What does this mean? If Japan split into 5 countries, each eating the same amount of fish per capita as now, would that somehow be more responsible?
If by "irresponsibly" you mean they failed to execute sufficiently draconian population control, it's hard to imagine anything more extreme than China's longstanding former One Child Policy - an exemplar of what you'd describe as responsible environmental behavior, right?
Who's more irresponsible? A Chinese family buying fish for 2 children or a Westerner buying twice as much food for themselves as they need?