Monday, November 9, 2015

Great Whale Gathrings - Part 2

Part 2: Baleen Whales of the Southern Hemisphere

Humpback Whale © Joshua Barton
In Part 1 [1] of this series, I looked at where the greatest of the great whale gatherings take place and focussed on baleen whales in the Northern hemisphere. In this part, I continue the discussion by discussing some of the spectacular gatherings of great baleen whales that have been recorded in the Southern hemisphere.
Antarctic Minke Whales
The phenomenal gathering of Grey Whales in Mexico is not to say that high concentrations of baleen whales do not occur in other parts of the world. Antarctica seems to be especially productive for great whales, probably as a result of the krill blooms that take place. Robert Pitman drew my attention to a reference of an aggregation of 400 Antarctic Minke Whales in the Encyclopaedia of Marine Mammals, 2nd edition by William Perrin, Bernd W├╝rsig and J.G.M. Hans Thewissen. I investigated the question of how frequently the Antarctic Minke Whales in gather into large aggregations in Antarctica. From the International Whaling Commission (IWC), I received ship-based survey data on 22,468 Minke Whale schools, where Minke was the first or only species recorded. The data was logged on 1,237 survey dates in the period from 25th December 1978 to 27th August 2010; a span of thirty-three years. Schools were classified as distinct, if groups were more than about 0.3 nautical miles apart. On 17th January 1987, when the large count of 400 Minke Whales in a school was made, 32 other schools were also recorded with sizes ranging from one to five, with the majority being a school size of one (i.e. a single whale). It is clear that the estimate of 400 was on the same basis as others and is a real figure and not a statistical extrapolation. Most papers I have seen on Antarctic Minke Whales are of a statistical nature and the sizes of the large schools are lost in low-value arithmetic means which reflect that Minke Whales typically occur in small schools. The mean school sizes in all the years ranged between two and five.
The count of 400 Minke Whales was recorded only once in 1987. The next highest counts of over 100 Minke Whales were as follows: 140 (once), 120 (once), 118 (once), 115 (twice) and 100 (seven times). During email correspondence in May 2015, I also asked a few scientists for details of the largest ‘in the field of view’ counts they have had of schools of Minke Whales. The feedback I received included from Paula Olson (‘...50-60 Minke Whales...’) and Paul Ensor (‘...Detections of large groups are also made from platforms other than the IWC research ships, for e.g. in Jan 2014, during helicopter surveys for Killer Whales in McMurdo Sound, I observed a group estimated at 60 individuals, all within 5 body lengths of a group member, and there were other groups in the area as well.....’). Minke Whales are not truly social animals but concentrate into large ephemeral gatherings for feeding. These concentrations are believed to have been higher nearer the pack ice. In dialogue with Trevor Branch and Mark Bravington, I gathered that the surveys moved away from the pack ice after 1984. Although the highest count was after this, it is possible that large concentrations in areas such as Prydz Bay close to the pack ice are now being missed. Antarctica seems to be very important for great whale concentrations of Minke Whales. However, this would not be evident from commercial whale watching cruises as they do not visit Prydz Bay in Eastern Antarctica. For example, Mark Carwardine who is a well-known author and populariser of whale watching has been to Antarctica around 23 times. However, he noted that he has not been to Prydz Bay and the largest school of Minke Whales he had seen had comprised of six whales [1].
I also received data from the IWC for Fin Whales, Humpback Whales and Southern Right Whales. I have shown the largest school sizes encountered in a single chart. The most notable is a school of 100 Fin Whales. Although Eastern Antarctica may in aggregate have the largest numbers of whales, it appears that to find large schools is difficult for these three species [3].
Dwarf Minke Whales
Dwarf Minke Whales are an undescribed sub-species of the Common Minke Whale found in the southern hemisphere. They aggregate in the northern Great Barrier Reef during the Austral winter. This is considered to be the only predictable, recurring aggregation of Dwarf Minkes and has led to a licensed swim with whales program since 2003.The whales are usually in small numbers with the largest schools in the field of view that have been seen ranging from 12-15. The Minke Whale Project of James Cook University has maintained records of the number of whales estimated to have been seen during a day. These total counts for the day attempt to exclude re-sighting but cannot be exact. There are several reports each year of Dwarf Minke Whale schools with counts in the 20-30+ range, most in the vicinity of Ribbon Reef No. 10. During correspondence in August 2015 with me, Dr. Matt Curnock provided information on the largest estimates of total day counts of unique whales. The largest estimated counts were 50 plus whales on 24th June 2003 at Ribbon Reef No. 10, approximately 50 whales on 14th July 2009 at Cairns Section, a minimum of 46 whales based on photo ID on 7th July 2010 at Ribbon Reef No. 10 and potentially 100 plus whales on 24th June 2012 at Ribbon Reef No. 10. Although the arrival and aggregation of the whales is seasonally predictable and provide for wonderful interactions, the chances of whale watchers encountering a large school appears to be low.
Right Whales
Right whales are also reported in large aggregations. Ocean Alliance in their website state that for years they have studied a population of Right Whales which uses the bays of Peninsula Valdes as a nursery ground. They say the study begun in 1970 follows the lives of 2,600 individual whales. Maurico Failla and others in their paper ‘Historical records of southern right whales (Eubalena australis) of the province Rio Negro, North Patagonia (1991-2008)’ documented 308 records comprising of 425 whales. The mean group size was 2 and the maximum was 7. It seems unlikely that the Southern Right Whales are found in concentrations which rival that of the other great whales discussed earlier. The North Atlantic Right Whale has been hunted close to extinction and only 400 are estimated to remain in the North Atlantic. The North Pacific Right Whale is rarely seen having also been pushed close to extinction.
Blue Whales
Blue Whales are not true social animals and are typically seen as individuals or in a mother and calf pair. They have until recent years been regarded as one of the hardest animals to see in the planet and not described in the scientific literature as being seen in large aggregations. In this article, I have shown that many of the baleen whale aggregations with the exception of the Grey Whales seem to occur unpredictably when there is a high concentration of krill. There are observations to suggest that in areas such as Trincomalee and Mirissa in Sri Lanka, there could be significant numbers of Blue Whales during the seasonal krill blooms. Not in the hundreds, but perhaps in aggregations no less noteworthy than what has been described for other baleen whales such as Bowhead Whales.
For example, on 24th April 2011 South of Mirissa I counted seven simultaneous Blue Whale spouts. At the same time, Dr. Charles Anderson, an experienced marine mammal observer was on another boat in the same locale and estimated that he had seen 17 individual Blue Whales in an approximately 5 kilometre square area (25 square kilometres). On 5th November 2010, Anoma Alagiyawadu, a Jetwing Lighthouse Hotel naturalist observed an astonishing 25 Blue Whales travelling together. At first, he thought it was a pod of Sperm Whales as he had never seen Blue Whales in such high numbers close to each other. Aerial surveys if conducted in the future may show that Blue Whales periodically gather in high concentrations off Mirissa and Trincomalee.
Continues the 9th of November...







Gehan de Silva Wijeyeratne
05 November, 2015

Via Wall Street International