Whales are marine mammals known for their gargantuan size. Most species of whales are hunted for their gargantuan size, which offers poachers plenty of meat and whale oils used in cosmetics. Despite several regulations that restrict whale harvesting, numbers still continue to dwindle. 

Being crucial parts of the marine ecosystem, most species of whales dominate their ecosystem and are integral to the survival of other species in the areas they inhabit. 

Recent surveys have shown that numbers continue to dip below historic standards, ringing alarm bells of conservationists across the globe. A study published in the journal Current Biology suggests that, in addition to smaller population sizes, those whales that survive are struggling. This comes from the study of North Atlantic Right Whales which show a significant decrease in size compared to the specimens studied in the area just 30 years ago.

Methods of Analysis 

According to Joshua Stewart of the National Oceanic and Atmospheric Administration (NOAA) in La Jolla, CAO the average right whale born today is expected to reach a total length about a meter shorter than a whale born in 1980, according to the paper published in Cell Biology. This average 7% decrease (much higher in some samples) in size is very concerning. Specimens are found to be up to a meter shorter than they should be compared to samples of whales born just a few decades ago. 

Parents of these smaller right whales all displayed much larger proportions and lengths at the same age as their offspring. This change comes in just 1-2 generations of whales. This reduction in size has been found in commercially farmed fish species that are regularly killed before they reach their full size (owing to commercial demand). But this is the first reported case of a marine mammal shrinking to adapt to possible changes in the environment. 

Stewart and his colleagues from NOAA, the New England Aquarium, Oregon State University, and Woods Hole Oceanographic Institution documented right whales in the North Atlantic using aerial photogrammetry measurements collected from crewed aircraft and remotely operated drones over a 20-year period, they looked for any changes in the body lengths of right whales.

“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,” said John Durban at Oregon State University (formerly with NOAA) in a ScienceDaily release. “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 whales in the area have been studied for a long duration. This allowed the team to access comprehensive historical data that allows for more detailed comparisons like fin length, fluke dimensions etc. Many individuals in the region have also been tagged with GPS devices, showing reproduction data and allowing researchers to track offspring of healthy adults. This 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 stressors such as vessel noise, ship strikes, and shifting prey availability.

“Fishing gear entanglements in this population are unfortunately fairly common, and entanglements resulting in attached gear and severe injuries have been generally increasing over the past several decades,” Stewart said. “Previous studies have shown that 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. In some cases, entanglements can be lethal, but it turns out that even sub-lethal entanglements can have lasting impacts on right whales.”

But the increasing entanglements with fishing gear might just be one of the stressors causing the reduced sizes. Smaller sizes could also cause life threatening entanglement with fishing equipment as smaller whales find it tougher to break free. The findings in right whales may have implications for other species of large whales around the world.

Also, food availability in the region over time was studied. The team reported that the region has an abundance of Calanus finmarchicus, a primary copepod prey item for right whales in the region. But the team also found that sighting rates of right whales in their typical foraging grounds have declined in the North Atlantic. The study concluded that this could be a result of other anthropogenic factors such as increasing vessel noise could also be interfering with foraging behavior and restricting growth 

Impact of Findings

“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,” Stewart explained. “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. This is by no means a problem unique to right whales — entanglements are a major threat for whales, marine mammals, and other marine species worldwide.”

“Because North Atlantic right whales have this incredibly detailed dataset with known ages, sizes, entanglement histories, and so forth, we could directly examine how these impacts are affecting growth rates,” Stewart continued. “My guess is that many other species are being similarly affected, but we just don’t have the ability to detect it in less well-studied populations.”

Based on the findings, the researchers call for stronger management actions to reduce the impacts of fishing gear and vessel operations.

“Implementing proven solutions such as reduced vessel speeds, lower breaking strength ropes, and ropeless fishing gear more broadly throughout their range are critical and urgent steps needed to stave off the extinction of this species,” said study co-author Amy Knowlton, New England Aquarium, Boston.

There needs to be a more detailed analysis of the food availability and other crucial factors that could affect whale sizes too. This drastic change is a signal to conservationists worldwide studying whale populations. Monitoring the size of offspring could provide early clues towards populations subjected to environmental stressors, showing the need for immediate intervention.