when从句剖析

SINCEMARCH 12th, when the first hickory shad of the year succumbed to a sparklylure, anglers of both sexes, several races and all sizes have been lining thebank of the Potomac in Washington, DC, like salmon-hungry bears. 我感觉看作定语从句和状语从句都可以，是如此么？

谢谢各位老师！

SINCE MARCH 12th, when the first hickory shad of the year succumbed to a sparkly lure, anglers of both sexes, several races and all sizes have been lining the bank of the Potomac in Washington, DC, like salmon-hungry bears. 

1. when the first hickory shad of the year succumbed to a sparkly lure，是定语从句，不是状语从句。先行词是MARCH 12th。

2. 句子谓语动词用了 “目前完成进行时”，时间状语自然是 SINCE MARCH 12th，不可能是“过去的一个时间点”，所以，排除 when 从句是状语从句的可能性。