HUMPBACK WHALES

Research on humpback whales (Megaptera novaeanagliae) isincluded as a component of the GAP project for two primary reasons:

1. Humpback whales are firmly established as apex predators in the Gulf of Alaska and eat a wide variety of prey, including several fish and zooplankton species. They can be found in Kodiak waters year round, with a peak in sightings occurring May through October. Therefore, the potential for competition between them and other predators, including man, may be significant.
2. Humpback whales were harvested commercially out of Port Hobron, Alaska from 1926 to 1937, resulted in the taking of nearly 1,600 humpback whales from the waters of the southeastern shores of Kodiak Island. It is generally believed that removing top predators like this, will lead to an increase in the amount of available prey to other predators, essentially reorganizing trophic relationships.

The relationship between the humpback’s decline due to commercial whaling and their role as apex predators within the Gulf of Alaska may be essential in understanding current and historic trends and predator-prey interactions in the Gulf. Data regarding the abundance and foraging of Kodiak Island humpback whales can be combined provide insight into the Kodiak marine ecosystem as a whole and help to determine which apex predators may have potential to compete with one another for prey resources.

A humpback whale lunges through its prey as near-by boaters look on. (Photo by Mary Crivello)

The remainants of the Port Hobron whaling station in eastern Kodiak Island.

1. Estimate Abundance and Seasonal Distribution

Humpback whale populations are often studied by using photo-identification of their tail flukes as a method of mark-recapture. Photo-identification studies allow for individual whales to be tracked within season and across years, estimation of regional abundances, and determination of migration routes. Current abundance is estimated for a portion of eastern Kodiak Island humpback whales based on photo-identification studies that are conducted on a seasonal basis. Historic abundance estimates of pre-whaling and immediate post-whaling abundances are also calculated using the current estimate of abundance, historic catch values, and biological parameters. Abundance in 2002 (N2002)was estimated at 157 animals and abunance prior to commerical exploitation(N0) was 343 animals. Abundance was reduced to just 27 whales immediately following the cessation of whaling out of the Port Hobron station (Abundance v. Time Chart). Photo-identification effort is on-going. Long-term effort will result in increasingly accurate estimates of abundance and expanded knowledge of seasonal habitat usage of Kodiak Island humpback whales.

Individual humpback whales can be identified from photographs of the black and white pigment patterns and other natural markings on the ventral surface of their tail flukes.

The low dorsal fin and hump are distinguishing characteristics of the humpback whale. Dorsal fin shape and scarring can also be used to indentify individual whales.

Baleen can be clearly seen on this feeding humpack whale.

Humpback whales are known to feed on a variety of fish species, including Pacific sandlance (top) and juvenile walleye pollock(bottom).

2. Determine Prey and Model Consumption

Consumption and biomass removal by humpback whales is modeled for both the current and pre-whaling humpback whale populations. To date, consumption has been modeled based on two hypothetical diets due to difficulties in directly determining targeted prey species of humpback whales. One diet was based on possible historic prey species as documented by the stomach content of humpback whales harvested at the Port Hobron whaling station. The second diet was based on average prey availability as shown by fish surveys in the Kodiak area. Modeling shows that the current humpback whale population may be removing as much as 9,600 tons of prey seasonally, while the historic population may have removed over 19,000 tons. These figures reflect consumption based on all available prey and do not account for prey selectivity. Currently, a combination of acoustic, video, associative, net sampling, and sonar techniques are being developed for use to identify prey species when feeding humpback whales are encountered . It is hoped that these techinques will improve estimates of biomass removal and better describe humpback whale selectivity and foraging habits.

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BALAENOPTERID WHALES

Large balaenopterid whales are considered significant components of marine ecosystems. However, most available distribution, prey, and habitat data are antiquated, having been derived from commercial whaling operations that ended in the North Pacific in 1976 and Kodiak nearshore waters in 1937. The goals of this study are to determine current summer (May-September) distribution of balaenopterids in Marmot and Chiniak Bays, northeast Kodiak Island, to measure several abiotic and biotic habitat characteristics that may relate to distribution, and to evaluate habitat partitioning among balaenopterid species.

Research began in 2002 with weekly whale-directed surveys and monthly 3-day hydroacoustic prey surveys. The former emphasized data collection and environmental measurements, using CTD (Conductivity-Temperature-Depth) casts and vertical zooplankton tows, at whale locations. The latter followed established transect lines. CTD and zooplankton sampling stations were pre-determined and mid-water trawls occurred when warranted by acoustic signal; stations in the vicinity of whales were coincidental. Whale-directed surveys yielded 96 humpback sightings (164 individuals), 131 fin whale sightings (239 individuals), 87 CTD casts, and 16 zooplankton tows. Thirty-six humpback sightings (68 individuals), 48 fin whale sightings (74 individuals),153 CTD casts, and 24 zooplankton tows occurred during hydroacoustic surveys. Preliminary analysis showed a significant difference (p < .0001) in mean water depth distribution for fin whales (120.8 ± 39.2 m) and humpback whales (79.2 ± 52.7 m), plus aggregations suggestive of high use areas. Distribution differences may relate to differences in prey preferences.

KILLER WHALES

Killer whales are included within the GAP project not as potential competitors of Steller sea lions, but as potential sea lion predators. Killer whale research initiates surveys observations, and collections needed to:

• document the number and identity of transient killer whales using northereastern Kodiak waters
• follow transient killer whale pods and document their attacks and predation of Steller sea lions and other marine mammals.

The degree to which killer whales prey on the western stock of Steller sea lions cannot be determined until photo-identification studies are conducted to distinguish transient (mammal eaters) from resident (fish eaters) populations. Documenting predation on mammals requires following pods and witnessing kill events first-hand. To increase the likelihood of encountering widely disperesed killer whale pods, we established a Killer Whale Hotline to receive reporst from pilots and mariners via VHF radio and cell phone.

"THE KODIAK KILLERS"

In the winter months, a group of transient killer whales have frequented Kodiak's harbor in search of a meal since at least 1993. Throughout the years the group has seen the birth and death of numerous calves, while three adult whales remain constant and include a large male with an easily recognized crooked fin. Through photographs of their dorsal fins, the whales have been identified as belonging to the AT group of transient killer whales which have been seen in Alaskan waters since 1984.

 These photos were taken on April 15th, 2002 when the "Kodiak Killers" attacked and killed a Steller sea lion in the Kodiak harbor. Note the crooked dorsal fin of the large male in the left picture.