-In the 2024-2025 season, 92 gray whales were recorded stranded in Baja California Sur, one of the highest numbers in decades.
-The number of calves fell by 90% compared to an average year and only 85 calves were counted in the main breeding ponds.
-The population of the North East Pacific fell to the third lowest figure since 1967: between 11,700 and 14,450 specimens.
-A decrease in food in the Arctic, due to the melting of ice and changes in water temperature, would be behind the problem.
On February 24, 2025, a gray whale (Eschrichtius robustus) was found dead in an unpopulated area off the coast of El Mogote, in La Paz, in northwestern Mexico. His body, over 13 meters tall, lay in an advanced state of decomposition.
The whale had traveled from the Bering Sea, off Canada, where it fed every year, to its breeding area in Baja California Sur (BCS). What is worrying is that this migratory trip was not the last only for this specimen, but for dozens of other gray whales.
The finding in El Mogote is one of 92 cases of stranded whales recorded during the last breeding season in Baja California Sur, which runs from December 2024 to April 2025, according to data from NOAA Fisheries (NMFS). The American scientific agency, which keeps track of this population along its migratory route, assures that this is one of the deadliest seasons for this species in recent history.
According to Francisco Javier Gómez Díaz, director of the Whale Museum in La Paz and an active member of the BCS Stranding Network, there is no evidence of human intervention in these stranded whales. Many probably died on the high seas and were washed away by coastal currents, he said.
In addition, the records detail a drastic decrease in the number of sightings; a significant drop in births; and a worrying increase in specimens in poor body conditions, that is, skinny animals, with fat reserves so low that, sometimes, bones are marked under the skin. Experts maintain the hypothesis that the decline in food in the Arctic, due to the loss of sea ice, combined with changes in water temperature, influenced the weakening of the whales and their death.
“What we have seen makes us think that they arrived malnourished, which made them much more vulnerable and prone to being stranded,” says Lorena Viloria Gomorra, a researcher at the Marine Mammal Research and Monitoring Program (PRIMMA).
Photo: PRIMMA.
A critical season in Baja California Sur
The last NOAA Fisheries census in BCS, which was carried out with field support from the Marine Mammal Research and Monitoring Program (PRIMMA) of the Autonomous University of BCS, took place during February 2025 in the state's main breeding and breeding sanctuaries: Laguna San Ignacio, Magdalena Bay, Puerto Chale, Punta Abrejos and the North Pacific area. There, the specialists carried out photoidentification to distinguish the different individuals, raised drones to observe their movements, placed marks on some specimens to be able to track them (CATS) and recorded the strandings, explains Viloria Gomorra, head of research in Magdalena Bay and member of PRIMMA.
Viloria Gomorra highlighted that none of the specimens analyzed showed signs of blows by boats or entanglements in nets. “None of them had cuts or signs of entanglement,” he explains.
Although most of the strandings occurred in the Ojo de Hare Lagoon, the main area where mammals congregate, strandings were also reported further south this year, in places such as Magdalena Bay, San Felipe, Guaymas, Mazatlán, Loreto and La Paz.
“This change in patterns in distribution may be related to alterations in migratory routes due to the search for food,” says Jorge Urbán Ramírez, researcher in the Academic Department of Marine Biology of the Autonomous University of Baja California Sur (UABCS) and coordinator of PRIMMA.
An unusual mortality event
The situation that alarms scientists today is not the first gray whale crisis. Urbán Ramírez confirmed that in 2019, the United States National Oceanic and Atmospheric Administration (NOAA) declared an unusual mortality event (UME) for this species.
During the UME, 83 deaths were recorded in 2019 and 88 in 2020, considered to be the most critical years of the event. Mortality remained high until 2022 and in the 2023 season, the UME was officially concluded when a decrease of 29 whales stranded off the Mexican coast was observed.
According to the researcher, this background created the expectation that the population would stabilize and begin to recover. However, the new spike in dead whales recorded in 2025 set off alarms again.
According to estimates from the NOAA Fisheries Southwest Fisheries Science Center, the Eastern North Pacific gray whale population has declined significantly since 2016, when nearly 27,000 were counted, one of the highest numbers recorded since counting began in 1967. However, after a series of adverse events in their arctic and subarctic feeding areas, this figure has fallen dramatically.
For the 2023 season, the estimate ranged from 13,230 to 15,960 gray whales, which corresponds to a decrease of between 41% and 51% compared to the peak of 2016, according to Urbán Ramírez.
The last available count (the 2024-2025 season) places the population between 11,700 and 14,450 individuals, the third lowest estimate in nearly six decades of monitoring.
Births are decreasing
According to data confirmed by NOAA Fisheries and PRIMMA, the 2024‑2025 season also recorded an all-time low birth rate record.
Biologist Urbán Ramírez warned that 2024-2025 surpasses 2023-2024 as the year with the lowest number of births in recent history.
“All those who have died are young or adult, but there are no babies, and there are no dead babies because the problem is that there are no live babies,” she says.
In the 2024-2025 season, only 85 whales were recorded in the three main breeding lagoons of Baja California Sur, representing a 90% decrease compared to an average year.
In Laguna de San Ignacio, northwest of BCS, for example, up to 138 mothers with babies were registered in 2014 on a single census day, while in 2025, only five babies were counted during the same monitoring day.
In the Bahía Magdalena lagoon complex, known as one of the main “nurseries” for the species, the numbers also plummeted: in 2016, 55 mothers were registered with babies in a single day and in 2025 there were only three babies counted during the entire season.
