When I was rowing internationally in the early 90's, we'd occasionally do 70 reps x 3 weights sessions with a pretty light weight. It was ground breaking back then, but weight training theory has caught up and passed that idea. For endurance you'll want to be doing 20 - 40 reps x 3 or 4 with a heavier weight, which will condition you better than doing lots 'n' lots of reps.