Sharks have more complex social lives than previously known, as shown by a study finding that gray reef sharks in the Pacific Ocean cultivate surprising social networks with one another and develop bonds that can endure for years.
The research focused on the social behavior of 41 reef sharks around the Palmyra Atoll, about 1,600km southwest of Hawaii, using acoustic transmitters to track them and camera tags to gain greater clarity into their interactions.
Far from being solitary creatures, the sharks formed social communities that remained rather stable over time, with some of the same individuals remaining together during the four years of the study.
Photo: Yannis Papastamatiou via Reuters 照片:延尼斯‧帕帕斯塔馬狄奧/路透
The researchers documented a daily pattern, with sharks spending mornings together in groups of sometimes close to 20 individuals in the same part of the reef, dispersing throughout the day and into the night, and reconvening the next morning.
“Sharks are incredible animals and still quite misunderstood,” said Florida International University marine biologist Yannis Papastamatiou, lead author of the research published on Aug. 12 in the journal Proceedings of the Royal Society. “I like to talk about their ‘secret social lives’ not because they want it to be a secret, but because only recently have we developed the tools to start seeing and understanding their social lives,” Papastamatiou added. “Not all sharks are social and some are likely solitary.”
The reef shark is medium-sized, reaching about 2m long. Its sociality bore similarities in terms of stability over time to certain birds and mammals but differed in that it did not involve nesting, mating, making vocalizations or friendly interactions.
The researchers suspect the sharks hang out together because it may help ensure that the various individuals find prey. “For some time we have known that sharks are capable of recognizing particular group mates and having social preferences,” said marine biologist and study co-author David Jacoby of the Institute of Zoology in London.
“Our study reveals for the first time that they are actually capable of maintaining social partners for multiple years. Further we offer a possible mechanism for such long-term social structure — namely that social groups likely operate as information centers from which individuals can follow one another to offshore feeding areas.”
(Reuters)
研究指出,鯊魚的社交生活比先前人類所知的還要複雜。該研究發現,太平洋的鈍吻真鯊(或稱灰礁鯊)族群會和彼此建立讓人驚異的社交網絡,並且發展出可以持續多年的連結。
此研究聚焦於巴美拉環礁周圍四十一隻鈍吻真鯊的社交行為,該地區位於夏威夷西南方約一千六百公里處。科學家藉由聲音發報器來追蹤鯊魚,並利用攝影機標籤,對它們的互動獲得更清晰的了解。
研究人員發現,這群鯊魚不但不是獨來獨往的生物,還建立起隨時間過去仍能保持相對穩定的數個社群,其中幾隻個體更在研究進行的四年之間一直聚在一起。
研究人員記錄下每日固定的規律:鯊魚們會群聚在這座環礁的同一個地方共度早晨,有時聚集的個體將近二十隻;接下來整個白天直到入夜,它們各自行動;隔天早上,鯊魚又重新聚首。
這篇論文的主要作者、佛羅里達國際大學的海洋生物學家延尼斯‧帕帕斯塔馬狄奧說:「鯊魚是難以置信的奇妙動物,它們直到今天仍然受到相當大的誤解。」該研究在八月十二日發表於《皇家學會報告》期刊。「我喜歡談論它們的『秘密社交生活』並不是因為它們想要保持神秘,而是因為一直到最近,我們才發展出合適的研究工具,開始觀察並了解它們的社交生活。」帕帕斯塔馬狄奧補充說:「不是所有的鯊魚都喜歡交際,有些可能比較偏向獨居。」
鈍吻真鯊屬於中型鯊,身長大約可達兩公尺。就長時間的穩定性而言,這種鯊魚的社交性格相似於某些鳥類或哺乳類。差別在於,鯊魚的社交活動並不包含築巢、交配、發聲或友善的互動。
研究人員懷疑,這些鯊魚聚在一起,可能是為了確保不同個體都有找到獵物。論文的共同作者、倫敦動物學研究所的海洋生物學家大衛‧雅克比表示:「我們已經知道,鯊魚能夠辨識出特定的族群夥伴,而且它們也有社交偏好。」
雅克比進一步指出:「我們的研究首次揭露出,鯊魚其實有能力維持社交夥伴長達數年。進一步而言,我們提出這種長期社會結構的潛在機制──也就是說,社交團體可能像是資訊交換中心那樣運作,藉此機制,個體可以互相跟隨,前往外海的覓食區。」
(台北時報章厚明譯)
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