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Right Whale Population Stabilizes but Entanglement Remains NMFS’s Priority

Things may be looking brighter for North Atlantic right whales. According to figures released in October 2023 by the National Marine Fisheries Service (NMFS), the North Atlantic right whale population decline is leveling off. The right whale population estimate for 2022 is 356 animals. The 2021 population, originally estimated at 340 whales, was increased to 364 whales due to the addition of newborn calves to the population.


Right whale and calf. NOAA photo.

According to NMFS, while current data indicate a “flattening” of the population decline, it is too soon to know if the population is beginning to recover. The agency reports that serious injury and mortality incidents among right whales continue to exceed the level allowed under the Marine Mammal Protection Act.


NMFS’s most recent data show that right whale births now exceed deaths. So far in 2023, two right whale deaths have been detected — one succumbed to a vessel strike while the other was an orphaned newborn calf — and twelve calves were born. In 2022, zero mortalities were observed and 15 calves were born.

However, NMFS assumes that for every right whale that is known to have died, two additional right whales died but were not seen. This is known as cryptic mortality.


Factoring in cryptic mortality, right whale births also exceeded deaths in 2021 and 2020. In 2021, two right whales were confirmed dead. One died as a result of a vessel strike and the other due to entanglement in Canadian snow crab gear. Based on cryptic mortality, NMFS recorded nine deaths and 20 calves that year. In 2020, two right whales were confirmed dead. One was killed by a vessel strike and the other was an infant mortality. NMFS recorded seven deaths and 10 calves that year.


These figures are in stark contrast to 2017 to 2019 when right whale mortalities reached record highs. Combined deaths for those three years, including cryptic mortality, totaled 92, while combined births totaled only 12. For cases where a cause of death was determined, the majority were traced to vessel strikes in the U.S. and Canada and entanglement in Canadian fishing gear.


Despite the striking improvement since 2019, the conservation community remains concerned. “While this is an encouraging change, the number of human-caused injuries that will likely lead to death or reduced reproduction in the future remains high,” said New England Aquarium senior scientist Philip Hamilton. “We need to continue to reduce human-caused death and harm to this species for the population to trend upward.”


Lobster industry leaders are more optimistic. “U.S. lobstermen have done our part to reverse the right whale decline by making our fishery even safer despite zero evidence that right whales are dying in our gear,” stated Kristan Porter, president of the Maine Lobstermen’s Association. “Now that right whales are successfully feeding again and Canada has put meaningful protections in place, I fully expect the right whale population will begin to rebound.”


In October, NMFS released the results of a new population viability analysis (VPA), its latest suite of computer models which predict the right whale population in 100 years based on different levels of entanglement in fishing gear, vessel strike rates, and availability of prey. The model results indicate that entanglement and vessel strike continue to pose significant threats to right whales.


The model assumes that conditions present in 2019 – when mortalities were high and calving was low – will continue for the next 100 years. The model concludes that without further management action, the right whale population remains at risk of decline.


The model examines different threat scenarios to determine the probability of extinction. Rather than looking at the probability that threats would result in the right whale population reaching zero, the VPA estimates the likelihood of “quasi-extinction” in 100 years, which is when right whales are still present but there are fewer than 50 proven females.


Under the 2019 baseline conditions, the model predicts a 93% probability of quasi-extinction for right whales in 100 years. The model then explores a variety of scenarios. For example, if the whale rules implemented in 2022 reduced entanglement by 50%, the population would be expected to increase by 52% in 100 years, reducing the probability of falling below 50 proven females to 35%.

The model also evaluated the relative impact of threats individually. If all other threats remain, removing all entanglement risk reduces probability of quasi-extinction from 93% to 5%; removing all vessel strike risk reduces it to 34%; while removing the threat of limited prey availability only reduces it to 88%.


NMFS Population Viability Analysis (VPA) Results

Probability of <50 proven females in 100 years (quasi-extinction)


Threat Scenario Probability of Quasi-extinction

No change (2019 baseline) 93%

Entanglement

Remove all entanglement risk, other threats remain 05%

Remove half entanglement risk, other threats remain 35%

Implement 50% weak rope, other threats remain 62%

Vessel Strike

Remove all vessel strike risk, other threats remain 34%

Prey Availability

Remove prey availability, other threats remain 88%


A peer review of the VPA was conducted by the Center for Independent Experts in 2022 and included guidance on next steps. The panel concluded that the VPA incorporated the best available science, but reviewers identified concerns and provided a suite of recommendations to improve the model as it is further developed.


The reviewers raised concern with certain elements of the model. One reviewer noted that the model used 2014-2019 data for entanglement injury and mortality rates while using 2010 to 2019 data for other analyses. The reviewer noted, “This is a critical assumption because estimated mortality jumps sharply in 2014 from low rates, and 2017 (17 reported deaths) is the only year since 1990 with more than 7 reported deaths (Pace et al. 2021).” Another reviewer noted that the lack of proper mathematical description of the model “has resulted in a ‘jury-rigged’ presentation of the model that remains unclear in parts and impossible for others to check the computations of the presented results.”


The Peer Review panel recommended that the VPA use a consistent time period — 2010-2019 — for all analysis, provide a proper mathematical description of the model and details of the analyses, and include a spatiotemporal structure to understand where right whales and human threats overlap so the model can meaningfully inform management.


According to NMFS, this model is a living tool that can be improved, adapted, and extended as new data, new methods, and new questions arise. Additional documentation on the underlying models and the model code will be available in a public data repository to promote further development and improvements.


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