Status of freshwater pearl mussel in Laxtjärnbäcken : Effects on freshwater pearl mussel in the presence of sediment load and brook trout

Abstract

The aim of this present study was to determine and evaluate whether the presence of brooktrout (Salvelinus fontinalis) and sediment load may be a threat against the reproduction anddistribution of freshwater pearl mussel (Margaritifera margaritifera) in a creek located innorthern Sweden. Freshwater pearl mussel is an endangered species and is dependent ofbrown trout (Salmo trutta) to reproduce. Therefore there are concerns of indirect effects onthe population of pearl mussel by competition between brown trout and brook trout. Ditchesfrom a nearby gravel road have been fixed to lower the sediment load into the creek. I tried toevaluate this action plan. Electrofishing, mussel- and habitat inventory was carried outwithin each locality to reveal results of the glochidia abundance on both brown trout andbrook trout. Data of pearl mussel dispersal and habitat use were collected. I found glochidiaon both brown trout and brook trout, but in much smaller numbers on brook trout. The pearlmussel is present in frequent numbers in the upper part of the creek, but downstream thenumber of mussels decrease, probably because of the previous ditch influence from thenearby gravel road. The creek cross the gravel road in one place and on the stretchdownstream no living mussels were found. The result suggest that sediment load might stillinfluence the pearl mussel population in some parts of the creek and that this effect is greaterthan the presence of brook trout