If the target bearing you get is from sonar ... and you cannot yet see the target ... turning toward the bearing will usually get you into visual range only if the target isn't moving ... or is moving along your course line (heading directly toward you or away). Otherwise, the target will drift one way or the other. If that's the case (your sonar operator can confirm it), you're not likely to get a visual if you try looking for it along the original bearing.
You need to head it off at the pass!