White sturgeon

White sturgeon are handled under some of the strictest rules applied to any sport fish, and the rules describe the handling problem accurately.

THE FISH MUST STAY IN THE WATER. Several of the major fisheries for this species have adopted rules forbidding a sturgeon to be lifted clear at all, and the reasoning is not decorative: a very large, elongated, heavy-bodied fish taken out of the water is unsupported along its length, and the internal damage is severe. There is no correct way to lift a large sturgeon, which is why the restriction is written as a prohibition rather than as advice. What applies where you are fishing is a question for the managing authority, and it changes.

THE SCUTES ARE THE HAZARD TO THE HANDLER. The rows of bony plates along the body are hard and sharp-edged, particularly on younger fish, and a hand run along a sturgeon's flank is cut. The animal is otherwise harmless — the mouth is a toothless protrusible tube for vacuuming the bottom and cannot injure anybody.

HANDLE IT ALONGSIDE, IN THE WATER, facing into current, with the fish supported and the hook removed with a long tool. Where a measurement is required, it is taken with the fish in the water.

AND THE REASON BEHIND ALL OF IT. Sturgeon are among the longest-lived and latest-maturing fish anybody catches. A large white sturgeon may be many decades old and may not have spawned many times. The species is depleted across much of its range and several populations are formally protected. The care is proportionate to how long it would take to replace one, which is longer than a human career.

White sturgeon reproduction combines two features that between them explain why this ancient lineage is in trouble almost everywhere it occurs.

THE FIRST IS INTERMITTENT SPAWNING. Females do not spawn annually. They accumulate the resources for a reproductive event over a period of years, spawn, and then rebuild — so at any moment only a fraction of the mature females in a population are reproductively active. The consequence is that a population's actual reproductive output is far smaller than its adult numbers suggest, and a count of large sturgeon substantially overstates how many are contributing in a given year. Combine that with very late maturity — many years before a fish spawns at all — and very long life, and you have an animal whose population arithmetic operates on a timescale of decades.

THE SECOND IS AN ABSOLUTE HABITAT REQUIREMENT. White sturgeon spawn in spring in fast flowing water over rock and cobble, broadcasting adhesive eggs that stick to the substrate and develop in the flow. That specific combination — high current, coarse clean substrate — occurs in particular reaches and nowhere else, and the fish must reach those reaches to spawn.

AND THAT IS WHAT DAMS REMOVE. A barrier between the adults and the spawning gravel does not reduce recruitment; it eliminates it. The adults persist — sturgeon live long enough that a population can appear stable for decades while producing nothing — and the population is functionally extinct long before it looks like it. Several white sturgeon populations are in exactly that state, maintained visibly by old fish with no natural recruitment behind them, which is why hatchery programmes exist for them.

IMPOUNDMENT DOES A SECOND THING, which is to remove the flow itself. A spawning reach behind a dam may still be accessible and no longer function, because the current that kept the gravel clean and oxygenated the eggs has gone.

SO THE CONSERVATION LOGIC FOR THIS SPECIES IS ABOUT RIVERS RATHER THAN ABOUT FISHING PRESSURE, and the fisheries that exist are managed accordingly. What is permitted where is current local information and varies enormously between river systems.

White sturgeon occupy deep river and estuary bottom, and the striking thing about their habitat is how much of a river system a single population requires.

THE ADULT HABITAT IS DEEP, SOFT-BOTTOMED WATER IN LARGE RIVERS AND ESTUARIES. Sturgeon work the bottom of deep holes, channels and slow reaches, feeding by touch and chemoreception with barbels and a protrusible tube of a mouth, taking invertebrates, molluscs, eggs and fish. They are benthic in the strictest sense — the fish is built to operate lying on the bed of a big river.

THEY MOVE BETWEEN FRESH AND SALT FREELY, and that is unusual and important. White sturgeon are anadromous in the loose sense: many individuals move into estuaries and coastal waters to feed and return to fresh water, while others remain in the river throughout. Some populations, landlocked above dams, complete the whole life cycle in fresh water. So the same species may be an estuarine feeder in one system and a purely riverine animal in another.

THE SPAWNING HABITAT IS SPECIFIC, DEEP AND FAST. Sturgeon spawn over coarse substrate in high-flow reaches during spring freshet, with adhesive eggs settling into the interstices of cobble and boulder in strong current. That combination — big flow, coarse clean substrate, adequate depth — occurs in a small number of places within a river, and it is precisely what impoundment removes: a dammed river loses its freshet, loses its high-flow reaches, and buries its coarse substrate under fine sediment.

WHICH IS WHY SEVERAL POPULATIONS ARE LOCKED IN AND FAILING TO RECRUIT. Above dams, adult sturgeon may persist for decades — this is an extremely long-lived fish — while producing almost no surviving young, so the population looks stable and is not. An ageing population of large fish with no juveniles is the diagnostic signature, and it is a habitat failure with a very long lag.

LONGEVITY MAKES THE HABITAT ACCOUNT A CENTURY-SCALE ONE. A large white sturgeon may have been in that river for many decades and matured slowly, so recovery from any habitat loss operates on the same timescale.

AND THE FISHERY IS SHAPED BY ALL OF IT. Where white sturgeon are fished recreationally they are frequently managed as a strict catch-and-release or slot fishery with substantial restrictions, and those arrangements differ by river, by reach and by jurisdiction. What applies on any particular water is a matter for the competent authority.

White sturgeon seasonality separates cleanly into two independent cycles — a reproductive one tied to river flow, and a feeding one that barely stops — and confusing them produces most of the misunderstanding about the species.

THE SPRING FRESHET IS THE REPRODUCTIVE TRIGGER. Snowmelt and rainfall raise flows in spring, and spawning is cued by that rise together with temperature. Adults move to specific high-flow reaches with coarse substrate, and the eggs settle into the interstices of cobble in strong current. The record's spawning material explains why that combination is so specific and why impoundment removes it: a regulated river with a flattened hydrograph has no freshet to trigger anything.

BUT THEY ARE NOT ANNUAL SPAWNERS. Individual white sturgeon spawn at intervals of several years rather than every year, so the spring event involves only part of the mature population. That is unusual and it means a poor year is not simply made up next season.

FEEDING IS A YEAR-ROUND ACTIVITY AND IT SLOWS RATHER THAN STOPS. Sturgeon work the bottom by touch and scent, which is unaffected by light or turbidity, and they continue feeding through winter at reduced intensity. That is why the species supports fisheries across most of the year while a salmonid in the same river does not.

WATER TEMPERATURE MODULATES ACTIVITY, with feeding strongest in the warmer months, and in tidal and estuarine reaches the movement between fresh and salt water follows both temperature and prey availability.

PREY PULSES DRIVE LOCAL SEASONALITY MORE THAN ANYTHING. A run of spawning salmon, a smelt or lamprey run, or an eulachon run concentrates sturgeon dramatically, and these seasonal food events are the single most reliable predictor of where fish will be — a seasonality inherited from another species entirely.

AND THE REGULATION IS SEASONAL, LOCAL AND CHANGEABLE. White sturgeon fisheries operate under slot limits, catch-and-release-only periods, area closures and in places complete prohibition, differing by river and by reach. Nothing above indicates what any of them are; the competent authority does.