Sharks
Scalloped Hammerhead
Sphyrna lewini · Cartilaginous fish — family Sphyrnidae
A scalloped hammerhead school is the sight that built entire liveaboard industries: dozens to hundreds of animals stacked into the current above a seamount, heads swinging in lazy unison, the edges of the formation dissolving into blue. Up close each shark is modest in size, notched along the front of its cephalofoil, and visibly nervous of divers — the school parts around exhaled bubbles like smoke. They gather by day and vanish at dusk to hunt squid in deep water. Heavy industrial and illegal fishing at the very seamounts that concentrate them has made this Critically Endangered species a symbol of high-seas protection.
どこで・いつ見られるか
「常駐（Resident）」とは、そのダイビングスポットでのほとんどのダイブで遭遇できることを意味します。「季節限定（Seasonal）」とは、記載された月に確実に見られることを意味します。それ以外の出会いはボーナスであり、計画の前提にはなりません。
| 目的地 | 信頼性 | 月 | メモ |
|---|---|---|---|
| Galápagos IslandsEcuador | Resident — seen on most dives | Year-round | |
| Cocos IslandCosta Rica | Resident — seen on most dives | Jun–Nov | |
| MalpeloColombia | Resident — seen on most dives | 年間を通じて | |
| Brothers, Daedalus & St John'sEgypt | Seasonal — reliable in season | May–Sep | |
| YonaguniJapan | Seasonal — reliable in season | Dec–Feb | |
| Port Sudan & SanganebSudan | Seasonal — reliable in season | Feb–May |
ベストな月、一目でわかる
| 月 | 安定して出会える目的地 |
|---|---|
| January | Galápagos Islands · Malpelo · Yonaguni |
| February | Galápagos Islands · Malpelo · Yonaguni · Port Sudan & Sanganeb |
| March | Galápagos Islands · Malpelo · Port Sudan & Sanganeb |
| April | Galápagos Islands · Malpelo · Port Sudan & Sanganeb |
| May | Galápagos Islands · Malpelo · Brothers, Daedalus & St John's · Port Sudan & Sanganeb |
| June | Galápagos Islands · Cocos Island · Malpelo · Brothers, Daedalus & St John's |
| July | Galápagos Islands · Cocos Island · Malpelo · Brothers, Daedalus & St John's |
| August | Galápagos Islands · Cocos Island · Malpelo · Brothers, Daedalus & St John's |
| September | Galápagos Islands · Cocos Island · Malpelo · Brothers, Daedalus & St John's |
| October | Galápagos Islands · Cocos Island · Malpelo |
| November | Galápagos Islands · Cocos Island · Malpelo |
| December | Galápagos Islands · Malpelo · Yonaguni |
理解を深める
ハビタット: Seamounts, offshore islands, and current-swept drop-offs by day; disperses into deep water at night to hunt
分布域: Circumglobal in warm temperate and tropical seas; the famous schools gather at Eastern Pacific seamounts, in the Red Sea, and off Japan
生態・行動: The schooling hammerhead. Hundreds of females may stack into slow-moving daytime schools around seamounts, thought to serve social and navigational functions between night feeding runs. Schools are famously shy of bubbles and noise — breath control and patience produce close passes, chasing produces an empty blue.
食性: Fish, squid, and rays taken on nocturnal hunts in deep water
サイズ: 目安は 2.5 m; 確認済みの最大記録 4.0 m (total length; schooling females at seamounts typically run 2–3 m).
出会ったときの正しいふるまい方
Tuck into the rocks down-current, slow your breathing or hold exhalations as the school passes, and never swim at the wall of sharks. Many operators brief a no-strobe or limited-strobe approach on first contact.
保全
Critically Endangered from decades of fin-driven overfishing; listed on CITES Appendix II. Marine reserves at Cocos, Malpelo, and Galápagos protect key aggregations, though enforcement on the surrounding high seas remains the weak point.
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