Production of Hexagenia limbata (Serville) and Ephemera simulans Walker (Ephemeroptera) in Dauphin Lake, Manitoba, with a Note on Weight Loss due to Preservatives

Abstract

Annual production and biomass of Hexagenia limbata (Serville) and Ephemera simulans Walker were estimated from samples taken from May through September of 1982 and 1983 in Dauphin Lake, Manitoba. The size-frequency estimates (.+-. 2 SE) of production of H. limbata were 12.6 .+-. 2.68 g/m2 (wet weight) in 1982 and 10.1 .+-. 2.10 g/m2 in 1983. Instantaneous growth production estimates were 9.51 and 9.76 g/m2 (1982) and 9.49 and 8.55 g/m2 (1983) based on life history interpretations of four versus seven cohorts, respectively. Elucidation of complex life histories involving overlapping cohorts may not be necessary in order to make accurate production estimates for similar semivoltine populations. Annual P/.hivin.B ratios for H. limbata ranged from 1.68 to2.38. Production estimates for E. simulans in 1983 were 9.02 .+-. 3.10 and 9.90 g/m2, using the size-frequency and instantaneous growth methods, respectively. Hexagenia limbata weight loss due to preservation in 10% formalin followed by 75% ethanol resulted in a production underestimate of 25%. Length changes of H. limbata in the same preservatives were not significant (p > 0.05). Hexagenia limbata was found at all stations having a silt/clay component. Ephemera simulans was found only on a matrix substrate of clay, silt, sand, and gravel.