ACS Research Committee Report

Southern Hemisphere Humpback Whales: the Longest Mammalian Migration
Source: Rasmussen, K., Palacios, D.M., Calambokidis, J., Saborio, M.T., Dalla Rosa, L., Secchi, E.R., Steiger, G.H., Allen, J.A., and Stone, G.S. 2007. Southern Hemisphere humpback whales wintering off Central America: insights from water temperature into the longest mammalian migration. Biol. Lett. Doi: 10.1098/rsbl.2007.0067.

Data were collected off Central America during winter 2001 to 2004 and off the Antarctic Peninsula during summer 1981 to 2004. Photographs were compared to identify individuals common to both regions.

A total of 207 whales were sighted in the Central America region, commonly off Panama and Costa Rica, during the study period. These whales included mother/calf pairs, groups of competing males and singing males; this behavior and group composition is indicative of a mating and calving ground. This wintering ground is likely an extension of the ground of Ecuador and Colombia.

Forty-one whales were identified based on photographs; of these, seven were matched to photographs taken off the Antarctic Peninsula. Three of these whales were seen within the same year.

The minimum distances between these locations, determined by great-circle distances between straight segments around land masses, ranged from 8299 to 8461km.

Photographs from the Central America region were also compared to photographs taken off of California and matches between these regions indicate that North Pacific humpbacks also winter in this area.

Anecdotal sightings of humpback whales have been reported monthly off Central America.

Eastern North and South Pacific humpback whale populations share genetic traits indicating a trans-equatorial exchange, most likely occurring off Central America.

The average sea surface temperature (SST) in the Central America wintering ground is 28°C. Temperatures of other wintering areas range from 21.1-28.3°C. Coastal upwelling and the Pacific cold tongue result in cooler SSTs extending from the South American coast into the eastern equatorial Pacific; therefore, SSTs great than 21.1°C only occur in this region north of the equator. This implies that South Pacific humpback whales need to migrate farther north to wintering grounds off Central America in order to reach waters that are warm enough for mating and calving activities.  

Humpback Whale Wintering Habitat in the Northwestern Hawaiian Islands
Source: Johnston, D.W., Chapla, M.E., Williams, L.E., and Mattila, D.K. 2007. Identification of humpback whale Megaptera novaeangliae wintering habitat in the Northwestern Hawaiian Islands using spatial habitat modeling. End. Sp. Res. 3: 249-257.

Historical evidence suggests that humpback whales did not utilize habitat surrounding the main Hawaiian Islands until about 200 years ago.

Visual surveys in this study were made from a NOAA oceanographic vessel from March 26 through April 12, 2007. The location, species, general behavior, and group size estimates for each cetacean encounter was recorded. Skin and blubber biopsies were obtained from individuals for genetic analyses and simultaneous acoustic observations were conducted using a towed hydrophone array.

The extent of potential humpback whale wintering habitat in the Hawaiian Archipelago was assessed using bathymetric and sea surface temperature (SST) data.

During the cruise, nine groups of humpback whales were observed. The best estimate of number of animals was 24. At least two groups had young calves and three groups were engaged in competitive behaviors.

There were 662 photographs taken of humpback whales, from which two distinct tail patterns and four distinct dorsal fin shapes were obtained for individual identification. These observations revealed the presence of humpback whales, several of which were engaged in competitive behaviors, in the Northwestern Hawaiian Islands (NWHI) during late winter.

All sightings were made in shallow water, at or within the 200m isobath, despite considerable effort in deeper areas. There were areas that were shallow with a SST less than 21°C that did not have any humpback whale sightings; likewise, there were deeper areas that had sufficiently warm SSTs in which there were also no sightings.

The behavior of sighted humpbacks suggests that at least some of these whales are using this region as a wintering ground, rather than a migratory pathway. This hypothesis is further supported by satellite tag data from migrating humpback whales, in which no whales moved across the NWHI on their migration.

