How a shark donated its body to science
LAST WEEK, STAFF arriving at the CSIRO’s Australian National Fish Collection labs on the River Derwent in Hobart were surprised to discover a large shark washed ashore near their carpark.
The right-place-at-the-right-time experts soon recognised the species as a broadnose sevengill shark (Notorynchus cepedianus) – and while a washed-up shark might usually remain on a beach for a few days as bird food and a curiosity, this one was promptly taken to the lab as a valuable specimen for future research and conservation.
While specimens normally arrive in the CSIRO’s biological collections as a result of careful research, they are sometimes donated by the public – usually birds or mammals that have been hit by cars. And, as in this case, occasionally they literally arrive on the scientists’ doorstep.
This shark was an adult female, 2.4m long and not pregnant. She joins three other sevengill sharks in the Austrlian National Fish Collection in Hobart, all from Tasmania.
This 2.4m female broadnose sevengill shark washed up next to the CSIRO’s Australian National Fish Collection labs in Hobart last week. (Image: CSIRO)
One of the lab’s resident icthyologists (fish scientists), John Pogonoski, explained how the shark will be kept:
“The shark was too large to retain whole, so we froze its head and fins for taxonomic and morphological studies, where we identify the species and describe its features. We also froze muscle tissue for future genetic studies. Shark fins are especially useful to retain when the whole animal cannot be kept. If fins of this species are ever used in the shark fin trade, we can match them to the samples in our collection,” he said.
John explained the shark was most likely line-hooked by a recreational fisher, either the night before or the morning it was found.
“The shark would have been gut-hooked rather than hooked in the mouth because there was no visible damage inside its mouth. It’s likely the fisher cut through the gut to extract their hook and then threw the shark back into the water,” he said.
“When we dissected the shark in the laboratory, it was obvious that the anterior [front] portion of the gut had been severed and removed. When we looked for stomach contents, there was no stomach,” he said.
John’s suggestion for fishers who hook a fish or shark and can’t see the hook in the fish’s mouth is to cut the line above the hook and leave it in place. “The hook would have eventually rusted and the shark may have survived, but that depends how exhausted the shark was after being caught and how much damage the hook had caused to the gut,” he said.
Sevengill sharks can grow up to 3m long. They are the most common sharks in Tasmania’s Derwent River and the largest resident shark. While most sharks have five or six gills, as its name suggests the broadnose sevengill has seven – a trait shared by primitive sharks more common in the Jurassic.
The sharks have a widespread distribution, occuring in the Atlantic, Indian and Pacific oceans, mainly in temperate waters. In southern Australia they have been reported from Sydney to Perth, including Tasmania.
This is an edited version of a CSIRO blog post. Read the original post here.
