bonito

Mr Scott, the chief mate, being a capital fisherman, the table was almost daily furnished with an albacore, bonito, or dolphin, and not unfrequently with all three, which he struck with a gig.

Making dashi is simple once you have katsuobushi (shaved, dried bonito flakes) and kombu (sea kelp), which have become increasingly easy to find across the United States. (You can also order them online.)