Cold Water
Australian Giant Cuttlefish
Sepia apama · Cephalopod mollusk — family Sepiidae; the largest cuttlefish species
Every austral winter the upper Spencer Gulf hosts the only known dense breeding aggregation of cuttlefish anywhere: tens of thousands of Sepia apama packed onto a few kilometers of shallow rocky reef near Whyalla, in green water that can drop below 12 °C. Males outnumber females several times over, so the reef becomes a tournament — meter-long heavyweights strobing zebra patterns at rivals while smaller sneaker males dim their colors, tuck their arms, and pass as females to slip through the cordon. It all happens in two to eight meters, snorkel-accessible, roughly May through August with a June–July peak. Across the rest of southern Australia the species lives as solitary, frankly curious reef residents that study divers as openly as they are studied. Bring drysuit-grade insulation, move slowly, and touch nothing: these animals breed once and die.
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 |
|---|---|---|---|
| South AustraliaAustralia | Seasonal — reliable in season | May–Aug |
ベストな月、一目でわかる
| 月 | 安定して出会える目的地 |
|---|---|
| May | South Australia |
| June | South Australia |
| July | South Australia |
| August | South Australia |
理解を深める
ハビタット: Temperate rocky reef, kelp, and seagrass; the famous breeding aggregation packs onto a few kilometers of shallow stone reef in the upper Spencer Gulf.
分布域: Southern Australian coast from Queensland's border waters around to Western Australia, including Tasmania.
生態・行動: Solitary and curious most of the year; each austral winter tens of thousands converge near Whyalla to breed, males dueling in color while smaller sneaker males dim their patterns and pass as females to reach mates.
食性: Crabs, shrimp, and fishes taken with ambush patience and tentacle strikes.
サイズ: 目安は 0.4 m; 確認済みの最大記録 0.5 m (mantle length; total length approaches 1 m and big males exceed 10 kg).
出会ったときの正しいふるまい方
Thick exposure protection, slow fins, and no touching at the aggregation — the animals die after breeding, and every disrupted pairing spends a genuine last chance. Follow local sanctuary-zone rules.
保全
Assessed Near Threatened; the Whyalla aggregation crashed in the early 2010s before rebounding under fishing closures and a sanctuary zone that remain load-bearing.
目撃情報で知られるダイブサイト
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