Spiking Ocean Temperatures a Threat to Dolphin Survival

(CN) – “Unprecedented” is the word researchers are using to once again describe the impacts of a climate change on wildlife and habitat, this time regarding a marine heatwave that will have long-lasting negative effects on birth rates and survival of the iconic dolphin population in Shark Bay, Western Australia.

The grim event has been documented in a study published Monday by researchers at University of Zurich in Switzerland.

A 2011 heatwave in Shark Bay, a UNESCO world heritage site, caused water temperatures to rise to more than four degrees above the annual average. The spike in water temperature damaged seagrass within the Shark Bay ecosystem that is vital to marine mammal survival.

Researchers investigated how this environmental damage affected survival and reproduction of dolphins and were surprised to find more far-reaching consequences than previously thought.

An analysis of long-term data on hundreds of animals collected from 2007 to 2017 revealed the dolphins’ survival rate had fallen by 12% following the heatwave. Moreover, female dolphins gave birth to fewer calves – a phenomenon that lasted at least until 2017.

“The extent of the negative influence of the heatwave surprised us,” first author and former University of Leeds doctoral candidate Sonja Wild said. “It is particularly unusual that the reproductive success of females appears to have not returned to normal levels, even after six years.”

Study authors acknowledge there are several other possible explanations for this phenomenon that they have yet to fully investigate. Neglect of calves, increased newborn mortality, delayed sexual maturity or a combination of these factors could also lead to reproductive failures.

The heatwave’s damage to seagrass did not equally affect all dolphin groups. Dolphins that socially learned a foraging technique of using sponges to locate food in deep water did not suffer as badly as those that do not use this technique. Even so, scientists are still concerned about the long-term ramifications of unprecedented changes in climate.

Dolphins are at the top of the food chain, and before this study scientists had only seen effects from increased temperatures in organisms lower on the food chain. Michael Krützen, University of Zurich anthropology professor and study leader, emphasized the long-term implications.

“Marine heatwaves are likely to occur more frequently in the future due to climate change,” Krützen said. “This is worrying not only for the long-term prospects of marine mammal populations, but also for the entire oceanic ecosystems.”

Swiss National Science Foundation, National Geographic Society, SeaWorld Research and Rescue Foundation, W.V. Scott Foundation and A.H. Schultz Foundation helped to fund the research.

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