Making a more accurate pregnancy test for humpback whales, Ars Technica

A / humpback whale and calf.

Peeing on a stick is nobody’s idea of ​​fun, but It’s a hell of a lot better than what whales have had to deal with: pregnancy test by dart gun. And if a blubber-sampling dart wasn’t bad enough, some dart gun pregnancy tests might not even be all accurate.

A recent paper in Nature Scientific Reports found evidence that the standard humpback whale pregnancy test was failing to spot a whole lot of pregnant females . There’s a better way of testing, the researchers suggest — and their results could help conservationists and researchers protect whales.

Counting whales

You can’t protect a species very effectively if you have no idea how many individuals are alive and whether their numbers are on the increase or decrease. Estimating populations of wild animals is always tricky, but for whales, it’s fiendish — huge territories, long migrations, and of course the whole problem of living underwater mean that scientists have to get inventive to figure out even (rough numbers)

One option is to record whale calls and try to extrapolate from that. Another method is just old-fashioned watching from boats. These techniques can give estimates of the current population — often with a broad range of uncertainty — but they won’t really track the trajectory of a population. To do that, you also need to know about deaths, pregnancies, and births. As we’ve seen with killer whales , a drop-off in pregnancy rates or an increase in infant mortality can set off alarm bells about the health of the population.

Humpback whales on the whole aren’t doing too badly these days, but four out of the world (populations are) still endangered , and another is considered threatened. They face a range of anthropogenic threats, including noise pollution, ocean contaminants, boat strikes, and fishing gear entanglements. Tracking even the healthy humpback whale populations offers an opportunity to get a read on how other, more endangered whale species might be doing in the same waters — if the humpbacks start floundering, chances are other species will, too.

Of course, figuring out if a whale is pregnant is no simple task. But researchers can get tissue samples using dart guns , with lightweight darts that bounce swiftly off the whale and float in the water with their precious cargo of blubber. But once you have that blubber, what do you test for? Chemist Greta Dalle Luche and her colleagues argue that the standard test has been missing important information.

More than one hormone

Currently, progesterone is seen as the smoking gun for humpback whale pregnancy. Across mammal species, progesterone is a crucial pregnancy hormone and can be orders of magnitude higher during pregnancy than at other times. Previous research on humpback whales found that females with higher levels of progesterone in their blubber showed up with calves a year later, confirming that they had been pregnant.

The problem is that hormones aren’t necessarily that simple. In a lot of mammal species, progesterone levels start to drop a few days before birth. And bottlenose dolphins and killer whales have been found to have a much earlier plummet in their progesterone levels — months before birth. If humpback whales are similar, testing only for progesterone could be failing to catch the whales at later stages of pregnancy.

Dalle Luche and her colleagues wanted to find out if there were other hormones that could be useful for humpback pregnancy tests. So they set about sampling humpback whales off the coast of Australia. They tracked them for three weeks during the summer of 2016 as the whales were heading northward to warm tropical waters where they generally give birth. This meant that many of them would probably be pregnant along the way. And they tracked them again during their southward migration in the fall, when recent mothers are joined by their newborn calves on their journey back to Antarctic and other females are often newly pregnant.

Based on the progesterone-only test in a sample of 96 female humpbacks, they found that only one appeared to be pregnant. That would be a remarkably low rate of pregnancy. But when they looked at a cluster of hormones together, they found that a third of the whales showed a similar pattern: high levels of testosterone and another hormone called androstenedione. The proportion of whales showing this pattern is about the number of pregnant whales that would be expected. High levels of these hormones have been found in other mammals during pregnancy, suggesting that this might be a better way to detect humpback pregnancies.

Better use of blubber

Female humpback whales on their southerly migration present a complicated picture: some might be in the early stages of detectable pregnancy, some too recently recently Pregnant for hormone changes to be detected in blubber, and some ovulating. It could be that Dalle Luche and her colleagues found such a low rate of pregnancy using progesterone because they tested at a different point in the breeding cycle compared to previous studies.

These results don’t necessarily mean that progesterone tests for humpbacks should be thrown out immediately, but they do indicate that it’s worth looking beyond progesterone for a more accurate test. They also make it clear that it’s crucial to account for how pregnancy hormones might differ across species and throughout a pregnancy and to look for profiles of multiple hormones that can paint a more accurate picture.

When it’s this difficult to gather data, sample sizes will always be small, which increases the uncertainty of the results. So there’s much more work to be done here on refining the test and establishing how it can best be used, which will all take time.

Aside from just being useful for humpback whale conservation, this technique highlights the way forward for developing more accurate tests for other species. It might not be possible to translate the test directly, but learning how to spot a pregnant humpback whale will make it easier to develop tests for critically endangered species and populations, like North Atlantic right whales

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