Endangered eel larvae make a tasty treat for fish in an ocean

first_img Endangered eel larvae make a tasty treat for fish in an ocean desert Country * Afghanistan Aland Islands Albania Algeria Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia, Plurinational State of Bonaire, Sint Eustatius and Saba Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d’Ivoire Croatia Cuba Curaçao Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard Island and McDonald Islands Holy See (Vatican City State) Honduras Hungary Iceland India Indonesia Iran, Islamic Republic of Iraq Ireland Isle of Man Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, Democratic People’s Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People’s Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macao Macedonia, the former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mayotte Mexico Moldova, Republic of Monaco Mongolia Montenegro Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Norway Oman Pakistan Palestine Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Qatar Reunion Romania Russian Federation Rwanda Saint Barthélemy Saint Helena, Ascension and Tristan da Cunha Saint Kitts and Nevis Saint Lucia Saint Martin (French part) Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia Seychelles Sierra Leone Singapore Sint Maarten (Dutch part) Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands South Sudan Spain Sri Lanka Sudan Suriname Svalbard and Jan Mayen Swaziland Sweden Switzerland Syrian Arab Republic Taiwan Tajikistan Tanzania, United Republic of Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Venezuela, Bolivarian Republic of Vietnam Virgin Islands, British Wallis and Futuna Western Sahara Yemen Zambia Zimbabwe European eels, besides being delicious, have mystified biologists for more than a century. They spend their adult lives in estuaries and rivers, and head to the Sargasso Sea near Bermuda to reproduce. Their tiny transparent larvae then hitch a ride back to Europe on the Gulf Stream. But eel populations have been mysteriously dropping, prompting desperate measures to replenish their numbers.Now, researchers have a clue about one peril young eels face during their journey: hungry fish. The larvae were once considered too difficult for most predators to spot and catch, but a new study that looks at DNA traces in the guts of fish near eel-breeding waters suggests at least six marine species can make quick work of baby eels.“The study shows that although eel larvae are likely difficult for predators to see, they do contribute to ocean food webs as prey for other species,” says Michael Miller, an eel expert at Nihon University in Fujisawa, Japan, who was not involved with the work. Sign up for our daily newsletter Get more great content like this delivered right to you! Country These endangered eel larvae are mysteriously declining. DNA in fish guts show where some of them end up. Click to view the privacy policy. Required fields are indicated by an asterisk (*)center_img By Elizabeth PennisiAug. 14, 2018 , 3:55 PM The European eel (Anguilla anguilla) was once quite common, but its numbers have declined precipitously in the past 45 years. Moreover, the number of larvae that finally make it to Europe as “glass eels” has dropped by 90%, leaving some to wonder what might be happening to the larvae. Was something eating them up?That didn’t seem likely. Eel larvae—which are about the size of a small willow leaf—had been detected only once, in the late 1800s, in the guts of other fish. It could also be that, once swallowed, they decayed so quickly that they disappeared without a trace. Intact, the eels are still difficult to find, “even in a tray of water,” says study co-author Mads Reinholdt Jensen, now a graduate student at Aarhus University in Denmark. As a result, researchers studying eel declines have looked at everything—everything, says Jensen, except who eats the eel larvae.Instead of searching for the larvae themselves, Jensen and his colleagues at the University of Copenhagen looked for their DNA in 62 fish collected and quickly frozen in 2014 by a Danish team that had searched in vain for spawning adult eels in the Sargasso Sea. Jensen’s team had to develop special eel-specific molecular tags that would latch on to any eel DNA in a fish’s gut. Ultimately, the researchers verified European eel DNA in six of the fish, each of them a different species, they report in the August issue of Marine Biology.That was a surprise to Tracey Sutton, a marine ecologist at Nova Southeastern University in Fort Lauderdale, Florida, who was not involved with the study. “It goes against the dogma that these fishes prey primarily on crustaceans,” he explains. “It shows a new [food web] pathway we didn’t have before.”The discovery is a “novel preliminary finding” that could help reveal the “true diets” of these predatory fish, and their role within the oceanic food web, says Ryan Saunders, a marine ecologist with the British Antarctic Survey, in Cambridge, who was not involved in the study. The Sargasso Sea is notoriously low in nutrients, he notes, and not much is known about the few fish that live there.The DNA techniques used in the new study could “revolutionize the way we study fish diets and food webs,” Saunders says. But Jensen notes they still won’t help the researchers estimate how many larvae the fish were eating or what proportion of the predators’ diet the eels represented. Calculating those numbers will be important to concluding anything about the role the fish are playing in the eel’s decline, Miller says. And Sutton is skeptical: “Predation on larvae is a normal thing,” he says. “The dramatic decline is almost surely human-induced.” Email Paulo Oliveira/Alamy Stock Photo last_img

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