developed techniques for rapidly identifying shark species based on small tis- sue samples, which, among other benefits, allowed identification of illegally caught species even after they had been chopped up. He had begun applying similar techniques to establishing genetic markers for various billfish species. Image courtesy of J. Foster/Guy Harvey Research Institute, Dania Beach, FL. When Shivji and colleagues analyzed Beerkircher’s samples, they were stunned. Photos of the two species side-by-side, white marlin (Top) and roundscale spearfish (Bottom). While the physical differences between the report in 2007 (5). The report highlighted based on only a nascent appreciation for species were subtle and missed by most, major uncertainties, both in absolute popu- roundscales. The picture soon turned more there was no mistaking the genetics. “They lation size and in the numbers of round- confusing. were not a little bit different from white scale fish misidentified as white marlin. After Shivji’s team established the round- marlin, they were really different,” says NOAA concluded that existing manage- scale genetics, they began working with Shivji of what proved to be roundscale ment efforts—controlling fishing seasons Beerkircher and others to figure out the ex- spearfish samples. They weren’t even in the and prohibiting certain practices that are tent of the species. In 2009 they published a same genus. The difference was so stark that more likely to snag white marlins—were paper showing that, at least in the Sargasso it ruled out interbreeding (3). sufficient for preventing further declines. Sea region of the Atlantic, the roundscales Also, the distinctions weren’t mere The report also said that, despite the uncer- are fairly common (4). On average, round- academic minutiae. The discovery of the tainty, there appeared to be a slight uptick scales made up about a quarter of the catch- roundscale would significantly affect the in the population of white marlin, which es deemed white marlin from certain fish- already limited understanding of the had been plummeting since the 1960s. ing tournaments and longliners. This raised white marlin. “This completely messed up Eric Prince, a fisheries biologist at the new questions about the accuracy of the the white marlin stock assessments,” says NOAA National Marine Fisheries Service, population estimates of white marlin that Shivji. Miami, who took part in the reviews, says were used to review its threatened status. The white marlin is recognized as one of one of the greatest sources of uncertainty “You’ve got these big predators running the most overexploited pelagic fishes in the over white marlins is that most countries, around [being] mistaken for each other and Atlantic (4). In some countries subsistence unlike the United States, do not report their no one knows the status,” says Shivji. fishermen target them, but for the most white marlin bycatches, leaving huge gaps The confusion does not end there. There part white marlin are the unfortunate by- in the data. A variety of estimates put the seems to be substantial variability in the rel- catch of commercial fishermen known as total white marlin population size in the ative number of roundscales and marlins, longliners who drag kilometers-long fish- Atlantic Ocean at about 200,000 fish, but not just from one study area to another, ing lines with baited hooks intended for this is largely based on analyses from a de- but also from year to year. For several years other species like tuna and swordfish. The cade ago that have neither been updated (6) now, John Graves, a fisheries biologist at white marlin are also prized by recreational nor corrected for possible roundscale mis- the Virginia Institute of Marine Science, sport fishermen, but regulations mostly call identifications. Gloucester Point, VA, and his colleagues, for them to be released alive, if possible, After the 2007 review, NOAA’s Endan- have found substantial variation in the when they’re caught. gered Species Division argued that because number of roundscales being caught at an of the uncertainties, NOAA should at least annual white marlin fishing tournament To List or Not to List retain the white marlin on its Species of in New Jersey. Some years there have been In 2001, scientists and environmentalists Concern list. This designation doesn’t pro- none and in others they’ve been plentiful. formally requested that the United States vide any special protection but can lead In some cases Graves discovered that it was consider listing the white marlin as ei- to more attention and research funding. roundscales winning the major prizes in ther threatened or endangered under the But in 2008, NOAA’s Office of Protected the tournament, which is allowed because Endangered Species Act. After a review, Resources, which had the final word, dis- the species are so outwardly hard to distin- NOAA rejected that petition, sparking a agreed and the white marlin was removed guish. legal challenge that led to another review. from the list. Researchers generally agree that this kind The second review resulted in a NOAA The arguments in those debates were of work has added to uncertainties over 4152 | www.pnas.org/cgi/doi/10.1073/pnas.1302602110 Schrope Downloaded by guest on September 24, 2021 white marlin populations. One way the listing issue a third time. Among other rea- sport fishermen; targeting the white marlin, roundscale confusion could have a major sons, the CBD pointed to confusion created even with catch-and-release fishing, would impact on our understanding of the white by the roundscale work as justification for have to end if the fish was deemed endan- NEWS FEATURE marlin’s current health would be if the the request.

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