Observation: Thousands of dead crabs were observed on west side of Denman island beach. This hasn't been seen before. - Roz Kleim, British Columbia.
Comment by LEO BC Coordinator: These crabs appear to be red rock crabs (Cancer productus), and it is reported that all the dead and stranded individuals were male. Autumn White, who was one of the observers of this event, forwarded some photos and observations from a Facebook thread about this event. Select comments from that Facebook thread are inserted below without names and dates. There is some speculation about the cause of this mortality event in this thread, but the cause of this event should be considered undetermined at this juncture until more information is available. An initial list of alternate hypotheses includes: (1) low temperature mortality, (2) domoic acid from algal blooms, (3) high ocean acidity due to high concentrations of atmospheric CO2, (4) effects of imazapyr to eradicate Spartina; see BC Progress Report and a Letter report from Delta - Dr. Tom Okey, Ocean Integrity Research -and- Adjunct Professor, UVic School of Environmental Studies..
Facebook post by Autumn White, followed by comments by other people: What's with all the large dead crabs on the west side beaches? There must be over 1000. Odd. They were ~five inches across and red. -- Autumn White, Denman Island.
I heard about the east coast die off…there's been a lot of die offs in recent years, The Real Coastal Warriors have a huge two part document from back in 2010 and 2011
They are whole crabs, not just shells. Seems like they are mostly if not all male as well. I'm not sure what type, but people do eat them. About 5-6 inches.
We've seen them from Hinton (470 of them there alone!) all the way to Scott rd.
Same thing happened around labour day. I didn't see first hand but it was reported by a friend. Can’t remember exactly where but I’ll check.
Labour day it was east side around Fillongley beaches.
It is very strange..lots at Millard Beach too. Anyone asked fisheries?
Macfarlane south on Lacon ….way too many crabs
Just phoned it in to Fisheries and mentioned FB photos.
Lots and lots of dead red rock crabs at Hinton Beach today. Oddly, no scavenger birds eating them.
I was curious why the birds weren't eating them as well.
Our shores were spared the chemical Spartina removal program. But I will say, the willingness to blame shellfish growers, without a shred of evidence, is telling.
A longer statement on the same Facebook thread (author unknown):
- The crab kill that is washing ashore on Denman triggered my interest in learning what poisons are now being permitted in the intertidal zone now that the ban on using chemicals has been lifted. Permits to use imazapyr to eradicate Spartina throughout coastal BC was the only information I could find.
The Spartina eradication program is described as a collaboration involving a partnership with the US, various Canadian federal and provincial ministries, including Health and the Environment), city councils, and Ducks Unlimited. Since Hornby and Denman islanders responded in the permit public comment period that our manual program was effective, our islands were spared.
Spartina Working Group used to support unanimously approving using imazapyr (and rodeo early on) was based on research used by Washington State to support permitting chemicals, which are banned in Europe, to eradicate spartina in the intertidal zone and to eradicate “pests” like burrowing shrimp in shellfish farms.
This research includes the familiar "no significant negative effects expected) and fails to address the long range, cumulative effects of using imazapyr on the marine ecosystem or the need for higher dosages now that Washington is reporting that Spartina “clones” are now appearing where the Spartina were “eradicated.”
Equally alarming is that, given the success of manual eradication on Denman and Hornby, why the Spartina Working Group did not support improving manual eradication programs and apply the precautionary principle given the absence of research on at the long range, cumulative effects of spraying imazapyr in the marine ecosystem already burdened by micro plastics and other pollutants. (Imazapyr is known to also kill nearby plants, for example.) Without this research, BC’s Spartina eradication program appears to violate Prime Minister’s mandate that DFO implement a science based/ecosystem management approach. And since the gate to spraying imazapyr in the marine zone is open, what other chemicals can we expect to be approved that could help us to understand why thousands of dead crabs are washing up on our shore.
Sources worth scanning are the 2015 British Columbia Spartina Eradication Program Progress Report, which includes a section on Denman and Hornby’s manual eradication plan, and maps of sprayed areas throughout coastal BC and Baynes Sound; and a 2012 letter from the Delta City Council to various ministries on their support of spraying over manual eradication.
References:
The Corporation of Delta . 2012. Spartina anglica (English Cordgrass) . October 15, 2012
Daily Mail Reporter. 2011. 40,000 'devil' crabs wash up on Kent coast after dying from hypothermia in freezing sea. Daily Mail 5 January 2011
DFO. Red Rock Crab Profile
DUC. 2015. British Columbia Spartina Eradication Program Progress Report. Ducks Unlimited Canada, on behalf of the BC Spartina Working Group.
Jurgens LJ, Rogers-Bennett L, Raimondi PT, Schiebelhut LM, Dawson MN, Grosberg RK, et al. (2015) Patterns of Mass Mortality among Rocky Shore Invertebrates across 100 km of Northeastern Pacific Coastline. PLoS ONE 10(6): e0126280. doi:10.1371/journal.pone.0126280
Shore, R. 2014. Acidic water blamed for West Coast scallop die-off. Vancouver Sun 26 Feb 2014.
2012 letter from the Delta City Council to various ministries on their support of spraying over manual eradication.
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Observations From Members