The Centuries-Long Cod Fishery Extended Along the Entire Continental Shelf

The centuries-long cod fishery extended along the entire continental shelf of the northeast coast of the United States until it collapsed in the 1990s.After the collapse, eggs and first-year juveniles existed only in certain coastal areas.When studying the fishery's recovery, ecologists made habitat surveys of coves or sections of coasts, but they could only measure cod density in relation to habitat in small areas (a few hundred square meters) , in which habitat varied greatly.This meant they were unable to estimate numbers of cod or their likely survival.The ecologists' difficulty resulted from

A) lack of adult cod in the survey.
B) inability to conduct experiments.
C) inability to build models of the fishery.
D) differences in scale of the two measurements.
E) differences in time periods of the two measurements.