Mortality, movement, and body size:: critical scales for Atlantic cod (Gadus morhua) in the Northwest Atlantic

The problem of scaling spatially and temporally limited data to larger scale questions can no longer be ignored as evidence accumulates that the importance of any given process, relative to another, depends on spatial and temporal scale. A recently developed graphical technique allows identification of critical space and time scales, which separate scales at which one rate prevails from scales at which another rate prevails. We used data from the literature to test a series of hypotheses concerning change in critical scales with change with life history stage in Atlantic cod (Gadus morhua). The critical scales for mortality relative to kinematics increased slightly for pelagic juveniles relative to drifting eggs, decreased substantially for demersal juveniles relative to pelagic juveniles, increased again in adults, and, contrary to expectation, remained high in large adults ("mother fish"). Critical time and space scales were found to be linked and cannot be taken as constants.