求助大伙来分析一下这个however的作用

bennywang2usa

Over the last 150 years, large stretches of salmonhabitat have been eliminated by human activity: mining, livestock grazing,timber harvesting, and agriculture as well as recreational and urbandevelopment. The numerical effect is obvious: there are fewer salmon indegraded regions than in pristine ones; however, habitat loss alsohas the potential to reduce genetic diversity. This is most evident incases where it results in the extinction of entire salmon populations. Indeed,most analysts believe that some kind of environmental degradation underlies the demise of many extinct salmon populations.Although some rivers have been recolonized, the unique genes of the original populations have been lost.
我对这一段的分析：【这段就是讲环境的改变对S的负面影响，特别是对基因的影响，甚至会导致整个S种群的灭绝。段位的although不过是个小让步而已，证明前面观点的客观性。但这个However是什么样的作用呢？】