Dave Petzal talks about both at Field and Stream, with a caution that the rules don't always apply.
For example, one cold winter afternoon I was shooting wood ducks near a small pond. The ducks were flying over the pond and you had to time your shot so that the duck didn't fall into the pond, or good sportsmanship required that you swim for your supper. I didn't mind, so much as home was just 200 yards away. Several afternoons I walked back, freezing, in my skivvies.
We tried to try to shoot the ducks when they wouldn't fall into the pond, but accidents happen. I had just connected with a little drake, and he fell into the water. The evening flight ended and I kicked off my boots, preparing to shuck my jeans and take a little late afternoon winter swim when I saw a big alligator surface near the defunct duck.
I sat down and put my boots back on. I don't mind swimming after a duck I shot, but I DO mind swimming with an alligator. The gator was welcome to the duck, with my compliments.
Do I always retrieve what I shoot? I try to, but gators have to eat too.