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Hartley Nature Center
Natural History. Stewardship. Sustainablility.


Crayfish are found in both Hartley Pond and Tischer Creek

Calico Crayfish

The species to the left is the Calico Crayfish, Orconectes immunis. It came from Hartley Pond in 2009. This is the first crayfish species to be identified from Hartley Park. It is probably the species usually captured and observed.  This widespread native species is not the only crayfish species living in the park.


Black Crayfish

This second species is the Black (or Northern) Crayfish, Orconectes virilis. It was discovered in Tischer Creek at the Newbridge site in the spring of 2009. It is seen infrequently, perhaps once a year.

image from Nature North

Rusty Crayfish

The Rusty Crayfish, Oronectes rusticus is not native to this area, but comes from the south. It is probably here by being fish bait released into our waters. In Hartley Pond & Tischer Creek, its numbers relative to the Calico Crayfish are unknown. It was first identified in Hartley Park in 2010 but needs confirmation. Elsewhere it has been found to be destructive outside of its original range. If it is indeed present in the park, judging by the monitoring of our yearly Citizen Scientists (grade school classes, mostly), there appears to be a steady equilibrium with its habitat. Another possibility is that this species has just arrived in this watershed and is just beginning to make changes in our aquatic environment.



We don’t know exactly which species of crayfish we’ve been measuring, but the data is still important. In the years we have taken data, there are no trends and only one large change (in 2009) in crayfish populations. Additionally, there were no trends and no large changes in the water quality detected in Tischer Creek and Hartley Pond in the years of crayfish sampling. This data provides us with base-line data that will make any future trends and large changes discernable and documentable. All the 2005 year data for unknown reasons is discernably consistently different from data of other years.


Crayfish Average Numbers

CHART 1 The fewer crayfish found per the number of samplings in 2007, 2008 and 2009 may be due to the midsummer droughts in those years resulting in probable low oxygen levels of the non-moving water in Tischer Creek during those times.  The numbers and sizes of the crayfish recovered quickly each year after the rains resumed.


CHARTS 2 and 3: Crayfish Length in Centimeters

Chart 2 shows the largest average minimum length of male crayfish having occurred in 2009. Chart 3 shows the lowest maximum average length of female crayfish having occurred in 2009, and the largest minimum length in 2010. All the other 2010 values in the two charts fall within previous years’ ranges. Male length patterns are very similar to female length patterns over the years.



The percentage of large males and females in 2010 falls within the range of values of previous years.



The 2010 percentage of males versus females fall within the range of previous percentages.


This project was funded in part by the Coastal Zone Management Act, by NOAA's Office of Ocean and Coastal Resource Management, in conjunction with Minnesota's Lake Superior Coastal Program.


Hartley Nature Center, 3001 Woodland Ave. Duluth, MN 55803       location map
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