Higher humpback whale pregnancy rates suggest they are rebounding

May 2, 2018 by Bob Yirka, Phys.org report
Credit: CC0 Public Domain

A team of researchers with members from several institutions in the U.S. has found that pregnancy rates for humpback whales living near Antarctica are increasing. In their paper published in Royal Society Open Science, the group describes studying the whales and what the increased rates may mean for them.

The was very nearly extinguished from the planet during the 18th and 19th centuries due to humans hunting—prior research has suggested that population levels dropped to 10 percent of pre-hunting days. But over the past half-century, laws protecting them have boosted survival. Those that live below the equator have fared so well since whaling regulations were enacted that they are no longer considered to be endangered. And now, it appears that global warming is actually helping them rebound even more, the new study suggests.

To assess how well the humpbacks are doing, the researchers traveled to the Western Antarctic Peninsula and used boats to take blubber samples using dart guns through the years 2010 to 2016. Blubber samples can be tested for progesterone levels and also gender. The team reports that they were able to test 268 females and 239 males. They report that 60 percent of the females tested appeared to be pregnant. The percentage rose as the years passed, suggesting a relatively constant upswing in whale rates. Increasing rates of pregnancies is a good sign for a population on the rebound, the team notes. The researchers suggest part of the reason for the increase in is global warming, which has provided an average of 80 more ice-free days per year, allowing the to feed on krill more easily.

But the long-term outlook is not so rosy, the researchers note. A reduction in sea ice due to will also mean a reduction in krill populations—they feed on the zooplankton that resides on the underside of the ice. Less krill to go around will make it more difficult for all of the creatures that feed on the tiny crustaceans.

Explore further: Researchers link Australian whale strandings to malnutrition

More information: Logan J. Pallin et al. High pregnancy rates in humpback whales ( Megaptera novaeangliae ) around the Western Antarctic Peninsula, evidence of a rapidly growing population, Royal Society Open Science (2018). DOI: 10.1098/rsos.180017

Abstract
Antarctic humpback whales are recovering from near extirpation from commercial whaling. To understand the dynamics of this recovery and establish a baseline to monitor impacts of a rapidly changing environment, we investigated sex ratios and pregnancy rates of females within the Western Antarctic Peninsula (WAP) feeding population. DNA profiling of 577 tissue samples (2010–2016) identified 239 males and 268 females. Blubber progesterone levels indicated 63.5% of the females biopsied were pregnant. This proportion varied significantly across years, from 36% in 2010 to 86% in 2014. A comparison of samples collected in summer versus fall showed significant increases in the proportion of females present (50% to 59%) and pregnant (59% to 72%), consistent with demographic variation in migratory timing. We also found evidence of annual reproduction among females; 54.5% of females accompanied by a calf were pregnant. These high pregnancy rates are consistent with a population recovering from past exploitation, but appear inconsistent with recent estimates of WAP humpback population growth. Thus, our results will help to better understand population growth potential and set a current baseline from which to determine the impact of climate change and variability on fecundity and reproductive rates.

Related Stories

Antarctic whales and the krill they eat

May 9, 2016

The Western Antarctic sector of the Southern Ocean is the regular feeding ground of a large number of fin and humpback whales of the Southern Hemisphere. Around 5,000 fin whales likely migrate to its ice-free waters during ...

Humpback whales rebounding on Brazil's coast

September 2, 2012

(AP)—An institute that tracks the population of Humpback whales that reproduce along Brazil's coast says the number of the once-threatened mammals has tripled over the last 10 years.

Recommended for you

How human brains became so big

May 23, 2018

The human brain is disproportionately large. And while abundant grey matter confers certain intellectual advantages, sustaining a big brain is costly—consuming a fifth of energy in the human body.

Rehabilitating lactate: From poison to cure

May 23, 2018

George Brooks has been trying to reshape thinking about lactate—in the lab, the clinic and on the training field—for more than 40 years, and finally, it seems, people are listening. Lactate, it's becoming clear, is not ...

Chimpanzee calls differ according to context

May 23, 2018

An important question in the evolution of language is what caused animal calls to diversify and to encode different information. A team of scientists led by Catherine Crockford of the Max Planck Institute for Evolutionary ...

How a cell knows when to divide

May 23, 2018

How does a cell know when to divide? We know that hundreds of genes contribute to a wave of activity linked to cell division, but to generate that wave new research shows that cells must first grow large enough to produce ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

skrotbil
not rated yet May 02, 2018

modtager alle slags biler: Personbiler, Varebiler, Skrotbiler , Skadede og defekte biler, Danmarks Højeste Skrotpræmie 2018

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.