Monday, March 04, 2013
ON Feb 18, five sperm whales were seen feeding off the northwest coast of Scotland.
Meanwhile, new research suggests humpback whale numbers have risen in the North Atlantic. But the news on whales isn’t all good; there is so much manmade noise in the sea that humpbacks and right whales have to ‘shout’ to be heard above the din. The highly endangered right whale also has a ‘road safety’ problem.
The sperm whales were spotted by fishermen off the island of Rona. These deep-water giants, of Moby Dick fame, live fairly solitary lives and venture this far north only in summer. According to Dr Peter Evans of Seawatch, this winter sighting of a group is notable not just for the time of year but for its inshore location. It could be a "reflection of climate change, with their main prey, squid, becoming more abundant locally in recent years, resulting in animals staying through the winter to feed, rather than travelling into lower warmer latitudes".
Sperm whales are visiting our waters more frequently than in the past; according to Prof Tom Hayden of UCD, almost half of the 28 strandings on Irish coasts during the 20th century occurred after 1980.
The humpback, like the sperm whale, is a widely distributed species. Found in temperate waters all over the world, it was, until recently, just an occasional visitor to our shores.
Only six humpbacks were landed at the Mayo whaling stations between 1908 and 1914 and none were caught between 1920 and 1922. There were only five strandings on the Irish coast up to 2000. Since then, however, the humpback has become an annual migrant. The good news on humpbacks isn’t confined to Ireland; numbers are up worldwide.
Whalers reduced the global population by 90% and only a few hundred remained in the North Atlantic when hunting ceased in 1955. There are now about 17,000.
The increase in numbers raises questions. At what stage can we say that the species has ‘recovered’? How many humpbacks were there before steam-powered whaling ships, fast enough to pursue humpbacks and equipped with explosive harpoons, arrived on the scene in the 19th century? With calls from some quarters for the ban on whaling to be relaxed, this is no mere academic question. Estimates derived from ‘bag totals’ in whalers’ logbooks suggest that there were 20,000 to 46,000 humpbacks before the onslaught began. However, many records are anecdotal and whalers often confused one species with another.
Genetic testing has produced a more accurate figure. An initial analysis of mitochondrial DNA suggested that there were about 240,000 in the pre-whaling population. However, only one segment of the DNA was sequenced. A more detailed study, led by Dr Kristen Ruegg of Stanford University and published in the current edition of Conservation Genetics, refined that estimate. He and his team examined nine sequences from the genome. They believe that there were between 45,000 and 235,000 humpbacks in pre-whaling times, an average of 112,000.
The Japanese, Norwegians and Icelanders still kill whales of selected species, but the number taken is small. Human activities, however, continue to affect sea mammals.
Researchers at Woods Hole Oceanographic Institution examined the impact of shipping on whales. Underwater noise levels are doubling every decade; whales now live in a 24-hour cacophony of engine sounds, pulses from submarine detectors and ‘air gun’ explosions used by oil industry seismologists. The problem is so acute that whales have difficulty hearing the songs when they try to communicate with each other. They have changed their singing patterns in areas where noise levels are high. It’s been suggested that stress from noise pollution might even be a killer.
One of the species affected is the Greenland right whale, of which only 500 remain. Right whales face another threat. They, and the other great whales, can be struck by vessels when they venture close to busy shipping lanes. Some progress has been made in getting captains to slow down or avoid sailing into areas frequented by whales, but collisions are an increasing problem.