<img class="styles__noscript__2rw2y" src="https://dsx.weather.com//util/image/w/ap_17179546435566_0.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0" srcset="https://dsx.weather.com//util/image/w/ap_17179546435566_0.jpg?v=at&w=485&h=273&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 400w, https://dsx.weather.com//util/image/w/ap_17179546435566_0.jpg?v=ap&w=980&h=551&api=7db9fe61-7414-47b5-9871-e17d87b8b6a0 800w" > In this 2012 photo provided by the Center for Whale Research, a dog trained to sniff for orca scat sits on a boat in the Salish Sea in Washington state. (Center for Whale Research via AP) (Center for Whale Research via AP)

Resident endangered killer whales that inhabit the waters off Washington state are having fewer pregnancies these days and it's likely because of a lack of food, a new study says.

Researchers from the Center for Conservation Biology at the University of Washington, along with partners at the National Oceanic and Atmospheric Administration’s Northwest Fisheries Science Center and the Center for Whale Research , found a link between the orca population’s low reproductive success to stress brought on by a lack of their staple diet in the area, Chinook salmon.

In the study published this week in PLOS ONE , researchers determined that more than two-thirds of orca pregnancies failed over a seven-year period by analyzing hormones found in excrement collected at sea. The orca scat was collected thanks to the help of dogs trained to smell out and find the excrement. They are able to detect scat up to one nautical mile away.

“Based on our analysis of whale health and pregnancy over this seven-year period, we believe that a low abundance of salmon is the primary factor for low reproductive success among southern resident killer whales,” lead author Sam Wasser , a UW professor of biology and director of the Center for Conservation Biology, said in a University of Washington press release . “During years of low salmon abundance, we see hormonal signs that nutritional stress is setting in and more pregnancies fail, and this trend has become increasingly common in recent years.”

The researchers believe the orcas experience miscarriages because the lack of food results in decreases in the hormones necessary to support the pregnancy.

This group of whales, which get 95 percent of their diet from the area's population of salmon, live in the area year-round, unlike other whales that are transient.

“These findings indicate that pregnancy failure — likely brought on by poor nutrition — is the major constraining force on population growth in southern resident killer whales,” Wasser said.

Boosting salmon runs in the Columbia and Fraser Rivers could help the orcas recover, Wasser said.

“As it stands now, the orca numbers just keep declining with no signs of recovery,” said Wasser. “We’re losing a valuable resource here.”