Potential Trophic Competition Between the European Perch <i>Perca fluviatilis</i> and Pikeperch <i>Sander lucioperca</i>

ABSTRACT The European perch Perca fluviatilis and pikeperch Sander lucioperca can co‐occur, potentially competing for food resources. However, few studies have addressed the potential feeding competition between these species. We used carbon and nitrogen stable isotope analysis to assess the potential trophic competition between these species in two Turkish ecosystems, a natural lake where both species are native (Lake Gala), and a reservoir where both have been introduced (Sığırcı). We found a significant positive relationship for S. lucioperca between δ 13 C and size in Lake Gala, suggesting higher consumption of benthic/littoral prey in bigger individuals, but not in the Sığırcı reservoir nor for P. fluviatilis . A positive relationship between δ 15 N and size was also found in the Sığırcı reservoir for both species, indicating that trophic position increased with age, while in Lake Gala P. fluviatilis showed a negative relationship, possibly due to consumption of abundant prey from lower trophic levels. In Lake Gala, the isotopic niches overlapped and were larger in S. lucioperca , while in the Sığırcı reservoir they were segregated and larger in P. fluviatilis . Our results show that the trophic niches of P. fluvatilis and S. lucioperca can overlap, leading to potential interspecific competition.