Decreasing stock since 50 years
According to an analysis of the data from the Queensland Shark Control Program, the decline in coastal sharks in Queensland has continued for 50 years, in sharp contrast to current assumptions – mainly from politicians - of "exploding" shark populations.
Researchers at the ARC Center of Excellence for Coral Reef Studies at the University of Queensland (CoralCoE) and Griffith University analyzed data from the program, which has been using drum and net lures since 1962 to minimize human and shark interactions now extends over 1,760 kilometres along the coast of Queensland.
The CoralCoE researcher and lead author of the new study George Roff says that historical numbers of shark populations in Queensland are largely unknown, despite a long history of shark hunting. The study was recently published in the journal Communications Biology.
"19th-century explorers once described the Australian coasts as 'full of sharks,' but we have no clear idea of how many sharks used to live on the beaches of Queensland, and shark populations have declined sharply across the world in recent decades Many species are considered endangered," Dr. Roff.
The researchers evaluated historical records of shark fangs to study changes in the number and size of sharks over the past half-century.
"We've found that the number of large sharks, such as hammerhead sharks, tiger sharks and white sharks, along the Queensland coast have decreased by 74 to 92 percent, and the average size of sharks has also fallen - tiger sharks and hammerhead sharks are becoming smaller," explains Dr. Roff.
"Our data shows radical changes in our coastal ecosystems since the 1960s, acting as window into the past. We now see what was natural off our beaches and it provides an important context for dealing with Shark numbers," warns Dr. Roff.
"Although sharks are often perceived as a threat, they play an important ecological role in coastal ecosystems, and the large losses of these large predators have probably altered the structure of coastal food webs over the past 50 years," explained Dr. Horse.
Link to the study: https://www.nature.com/articles/s42003-018-0233-1.