Use the ichthy they said... it's immune to shocks they said... that's fine I'll quickly swim done with no scuba gear and lure one to the surface...zap... surface is so near yet so far... manta finish the job
While your tame still might die anyway if you have a high hp dino that gets zapped by these whistle followall and swim away. If you can i managed to rescue my 140 rex that way. She had 8k health and lost around half with a normal saddle. I came back with my re and killed them with rock throw. (It was super effective)
The dossier flat out lies, these things will agro from a fairly long range and pursue you quite insistently they also spawn in the shallows A LOT so if you planned to build a comfy open dock from which you could appreciate the sunset, well tough luck get used to your drab behemoth gates.