Video length is always a concern for most of us. If you are publishing to uknown audience (web, YouTube, etc...) keep it to as short as possible as Pajjpen mentioned above. One idea I was flirting with is to have a main long video to to tell the whole story for 5-10min for example and other mini clips 1-3 min to show a single fish/creature in action. In the main long video the single clip about the creature will be in shown in for few seconds only. Of course, you need include only the absolute must show clips (the winning clips).
To help short list the winning clips good workflow is to start selections process as early as possible and preferably on the same day cause the shots are still in your head. Another helping tip is not to shoot just anything that moves underwater cause you have ample storage and battery life, this will help you minimize the number clips.
Some good cinematographer try to plan the shots as much as possible and yes one has to improvise in our case a lot.
Compile the clips into the main video through rough edits/cuts (no edit, no color correction at all) to ensure you story is achievable within the time limit you sat. Only then start your color correction process.
Whatever workflow you choose, one can not emphasize enough on good lighting and white balance to help get the correct colors and thus saving tedious color correction work.
For those who already familiar with the above, please forgive me for the long message.