1. Let's have a look at the first pair of pictures. The lighting was not perfect when taking this pictures, and it resulted in a bit blurred left side trees (though they were supposed to be sharp and too white sky in the right top corner. That is why, I have cropped these two elements that I did not like. I think the composition has even won from this, as there is now more attention to the bridge, which became more central than on the initial picture.
2. The nose and eyes of the seal were from the very beginning planned as central object. As it was not possible to come closer to the object than it is, I centralized and cropped the needed details. I also decided to leave some waves and bubbles to save the movement effec
3. For cropping this shot I referred to the exercise on the positioning the horizon. As it was advised there, placing the horizon line exactly in the center makes the composition static. Also there was nothing really interesting in this sky to make it half of the shot. That's why I decided to cut some sky. I have also sacrificed some sand in the bottom to make the shot look more like panorama and attract more attention to the grass and reflections.
Summarizing this exercise, I can conclude that cropping is a tool that should not be forgotten, if you are not very happy with the composition of a shot or some details are rather irritating.