Site fidelity and condition metrics suggest sequential habitat use by juvenile common snook

The common snook Centropomus undecimalis is an estuarine-dependent fish that relies on landward wetlands as nursery habitat. Despite its economic importance, portions of the snook's early life history are poorly understood. We compared habitat use of young-of-the-year (YOY) snook in 2 geomorphic mesohabitats (tidal pond and tidal creek) along an estuarine gradient (upstream vs. downstream) within a single wetland during fall recruitment. We used abundance, length, condition indices, and stable isotopes to assess ontogenetic mesohabitat use and site fidelity. We found that (1) YOY snook were more abundant within the upstream creek and ponds; (2) the smallest snook were found only in ponds; (3) snook from ponds had lower condition (Fulton's K and hepatosomatic index); (4) snook began moving from ponds to the creek at similar to 40 mm standard length; and (5) snook from the 2 mesohabitats were isotopically distinct, indicating high site fidelity at rather small spatial scales. Collectively, these data identified sequential use of mesohabitats, wherein seaward-spawned YOY snook moved landward and recruited to pond habitats, where they dedicated energy to growth (as length) before making an ontogenetic habitat shift to the creek. Once in the creek, YOY snook condition improved as they approached maturity and started the downstream return towards seaward locations. The wetland network that was previously viewed as generalized nursery habitat instead consists of mesohabitats that support different life stages in sequence. This represents ontogenetic habitat complementation, in which lower availability of a required mesohabitat type may limit the entire wetland's contribution to the adult population.