Responsa zu Dewarim 20:19

Furthermore, the main prohibition of bal tashhit, though rabbinic, is nevertheless rooted in the Torah’s prohibition of cutting down fruit trees. And there it is written: “For you shall eat it and not cut it down…” (Devarim 20:19). Thus, since whatever the rabbis instituted was modeled on Torah law, one may not destroy something that man can benefit from; one may not destroy and debase that benefit. Perhaps this even applies to something ownerless. However, bal tashhit does not apply to something whose loss that will not cause the loss of benefit to any man. Therefore, those animals of the forest, while they are alive, give benefit to no man. Their main benefit is in their death—through their pelts and meat. So how can we say that it is forbidden to kill them because of bal tashhit?