It is possible that humpback whales have used the NWHI as a wintering ground consistently, but remained undetected due to minimal to no survey effort. Alternatively, humpback whales may be expanding their range as their population recovers.  

Acoustic Clicks and Buzzes by Foraging Humpback Whales
Source: Stimpert, A.K., Wiley, D.N., Au, W.W.L., Johnson, M.P., and Arsenault, R. 2007. "Megapclicks": acoustic click trains and buzzes produced during night-time foraging of humpback whales (Megaptera novaeangliae). Biol. Let. 3: 467-470.

Humpback whales were studied using DTAGs, which are suction-cup tags that record sound and body orientation of tagged individuals.

Nine humpback whales, five in 2004 and four in 2005, were tagged in the Gulf of Maine. Two tagged animals displayed a previously-unreported acoustic behavior: multiple bouts of broadband clicks that were termed "megapclicks."

A total of 101 bouts containing 34,026 clicks, were identified from two whales on different days. The sounds had peak frequencies of approximately 800-1700 Hz, and received levels at the DTAG of approximately 143-154 dB.

During click bouts, 98% of inter-click intervals (ICIs) were between 19 and 200 ms. The shortest ICIs generally occurred at the end of bouts as part of acceleration in click rate.

This pattern was similar to Odontocete or bat "terminal buzz." Buzzes contained megapclicks with ICIs of 25 ms or less and had durations of at least 0.5s.

All megapclick bouts occurred during night-time hours and generally near the bottom of dives (average depth 38m, which was near the ocean floor in the study location).

All bouts that ended in buzzes also ended with a sharp body roll by the tagged animal. Rolls of similar magnitudes and angular rates occurred frequently during tag attachment without accompanying buzzes; these rolls were thought to represent feeding events.

The rolling behavior being associated with buzzes suggests that this acoustic behavior has a foraging function. Sounds with these characteristics could be useful for some form of rough acoustic detection such as identifying the seafloor or other large target. Alternatively, megapclicks may be used to manipulate prey, such as flushing prey from the bottom into the water column. Humpback whales have previously been documented to manipulate prey in other non-acoustic ways.  

Increasing Abundance of Bowhead Whales in West Greenland
Source: Heide-Jørgensen, M.P., Laidre, K., Borchers, D., Samarra, F., and Stern, H. 2007. Increasing abundance of bowhead whales in West Greenland. Biol. Lett. 3: 577-580.

Commercial whaling in Baffin Bay removed at least 28,700 bowhead whales between 1719 and 1900. In 1825, the bowhead population was estimated at 11,000 whales; by the end of the 19th century, the stock was so reduced that commercial whaling was no longer viable. In 100 years, there has been little apparent recovery of this population.

This study used a combination of aerial surveys conducted between March and April, 2006, and satellite tagging conducted in April of the same year to determine population size. Nine bowhead whales were tagged during this period. Aerial surveys were conducted in the area used by tagged whales and in the waters adjacent to their tracks.

Eighty-nine percent of sightings occurred inside the area used by satellite tagged whales; 11% of sightings occurred in waters adjacent to the tagged whale's track. There were 33 sightings of bowhead whales from aerial surveys. Satellite tags demonstrated that bowhead whales spend 24% of their time at or above 2m depth, where they would be visible to aerial surveys. Taking this into account, estimated abundance when corrected for perception bias was 1229 whales.

This region has been surveyed extensively since 1981 with comparable methods; however, all previous studies have sighted too few whales to allow for reliable abundance estimates.

The low number of sightings in the 1980s and 1990s, followed by an abundance estimate of over 1200 in 2006 can not be explained by growth rates that have been documented in this species in other regions. One possible explanation is that the decreased sea ice in West Greenland has recently allowed better access to coastal feeding grounds. Whatever the cause for the increase in sightings, the authors hypothesize that this significant increase in sightings indicates population growth in this region.  

   

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