Orca-moose predation
October 23, 2019 7:57 AM   Subscribe

I saw recently a factoid about how orcas eat moose when they are swimming. How common is this as a way for moose to die? I am looking ideally for a number backed up by a citation.
posted by jeather to Science & Nature (5 answers total) 3 users marked this as a favorite
How common is this as a way for moose to die?
Not very common, at all. This study says wolf predation and food competition explained 80% of population variation.

Here's another study that is exclusively about causes and rates of moose mortality, it has no mention of orca predation whatsoever, though it does mark a few calves killed by "unknown predator". The vast majority of moose kills are by wolves, grizzly bear, and black bear, and mostly concentrated on calves, not adults. Here's another study of moose mortality with no evidence of a single orca strike.

A recent GPS collar study focused on causes of moose calf mortality found Twenty‐five of 34 calves (74%) died of natural causes as of 31 December 2013, including 1 after natural abandonment, 1 after abandonment of unknown cause, 1 drowning, 1 unknown predator kill, 1 lethal infection from wolf (Canis lupus) bites, 4 black bear (Ursus americanus) kills, 12 wolf kills, and 4 “probable wolf kills.”

Each of these studies is for a particular place and time, not one of them documented a single orca kill. There are many more studies on moose mortality. It is possible some specific herd of moose ends up spending a lot of time in the water, and perhaps orca-deaths would register in that population. But in general:

TLDR I (a biologist but not a moose demographer) find no evidence of orca predation of moose being anything other than a rare but notable occurrence, perhaps similar to humans killed by lightning, sharks, or coconuts.
posted by SaltySalticid at 9:06 AM on October 23, 2019 [5 favorites]

This seems like a bizarre factoid to me. I think SaltySalticid has you covered for science, but if you want anecdata: I live right on the ocean in an area of high moose population density. I have never seen a moose swimming or wading in the ocean (yes, lakes and on a few occasion marshes- but wading, not swimming). I have spent considerable amounts of time (entire months in the summer) in other beachy areas of high moose population density that also feature reasonable orca populations. I have seen neither moose swimming in the ocean nor orcas snacking on anything besides stuff regularly found in the ocean.
posted by charmedimsure at 9:18 AM on October 23, 2019 [3 favorites]

The information appears to come from analysis of orca stomach contents:

Stomach contents from animals taken in whaling operations or from stranded individuals have provided extensive information on species consumed...Killer whales are top predators, with an extreme range in food items reported taken, including...occasional reports of terrestrial mammals such as deer, moose, and pigs (Heyning and Dahlheim 1988; Guinet 1992; Jefferson et al. 1991)
posted by AzraelBrown at 10:03 AM on October 23, 2019 [3 favorites]

An article on Prey selection of offshore killer whales says "their diet comprises a wide array of prey, including fish, cephalopods, pinnipeds, cetaceans, birds, and even moose," which suggests it's a rare occurrence.
posted by Mr.Know-it-some at 10:18 AM on October 23, 2019 [1 favorite]

Also: orca stomachs containing moose does not neccessarily mean predation. They could be scavenging moose that have
- drowned
- died of hypothermia
- died of infectious disease
- died from injuries inflicted by a non orca predator
posted by Murderbot at 11:00 AM on October 23, 2019 [4 favorites]

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