Answer:
- He can only catch old fish (past the reproductive age).
Explanation:
As per the given description, the strategy that the commercial fisherman can employ to ensure the sustenance of population of tuna fishes in long-term would be 'catching only the old fish past their reproductive age' as it would give time and space to tuna population present in the water to reproduce and multiply its population in the meantime. This technique is recognized as 'purse seining' where the fisherman would target the old fishes and reduce the bycatch of tuna fishes so that its over-exploitation could be held for a while and give them required time to regain their population.
