Research press release


Nature Communications

Ecology: Where predators lurk in the open oceans

サメ、マグロ、バショウカジキ、マカジキなどの大型魚による捕食は、赤道付近よりも温帯海域の方が多いことを報告する論文が、Nature Communicationsに掲載される。この新知見は、捕食が、赤道付近で最も強く、魚類種の多様性の増加に関連しているという従来の仮説に疑問を投げ掛けている。


今回、Marius Roestiたちの研究チームは、餌を付けた縄に対する大型捕食魚類の攻撃(9億回以上)を記録した1960~2014年の遠洋延縄漁のデータセットの解析を行った。その結果分かったのは、捕食魚類の攻撃が、赤道付近よりも温帯(南緯・北緯約30~60度の中緯度帯)で頻繁に起こり、このパターンは、時がたっても変化せず、4つの海盆の全てで見られた。海洋哺乳類、海鳥類、深海魚類が主な捕食者となる南北の極域に近づくと、外洋性魚類による捕食は、再び減少した。


Predation by large fish such as sharks, tuna, sailfish and marlin is higher in the temperate regions of the oceans than near the equator, reports a study published in Nature Communications. The findings challenge previous assumptions that predation is strongest near the equator and associated with an increasing diversity of fish species.

Both terrestrial and marine biodiversity tend to increase towards the equator. However, studies of terrestrial ecosystems have found mixed evidence that interactions among species are strongest near the equator. Meanwhile, little is known about geographical variation in species interactions in the open ocean.

Marius Roesti and colleagues analysed datasets of pelagic (open ocean) longline fishing that record over 900 million attacks on baited lines by large fish predators between 1960 and 2014. They found that predator attacks were more frequent in temperate regions (the mid-latitudes that exist roughly between 30 and 60 degrees north and south) than around the equator and that this pattern was consistent over time and across four ocean basins. Predation by pelagic fish decreased again towards the poles, where the main predators are marine mammals, seabirds and deep-water fish.

Predator attacks were also negatively correlated with the number of open ocean fish species. These results may help explain recent findings that speciation rates (the formation of new and distinct species) in marine fish increase away from the equator, as it has been previously suggested that interactions between species can promote speciation.

doi: 10.1038/s41467-020-15335-4

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