Environmental Variability & Subsistence Hunting

Environmental Variability, Bowhead Whale Distributions and Iñupiat Subsistence Whaling

Summary:

Project completed in 2006. Reports and journal articles below. Stomach samples were collected under NMFS permit #814-1899-03.

Overview of Project:

Bowhead whales are typically found on the shelf along northern Alaska and are hunted there. We are interested in why the whales aggregate there every year during their migration, how climate change or variability might affect their behavior, and how these factors influence Iñupiat subsistence whaling success. Whales pause during their migration at favorable food spots to feed. There are two basic types of sea water near Barrow, Bering Sea water and Arctic Ocean water. Copepods are found in both and euphausiids are more common in Bering Sea water.

What do bowhead whales eat?

Copepods	Copepods
Euphausiids (krill)	Euphausiids (krill)

So, why do whales stop along the coast during their migrations?

• Good “bowhead food” environments are found there. Whales need high concentrations of plankton to feed efficiently; therefore, they seek “hotspots” of food. See Krill Trap below.
• At Barrow, whales might find concentrations of euphausiids associated with Bering Sea water.
• Changes in the ocean environment may change the availability of food and, therefore, the behavior of the whales.

How does the amount of Bering Sea water vary?

There are two basic climate regimes along the north coast of Alaska, Regime I and Regime II.

Regime I occurs during a negative Arctic Oscillation (AO) with a strong Beaufort gyre. (Beaufort gyre = gray arrows, Bering Sea water = white arrows) This strong Beaufort gyre causes a greater influence of Arctic water and less movement of Bering Sea water across the Beaufort Shelf. (Source: Wieslaw Maslowski)

Regime II occurs during a positive AO with a weak Beaufort gyre. The weaker Beaufort gyre allows the movement of Bering Sea water across the Beaufort Shelf, bringing euphausiids with it. (Source: Wieslaw Maslowski)

Map showing sightings of bowhead and beluga whales along the Beaufort Sea shelf. (Source: Sue Moore)

Hypothesis:

• Bowhead whale distribution is influenced by variability in plankton concentration that is linked to physical and biological oceanography and the AO regimes.
• Bowhead whales congregate at Barrow because of plankton patches that form there at certain physical features that cause eddies, fronts, and convergences of waters.

Research Questions:

• What are the oceanographic conditions favorable to the development of plankton aggregations at Barrow? How will this differ between the 2 regimes?
• How does zooplankton composition (e.g., euphausiids vs. copepods) differ between the regimes?
• Can bowhead whale residence time near whaling villages be predicted by the AO regime, oceanographic conditions, and prey availability?
• Is the Iñupiat fall whaling tradition resilient to contemporary changes in climate variability and bowhead whale ecology?

Approach: Interdisciplinary integration of the ecological and social systems

• Biological-physical modeling of the ice-ocean system.
• Field Study – High resolution study of the coastal ocean to identify hydrographic and biological features to verify predictions.
• System Analysis – 20 year study of past climate and ocean conditions, plankton and whale distributions, and hunting success.
• Ground-truthing – analysis and integration of traditional ecological knowledge through interaction and involvement of whaling captains.

Results from oceanographic field work in 2005 and 2006:

• Multiple water masses were observed.
• Variability in water masses was associated with changes in wind speed and direction.
• Aggregations of 50-100 bowhead whales were observed in early September of both years.
• Locations of aggregations were consistent with traditional ecological knowledge.
• Analysis of records from 1984-2004 showed aggregations associated with wind speed and direction.
• Euphausiids and copepods appear to be upwelled on to the Beaufort shelf during easterly or southeasterly winds.
• Westward Beaufort shelf currents converging with the coastal current flowing northeast (along the eastern edge of Barrow Canyon) seem to hold and concentrate the plankton, forming a “hot spot”.

Results from ethnographic work on subsistence harvest:

• Future weather conditions might deteriorate if wind patterns are altered by climate change.
• More windy days and higher wave size.
• Whale migration pathways could be altered due to whale prey availability or to human activity.
• Requiring longer travel distances for whaling crews to harvest whales.
• Under any of these conditions, whaling could become more dangerous, difficult, and less successful.
• Alternatively, climate change could result in greater transport of Pacific Water, and euphausiids, to the Barrow region.
• Enhancing the feeding opportunities for bowhead whales near Barrow and potentially extending the period during which bowhead whales are present in the fall.
• Extending the length of the hunting season.

Krill Trap Model:

These illustrations show how a “krill trap” can be formed. The circles indicate concentrations of krill. The second illustration shows the krill concentration located in the Barrow “hot spot.”

Results from aerial surveys and stomach contents analysis in 2005 and 2006 (excerpts taken from this journal article):

• In 2005, 145 whales were seen, mostly in two distinct aggregations: one (ca. 40 whales) in deep water in Barrow Canyon and the other (ca. 70 whales) in very shallow (< 10 m) water just seaward of the barrier islands.
• Feeding behaviors observed in the latter group included whales lying on their sides with mouths agape and groups of 5–10 whales swimming synchronously.
• In 2006, 78 bowheads were seen, with about 40 whales feeding in dispersed groups of 3–11 whales.
• Feeding behaviors observed included surface skimming, echelon swimming, and synchronous diving and surfacing.
• Surfacing behavior included head lunges by single animals and groups of 2–4 whales.
• Of 29 whales harvested at Barrow, 24 had been feeding.
• Euphausiids were the dominant prey in 2006 (10 of 13 stomachs), but not in 2005 (4 of 11 stomachs).
• In 2005, euphausiids were dominant in 4 of 11 stomachs, mysiids in 4 stomachs, isopods in 2 and amphipods in one stomach.
• Copepods were the dominant prey in the stomachs of three whales harvested near Barrow Canyon in 2005.

Publications:

• Krill Trap – read this blog for more of the story
• Ashjian, C.J., et al. 2010. Climate variability, oceanography, bowhead whale distribution, and Iñupiat subsistence whaling near Barrow, Alaska. Arctic 63(2):179-194.
• Ferguson, M. 2016. Observations of Bowhead Whale Foraging near Barrow, Alaska, in 2015 Support the Krill Trap. Poster presentation.
• Moore, S.E., et al. 2010. Bowhead whale distribution and feeding near Barrow, Alaska, during late summer, 2005-06. Arctic 63(2):195-205.