Study suggests climate change could prevent recovery of southern right whales

Study suggests climate change could prevent recovery of southern right whales
Fig. 1. SRW female survival and climate change. (A) Female survival probabilities for SRWs (E. australis) identified between 1971 and 2017 at Península Valdés, Argentina. Estimated survival in year t should be read as the probability of surviving to the end of that annual period. Estimates are shown with 95% CI (error bars). Years are categorized by ENSO phase (color code). (B) Oceanic El Niño Index (ONI) representing 3 months running mean sea surface temperature (SST) anomalies in El Niño 3.4 region from 1970 to 2019 (ONI values greater than 0.5, red line, represent the warm phase/El Niño; ONI values lower than −0.5, blue line, represent the cool phase/La Niña; ONI values between 0.5 and −0.5, black line, represent the neutral phase). Data are taken from the rsoi R package. (C) Mean monthly SST of SW Atlantic Ocean (30°W to 70°W, 42°S to 77°S) from 1970 to 2019. Data are taken from the COBE Dataset ( (D) Mean density (individuals m−2) of Antarctic krill (Euphausia superba) within the SW Atlantic Ocean, based on standardized densities. Years with >50 (black) and <50 (red) stations are plotted, yielding 6544 stations from the updated KRILLBASE database from 1981 to 2016 ( (E) Relationship between female survival probability and ONI [logit(φ = 5.359 − 1.371 * ONI)] during cool phase/La Niña (blue), neutral phase (gray), and warm phase/El Niño (red). Estimates are shown with 95% CI (error bars). SRW and krill illustrations are by A. Díaz. Credit: DOI: 10.1126/sciadv.abh2823

An international team of researchers has found evidence suggesting that if global warming continues, the recovery of southern right whales may be stifled. In their paper published in the journal Science Advances, the group describes their study of the whales and what they learned about them.

Southern right whales are a type of baleen whale that live in the Southern Hemisphere and are currently listed as endangered. Prior to modern whaling, their population is believed to have been approximately 35,000. Their numbers dwindled significantly until the 1930's when protection laws were put in place. In this new effort, the researchers have found evidence suggesting the recovery of the whales may run into trouble if continues.

The work by the team focused on the Southern Right Whale Program, a project involving the study and preservation of the whales that includes 50+ years of data. Included in the data are population numbers of whales that calf near the Valdes peninsula each year, which is a measure of population growth in general. The researchers noted population dips following El Niño years—both in 1997–1998 and 2015–2016. They suggest the dips were the result of warmer waters melting more glacial ice in Antarctica resulting in reductions in krill, which is the main food source for . Noting that prior studies have suggested that as the planet continues to grow warmer, El Niño events are likely to occur more often, they built a model to find out how global warming may impact southern right whale population growth.

The model showed that if the frequency and intensity of El Niño events remain as they are now, the population of the whales will continue to grow—reaching approximately 85% of their pre-whaling days numbers over the next century. But if the frequency and intensity of El Niño events increase due to global warming, the situation grows dire. The (a 4.4°C global rise in temperatures over the next century) showed the increase in population slowing to the point that the would never reach their former numbers.

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More information: Macarena Agrelo et al, Ocean warming threatens southern right whale population recovery, Science Advances (2021). DOI: 10.1126/sciadv.abh2823
Journal information: Science Advances

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