Whitespotted char

Its range

The species holds the northwest Pacific: Japan and the northeastern Korean Peninsula, through Sakhalin and the Kuril Islands to Kamchatka.

That is an island-and-peninsula range rather than a continental one, and it matters for the resident form. Each cold headwater on each island is effectively its own population, with no route to the next, so what looks on a map like a single distribution is in practice a long line of separate small ones.

Breeding

Pairing is distinct — one male to one female, rather than the crowd of satellites that attends many salmonid spawnings.

The sea-run form runs on a fixed schedule. Young enter the sea at two years old and return to the rivers to spawn at four years or older. That gives at least two years of marine growth before the first spawning, and it is what produces the size difference between the two forms.

The water it needs

The species exists in two forms, and they use quite different water.

The landlocked form prefers cold streams, below 15°C. Summer records put the fish in water of 13 to 15°C — a ceiling with no margin in it, and one that a warming summer erases rather than shifts.

The sea-run form is anadromous, reaching depths of 50 m at sea, within an overall temperature range of 4 to 18°C.

What it eats

It is carnivorous, feeding on insects and plankton.

Plankton in the diet of a char is worth noticing. It implies feeding in open water rather than picking drift from a current, which fits a fish that spends part of its life at sea and part in lakes.

How to catch it

Which form you are fishing for decides everything. The resident is a cold-stream fish with a hard ceiling at 15°C, so it holds the coldest water in a catchment through the summer. The sea-run fish arrives on a schedule and is a different proposition in size and in timing.

A diet of insects and plankton points at small imitations rather than at fish patterns, which is unusual for a char that grows as large as this one.

The maximum recorded age is only nine years — fast growth for a cold-water char.

Conservation

The 15°C ceiling on the resident form is the mechanism, and it is arithmetic rather than opinion: summer water that already sits at 13 to 15°C has nowhere left to go. Each warm year pushes the resident populations further up their catchments, and the ones already at the top have no further to move.

The sea-run form needs the river passable in both directions on a two-year and four-year cycle, which makes any barrier costly out of proportion to its size.

Other names

White-spotted char in English, ame-masu and iwana in Japanese — the two names distinguishing the sea-run and resident forms, which English does not. That distinction is useful, since the two are so different in size and habits that treating them as one fish loses most of what matters.