The invasive Asian carps seem to have bypassed the electric barrier built to protect the North American Great Lakes from potential ecological disaster.

Bighead and Silver carp DNA has been found in the Calumet River, Des Plaines River and at the confluence of the Calumet Sag Channel and the Chicago Sanitary and Ship Canal, federal and state officials announced Friday.

U.S. authorities regularly test for Asian carp DNA in suspended particles floating in river currents in this region, and positive test results have now appeared less than seven miles from Lake Michigan.

The carps are believed to have jumped over the electrical barrier commonly referred to as the “last line of defense” for the Great Lakes.

Authorities are now trying to locate the carps and catch them.

Why are the Asian carps such unwelcomed visitors?

The Asian carps wreck havoc with the native ecosystem by outcompeting local species for food.

They were deliberately brought to North America by catfish farmers to keep farm ponds clean, but managed to escape into the wild during a series of powerful flooding incidents in the 1990s. Since then, they have gradually expanded their range up the Mississippi and Illinois rivers.

Scientists tagging sharks off the Irish coast have tagged a surprisingly high number of Basking sharks this year: 50 specimens in just three days.

“I would normally expect to be lucky if we tagged 50 in a whole year,” said Dr Simon Berrow of the Irish Whale and Dolphin Group.

Basking SharkA record

Together with National Parks and Wildlife Service conservation ranger Emmett Johnston, Dr Berrow set out earlier this week to tag sharks off Donegal, as part of a project funded by the Heritage Council.

“In two hours last Monday we tagged 23 sharks, and we found 19 the following day – four of which had been tagged the day before,” Dr Berrow said. By the third day, they had tagged their 50^th basking shark.

Basking sharks were once a significant source of income for Irish whalers and the coastal towns of Galway and Waterford did for instance have street lights lit with basking shark oil as early as the 18^th century.

The importance of Basking sharks in Irish culture is evident in the number of names and monikers give to these peculiar creatures. In Irish, this “monster with sails” is known under the names Liabhán chor gréine (Great fish of the sun), Liop an dá (unwieldy beast with two finns) and Liabhán mór (great leviathan) – just to mention a few. The epithets “Fish of the sun” and “Sunfish” both pertains to its fondness of swimming just under the surface.

In the mid-1970s the Irish stopped their whaling, but the problems weren’t over for these sharks since they frequently ended up as by-catch in drift nets; a fishing method now outlawed in Irish waters. In addition to this, Norwegian whalers continued to hunt for shark off the Irish coast until 1986.

The Basking shark (Cetorhinus maximus) is listed as Vulnerable on the IUCN Red List of Threatened Species, and is a protected species in Great Britain but not in Ireland. However, the European Union has just placed a moratorium on fishing for Basking sharks in these waters.

If you spot a Basking shark in Irish waters, the Irish Whale and Dolphin Group would very much like to know any details about the sighting. You can find more information at www.baskingshark.ie.

Want to know more about Basking sharks and where they head when the Northern Seas become too cold for comfort? Check out our earlier blog post on Sharks of the Caribbean.

An expansion of vertical seagrass occurring some 25 million years ago was probably what prompted seahorses to evolve from horizontal swimmers to upright creatures. If you live in vertical seagrass, an upright position is ideal since it allows you to stay hidden among the vertical blades.

This new idea is put forward in a report by Professor Beheregaray* and Dr Teske** published in the journal Biology Letters on May 6.

Sea horse picture from our Seahorse section.

Only two known fossils of seahorse have been found and this scarcity of fossil records has made it difficult for scientists to determine when seahorses evolved to swim upright. The older of the two fossils is “just” 13 million years old and no links between the two fossils and horizontally-swimming fish has been found.

“When you look back in time, you don’t see intermediate seahorse-like fish,” Beheregaray explains. There are however fish alive today that look like horizontally-swimming seahorses and Beheregaray and Teske have therefore studied them in hope of finding clues as to when seahorses made the transition from horizontal to vertical swimming.

By comparing DNA from seahorses with DNA from other species of the same family, Beheregaray and Teske were able to determine who the closest living relative to seahorses was.

“The pygmy pipehorses are by far the most seahorse-like fish on earth, says Beheregaray. “They do look like the seahorses, but they swim horizontally“.

When you have two closely related species, you can use molecular dating techniques to calculate when the two species diverged from each other. Beheregaray and Teske used a molecular dating technique that relies on the accumulation of differences in the DNA between the two species, and then used the two existing fossils to calibrate the rate of evolution of DNA in their molecular clock. By doing so, the two researchers could conclude that the last common ancestor of seahorses and pygmy pipehorses lived around 25 to 28 million years ago. At this point, something must have happened that led to the formation of two distinct species, and Beheregaray and Teske believe that this “thing” was the expansion of seagrass in the habitat where seahorses first evolved.

The time in history when seahorses arose, the Oligocene epoch, coincided with the formation of vast areas of shallow water in Austalasia. These shallow waters became overgrown with seagrass and turned into the perfect habitat for upright swimming seahorses that could remain hidden from predators among the vertical blades. The pygmy pipehorse on the other hand lived in large algae on reefs and had no use for an upright position, hence it continued to swim horizontally just like their common ancestor.

“The two groups split in a period when there were conditions favouring that split,” says Beheregaray. “It’s like us. We started walking upright when we moved to the savannahs. On the other hand, the seahorses invaded the new vast areas of seagrass.”

* Associate Professor Luciano Beheregaray of Flinders University

http://www.flinders.edu.au

** Dr Peter Teske of Macquarie University

http://www.macquarie.edu.au