Complex sentence: Since the original Asian and Atlantic populations have become seemingly extinct, it is difficult to figure the unique features among whales in these stocks, however, there have been observations of some whales showing distinctive, blackish body colors in recent years.
Split into simpler sentences: Since the original Asian and Atlantic populations have become extinct, it is difficult to determine the unique features among whales in these stocks. However, there have been observations of some whales showing distinctive, blackish body colors in recent years.