My thoughts are that OS & Echo have pretty much localised the search area.
The 21 fish could not originally access the area due to depth constraints [ie <4500m].
They have over come this not through 'certification' but by trialing the fish deeper.
The best way of describing marine salvage is as -
"A science of vague assumptions based on debatable figures taken from inconclusive experiments and performed with instruments of problematic accuracy by persons of doubtful reliability and questionable mentality".
Let the experts do what they know best.