Human infrastructure can hinder the mobility of marine animals.
The ocean feels infinite. If you were to start swimming from shore, it’s easy to believe—fitness and oxygen aside—you could continue forever. That’s a far different experience to overland travel, where mountains, rivers, and six-lane highways buzzing with traffic thwart easy passage.
It’s equally easy to believe that fish and other highly mobile marine creatures experience the ocean in such an unrestrained fashion. These animals, adapted over millennia to navigate the ocean, must easily bypass any barrier around which they can theoretically swim. That assumption, though, is wrong.
According to Karissa Lear, an aquatic ecologist at Australia’s Murdoch University, it’s common for many marine species to stick to specific habitats and only seldom venture beyond them. That is especially true for many juvenile animals, she says, which are small and vulnerable to predation. This timidness can cause unexpectedly big problems for marine species, especially when infrastructure gets in the way.
Take, for example, the green sawfish living near the mouth of the Ashburton River in the Pilbara region of Western Australia.
In 2017, engineers working on a local oil and gas processing plant built a new loading facility consisting of a large piling jetty and solid rock wall, which stretched 500 meters offshore. At the time, Lear and her colleagues were concerned with how the construction would affect the critically endangered green sawfish, which uses the region as a nursery.
As time went on, however, the scientists realized that the green sawfish were unable, or unwilling, to pass around the barrier. That could prevent the animals from reaching valuable feeding grounds and other habitat. The juvenile green sawfish, says Lear, are probably too scared of getting nabbed by predators to leave the safety of their nearshore habitat to swim out and around the jetty.
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