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Posted on: October 4, 2010
Whale Migratory Routes More Complex Than Earlier Believed
MAALAEA (MAUI), HI -- Maps showing the migratory routes of humpback whales around Australia often use wide brush strokes to show the whales moving in a simple north-south line between their feeding areas near Antarctica and their breeding areas in warmer waters nearer to the equator.
But a recent Pacific Whale Foundation research paper demonstrates how the movements and population structure of humpback whales in this region may be much more complex than has been previously described.
The paper, written by Pacific Whale Foundation Research Director Quincy Gibson, PhD, President and Founder Gregory D. Kaufman, and Vice President, Paul Forestell, PhD, was delivered to a meeting of the International Whaling Commission (IWC) on June 6. It summarizes the continuing work of Pacific Whale Foundation to examine migratory patterns of east Australian humpback whales through its photo-identification studies over the past 25 years. (To download a PDF of the paper, click here.)
This work includes a catalogue of 4,196 uniquely identified animals which has been developed by Pacific Whale Foundation since 1984. Images obtained from multiple sites along the east coast of Australia since 1984 have been examined for evidence of multiple sightings of identified animals at different locations both within and between years. The data suggest complex patterns of migratory movement that may require reassessment of current definitions of breeding stocks.
"Historically, it has been suggested that the group of whales known as Area V humpback whales segregate after feeding in Antarctic waters and travel along the east Australian and New Zealand coasts towards their northern breeding grounds," says Kaufman. "These humpbacks migrating along the east coast of Australia are believed to breed in the northern tropical waters of the Great Barrier Reef Marine Park and beyond."
"But what we are finding is that during their northward migration, some whales may branch out from central Queensland and head off to a variety of destinations," said Kaufman. "It's important to find out where they are going to mate, breed and care for their young."
"Old assumptions about a straight north-south route were primarily based on research from the 1950s and 1960s that used Discovery tags on the whales," says Kaufman. "A permanent tag placed on a whale would be removed when the whale was killed by whaling ships. The result would be two points of information about the whale -- where the tag was first placed on the animal and where the tag was retrieved when the whale was killed. The results mainly pointed to a north-south migration route."
Today, most whale research involves photoidentification, a noninvasive practice that involves photographing the underside of the whale's tail, or its flukes, as they are commonly called. Each whale's flukes have unique shapes, markings and pigmentation patterns, allowing it to serve as a type of "fingerprint" that's unique to the individual whale. As researchers gather these "fluke i.d. photos" they are also recording GPS data on the exact location where each fluke photo is taken, the whale's behaviors at the time and its pod composition.
By comparing these fluke i.d. photos against other photos from different areas, researchers can identify "resights" of the same whale in multiple locations.
As researchers gather more whale fluke i.d. photos and also pool their fluke i.d. photos with those of other researchers, they are able to identify more and more resights, allowing them to make new discoveries about the migratory pathways of the whales.
"That's exactly what's been happening around Australia," says Kaufman. "Since 1983, data has been collected by Pacific Whale Foundation and/or submitted from collaborators working in the following areas in eastern Australia and Oceania: the Whitsunday Islands, Great Barrier Reef (excluding WI), Hervey Bay and Point Lookout, Queensland; Byron
Bay, Coffs Harbour, Eden, New South Wales; Tonga, American Samoa and Antarctica. We're now able to study these information on these 4,196 individual humpback whales, to learn about their migratory paths."
From 1993 – 1999 Pacific Whale Foundation collected photo-ID images from Eden, Hervey Bay and the Whitsunday Islands during each season. Those data provided an opportunity to look at how many of the identified animals were observed in one, two or three locations within the same season. "One
might reasonably assume that if animals are moving along a migratory corridor there should be a high incidence of re-sights in multiple areas," says Kaufman.
"What we found surprised us," says Kaufman. "We had expected to see that whales that began migrating northward along Australia's eastern coast would just follow the coastline, all the way up to the Whitsundays."
"But instead, we found that there was a low rate of resights of whales between these three areas along that coastline," he noted. "As a result, we are now hypothesizing that some of these whales may not follow the coastline, but may branch off at some point and go to different mating and breeding areas."
"From 1993 – 1999 there were 1,543 individuals photographically identified in the Whitsunday Islands, Hervey Bay and Eden a total of 2,013 times. Of the total number of sightings, 1,940 (96.4%) were sightings of animals seen in only one location in a given year. Seventy-two of those sightings (3.5%) were sightings of animals seen in two locations in a given year. In one year, one animal was seen in three locations," he says. " Clearly the interchange rate within season was at an extremely low rate and is inconsistent with the concept of a simple north-south migratory corridor."
The second set of data considers images collected between 1984 – 2007 from all the sites noted above plus Point Lookout. These observations were not collected in all areas in each year, but are useful for looking at patterns of interchange across seasons during 24 years of photo-identification effort.
What the researchers found is that only a small percentage of whales sighted in Hervey Bay or North Stradbroke Island were identified further north along Australia's coast. "In other words, whales found in Hervey Bay and off North Stradbroke Island appear not to be a representative sub-set of the whales found in the Great Barrier Reef and in other areas to the north," said Kaufman. "So our question is: if the whales that are not staying along the coast when they migrate north, where exactly are they going to, in order to mate and give birth?"
"Comparison of photo-IDs from east Australia and Oceania suggests that some whales may branch out from central Queensland during the northward migration to a variety of destinations," said Kaufman. "There is increasing information that suggests more complex broadly based movement patterns with extensive east-west movement by the whales."
"Different populations of whales may be overlapping along portions of the same migratory pathways," he notes. "Different subsets of whale populations may be using the east Australia corridor for a portion of their migration and then branching off to other breeding grounds. In fact, individuals from separate breeding areas may be overlapping along portions of the same migratory pathways."
"We had this publication presented to the IWC, to demonstrate that so little is known about the breeding populations of humpback whales in the South Pacific," notes Kaufman.
" To allow the hunting of humpback whales in this area at a time when we know so little about the whales' populations and migratory pathways would be criminal," he says. "Killing even a few whales could wipe out an entire breeding population."
Pacific Whale Foundation is continuing to make its photo-ID catalogue available to other groups for comparison. "We are currently in discussions with the South Pacific Whale Research Consortium regarding limited analysis of our combined holdings, and are in the planning phase for a collaborative effort with the College of the Atlantic to establish a comprehensive Southern Ocean Catalog for humpback whales," he says. "I"m very excited about having a chance to expand upon our hypothesis by looking for resights in these other data pools."
Pacific Whale Foundation's research team, guided by Greg Kaufman, will travel to Australia this summer to study whales and gather photoidentification data in Port Douglas, Hervey Bay and Eden.
Pacific Whale Foundation is a nonprofit organization dedicated to promoting appreciation, understanding and protection of whales, dolphins, coral reefs and our planet's oceans. We accomplish this by educating the public -- from a scientific perspective -- about the marine environment. We support and conduct responsible marine research and address marine conservation issues in Hawaii and the Pacific. Through educational ecotours, we model and promote sound ecotourism practices and responsible wildlife watching. To learn more, visit www.pacificwhale.org <http://www.pacificwhale.org> .