Fish habitats and the abundance and composition of fish populations in each habitat are determined and compared with populations in unchannelized or unmodified sections of this stretch of river.
(the abundance and composition of fish populations in each habitat; are; determined and compared with populations in unchannelized or unmodified sections of this stretch of river)
the abundance and composition of fish populations in each habitat
are
determined and compared with populations in unchannelized or unmodified sections of this stretch of river