Humpback Whitefish

Identification

The name is the field mark. Adults develop a pronounced hump behind the head, and beneath it sits an inferior mouth that points downward toward the substrate. Colour runs dark brown to midnight blue on the back, fading through silver on the sides to a white belly. The adipose fin is well developed and is typically larger in males. The tail carries a dark posterior edge (ADF&G).

It is a medium-sized fish. ADF&G gives a maximum length of about 20 inches and notes that most fish are smaller; the department’s education material describes fish reaching 22 inches and 5 pounds at eight years. Sampling in the Chatanika River has produced fish from 275 to 560 mm fork length, with the bulk of the mature run between 430 and 500 mm.

Distinguishing humpback whitefish from the other coregonines sharing its water is not straightforward and is one reason harvest records from the Interior lump them. Broad whitefish (Coregonus nasus) is the larger, heavier-bodied fish of lowland floodplains. Least cisco (C. sardinella) is smaller and more terete, seldom exceeding 14 inches in lakes though Chatanika River fish reach 19 inches and 4.5 pounds. Round whitefish (Prosopium cylindraceum) is a different genus altogether — cylindrical, seldom over 16 inches, and the resident whitefish of clear upland streams north of the Alaska Range (ADF&G, Whitefish Species of Alaska).

Taxonomy, which is genuinely unsettled

This is not a case of pedantic disagreement over a name. Authorities in current use disagree about how many species exist.

ADF&G calls this fish Coregonus pidschian, and so do ADF&G’s fishery management reports for the Tanana drainage. The Integrated Taxonomic Information System lists Coregonus pidschian as valid, with the common name humpback whitefish — and also lists Coregonus nelsonii, Alaska whitefish, as a separate valid species occurring in Alaska and Canada. The U.S. Fish and Wildlife Service maintains species pages for both names.

Against that, the most thorough synthesis of Alaskan whitefish biology treats the whole group as one species. Brown and colleagues describe a “Coregonus clupeaformis complex” containing three forms — C. clupeaformis, C. pidschian and C. nelsonii — and adopt the recommendation of McDermid et al. (2007) that there is a single North American species of humpback whitefish, which they call C. clupeaformis throughout (U.S. Fish and Wildlife Service, Alaska Fisheries Data Series 2012-4).

So the same fish is C. pidschian to the state agency that manages it, potentially C. nelsonii to a taxonomic database, and C. clupeaformis to the federal synthesis. This article uses C. pidschian because that is what ADF&G uses in Alaska, but readers should treat the binomial as a label of convenience rather than a settled fact.

Range and distribution

In Alaska the species occupies water bodies within the Yukon, Kuskokwim, Tanana, Kvichak, Susitna, Copper and Alsek river drainages, and ADF&G’s education material describes it as distributed throughout all drainages north of the Alaska Range. Six coregonine species are documented in the Tanana drainage alone: sheefish, broad whitefish, humpback whitefish, least cisco, Bering cisco and round whitefish.

Within the Tanana system the centre of humpback whitefish abundance is the Minto Flats wetland complex and the Chatanika River that drains it. Fish move out of Minto Flats into the Chatanika beginning in early June and spawn there in the fall (ADF&G Fishery Data Series 14-12). Radio-telemetry work summarised by the University of Alaska Fairbanks found a second, previously undocumented spawning area in the Tanana mainstem between Fairbanks and the mouth of the Salcha River: of 100 fish tagged in Minto Flats in 2009, 61 moved into the Chatanika and 39 entered the Tanana instead (UAF). ADF&G subsequently confirmed that the braided middle Tanana between the mouths of the Chena and Delta rivers supports humpback whitefish spawning (Fishery Data Series 18-36).

A point of precision matters for the clear-water tributaries near Fairbanks. Pre-spawning female humpback whitefish were captured in the Chena River (Alt 1987, cited in the USFWS synthesis), so the species does occur there. But the documented spawning waters in this drainage are the Chatanika and the Tanana mainstem, not the Chena or Salcha. ADF&G’s own description of the Chena is of “a clear to slightly tannic-stained stream containing resident populations of Arctic grayling and whitefish throughout its length” (Parker and Viavant 2000) — and a whitefish resident along the whole length of a clear upland stream is far more likely to be round whitefish, Prosopium cylindraceum, which is not a Coregonus at all. Anglers who catch a whitefish in the Chena or Salcha have probably caught a round whitefish; anglers on the Chatanika in fall have probably caught this one.

