Vaquitas not doomed to extinction by inbreeding depression

Mother and calf vaquita surface near San Felipe, Mexico. Credit: Paula Olson

New research shows that the endangered vaquita in the Gulf of California in Mexico remains genetically healthy enough for the species to recover if illegal gillnetting stops killing them.  The paper, “The critically endangered vaquita is not doomed to extinction by inbreeding depression” is based on full genome sequencing of 20 individuals collected by Mexican researchers since the 1980s and was published today in Science The scientists ran computer simulations based on the genetics of archived vaquita samples to project how the population would fare under different scenarios for their protection. They found that immediate and complete elimination of mortality from gillnets led to a high probability that the species will recover. Even low levels of continuing gillnet mortality rapidly reduced the species’ chances of survival, however.

Illegal fishing remains the sole immediate threat to vaquitas

Recent claims have been made that a reduction in illegal gillnet fishing in the northern Gulf of California is allowing for a gradual population recovery of the vaquita, Mexico’s endemic, critically endangered porpoise. Earlier recommendations by the Vaquita Recovery Team (CIRVA—Comité Internacional para la Recuperación de la Vaquita) had stressed that the vaquita could be saved from extinction only if gillnets were banned throughout its range and fishers adopted viable vaquita-safe fishing methods. In 2020, a 12 x 24 km area where the few remaining individuals were regularly found was designated a Zero Tolerance Area (ZTA), where the gillnet ban would be strictly enforced. Recent observations, however, indicate that illegal fishing is still rampant within the ZTA: during the shrimp season in October/November 2021 (Report here), 117 pangas were documented in the ZTA – the combined length of their nets could have spanned the 24-km length of the ZTA at least five times. 30 counts of pangas within the ZTA were made from the SSCS ship that indicate daily presence of illegal fishing ( see full report in English and in Spanish). On 19 January 2022 (Report here), during totoaba season, 58 pangas were counted fishing inside the ZTA, at a time when a new accord between the Mexican Navy and the Sea Shepherd Conservation Society was supposed to have greatly reduced illegal fishing within the ZTA. If vaquitas are to be saved from extinction, at a minimum, the ban on gillnet fishing in the ZTA must be enforced, and current evidence indicates that this is not happening.

 

Documenting illegal fishing has been difficult but photographs taken during the 2019 and 2021 vaquita surveys within the ZTA (see below) show gillnets clearly visible on pangas in the launch areas and in use within the ZTA. A video of pangas  launching from downtown San Felipe, with gillnets clearly visible as the only gear in use  is provided here.

Last Mekong dolphin in the Cambodia-Laos transboundary pool dies

The most recent of the seven news items on this website concerning the Critically Endangered population of Irrawaddy dolphins (Orcaella brevirostris) in the Mekong River was posted almost exactly four years ago. Since that time, the information on this population in the Focal Taxa section of the website was updated in August 2021.

In late October 2021, the Cambodia Fisheries Administration and WWF-Cambodia posted a joint press release entitled “Time is running out for saving the transboundary dolphins of the Mekong.” The important message conveyed in the press release was that as of 2021, only a single individual dolphin remained in Chheu Teal transboundary pool on the Laos-Cambodia border. Dolphins in Chheu Teal pool have long been regarded as an isolated sub-population because, since 2001, there have been no records of new dolphins entering the pool which is at the upstream extent of the population’s present-day (relict) range.  Seventeen dolphins were reported in the trans-boundary pool in 1993 (Baird et al., 1994; Stacey & Hvengaard, 2002). Regular photo-identification surveys have documented the decline of dolphins in that small fragment of habitat, from seven in 2009, to six in 2012, three in 2018 and only one in 2021.

On February 15, 2022 the last river dolphin in the transboundary pool (ID#035) on the Cambodia-Laos border was found dead.  A statement released by WWF-Cambodia indicates that this death almost certainly represents the national-level extirpation of O. brevirostris in Laos.

Both WWF and Cambodia’s Fisheries Administration are saddened by the death of the last known river dolphin in the transboundary pool. The numbers in the pool have plummeted over the last few years, due to multiple threats including hydro-power dam construction causing disruptions to river flow and reduced fish abundance, drowning in gill-nets, and the use of damaging fishing practices such as electrofishing and overfishing.

Dorsal fin photo of the last remaining dolphin, ID#35, in Chheu Teal pool on the Lao / Cambodia border which was found dead on 15th March 2022 © Tan Somethbunwath / FiA / WWF-Cambodia

In the press release, CSG members Uzma Khan, who serves as Asia Coordinator for WWF’s River Dolphin Rivers Initiative, and Somany Phay, Deputy Director of Cambodia’s Fisheries Conservation Department and the Government Liaison at WWF-Cambodia, called on the governments of Laos and Cambodia to acknowledge the extirpation of the transboundary population and stressed the importance of using the lessons learnt from this loss to push for stronger protection of the remaining animals in Cambodia, in particular by stopping the use of gill-nets and other illegal fishing methods. They urged the governments to take measures to restore habitat in the trans-boundary area and elsewhere in the Mekong ecosystem by maintaining flows and providing meaningful protection to dolphins as well as the river’s other biota.

In December 2020 a Trinational Workshop on the Irrawaddy dolphin was held virtually and brought together those working with the three freshwater riverine populations. Recommendations were made with regards to continuing the successful river guards programme and regularly monitoring Mekong dolphins to estimate their abundance and track their movements.

The Cambodia Government’s Fisheries Administration and WWF are actively working with the provincial authorities, local communities and other partners to implement strict enforcement of the fisheries law, stop the use of illegal gill-nets in protected dolphin habitat and provide alternative livelihood opportunities for communities along the Mekong. These actions are of paramount importance for the survival of Mekong River dolphins.

Further details regarding the Mekong River dolphin conservation status are summarised in a recent Report.

References

Phay, Somany, Eam, S. U. , Hang, Sereyvuth, Tan, S. B., Lor Kimsan,  DET Chamnan. 2022. Summary report on the Status of the transboundary dolphins between Cambodia and Lao’s PDR. Unpublished report.  The Fisheries Administration Cambodia, World Wide Fund for Nature (WWF) and IUCN Cetacean Specialist Group.

 

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