Ok for everyone looking for an easy way to get tons of shocking tranq darts just get a CROSSBOW not a normal bow a CROSSBOW go in the water and get them to follow you (you can shoot or just get close) then you can just kill em in the water cause crossbows can be shot underwater! Yay! no dead dinos except for the Cnidaria!
Use a basilosaurus to fight them. Since all their attacks involve electricity unlike the electric eels which can bite, they are doing no damage to the basilosaurus. Just spam the attack button and don’t forget to harvest their body for toxin too!