Reserves dumb down fishes' survival instincts
Marine reserves seem to dumb down survival instincts among protected fishes, especially when it comes to avoiding spear fishers outside the protected zone, according to an Australian study.
Researchers from ARC Centre of Excellence for Coral Reef Studies at James Cook University said big, innocent fishes wandering out of the reserve present an unexpected windfall to spear fishers awaiting them.
"There are plenty of reports of fish, both adults and juveniles, moving out of reserves and into the surrounding sea. Having grown up in an area where they were protected from hunting, we wondered how naive they would be with regard to avoiding danger from humans," says Fraser Januchowski-Hartley of the ARC centre.
The answer is: pretty naive. "Educated fish normally turn tail and flee when a diver armed with a spear gun approaches within firing range of them. The typical flight distance is usually just over four metres," the journal Ecology Letters reports.
"However, in our studies of marine reserves in the Philippines, Vanuatu and Papua New Guinea, where spearfishing remains a major way of harvesting table fish, we discovered that reserve-reared fish... are literally more catchable," it said.
The team studied fish across the boundaries of marine reserves from 200 metres inside the protected areas to 200 metres into the fished areas, according to an ARC statement.
They used underwater markers and measuring tapes to measure the 'flight initiation distance' of fish targeted locally by spear fishers. This indicates how close a skin diver can approach to a large fish before it decides to turn and flee.
They found that target fish living in fished areas were typically much warier of divers, and took flight at distances a metre or two farther away, than ones living within the reserve.
They also established that the 'naivete radius', whereby more catchable fishes spill out of the marine reserves extended for at least 150 metres from the boundary.