Abstract Niklitschek, E. J., Secor, D., Toledo, P., Valenzuela, X., Cubillos, L., and Zuleta, A. 2014. Nursery systems for Patagonian grenadier off Western Patagonia: large inner sea or narrow continental shelf? – ICES Journal of Marine Science, 71: 374–390. Adjacent to Chile's long and narrow continental shelf, the Patagonian Inner Sea (PES) is among the largest and most complex estuarine systems in the world. The PES harbours high concentrations of juveniles and adults of important groundfishes, which spawn within or in near proximity to it. A dominant view is that recruitment primarily originates here rather than in adjacent coastal regions. We used otolith stable isotopes to evaluate the relative contribution of several PES and continental shelf regions to recruitment of Patagonian grenadier, one of the most abundant groundfishes in the area. Seawater chemistry confirmed that δ13C and δ18O differentiated these nursery and feeding regions. Estimated recruitments from PES nurseries to adult feeding regions were important (10–35%), but lower than dominant contributions from shelf nurseries (64–85%). Stable isotope differences within otoliths indicated, however, that most adults had previously used PES habitats as subadults. Adults exhibited stronger homing to feeding habitats in the PES than to shelf regions, suggestive of seasonal site fidelity or partial migration behaviours. The proximity of principal spawning areas to the bifurcation of the West Wind Drift Current may cause large interannual and decadal variations in larvae transport and the relative contribution of different shelf and PES nurseries to recruitment.