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.
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