Complex sentence: The problems seem to arise from a large collection of vessels using sonar actively to scan a particular area, while on their own they only cause minor irritation to the marine species but collectively the problem is exacerbated.
Split into simpler sentences: The problems seem to arise from a large collection of vessels using sonar actively to scan a particular area at once. Whilst on their own they only cause minor irritation to the marine species but collectively the problem is exacerbated.