生まれたてのホホジロザメ、初観察か　米カリフォルニア沖

【パリＡＦＰ＝時事】米カリフォルニア州沖で、生まれたてのホホジロザメの姿が初めて観察された可能性があることが、新たな研究で明らかになった。野生のホホジロザメの幼魚はこれまでにも目撃されているものの、今回の個体は背びれが丸みを帯びており、生後数時間の稚魚だったとみられている。（写真は、米カリフォルニア州サンタバーバラ近郊沖でドローンに搭載したカメラで撮影された、生後数時間とみられるホホジロザメ。カルロス・ガウナ氏提供）
　このホホジロザメは２０２３年７月初旬、野生動物ドキュメンタリー作家のカルロス・ガウナ氏と米カリフォルニア大学リバーサイド校生物学博士課程の学生フィリップ・スターンズ氏が、カリフォルニア州サンタバーバラ近郊沖でドローンに搭載したカメラで撮影した。
　最初に目撃されたのは雌のホホジロザメで、臨月に近い個体とみられた。この雌が水中深く潜ったように見えた後、今度はより小さい、１．５メートル程度の個体が海面に顔を出し、上空でホバリングしていたドローンのカメラの方を真っすぐ向いた。
　ホホジロザメは、背側が灰色で腹側が白い。だがこの個体は全身が白く見えたため、ガウナ氏は最初、アルビノ（先天性色素欠乏症）ではないかと考えたが、不器用そうに泳ぎ回っているうちに、体から白い膜がはがれ落ちたように見えたという。
　両氏は学術誌エンバイロメンタル・バイオロジー・オブ・フィッシーズに２９日に掲載された記録の中で、この白い「膜」は子宮内で子どもに栄養を与えるために分泌されるミルク様物質による組織層で、誕生後すぐにはがれ落ちたのではないかと述べた。ただし、皮膚疾患の可能性も考えられるという。
　ホホジロザメは国際自然保護連合の「レッドリスト」で、絶滅危惧種に指定されている。
　カリフォルニア州南部は若いホホジロザメの生育場として、また同州中部沿岸は出産スポットとして知られており、ガウナ氏はこれまでにも妊娠中の雌や幼魚を目撃してきた。
　ただし、「サメが生まれる場所がピンポイントで特定されたことはなく、生まれたばかりの稚魚を見た者もこれまではいない」とガウナ氏。
　またスターンズ氏は、「これは野生の稚魚が確認された最初の証拠であり、出産場所とみて間違いないだろう」と述べ、周辺海域に広げたさらなる調査や保護を求めるロビー活動が必要になるとの見解を示した。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2024/02/01-16:42）

Drone footage of a young shark emerging to the ocean surface could be the first sighting of a newborn great white, according to new research, potentially revealing a birthing site for the threatened ocean predators.
While juvenile great whites have been previously spotted in the wild, experts said footage of a newly born pup, believed to be just hours old because of its rounded dorsal fin, could shed light on a longstanding mystery in shark science and improve conservation efforts.
Where white sharks give birth is one of the holy grails of shark science, said wildlife filmmaker and photographer Carlos Gauna, who captured the moment on camera.
No one has ever been able to pinpoint where they are born, nor has anyone seen a newborn baby shark alive.
In early July 2023, Gauna -- known online as The Malibu Artist -? and UC Riverside biology doctoral student Phillip Sternes observed an apparently heavily pregnant great white shark off the Californian coast near Santa Barbara.
The shark appeared to dive deep into the water and not long after, a smaller shark emerged at the surface, and looked directly towards the camera hovering above.
Gauna said they initially thought the completely white little shark was an albino, because great white sharks -- referred to only as white sharks by scientists -- are actually grey on top and white only on their undersides.
But then they saw the shark appear to shed the white layer from its body as it clumsily swam around, he told AFP.
In an account of the sighting, published in the journal Environmental Biology of Fishes on Monday, Gauna and Sternes said they now believe that this white skin was in fact an embryonic layer of intrauterine milk, which is secreted in utero to nourish shark pups and is shed soon after birth.
They also gave an alternative explanation -- that the five-foot (1.5 metre) long shark could have been suffering from a skin condition.
- Protecting the predator -
Southern California is known to be a nursing ground for young white sharks, while the central Californian coast has been tipped as a potential birthing spot and Gauana had seen pregnant and young white sharks in the area before this sighting.
This may well be the first evidence we have of a pup in the wild, making this a definitive birthing location, Sternes said in a press release, adding that more research would be needed to confirm the area more generally as a birthing ground.
If it is, Sternes said that would put pressure on lawmakers to protect the waters.
This paper rightly claims that it is the first immediate post-birth sighting of a white shark, said Heike Zidowitz, senior programme officer for marine species conservation at the World Wildlife Fund in Germany, who was not associated with the study.
That would be significant in helping to strengthen conservation of great whites.
The sharks are listed as vulnerable by the International Union for the Conservation of Nature, which says that, as top predators, great white sharks help maintain the intricate ocean food webs.
While shark attacks on humans are relatively rare, the great whites have a fearsome reputation that can lead to campaigns that kill not only endangered sharks, but also other non-target species.
White sharks are one of the most wide ranging sharks and knowing exactly where they go to give birth will enable us to protect these areas from man-made negative impacts, such as fishing activities, habitat destruction, shipping noise, etc, Zidowitz told AFP.