Some of the muscles worked are the lats, shoulders, pecs, triceps, biceps, fore arms and grip/hand strength. Pull-ups will do more for you than push-ups simply because of the pull motion vs. the push motion. This is not to say you shouldn't do other things like push-ups, no one wants to over-build one muscle group. It's all about balance.
One of the main reasons I know pull-ups work my paddling muscle groups is because if I paddle the day after I have done a work-out that involves a lot of pull-ups, every muscle I mentioned above hurts during my stroke. That's good enough reason for me right there. And when I have been doing pull-ups consistently, I feel like I'm paddling stronger.
Every 3rd day I am stuck at a fire station and have to work out indoors. I try to do 100 pull-ups on those days, mixed in with other core exercises. I usually have to do sets of 10-15 with a minute rest in between. Another great work-out is called "The Murph" so named for Navy SEAL Michael Murphy who was killed in Afghanistan. You start with a 1 mile run on a track or tread mill, then do 300 squats (w/o weight), 200 push-ups, and 100 pull-ups. Then another mile run. All for time. You can do the exercises in any order or number, like 30 squats, 20 push-ups, 10 pull-ups, repeat. Some of the fittest people in the world can do this right around 20 minutes! But don't be surprised if you are double or triple this time.
And there are many people out there that pull-ups are just out of the question right now. You can substitute a full pull-up by using the lat pull-down machine at the gym. You can set a lower weight and work-up until you can do a full pull up. You don't want to injure yourself which means no paddling! And remember, nothing replaces actual paddling and water time. Enjoy.