Shark fish-out changes schools of fish
New light has been shed on the cascading effects of over-fishing shark populations off the coast of Australia.
New research suggests there have been significant body-shape changes in fish, due to shark population declines from overfishing.
Scientists at the University of WA have teamed up with the Australian Institute of Marine Science, the University of Miami and Rosenstiel School of Marine and Atmospheric Science, and analysed seven different fish species from two neighbouring coral-reef systems off the coast of north-west Australia.
With targeted shark-fishing intensified in the region in recent decades to flavour shark-fin soup, populations have declined, causing fish sizes to decrease.
Lead author Neil Hammerschlag, a research assistant professor at the UM Rosenstiel School and UM Abess Center for Ecosystem Science and Policy, said the removal of sharks by humans had potentially caused a reduction in the size of fish body parts that are important for shark detection and evasion.
“Eye size is critical for detecting predators, especially under low-light conditions when many sharks usually hunt, and tail shape enables burst speed and rapid escape from sharks,” he said.
“There is an urgent need to understand the potential cascading ecosystem consequences of shark declines, especially on coral reefs that we rely heavily on for tourism, food and recreation.”
Despite the research evidence, the effect has not yet reached the Pilbara coast, say local anglers.
Port Hedland Game Fishers Club president Gavin Jones said anecdotally he has not seen low numbers in sharks or smaller fish off the Hedland coast.
“We go through patches where we get what I describe as nursery days where all you get is smaller fish but whether that’s more prevalent now I don’t think so yet. We also haven’t seen a smaller population in sharks; in fact, this time of year people find it’s shark city,” he said.
“We’ve always had a good population of sharks up here.”
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