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A strategic cycle
When the water reaches 6 to 12°C and winter floods inundate the edges, the spawning pike (males from 2 to 3 years of age, 35 to 45 cm, and females from 3 to 4 years of age, 45 to 55 cm) move to submerged meadows, reedbeds and calm annexes. The female releases her eggs onto the submerged vegetation, where they attach themselves thanks to their adhesive envelope.
The males deposit their milt to fertilize them. Fertility is high: a female generally produces between 15,000 and 40,000 eggs per kilogram of body weight. A 6 kg female can lay between 90,000 and 240,000 eggs, and a very large 10 kg female can lay over 300,000 eggs.
We now know that large females play a decisive role in population renewal. Not only do they produce more eggs, they also produce better quality eggs. For this reason, some federations have implemented a reverse mesh, or catch window: fish below a minimum size remain protected, but very large individuals are also protected, in order to preserve the best spawners. The aim of this approach is to maintain a balanced age pyramid and secure the reproductive potential of the environment, in keeping with the protection of the spawning period.
Incubation and degree-days: precise thermal mechanics
Hatching does not depend on a fixed number of days, but on a thermal accumulation expressed in degree-days. The principle is simple: average water temperature multiplied by the number of days. For pike, it takes around 120 degree-days to reach hatching, which means that in water at 10°C, incubation lasts around 12 days (10 × 12 = 120). At 8°C, incubation takes around 15 days. At 6°C, it will take almost 20 days.
Throughout this period, the eggs must remain submerged and properly oxygenated. A premature drop in water level or clogging of the seagrass beds can lead to massive mortality. In correct but not optimal natural conditions, studies show that 30 to 70% of fertilized eggs hatch, whereas in a degraded context (clogging, asphyxia, water withdrawal), this rate can fall below 20%. Taking a theoretical example of an 8 kg female laying 200,000 eggs, if 60% hatch, this represents 120,000 larvae. The figure still seems considerable. But this is where the most critical phase begins.
The larval and post-larval phase: the silent hecatomb
After hatching, the larvae remain attached to the vegetation for a few days, living on their yolk sac (food reserve). Then they become planktonophagous. There are many causes for this: predation by aquatic invertebrates, predation by whitefish, temperature variations, drying up of shallow areas, lack of planktonic resources, etc.
In most natural environments, less than 5% of larvae reach the juvenile stage of a few centimetres in length. 120,000 larvae with a survival rate of only 5% = 6,000 fry of a few centimetres in length.
Pike are fish-eaters from an early age. As soon as a size differential appears, the most developed individuals consume their congeners. This early cannibalism is a natural regulatory mechanism. It enables dominant individuals to grow rapidly, benefiting from a rich energy resource. In some cases, up to 30-50% of post-larval losses can be attributed to cannibalism.
This phenomenon is accentuated when flooded areas are small, initial densities are high or alternative food resources are limited. For example, of the 6,000 fry in our example, it is not unusual for only 1,000 to 2,000 to reach the end of the first summer.
From juvenile to adult: a progressive filter
Mortality doesn't stop there. Predation by fish-eating birds, by other carnivores, harsh winters, disease, fishing pressure... each year further reduces numbers. Under typical natural conditions, less than 1% of eggs laid reach the age of one year, and only 0.1 to 0.5% reach sexual maturity.
In concrete terms, out of 200,000 eggs laid, a few hundred will become pikelets of the year, a few dozen will reach two or three years of age and only a handful will become breeding adults. These ratios show that high initial fecundity compensates for extreme mortality. This is not a comfortable surplus, but a fragile balance.
The complete cycle therefore relies on three major conditions: reaching the 120 degree-days required for hatching without premature water withdrawal, maintaining flooding for three to four weeks to allow feeding to begin, and providing a sufficiently large habitat to limit density and hence excessive cannibalism. However, the damming of rivers, the reduction of flood plains, agricultural drainage and climatic variability are reducing the duration of floods. Water sometimes withdraws before the necessary thermal accumulation is reached.
A closure that protects a process, not just fish
During spawning, pike are grouped together in little water. They are vulnerable. Catching them at this time, even if no-kill, can disrupt reproduction and reduce the synchronization of spawning. But beyond the protection of individuals, the closure protects a short biological window, measurable in a few hundred degree-days. A hydrological interruption or repeated disturbance during this phase can compromise an entire age class.
Pike reproduction is not a surplus-producing machine. It's a tight equation where every parameter counts. Respecting the spawning period means allowing these few hundred degree-days to occur without disturbance. It means accepting that only a handful of individuals will ensure the next generation.
Beneath the surface, everything is silent and fragile. And these figures remind us of one essential thing: if nature produces much, it wastes nothing.
