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Species distribution models (SDMs) are key tools in ecology, conservation and management of natural resources. They are commonly trained by scientific survey data but, since surveys are expensive, there is a need for complementary sources of information to train them. To this end, several authors have proposed to use expert elicitation since local citizen and substance area experts can hold valuable information on species distributions. Expert knowledge has been incorporated within SDMs, for example, through informative priors. However, existing approaches pose challenges related to assessment of the reliability of the experts. Since expert knowledge is inherently subjective and prone to biases, we should optimally calibrate experts' assessments and make inference on their reliability. Moreover, demonstrated examples of improved species distribution predictions using expert elicitation compared to using only survey data are few as well. In this work, we propose a novel approach to use expert knowledge on species distribution within SDMs and demonstrate that it leads to significantly better predictions. First, we propose expert elicitation process where experts summarize their belief on a species occurrence proability with maps. Second, we collect survey data to calibrate the expert assessments. Third, we propose a hierarchical Bayesian model that combines the two information sources and can be used to make predictions over the study area. We apply our methods to study the distribution of spring spawning pikeperch larvae in a coastal area of the Gulf of Finland. According to our results, the expert information significantly improves species distribution predictions compared to predictions conditioned on survey data only. However, experts' reliability also varies considerably, and even generally reliable experts had spatially structured biases in their assessments.