Evaluating recruitment synchrony of vendace (Coregonus albula) and smelt (Osmerus eperlanus) in three large Swedish lakes

Fish recruitment varies widely interannually and is often difficult to predict. This variation may reflect responses to key environmental factors, including annual climatic conditions. Such factors are often correlated across broad spatial scales, leading to recruitment synchrony among spatially separated populations (i.e., the Moran effect), especially in large lakes and marine systems. We examined interannual variation in the relative year-class strength (RYCS) of vendace ( Coregonus albula ) and smelt ( Osmerus eperlanus ) in three large Swedish lakes—Vättern, Vänern, and Mälaren—to assess whether there was evidence of intraspecific and/or interspecific recruitment synchrony. We used catch-curve residuals to index RYCS and compared populations using Z scores to test for synchrony. Additionally, we examined relationships between RYCS and climatic variables (monthly precipitation, wind speed, and temperature) to identify potential drivers of synchrony. Our results revealed no evidence of synchrony among smelt populations, but demonstrated strong, positive intraspecific recruitment synchrony for vendace. Several significant climate associations emerged for vendace RYCS, including a positive association with May mean temperature and negative associations with May and September precipitation, suggesting that vendace recruitment success is influenced by climate. Additionally, we found interspecific recruitment synchrony between smelt and vendace in lakes Vättern and Vänern, which are deeper and more oligotrophic than Lake Mälaren. These findings suggest that recruitment synchrony in these large freshwater systems may occur at broader spatial scales than indexed by some previous studies, and that climate plays a significant role in vendace recruitment success across all three lakes.