Coho salmon

Coho salmon habitat is unusual among Pacific salmon because the freshwater phase is long and the habitat it requires is small.

JUVENILES SPEND A FULL YEAR OR MORE IN FRESH WATER, unlike pink or chum salmon which go to sea almost immediately. That extended rearing makes coho more dependent on freshwater habitat quality than any other Pacific salmon.

AND THE HABITAT THEY NEED IS SLOW, COMPLEX AND SMALL. Juvenile coho use pools, side channels, beaver ponds, off-channel wetlands and woody debris — low-velocity, structurally complex water rather than the fast riffles other salmonids favour. Winter refuge habitat of this kind is frequently the limiting factor on a whole population.

WHICH IS WHY CHANNELISATION HURTS THEM MOST. Straightening a stream, removing wood and disconnecting side channels removes exactly the habitat coho juveniles depend on, and coho declines in developed catchments track that loss closely.

SMALL COASTAL STREAMS SUPPORT THEM DISPROPORTIONATELY, and coho use tributaries too small for larger salmon.

ADULTS AT SEA OCCUPY COASTAL AND SHELF WATERS, generally closer inshore and for a shorter period than chinook, before returning.

AND ESTUARIES ARE A REAL TRANSITION HABITAT, used for physiological adjustment and feeding in both directions, and frequently the most degraded part of the whole path.

Coho spawning follows the Pacific salmon pattern — a single reproductive event followed by death — with a distinctive preference for small water.

ADULTS RETURN IN AUTUMN AND EARLY WINTER, entering rivers on rising flows after autumn rain, and they penetrate far into small tributaries that larger salmon cannot use.

THE FEMALE CUTS A REDD in clean gravel, generally in the tail of a pool or the head of a riffle where flow draws water down through the substrate. She defends it after spawning until she dies.

SPAWNING IS SEMELPAROUS. Adults die after spawning, and the carcasses deliver marine-derived nutrients into the stream — a genuinely important input to the productivity of the whole system, including the food supply of the next generation.

INCUBATION RUNS THROUGH WINTER, with emergence in spring, and fry then remain in fresh water for a year or more.

RAIN AND FLOW ARE THE PROXIMATE TRIGGER for river entry, so run timing shifts with the weather rather than with a date, and a dry autumn holds fish in the estuary.

JACKS ARE PART OF THE STRATEGY. A proportion of males return precociously after only a short time at sea, sneaking spawnings rather than competing directly, which is a genuine alternative reproductive tactic rather than an anomaly.

AND HATCHERY INFLUENCE IS PERVASIVE across much of the range, which complicates any statement about wild coho reproduction and is worth knowing before reading run statistics.

Coho pass through a physiological transformation between the sea and the gravel, and a fish's position along that path decides how much handling it can survive — which means the same technique produces different results on the same river in the same week.

A BRIGHT FISH, freshly in from salt water, is at its physiological peak: full energy reserves, intact scales, a working immune system, an unmodified body. It can absorb a fight and a release, and it has the reserves to complete everything that follows.

A COLOURED FISH, weeks into fresh water and into spawning condition, is a different animal. The body has been reabsorbing itself to fuel the migration and to build gonads. The skin thickens and the scales become embedded but the mucus layer and immune function decline, fungal infection becomes common, and the fish is running down a reserve that is visibly close to exhausted. It has less to spend on recovering from a fight and less capacity to resist an infection introduced by a hand that removed its mucus.

THE PRACTICAL CONSEQUENCE IS THAT HANDLING SHOULD GET MORE CONSERVATIVE AS THE SEASON GOES ON, which is the opposite of what usually happens — anglers get more casual as fish get more numerous and less valuable-looking.

What the fish needs is the same in both cases and matters more in the second: a short fight, wet hands or none at all, no lifting clear of the water, no contact with dry gravel or a dry bank, and a release facing into current until it holds itself. Coloured fish especially should be handled through the net or not at all.

AND THE FISH ON THE REDDS ARE OFF LIMITS, for the same reason as every other Pacific salmon: they are doing the only thing left that they exist to do, and in most places targeting them is a legal question answered locally rather than a judgement call.

Coho seasonality is more consistent than chinook's and it is defined by two features: a late run, and an unusually long freshwater juvenile stage.

THE ADULT RUN IS LATE AND RAIN-DRIVEN. Coho typically return to fresh water in autumn and early winter, and entry is strongly cued by rainfall raising river levels — a dry autumn holds fish off the coast and a heavy rain event moves them in a rush. That makes coho river fishing far more responsive to weather than to date: the same week can be empty or full depending on what the sky did.

THEY SPAWN IN SMALL TRIBUTARIES, WHICH SHAPES EVERYTHING. Coho favour small streams and headwater tributaries rather than main stems, and that is a habitat preference with a seasonal consequence — those small waters are only accessible when flows are up, so the run timing and the rainfall are functionally the same variable.

THE JUVENILE STAGE IS THE LONG PART AND IT IS THE BOTTLENECK. Coho fry typically spend a full year or more in fresh water before smolting, holding in pools, side channels, off-channel ponds and beaver ponds. That means a coho population depends on year-round freshwater habitat quality — summer low flows, winter high flows, and refuge from both. Winter habitat in particular, where juveniles shelter from scouring flows, is a recognised limiting factor.

SO THE SEASONS THAT MATTER MOST ARE NOT THE ONES ANGLERS SEE. Summer drought and winter flood in a small tributary determine how many fish return two or three years later, and neither event involves an adult salmon.

AT SEA THEY ARE SHALLOWER AND MORE SURFACE-ORIENTED THAN CHINOOK, feeding aggressively on baitfish in coastal waters through the summer and putting on weight rapidly in the final months before returning. The late-summer coastal fishery is that feeding phase, and the fish are in prime condition then and deteriorate rapidly once they enter fresh water.

JACKS COMPLICATE THE PICTURE and are worth naming. A proportion of males return a year early at small size, which changes the size composition of a run and is a normal part of the life history rather than a defect.

AND FISHERIES FOR THEM ARE MANAGED IN-SEASON AND BY POPULATION. Wild and hatchery fish are frequently treated differently, and marking, retention and closure rules change year to year. The competent authority is the only source.