Habitat and water temperature

Humpback whitefish use the full gradient of an Interior river system across a year: lowland wetland complexes and floodplain lakes for feeding, mainstem rivers as migration corridors, and gravel-bottomed flowing reaches for spawning. They are bottom-oriented in all of them.

There is no published thermal optimum, stress threshold or lethal temperature for this species. That is worth stating plainly rather than substituting figures borrowed from lake whitefish or mountain whitefish. What can be sourced are the water quality criteria Alaska applies to fresh waters that support the growth and propagation of fish: such waters “may not exceed 20°C” (68°F) at any time, with 15°C (59°F) for migration routes and rearing areas and 13°C (55°F) for spawning areas and egg and fry incubation (Alaska Department of Environmental Conservation, 18 AAC 70). Those are regulatory criteria, not measurements of what this fish can survive, but they bracket the conditions Interior rivers are managed to hold.

What is documented biologically is the cold end. Eggs are deposited in fall and incubate through the winter at water temperatures only slightly greater than 0°C, hatching the following spring. In practical terms, a river’s whitefish spawning success is set by conditions under the ice, months after the fish that produced the eggs have left.

Life history

The migrations are the striking part. ADF&G documents spawning movements of over 500 miles up the Kuskokwim River and over 1,300 miles up the Yukon. Spawning occurs from September through November depending on the system, over gravel in flowing water. In the Chatanika it is concentrated between mid-September and early October, with the downriver migration executed immediately afterward.

Age at first maturity varies enormously with latitude and productivity — as young as 4 years in the Kuskokwim, as late as 11 years near the Arctic Ocean. Some populations are anadromous.

These are long-lived fish, and older than most anglers assume. In the Chatanika, otolith ageing showed that the 430–469 mm length classes making up 47 percent of the population were 10 to 16 years old, and fish of 500 mm or more ranged from 12 to 27 years. Recruitment into the assessed population occurs at age 5 to 8, at roughly 380 to 409 mm fork length. A 20-inch Chatanika whitefish is plausibly older than the angler holding it.

Diet

Juveniles feed mainly on zooplankton. Adults are benthic feeders, taking mollusks, crustaceans and chironomid larvae, and the inferior mouth is the tool for it — clams, snails, aquatic insects and larvae worked off the bottom of streams and lake margins. This bottom-feeding habit is what makes whitefish central to subsistence food webs and also what makes them useful as an integrator of benthic productivity in systems where few other fish occupy that niche.

Angling

Humpback whitefish are among the most important subsistence fish in Alaska, taken across the Colville, Kuskokwim, Yukon and Kvichak drainages, and in the Tanana they are regularly taken in food fisheries at Nenana and Minto alongside sheefish and broad whitefish.

The Chatanika River is the exception in recreational terms: it has supported a prolific and popular recreational spear fishery targeting humpback whitefish since the 1970s, prosecuted at night in late fall when the fish are staged on the spawning gravels and visible in shallow, clear water. It is a genuinely distinctive Interior Alaska fishery, and it is a visual one — the fish are found by light rather than by fly or bait.

Rod-and-line encounters are incidental. The small inferior mouth and benthic diet mean humpback whitefish are rarely the fish a Tanana-drainage angler is targeting; ADF&G’s Tanana management report notes only that humpback, broad and round whitefish “are caught occasionally by sport anglers.”

Conservation

The species carries no federal Endangered Species Act listing. The management story that matters is the Chatanika.

The spear fishery peaked in 1987 at more than 25,000 fish taken, then collapsed. The directed fishery was closed from 1994 to 2007. Stock assessment resumed afterwards: in 2008 ADF&G estimated 22,490 humpback whitefish of 360 mm or larger in the study reach, with about 60 percent of sampled fish at 440 mm or larger and relatively few small fish present — a population weighted toward old, large individuals with weak recruitment behind them (Wuttig 2009). By 2012 the estimate for the 50 km study area was 12,755 fish of 360 mm or larger, with 71 percent between 430 and 499 mm.

The University of Alaska Fairbanks assessment of the same period was cautiously positive. Comparing size, age, growth and mortality rates, Trent Sutton concluded that “humpback whitefish appear to have recovered.” The two ADF&G abundance estimates, taken alone, do not obviously support that reading; the difference lies in what is being measured — demographic structure versus a point estimate of numbers in a defined reach — and readers should note that the assessments emphasise different things rather than assume one supersedes the other.

The broader concern for the species is not harvest but the taxonomic uncertainty itself. A management unit whose species boundaries are contested is a management unit whose stocks are hard to define, and the Interior Alaska coregonines are managed and reported as a group precisely because separating them in the field and in the catch record is difficult. That is a live problem, not a resolved one.