Natural History. Stewardship. Sustainablility.
2002-2007 CRAYFISH IN TISCHER CREEK & HARTLEY POND, HARTLEY PARK
Average Number of Crayfish in Hartley Pond and Tischer Creek 2002-2007
The data in Chart 1 confirm observations that the number of crayfish sampled by elementary classes in Tischer Creek and Hartley Pond was noticeably fewer than in past years.
Percent of Female Crayfish in Hartley Pond and Tischer Creek 2002-2007
The data in Chart 2 shows that the percentage of females in all samples was not noticeably different in 2007 from previous years. The percentage in 2007 falls in the range of such values of the earlier years.
Average length of Male Crayfish 2002-2007
CHARTS 3 &4 show that the larger average sizes of of both sexes
of crayfish in 2007 fell within the range of the same sizes in previous years. However, the the average minimum sizes of both male and female crayfish were somewhat greater than previous years.
Average length of Female Crayfish 2002-2007
Number of Individuals Longer than 7cm 2002-2007
Charts 5&6 show that a count of samples that had at least one large crayfish, male and female, in 2007, was greater than in previous years. The count was not of how many of the larger ones occurred in each sampling, because only the maximum size was recorded.
Percentage of all individuals 7cm long and above 2002-2007
Whatever was causing the decreased number of individual crayfish in 2007 may or may not have had an effect on the few changes seen in the 2007 crayfish relative to crayfish sampled in previous years.
There were 2 observable changes that we know of in the Tischer-Hartley watershed. One is the very recent increase of large houses in the watershed which may mean increased fertilizer or pesticide pollution as the critical factor leading to the reduced numbers of crayfish in these waters. The other change is the reduction of the flow in Tischer Creek to zero for several weeks. Oxygen may have been limiting to crayfish presence in the parts of the creek that was sampled. The latter seems to be the only or major reason, as after the great increase in rainfall in late September the number of crayfish caught increased.
This spring’s testing of these waters showed no detectable nitrate, chloride, and phosphate. No algae bloom has developed nor has there been a large number of dead fish or other aquatic animals in these waters.
There appeared to be a normal seasonal development of the pond weed beds in Hartley Pond this summer.