Humpback whale faeces spin surprising tales

Alf Wilson, Science

Faecal plume in the water behind humpback whale tail
Humpback whale faecal plume visible behind its tail.   Credit: Rhonda Reidy

People have been giving Rhonda Reidy a lot of "crap" over the past several years, but don't worry – she's been asking for it. Reidy, fresh from defending her PhD, published a paper that pulls together a unique collaboration, a record number of faecal samples, and DNA analysis to tell the surprising story of what some humpback whales in the Salish Sea were eating.

But this story started in 1999 when Reidy, crewing on a BC whale watching boat, saw her first humpback whale. After decades humpbacks were returning to BC waters. A question stuck with Reidy over the years: how might increasing humpback whale predation impact commercial BC fish populations. She approached UVic Professors Laura Cowen (Statistics) and Francis Juanes (Biology) about doing a graduate degree to statistically model humpback whale predation. But there was one big problem: no one knows precisely what humpbacks in BC eat at depths of fifty to two-hundred metres underwater, where they primarily feed.

"All of the current data in BC is for humpback whales feeding at the surface. I dug through the literature," Reidy recalled "and I just couldn't find information on what humpback whales are eating underwater, where they spend most of their time."

Reidy used leading tools to study humpback whale deep-water foraging behaviour: acoustic prey mapping (think sophisticated fish finder) and suction-cup tags that collect three-dimensional whale movement.

We now know where they like to feed, are most often found, and we have pretty good information about their diving behaviour, what the prey in the water column look like, in terms of density and abundance. But other than broad categories of fish and zooplankton, we still don't know precisely what they're consuming underwater. And that's why I turned to molecular biology.
— Rhonda Reidy, Biology

Reidy chose DNA-metabarcoding, a type of PCR test. The Hakai Institute's Matthew Lemay and Rute Clemente-Carvalho did the DNA analysis and they're already planning to reanalyze Reidy's samples using techniques that could reveal more details.

"The DNA detections only tell us what is present in the feces. But if there was a high sequence abundance of a specific species, it tells us that's important prey to pay attention to: either the whale was frequently feeding on that species, or it recently fed on that species."

As expected, krill was prevalent in thirteen of the fourteen samples. But Pacific herring, hake, and eulachon were also prevalent. Walleye, pollock, and sablefish were strongly detected but only in one sample each, so not prevalent. It is not known if this was opportunistic or if the whales were targeting those fish species.

The interesting result was that the whales may be targeting higher trophic-level fish like pollock and hake, in addition to lower trophic-level fish like herring and anchovy and invertebrates like krill.
— Rhonda Reidy, Biology

Rhonda Reidy on a boat using a laptop, researching humpback whales
Rhonda Reidy prepares to deploy acoustic prey mapping apparatus. Credit: Jessica Qualley

But collecting humpback poop requires good luck, timing, and reflexes – it rapidly dissipates, some sinking and some floating away. It's why humpback feces-collection expeditions have mostly left researchers empty-handed.

"People have tried dedicated humpback whale faecal sampling programs and it just – so far – hasn't worked very well. You never know when a whale is going to defecate," Reidy chuckled. "They roam vast areas. You can go days and days without a faecal sample."

Reidy's journey, from whale-watching crew to boat skipper to academic, provided unique connections. Reidy was savvy enough to recognize her access to – and the respect of – highly qualified personnel.

"I called on my colleagues in the Pacific Whale Watching Association who are out on the water daily – who I trust and know," Reidy explained. "They know what they're looking at and they know the animals and they know to follow the very strict boating rules around the whales."

Reidy was able to get eighteen samples over four seasons for humpback whales in the Salish Sea (around the southern tip of Vancouver Island). Of these, fourteen contained faecal matter. No one had ever collected so many Salish Sea humpback faecal samples in such a short time.

So, how is humpback whale poop collected?

"Sometimes you can see the humpback defecate. You bring the boat alongside the faeces and I use a pool-skimmer net to scoop as much as I can. Then I scrape it into a new Ziploc bag." Reidy detailed. "I had a couple of colleagues on a larger boat use a bucket. I had somebody use a water bottle"

Like any leading-edge research, more questions have been raised. But Reidy explains that one thing is now certain.

All of the work that I have done, tells me, that we cannot assume what the humpback whales are eating underwater. Not precisely at the species level.
— Rhonda Reidy, Biology

But thanks to Reidy's research, we're starting to find out.

Check out her recent publication "Fine-scale diversity of prey detected in humpback whale feces"

Reidy's research with supervisors Francis Juanes (biology) and Laura Cowen (statistics) reflects UVic’s ongoing commitment to the United Nations Sustainable Development Goals (SDG) 14, life below water. Learn more about the UVic’s 2022 SDG assessment by the Times Higher Education Impact Rankings.

Humpback whale faecal plume
Humpback whale faecal plume spreads in the Salish Sea.   Credit: Rhonda Reidy