Resources utilization and trophic niche between silver carp and bighead carp in two mesotrophic deep reservoirs

Abstract

Resources utilization and trophic structure in aquatic food webs play important roles in the ecosystem stability and functioning. Silver carp (SC, Hypophthalmichthys molitrix) and bighead carp (BC, Hypophthalmichthys nobilis) are intensively stocked in lakes and reservoirs in China and share similar food resources and trophic positions in water bodies. To better understand the ecological roles of SC and BC in natural freshwater, two mesotrophic reservoirs (Nanwan and Nianyushan) were selected to compare resource utilization and the trophic niche of these two fish species. Data analysis using Bayesian mixing model showed that SC was more like a fine particulate organic matter (fPOM) feeder, while BC consumed more coarse particulate organic matter (cPOM) and displayed a higher trophic position in both reservoirs. In contrast, niche breadths represented by the corrected standard ellipse area (SEAC) were essentially the same for SC and BC in Nanwan (SEAC = 6.1 for SC and BC), but much larger for silver carp in Nianyushan (SEAC for SC: 11.6, SEAC for BC: 4.2). The high stocking ratio of SC/BC in Nianyushan was the probable reason for the large SEAC of silver carp, which suggested that silver carp could use more food resources and become more competitive with a higher stocking biomass ratio. The results indicated that the trophic partitioning of filter feeders might be regulated by the stocking biomass ratio of the fish to some extent.