Shetland: Man spots killer whales chasing seal onto rocks

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Dr Joshua Stewart, of the National Oceanic and Atmospheric Administration in California, said: “The increased drag from entangling gear requires right whales to spend a lot of extra energy just to go about their normal activities, and that is energy they might otherwise spend on growth or reproduction. “Even sub-lethal entanglements can have lasting impacts on right whales.” Dr. Stewart and his colleagues wanted to document the challenges faced by right whales as indicated by changes in their life history characteristics, including size.

Using aerial photogrammetry measurements collected from aircraft and remotely operated drones over a 20-year period, they looked for any changes in the body lengths of right whales.

Dr John Durban, of Oregon State University, said: “We were able to build on our previous work that used conventional aircraft in the early 2000s by adopting new drone technology to extend the time series in recent years.

“In both cases, we were able to measure whales by flying a camera high above them, essentially giving them a health check without them knowing we were there.”

The researchers said that the whales were an “ideal” case study because they’ve been monitored consistently since the 1980s, with individual-level information on age and size and detailed records of attached-gear entanglements.

The intensive monitoring made it possible to begin to evaluate the effects that severe and prolonged entanglements may have on the long-term fitness of individuals, as well as the potential effects of other stress factors such as vessel noise, ship strikes, and shifting prey availability.

He said that the data collected showed that serious entanglements in fishing gear are one stressor associated with shorter whales.

Dr Stewart suggested that the stunted growth may lead to reduced reproductive success and a greater likelihood of life-threatening gear entanglements.

And he believes the findings in right whales may have implications for other species of large whales around the world.

Dr Stewart said: “The smaller you are, the less energetic reserves you have, and the harder it might be to survive a serious entanglement or sustained food shortage.

“So it’s possible that these life history changes could translate into population viability impacts. But this really makes me wonder about how large whales worldwide are being impacted by entanglements.“

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