Does anyone know why the USN pinger locator system doesn't use an array of transducers to determine the bearing to the back box acoustic pinger? There are many commercially available systems which use transponders to measure range and bearing to determine positions of underwater targets like ROV's. You can't get range from a free running pinger but you can get bearing. An example Ultra Short Base Line (USBL) system is covered in the link below.
USBL - All Systems
From the description.
"The second is that the bearing can be determined by knowing the discreet difference in phase between the reception of the signal at the multiple transducers present in the transceiver. This allows the USBL system to determine a time-phase difference for each transducer and therefore calculate the angle of the arriving signal."
All you would need is a compass on the fish along with the derived angle to get the bearing. This would allow the pinger to be found MUCH faster. Using a single transducer seems to be very inefficient.