The shallow Patagonian Shelf off Península Valdés limits the dive depth of southern elephant seals (Mirounga leonina) to <100 m, an unusual circumstance for this deep-diving species. Beyond the shelf water depths of >1,000 m enable the seals to forage deeper and use the entire water column. We compared the diving pattern of 10 juveniles instrumented with light–temperature loggers to determine if diving effort, measured as dive durations longer than the estimated aerobic dive limit, differed between on-shelf and off-shelf waters. The productive Patagonian Shelf, an environment where juveniles showed lower diving effort, also was used commonly by older seals, which likely displaced juveniles off-shelf periodically, where they exhibited increased diving effort.