2015–2016 Large Whale Unusual Mortality Event in the Western Gulf of Alaska, United States and British Columbia (Closed)

NOAA Fisheries declared an unusual mortality event for large whale strandings in the Western Gulf of Alaska. Whale strandings were also elevated in British Columbia, Canada.

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Frequent Questions: 2015–2016 Large Whale Unusual Mortality Event in the Western Gulf of Alaska and British Columbia

Submitted by jaclyn.taylor on Wed, 07/10/2019 - 13:13

A joint investigation was conducted between NOAA Fisheries and the Department of Fisheries and Oceans, Canada. The UME was defined as occurring from May 22, 2015 to December 31, 2015 in Alaska and from April 23, 2015 to April 16, 2016 in British Columbia. The number of dead fin and humpback whales in the UME totaled 34 for Alaska and 12 for BC.

Why are you closing the 2015–2016 large whale mortality event in the Western Gulf of Alaska and British Columbia when no cause has been determined?

The conditions under which the UME was declared are no longer occurring. Scientists are no longer documenting a marked increase in strandings, or a temporal shift in strandings. Although the international team of scientists who investigated this UME was not able to pinpoint a definitive cause, they say the most likely culprit was unusual oceanographic/climatic conditions, which occurred in 2015. These conditions may have led to shifts in prey distribution and/or harmful algal bloom exposure, ultimately causing malnutrition and/or toxicity. In many UME cases, a definitive cause is never determined.

How widespread was the 2015–2016 large whale UME in the Western Gulf of Alaska and British Columbia?

Increased mortalities of large whales were observed along the Western Gulf of Alaska, encompassing the areas around Kodiak Island, Afognak Island, Chirikof Island, the Semidi Islands, and the southern shoreline of the Alaska Peninsula. Additionally, large whale strandings also increased in the Pacific waters along the central British Columbia coast, from the northern tip of Haida Gwaii (formerly, the Queen Charlotte Islands) to Southern Vancouver Island.

What are the dates for this unusual mortality event? How many whales are included in this UME?

The UME is defined as occurring from May 22, 2015 to December 31, 2015 in Alaska and from April 23, 2015 to April 16, 2016 in British Columbia. The peak increase in fin whale stranding numbers and frequency of occurrence was observed from May 22 to June 17, 2015 for Alaska.  For British Columbia whales, the peak extended from April 23, 2015 to November 30, 2015 and subsequent strandings have returned to baseline. The number of dead fin and humpback whales in the UME totaled 34 for Alaska and 12 for BC.

What do scientists believe is the most likely cause of this unusual mortality event?

After analyzing various differentials relative to available data, scientists say the most likely cause of this UME was exposure to abnormal environmental conditions such as increased algal toxins, ocean temperature changes, or prey changes that may have resulted in malnutrition. It is possible that there was more than one ecological cause for these mortalities.

What unusual ocean conditions occurred in 2015? Did those conditions continue into 2016?

Unusual ocean conditions in 2015 included:

  • “The Blob”—changing centers of surface heat anomalies in the North Pacific and Bering Sea.
  • One of the strongest El Niño weather patterns on record.
  • Decreasing ice extent in the Bering Sea.
  • Second warmest year on record in Alaska (air temperature).
  • Deep heat: heat in the ocean reached depths of 200 m or more below the surface.
  • Largest harmful algal bloom along the Pacific coast ever recorded.

Some of these conditions persisted into 2016, including “The Blob” and El Niño. Alaska had its warmest year on record in 2016.

What did scientists test for? What did they find?

Although many carcasses were too decomposed and/or too remotely located to allow for necropsies, the samples scientists were able to gather were tested for infectious diseases, predation, algal toxin exposure, impacts from sonar and seismic testing, radiation, ship strikes, and starvation. Samples from one Alaskan whale and eight Canadian whales were tested for a variety of bacterial and viral pathogens, with no evidence of infectious disease present. These animals were also tested for two algal neurotoxins (domoic acid and saxitoxin). The Alaska whale was negative for both toxins; tests for both harmful algal toxins on the British Columbia whales came back positive in seven of eight whales, with values in two whales in the realm of those found in West Coast pinnipeds exhibiting clinical signs of toxicity.

What types of large whales did this unusual mortality event effect?

This event involved principally fin and humpback whales. Although other species of whales were initially included in the UME, they were later determined not to be part of this event.

Were other marine mammals or animals affected by this die-off event?

Other animals that may have been affected by unusual oceanographic conditions include seabirds and sea otters. A seabird die-off event involving mostly common murres occurred across the largest geographic extent ever recorded in Alaska. Findings were consistent with emaciation and starvation. Higher numbers of Northern sea otter mortalities were also reported, mainly in lower Cook Inlet. Scientists point to Streptococcal bacterial endocarditis, encephalitis and septicemia as the culprit. We do not know whether these mortality incidents are related to whatever killed the whales.

What is the current large whale population in the Western Gulf of Alaska? Which species are endangered?

Although fin whales are still listed as endangered (a status they were accorded under the Endangered Species Act in 1973), the North Pacific population is generally believed to have grown substantially in the last few decades.  The minimum population estimate is approximately 1,300 according to this 2015 marine mammal stock assessment report.

A multi-national ocean-wide study called SPLASH recently estimated the North Pacific humpback population at 21,000 animals. Of the three humpback populations that migrate to Alaska waters, the Hawaii population has recovered and been removed from the list of endangered species, while the Mexico population is threatened, and the Western North Pacific population remains endangered.

The minimum population estimate for Eastern North Pacific gray whales is 20,125, according to the NOAA Fisheries 2014 stock assessment. The Eastern North Pacific population of gray whales was removed from the Endangered Species list in 1994. The population is stable.

What is next now that the UME has been closed?

Scientists plan to continue post-UME monitoring for one to two years. They may also broaden the assessment of 2016 samples, and will continue to monitor trophic level changes and associated environmental shifts. Expected steps include:

  • Analyzing data for 2016 samples taken from fin and humpback whales throughout Alaska waters.
  • Monitoring other indicators of feeding ecology to investigate foraging patterns and potential nutritional deficiencies for many species.
  • Conducting necropsies and sample collection on future whale strandings and continuing to test for harmful algal blooms, look for unusual stranding patterns, and investigate changing behavior or presence of large whales.

Concern about radiation in the marine environment followed the Japanese Fukushima nuclear reactor leak in 2011. The level of Cs-134 in the Alaskan fin whale aqueous humor was below minimum detectable levels. Similar radioisotope levels below detection limits were identified in three British Columbia fin whales. There is currently no evidence to indicate that radioactive contamination from the Fukushima event is affecting the health of marine mammals in Alaska. Radionuclide testing in Northern fur seals in 2014 also revealed very low levels of radionuclides.

No evidence has been found linking the whale deaths to military activities. The 2015 Navy Major Training Exercise titled, “Northern Edge 2015,” was conducted between June 15 and June 26, 2015, after the spike in fin whale strandings. There was no indication of an increase in strandings after completion of the exercises. If you have further questions, please follow-up with U.S. Navy Third Fleet Public Affairs at (619) 767-4383.

How many large whale unusual mortality events have previously occurred in Alaska?

This is the first large whale UME in Alaska. Only two other UMEs have been declared in Alaska. One involved pinnipeds in 2011 and the other involved sea otters in 2006.

NOAA Fisheries declared an unusual mortality event for large whale strandings in the Western Gulf of Alaska. Whale strandings were also elevated in British Columbia, Canada.
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