Photo: Francisco Javier Gómez Díaz.
Skinny whales
In addition to the low number of births and the increase in stranded whales, another warning sign is the high proportion of specimens with poor body condition.
According to Lorena Viloria Gomorra, 980 whales were photoidentified during the monitoring of the Magdalena Bay lagoon complex, of which 244 had poor body conditions, that is, they looked weak and weakened. In Laguna de San Ignacio, 72 individuals were observed in poor condition.
Viloria Gomorra explains that the body condition of whales is determined based on visual and photographic evaluations, classifying individuals into three categories: good, regular and bad.
A whale in good condition maintains a straight line from head to back, retaining its thick layer of fat and musculature. However, when they have marked curvatures behind the head, what experts call a visible “neck”, it means that their energy reserve has diminished.
In the most serious cases, you can even distinguish the scapular bone —equivalent to our shoulder blade—, something that should never be noticed in a healthy whale. This confirms a severe loss of fat and muscle mass, reflecting food deficiencies in their migratory route.
“Seeing whales with marked bones, without reservations, is very worrying because it means that they have no energy either to reproduce or to migrate successfully,” says Viloria Gomorra.
Scientists such as John Calambokidis, from the Cascadia Research Collective organization, a non-profit scientific institute based in Washington, United States, specialized in the study of cetaceans and marine mammals, say that whales are suffering from a reduction in food sources in the Arctic. This is mainly due to the melting of sea ice, which affects the production of subglacial algae and, therefore, benthic amphipods, which are its main prey.
This is also stated by the scientific journal Polar Journal and experts such as Josh Stewart, from the Marine Mammal Institute, OSU, who say that the reduction of ice reduces the production of algae that grow under it, fertilize the seabed and feed key crustaceans.
Atypical gray whale watching
In February 2025, the National Commission for Protected Natural Areas (CONANP) reported the presence of at least 50 gray whale specimens in Cabo Pulmo National Park, located in the state of Baja California Sur. This is an unprecedented phenomenon, since it is the first time that a concentration of such magnitude has been recorded in this protected marine area.
This sighting reinforces the experts' hypothesis about variations in whale migration routes. The positive thing is that its presence near the coral reefs of the national park could be a positive sign of the health of the marine ecosystem.
“Local guides have documented the presence of whales at various points in the park, which also represents a valuable opportunity to continue research on marine biodiversity in Cabo Pulmo,” said CONANP.
Researcher Viloria Gomorra attributes this unusual behavior mainly to the effects of the La Niña climate phenomenon in 2025, which caused colder temperatures in breeding waters. This, he explains, forced the whales to move south in search of warmer waters within their tolerable range, which ranges from 18° C to 23° C. For example, in Magdalena Bay, temperatures of up to 17° C were recorded, outside the ideal range for the species, which motivated these atypical migrations.
According to experts, the extra energy invested in moving to these new sites would also be affecting the health of the whales.
The gray whale is one of the most extensively migrating mammals on the planet. Each year, it travels between 16,000 and 20,000 kilometers from feeding areas in the Arctic to breeding lagoons in Baja California Sur, Mexico. Researcher Urbán Ramírez pointed out that in some cases it has been documented that these routes can reach up to 23 thousand kilometers.
Photo: PRIMMA.
However, “during this migration, the whales do not feed actively”, explains Urbán Ramírez, but “they depend on the energy reserves accumulated during the summer [that is, during the time they were feeding in the Arctic] to complete their migratory, reproductive and lactation cycle.”
During its feeding phase, an adult female gray whale requires, on average, between 3400 and 4500 megajoules (mj) per day (measured by the amount of energy that a whale stores with respect to its mass), so in each biannual reproductive cycle, it accumulates between 130,000 and 136,000 mj. This reserve must sustain energy expenditure during migration, childbirth, breastfeeding and return to the north.
“If a whale loses more than 40% of its total energy accumulated during the trip, its survival is compromised, also affecting reproductive success,” says Urbán Ramírez.
The increase in travel to atypical areas, as observed in the last season, increases energy expenditure and reduces the likelihood of survival and reproduction, which could explain the increase in mortality reported for this species, adds the expert.
PRIMMA researchers explain that the combination of abnormal temperatures in breeding areas and the decline of food in the Arctic is forcing these ocean giants to modify their ancient routes, with an energy cost that may compromise their survival.
Faced with this scenario, scientists warn that what was observed in 2025 would be a warning sign about the cumulative effects of global warming on migratory species, and stress the urgency of strengthening research and conservation of critical habitats across the Pacific.
They ask to raise protected status
Urbán Ramírez reported that scientists from PRIMMA and UABCS submitted an evaluation at the end of July to the General Directorate of Wildlife (DGVS) of the Secretariat of Environment and Natural Resources, with the purpose of proposing the change of category of gray whales in the Official Mexican Standard NOM-059.
Currently, the species is under the category of Special Protection, but the proposal seeks to recognize it as a threatened species, which would make it possible to strengthen conservation, protection and responsible management actions.
As explained by the researcher, this measure does not seek to curb tourist observation activities, but rather to ensure that they are carried out under criteria that minimize stress and disturbance to the specimens, especially in a year as critical as 2025.
“We are not thinking of stopping the observation of gray whales, care must be reinforced to interact with them, because when they are not well nourished, increasing the stress of the whales must be avoided,” explains Urbán Ramírez.
* This text was made possible thanks to the financial support and editorial support of Mongabay and Causa Natura.
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