Life histories, abundance and distribution of stoneflies in the Flathead River Basin Montana (USA): continuity over 30 years.

MISERENDINO, M. L; STANFORD JACK ARTHUR

Flathead lake Biological Station, Montana

Conferencia; XI International Conference on Ephemeroptera. XV International Symposium on Plecoptera; 2004

International Society of Plecoptera and Ephemeroptera

Abstract: The species richness, distribution and life histories of the stoneflies in the Flathead River basin (Montana-USA) were studied in 1972-1973 and 2001-2002. Stoneflies were collected from 1- 6th order sites including reaches regulated by dam discharges.  Stonefly species were distributed in relation to temperature patterns which varied between sites and composition did not differ between the two study periods, except Hungry Horse Dam tailwaters where several “riverine” species recolonized after restoration of normative temperatures was accomplished by retrofitting the dam for depth-selective discharge. We recorded multivoltine species as C. sabulosa and Hesperoperla pacifica that were absent during the first study at this site. However, total Plecoptera density at this site still remained 80% lower than in the unregulated reaches where sites typically had more than 40 species.  Across all sites we recorded 72 species.  Emergence was synchronous, starting in Febuary (cold-stenothermic capniids) and continuing until mid-September (Claasenia sabulosa, Calineura californica).  Maximum population density was reached in November to January at river sites as small larvae were apparently recruited from late summer and fall hatching. Species/area was highest in late fall, corresponding to the recruitment of small naiads of the many univoltine species. The unusually high plecopteran diversity at the Flathead River Basin is related to the heterogeneity of the system in terms of thermal and trophic cycles and the multidimensional habitat, coupled with unique position of the river system on the continent in a zoogeographic context.