There is one big issue that isn't addressed in this documentary. The makers attack commercial fishing, and they tell people to stop eating fish. The evidence for that is extremely in your face, and I don't necessarily disagree.
However, the creators of this film continually move up the chain until they reach this alarmingly large scale issue, but then don't continue to move up. Fishing is done to make money for and to feed people.
Conservation is about enforcing the rights of animals to live a deserved and decent life, and in doing so, aid in the overall ecosystem to ensure that life for all of us can continue onwards after that animal has died. If any one of those animals begins to overpopulate an area, nature has a way of dealing with it, namely the loss of a food source. Overeating by a species causes the food to die, then the species starves off until the numbers go back down, and life continuous in a renewed balance.
It's overpopulation by humans that is affecting these changes. Oh but wait, don't humans have the right to live? The answer is the same for any other creature, yes, but the amount of our species, like any other, must be kept in check or nature will do it for us. And that is the main takeaway from this documentary.
This is simply nature at it's best, we overpopulate, our food runs out, we starve, die off, then balance is restored. Or in the case of humans, we just kill the whole thing. But it's overpopulation by humans that is the root problem. One man fishing in his pond to feed his family is fine, but billions of people wanting fish becomes an industry. If we move to eating just plants, they are more sustainable yes, but there is only so much land, so much space to take up for plants to feed billions. The humans will simply outgrow that as well until there is no more solution. Plant based foods is a bandage. We must learn to understand and work with the balance of population for a long term solution.