A grey whale mother-calf pair migrating alongside the central California coast from the wintering grounds in Mexico to the summer season feeding grounds within the Arctic. Credit: NOAA Fisheries
Gray whales that migrate alongside the West Coast of North America continued to say no in quantity over the past 2 years, based on a brand new NOAA Fisheries evaluation. The inhabitants is now down 38 % from its peak in 2015 and 2016, as researchers probe the underlying causes.
The inhabitants additionally produced the fewest calves on document this 12 months since counts started in 1994, an accompanying report explains.
The 38 % decline from a peak of about 27,000 whales in 2016 to 16,650 this 12 months resembles previous fluctuations within the jap North Pacific inhabitants. Researchers on the Southwest Fisheries Science Center mentioned it warrants continued shut monitoring. Population counts for jap North Pacific grey whales are usually carried out over the course of a 2-year interval. However, NOAA Fisheries will add a 3rd 12 months counting grey whales that go alongside the Central California Coast to this survey, from late December to mid-February 2023.
“Given the persevering with decline in numbers since 2016, we must be carefully monitoring the inhabitants to assist perceive what could also be driving the pattern,” mentioned Dr. David Weller, Director of the Marine Mammal and Turtle Division on the science middle. “We have noticed the inhabitants altering over time, and we wish to keep on high of that.”
An improve in grey whale strandings led NOAA Fisheries to declare an Unusual Mortality Event for the inhabitants in 2019, prompting an investigation into the probably causes. That ongoing investigation has recognized a number of probably contributors. These embrace ecological modifications within the Arctic affecting the seafloor and the amphipods and different invertebrates dwelling in and above the sediment and within the water column that grey whales feed on every summer season, based on new analysis revealed earlier this 12 months.
Some grey whales could have struggled to search out meals amid these shifts, mentioned Dr. Sue Ellen Moore, a University of Washington researcher who leads the UME workforce assessing ecological influences. She famous that grey whales feed on all kinds of prey over an unlimited vary, so there might be many variables affecting how, when, and the place they discover meals.
While lots of the roughly 600 useless whales recorded from 2019 to 2022 appeared malnourished, some didn’t. Some stranded whales had clearly died of different causes similar to getting hit by ships or predation by killer whales. The variety of strandings initially spiked in 2019 however then fell in subsequent years. That means that many of the grey whale inhabitants decline most likely occurred within the years shortly after the UME was declared.
“There is nobody factor that we will level to that explains the entire strandings,” mentioned Deborah Fauquier, Veterinary Medical Officer in NOAA Fisheries’ Marine Mammal Health and Stranding Response Program, who coordinates the UME investigation. “There seems to be a number of components that we’re nonetheless working to grasp.”
Population Reflects Changing Ocean Conditions
Gray whales are identified for his or her seen migration alongside the West Coast annually. The inhabitants has fluctuated extensively earlier than, together with an analogous drop of roughly 40 % from the late Eighties to the early Nineties. The inhabitants later rebounded to a brand new excessive level. Gray whales within the jap Pacific Ocean are totally recovered from the times of business whaling, and have been faraway from the listing of endangered species in 1994.
An analogous spike in strandings led to the declaration of an earlier Unusual Mortality Event in 1999 and 2000, when the inhabitants declined by round 25 %. It later climbed again to a peak in 2015-2016. (While Table 1 within the report features a larger estimate for 2014-2015, that quantity was much less exact, so scientists depend on the 2015-2016 estimate.)
Gray whale abundance and annual calf manufacturing. Credit: NOAA Fisheries
Most grey whales migrate between feeding grounds within the Arctic throughout summer season and lagoons in Baja Mexico within the winter the place they nourish their new child calves. This annual roundtrip of greater than 10,000 miles exposes them to many stressors alongside the best way. A small group of grey whales additionally spends the summer season feeding alongside and across the Pacific Northwest Coast.
The inhabitants has probably at all times fluctuated in response to modifications in its surroundings, with out lasting results, mentioned biologist Dr. Tomo Eguchi, lead creator of the brand new NOAA Fisheries studies on the whale inhabitants abundance and calf manufacturing. “The inhabitants has rebounded a number of occasions from low counts prior to now,” he mentioned. “We are cautiously optimistic that the identical will occur this time. Continued monitoring will decide whether or not and after they rebound.”
Calf Numbers Also Decline
NOAA Fisheries researchers observe the numbers of grey whales within the inhabitants by counting southbound whales heading for Mexico. They monitor calf manufacturing by counting moms and calves migrating north every spring from lagoons in Baja California, the place some whales give start. The most up-to-date depend that concluded in May estimated the entire calf manufacturing this 12 months at about 217. This quantity was down from 383 calves final 12 months and the bottom for the reason that counts started in 1994.
Like the grey whale inhabitants as an entire, the variety of calves born annually has additionally fluctuated. Low calf counts have been recorded for intervals of three to 4 years at a time earlier than rebounding. Two of the three prior intervals of low calf manufacturing have coincided with Unusual Mortality Events and declines within the inhabitants. This means that the identical components that have an effect on grey whale survival probably additionally have an effect on their copy, the report on calf numbers concludes.
Aerial images of grey whales within the lagoons in Mexico confirmed declines within the physique situation of many grownup whales, underscoring that connection. “Depending upon the age of the whales, this decrease physique situation could have led to delayed copy and decrease calf counts, and/or diminished survival in skinny whales,” scientists reported.
In December, groups will start the subsequent depend by coaching binoculars on whales migrating south previous Granite Canyon, simply south of Monterey Bay in California. “What we hope to see within the subsequent few years is that the abundance stabilizes after which begins to indicate indicators of improve,” mentioned Dr. Aimee Lang, a coauthor of the brand new studies. “We shall be watching carefully.”
Gray whale inhabitants drops by quarter off U.S. West Coast
More info:
Abundance and Migratory Phenology of Eastern North Pacific Gray Whales 2021/2022ABUNDANCE AND MIGRATORY PHENOLOGY OF EASTERN NORTH PACIFIC GRAY WHALES 2021/2022, DOI: 10.25923/x88y-8p07
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NOAA Fisheries West Coast Region
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Gray whale numbers proceed decline; NOAA fisheries will proceed monitoring (2022, October 7)
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