Date: August 6, 2019
Source: Zoological Society of London
A team of researchers has discovered that sharks are much rarer in habitats nearer large human populations and fish markets. The team also found that the average body size of sharks and other marine predators fell dramatically in these areas, where sharks are caught and killed intensively for their meat and fins.
The study, published today in the journal PLOS Biology, shows that the average body size and number of sharks and other marine predators -- vital to maintaining healthy ocean ecosystems -- fell significantly in proximity to cities with more than 10,000 people and associated fishing fleets.
The minimum distance from people and fishing which had no measurable effect was 1,250 kilometres. This is far further than previous studies have suggested and probably reflects the increased distances fishing boats can now travel. As a result, sharks were only observed at 12% of sites monitored.
Interestingly, researchers also found that sea surface temperature had a strong influence on predators' average body size, with a marked decrease at more than 28°C. While this is consistent with normal biogeographic patterns -- it is known that many smaller species live in tropical waters, for example -- it could become a problem as global temperatures continue to rise. (...)
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