It may bring a reprieve for the whale populations currently protected in international waters but at a very high price.

分析：这里与but后面的内容是与前面It may bring a reprieve for the whale populations currently protected in international waters 并列，but后面是一个省略结构，不省略的是 (It may bring a reprieve for the whale populations currently protected in international waters) at a very high price。

句意为：这也许会给目前在国际水域受到保护的鲸鱼种群带来一段暂缓期，但这也许会以很高的代价给目前在国际水域受到保护的鲸鱼种群带来一段暂缓期。

简化后：这也许会给目前在国际水域受到保护的鲸鱼种群带来一段暂缓期，但付出的代价很高。

以下类似的用法，请体会：

They reached an agreement, but at a high price. 他们达成了协议，但代价很高。

Most goods are available, but at a high price. 大部分商品都可以买到，但价格昂贵。

The bottle was won, but at a heavy cost in casualties. 战斗取得了胜利，但却是以人员的重大伤亡为代价的。

Sales are growing for premium wines, but at a bare 2 percent a year. 优质葡萄酒的销量在上涨，但每年仅涨2%。

He managed to get a TV celebrity to open the theatre, but at a whopping fee. 他设法请来了一位电视名人主持剧院的开幕典礼，但费用高得惊人。