Species distribution models (SDMs) are essential tools for understanding the spatial dynamics of fish populations. Traditionally, SDMs estimate species abundance, biomass, or occurrence, either for entire populations or specific life stages, such as juveniles and adults. This study introduces a novel length-based spatially explicit SDM designed to estimate length frequency distributions (LFD) in continuous space. By integrating covariate-length and space-length correlations, the model provides a powerful tool for understanding spatial population structure dynamics. We describe the generalised length-based spatially explicit SDM and validate the model through simulation and apply it to a European hake ({\it Merluccius merluccius}, Merlucciidae) case study in the northeastern Atlantic, demonstrating its potential for real-world applications. We follow by discussing the utility of model-based LFD estimates, particularly in the fields of stock assessment, spatial fisheries management, climate change and ecosystem based fisheries management. Finally, we propose a number of model extensions departing from the proposed length-based SDM that could profoundly enhance our understanding of population dynamics and refine future fisheries management models.