By Rodrigo Manterola
An unusual mortality event is exactly that, an event where individuals start stranding and dying in larger numbers than usual, and the one of 2019 wasn’t the first one
UMEs are not a rare thing, and according to NOAA since 1990, 70 UMEs have been registered, involving all kinds of species and populations, many without a clear cause or a definitive solution.
Factors like disease, pollution, biotoxins, and other man related and unrelated events have been recorded and attributed as causing factors for past UMEs
In the winter of 1999, the gray whale population showed signs of nutritional stress just like in 2019, and a UME was declared by NOAA with more than 600 individuals reported dead and washing off the shores of Canada, the USA, and Mexico alone, not accounting for the ones that don’t reach the coast and just sink and disappear without revealing any data. It is estimated that only around 10% of the carcasses make it to shore.
Eventually, and as gray whales have shown to us, their numbers started to bounce back and for almost two decades almost no issues were reported in the eastern Pacific gray whale population whatsoever.
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The 2019-2021 Unusual Mortality Event
When we started our operation in January, only a small number of gray whales was present in the lagoon, as this is early in the season and whales are still traveling south from their feeding grounds; San Ignacio lagoon hosts some 300 individuals at the peak of the season around mid-March.
By the second week of February, it was evident that something was wrong; many skinny whales, very few calves, and low average numbers were starting to pop in the data.
By the end of February, we were already seeing some dead whales washing ashore and reports of similar situations were received from other camps and scientists along the west coast of North America.
As from 2019 and up to February of 2021 almost 400 whales have been reported dead, most of them due to emaciation.,
So far the 2019 UME seems to be extending for longer than expected and the reasons are still unknown, but some usual suspects are being mentioned.
What’s killing the gray whales?
Since the very beginning of the 2019 UME, just as with the one from 1999-2000, nutritional distress was the common factor found in the necropsies performed in some of the carcasses leading scientists to believe the cause was the lack of food in the feeding grounds.
What caused this change in the food chain is still unknown but climatic disturbances in the pacific ocean were pointed at.
Warming waters in the arctic feeding grounds are probably caused by an event known as “the blub” first recorded in 2014.
The “blub” is the unusual warming of surface waters that disrupts oceanic currents and the distribution of nutrients and cold water across the northern pacific ocean.
The cause is linked to a slow rate of heat dissipation in the water probably caused by atmospheric high pressure in the area known as the ridiculously resilient ridge.
Other consequences of this phenomenon include:
- The largest harmful algal bloom recorded on the West Coast, which shut down crabbing and clamming for months.
- Thousands of young California sea lions stranding on beaches.
- Multiple declared fishery disasters.
This “blub” is, in simple terms, static water preventing the natural circulation of oceanic currents, and yes, scientists think is a bit serious and the implications of this are still debated.
These conditions are less than ideal for all life in the ocean, and it’s particularly damaging to the smallest creatures like zooplankton and phytoplankton. Remember what our whales eat?
The cause of these conditions is still avoiding the scientist, at least for most of it, and its implications are scary at best, and human activity hasn’t been ruled out as a causing factor
The fluctuating numbers
According to NOAA’s recent study, the gray whale population has reduced by 24% since 2016 with 20,580 individuals in 2021 versus 26,960 in 2016, in a very similar trend as the UME reported in 1999-2000.
As an interesting fact, the gray whale population bounced back to greater numbers after the 1999-2000 UME.
Gray whales are considered sentinel species, this is; species that reflect the environmental health of the ecosystem they belong to just like dead fish in a river would indicate health issues within such a river.
To see such stranding numbers should be at least worrying as these strandings indicate a bigger problem within our oceans.
But is that the whole story?
As mentioned before, these types of events, (UME) have bounced into a larger population after just a few years from the event.
The population dropped by 23%, from 21,135 whales in 1997 to 16,369 whales in the 199- 2000 UME. just to climb back up, peaking at almost 27,000 in 2016.
The population bottleneck
Are the gray whales in a genetic bottleneck?
To understand this we first need to clearly understand what a population bottleneck is and how this affects a particular species and an entire ecosystem.
A population bottleneck is a type of event that dramatically reduces the size of a population, this may be caused by various, and not necessarily related events, such as a natural disaster with large environmental destruction, human activities like the hunting of a species to the point of extinction, or any other habitat destruction that results in the deaths of the organisms that conform it.
The population bottleneck produces a decrease in the gene pool of the population because of the loss of gene variants that were present in the original population.
Due to this, the remaining population has a very low level of genetic diversity, and the population as a whole has fewer genetic characteristics.
Due to the loss of genetic variation, the new population can become genetically distinct from the original population, which has led to the hypothesis that population bottlenecks can lead to the evolution of new species just as the extinction of the old species.
What the future looks like for the gray whale?
While these are conditions that will bring more than a disruption in the whale population, as implications include, weather and therefore agricultural and social issues beyond our comprehension, the future of the eastern Pacific gray whale population is uncertain at best, but not all is lost.
These whales have shown us the power of resilience and adaptability, not for nothing this whale is the only survivor of its species, but it also has shown its capability to come back from threatening circumstances before.
Maybe it’s us who should be worried about these oceanic changes and the direct repercussions they will have on our way of life. Recent events have shown us how unprepared we are to face situations mother nature throws at us and how important it is to be prepared as a society.
Whatever the future is for both the gray whale and us, and all other species on our planet, something is clear; maybe it’s time to take more seriously how the world interconnects, and the fact that we are not a separated species but one more of the millions of species we share the world with.
What can you do if you find a stranded marine mammal?
NOAA’s Marine Mammal Health and Stranding Response Program is the program in charge of emergency responses to sick, injured, distressed, or dead seals, sea lions, dolphins, porpoises, and whales.
The MMHSRP works with volunteer stranding and entanglement networks as well as local, tribal, state, and federal government agencies to coordinate and conduct emergency responses to stranded or entangled marine mammals.
The Program provides network members with a Stranding Agreement from the NOAA Fisheries regional offices to ensure that all activities performed are safe for both responders and animals.
The network members provide staff and local response capabilities, independently raising funds to cover the majority of their costs.
The stranding and entanglement networks also perform a valuable biosurveillance role, as they are often the first to detect threats to marine mammal populations.
To that end, stranding networks provide data to the MMHSRP by using the Level A Stranding Report form