Foraging morphology and diet divergence of European whitefish (Coregonus lavaretus) in water courses of Murmansk region

Abstract

European whitefish (Coregonus lavaretus) is a highly polymorphic species. In general, it is assumed that the divergence in whitefish is a form of a specialization in the use of the resources (including food) of the main limnological zones – pelagic (plankton), littoral (benthos, plankton), profundal (benthos) – and the morphological adaptations of the shape of the body and head simultaneously determine the direction of the process. The shape and number of gill rakers, which are responsible in whitefish for prey retention, are considered the most important adaptive trait and are most often used to distinguish between its sympatric morphs or ecotypes. Current study will be devoted to foraging morphology and diet divergence of whitefish in water courses of Murmansk region. Our study of the water bodies in three major river basins of Murmansk region revealed the presence of two whitefish morphs: sparsely rakered (further sr) and medium rakered (mr). The mr morph is less common and observed only alongside the sr whitefish. In general, in sr whitefish the number of gill rakers ranges between 15 and 31, and in mr whitefish between 27 and 44. Among whitefishes with 27–31 gill rakers, both sr and mr morphs were observed and distinguishable by the shape of the rakers. In the studied sr whitefish populations, relatively long and short rakered whitefish morphs were found. In Lake Kuetsjärvi (Pasvik River basin), the sr and mr whitefish formed additional slow- and fast-growing ecological morphs. In the water bodies of the Murmansk region, the greatest diversity of sympatric morphs of whitefish (from two – sr and dr to four morphs – sr1, sr2, mr1, mr2) is observed in the most polluted water bodies with higher productivity and a large abundance of such generalists as perch and European smelt. The diet of sr and mr whitefish morphs in the studied water bodies of Murmansk region in summer-autumn period is associated with hydrobiological features of fish habitats. Sr whitefish morph from the Pasvik, Tuloma and Niva Rivers basins, inhabiting mainly littoral and profundal areas of water bodies, have a benthic diet. Mr whitefish morph, inhabiting mainly littoral and pelagic areas of water bodies, have both benthic and mixed feeding types. According to our data, coexistence of four morphs of whitefish in Lake Kuetsjärvi (lower Pasvik River) – sr1, mr1, sr2 and mr2 have the low specialization and use the most abundant recourses in lake. The most extensive overlapping of feeding spectra is found in small morphs in Lake Kuetsjärvi – sr1 and mr1. On the basis of our data on whitefish from water bodies of Murmansk region we found active gill apparatus functioning in fish, as minimum length of food organisms in sr and mr whitefish morphs were sometimes less than or equal to gill rakers distances of fish.