Rusty Crayfish in Brassills Creek, 2006

HARVEST OF AN INVASIVE ALIEN

In 2001, Fred Schueler and Jhil Kar discovered the large population of this invasive crayfish in Brassills Creek at the Paden Road Bridge, north of Burritts Rapids on the Smiths Falls Limestone Plain, south of Ottawa, Canada. In July, 2006, Fred heard that the Ottawa Stewardship Rangers, sampling creeks in Ottawa-Carleton, were going up Brassills Creek. He suggested that they look out for the invasive Rusty Crayfish there. Around Paden Road they found such a large concentration of the invasive species that they decided to remove as many as possible from the creek, and asked us how to dispose of them.

Coincidentally, a week earlier BMNHC had held its first research-based "Crayfish Camp", sampling selected eastern Ontario creeks and lakes for introduced crayfish, and at the Paden Road bridge over Brassils Creek we saw the "Rusties," Orconectes rusticus, the "Crayfish that ate Wisconsin", flaunting themselves all over the bottom at densities of 2-4 crayfish/sq m, with no native crayfish to be seen. This inspired plans of harvesting and boiling them for a picnic feast. There's no problem disposing of captured Crayfish if you're working with hungry People, and we suggested this to the Stewardship Rangers, who responded by setting a date for the harvest, with BMNHC hosting the picnic at the Andrewsville Locks on the Rideau River.

Brassils Creek enters the Rideau from the north just above Burritts Rapids, and in its lower stretches, running mostly over stepped limestone bedrock, it doesn't have any flow in many summers. The local Crayfish, up to 1999, have been Orconectes virilis and Orconectes propinquus. As as one goes upstream, over the steps by which the Dwyer Hill Road ascends to the plateau north of the Rideau, Brassils Creek becomes a peaty Beaver-impounded stream, and Orconectes virilis has been the only Crayfish.

Brassills Creek may be the smallest, most intermittant creek in which we've found Rusty Crayfish in eastern Ontario. Since we found O. rusticus at Paden Road in 2001, we fully expected it to have spread both up and downstream of there in five years, and now our interest in Brassils Creek is why the Rusties are limited to the one stretch of the creek. Morphologically, these are very different from the Rusties in the Rideau or the Jock, so they may be an independent introduction.

On 2 August 2006, Fred Schueler and Ryan Hawke of BMNHC met the Ottawa Stewardship Rangers crew (Cory Wilson, Shane Dool, Kim Judge, and Brad Stimson, led by crew Martha Loewen) at the Paden Rd bridge, and spent the morning dipnetting and seining for Rusty Crayfish. We churned up the creek by seine and dipnet, mostly going after Crayfish that were out from under cover. Many had old blackened shells, but others -- mostly females and Form II males -- were freshly molted and there were about 4 softshelled individuals.

At first we worked above the bridge, then the Rangers went to the bedrock area about 200m downstream, where they remembered seeing a lot or Rusties at their previous visit, while Martha and Fred continued seining and Ryan dipnetting first near the bridge, and then about halfway downstream.

After the Rangers came back, they resampled with seine and dipnet around the bridge, with about the same Catch-per-unit-Effort as we had initially, which shows we hadn't wiped out the population. In all they covered a stretch of about 250 metres, mostly downstream of the bridge.

One hundersd of the largest Crayfish were measured with a ruler while alive, cooked, and eaten at the lunch picnic. About 250 of the smallest were preserved in alcohol, to measure later, and the rest were cooked after the picnic and then measured. The total was about 500 Rusty Crayfish, removed from Brassils Creek and used for both food and science.

We arrived at the picnic site at Andrewsville around noon, set up a camp stove to heat a big pot of salted water while the crayfish were measured.

The largest is pretty awesome. A good characteristic to identify Orconectes rusticus is curved claws. Another is the rusty spot on either side of the carapace, and a third is the slightly pinched-looking "rostrum," the part of the carapace that projects forward between the eyes.

When the pot finally boiled, 100 measured crayfish were quickly dumped in all at once.

All movement stopped within a few seconds, and their shells turned bright vermillion. When the water returned to a rolling boil, our crayfish were ready to eat.

We peeled the tails like shrimp, and the taste was like lobster, with the texture of shrimp. They were also nice dipped in garlic butter or sea food sauce.

A few of them had newly shed skins, very bright, easy to peel, and just as delicious as the others (though the true practitioners of cancrivory chewed up the softshells entire)..

The Ottawa Stewardship Rangers and staff & volunteers of Bishops Mills Natural History Centre, replete after a full morning's work harvesting invasive aliens, followed by a great picnic - counting, sexing, measuring, and making a lunch of them!

Shall we make it an annual event? Contact Fred at bckcdb@istar.ca or Aleta at karstad@pinicola.ca
(613)258-3107 And also visit Bishops Mills Natural History Centre
30 Main Street, Bishops Mills
RR #2 Oxford Station
Ontario K0G 1T0 Canada