It's more straightforward, but i think you are
By your negligence I may run, but faced with the choice, most would prefer to swim
This snake could be a water snake. If a snake is approached it will most likely retreat unless cornered of attacked. They can also traverse land, but are most proficient at swimming.
Im the goal of sharks, who could surely fall,
Snakes are great at catching food and defending themselves
If they once fail to make good on their call.
If a shark is killed, they my wish they had the same hiding abilities as a snake
On both your time and your waste I am quite a drain,
The poison can end your life, ending your time and the potential waste that you will produce in the future
and when all else is taken, I will remain.
The snake is coiled up, when a small animal is taken by the snake, the snake then proceeds to coiling up again
I suck up heat but am cool while I thus feed,
They spend their days in the sun to warm up, but during the night they hunt
And my boats house the fish that don't catch my lead.
Humans may turn back from fishing if they find snakes in the water, so fish that are ahead of the snake are less likely to be caught