Fly fisherman using flyfishing rod in beautiful river.

The reproduction of trout and salmon on our Gaves

This article is written using the example of the reproduction of salmonid populations in USA. More precisely, the gaves basin in the Pyrénées-Atlantiques.

Do not hesitate to browse it because the information there is certainly very close to that which you will find on your territory. 

Observation of reproduction and counting of spawning grounds :

We are at the beginning of December and the reproduction of salmonids is preparing on our Gaves. The salmon and trout select the spawning grounds and there is no doubt that they will soon be busy!

This year, after a month of November under the sign of rain (400 millimeters fallen on the foothills), the substrate will be loose, which suggests a reproduction with high oxygenation of the buried eggs and therefore probably a high survival rate of fry. Still to be confirmed depending on upcoming events.

I invite you to enjoy the show which will last a few weeks on the gaves and their tributaries.

Observation of the spawning grounds during the reproduction of trout and salmon on the gaves

To find out a little more, I invite you to read this article on the reproduction and functioning of the spawning grounds.

If you do not know the mechanism of the reproduction of brown trout and Atlantic salmon, you will learn the essentials when you read it.

The reproduction of salmon trout fario and Atlantic salmon:

Salmonids, “Salmo trutta” trout and “Salmo salar” Atlantic salmon, represent the reference species inhabiting rivers with fresh and flowing waters.

Each year at the same time, these species are governed by their biological cycle. One of the stages of this mechanical cycle ensures the natural renewal of the workforce, this is the reproduction period.

This act delivers a visual spectacle of rare beauty to those who are interested in the life of aquatic environments and have a simple sense of observation.

The analysis of this period can (in the same way as monitoring of catches during the fishing season, or a fish inventory by electric fishing in autumn) indicate to the environment managers the evolution of the numbers present in the fishing grounds. 1st category of water.

Spawning ground observed on the Aspe river

This winter monitoring makes it possible to ensure overall control of the populations and also to assess the possible recruitment to hope for the next fishery years.

It also makes it possible to keep watch over rivers during a period when its surroundings are deserted, a period which is however so crucial for the development of fish populations.

These fish, manipulated by the importance of the act, become less savage and can be subject to poaching.

Fortunately, this malevolence is isolated and rather rare; lovers will then take advantage of the exceptional opportunity to get up close to the salmonids that spawn right there in front of us, a few meters from the shore.

These observations, which have been renewed over the years, also lead to examining the evolution of habitats, flows, water quality, weather, etc.

The indications of possible modifications directly influence the overall result of the spawning (modification of the aggregate of the spawning grounds, the variability of the currents, submerged surfaces, tides due to hydroelectricity, progressive amplification of the temperature, erosion of the banks, depletion of riparian, clogging, effects of floods …).

Unfortunately, most of these changes are directly related to human actions and the need for comfort in the modern world.

Preservation requires constant awareness, public awareness seems to be on the right track. The defense of the living in the face of the collapse of biodiversity gives even more weight to the safeguard of our aquatic environments.

Although lobbying is still our steward for a while, it is good to hope for a better future and much more respectful of mother nature.

Beautiful spawning grounds have seen on the Gave d’Oloron

By the way, I come back to the subject of the reproduction period and I will give you some information necessary to better understand this phase of the salmonid cycle.

Principles of the reproductive phase:

For trout, the reproduction time window is between the months of November to February with a peak in December.

Salmon spawn during a shorter window, from the beginning of December to the end of January, but often following the peak of activity of the various.

Photoperiod plays an important role in the stimulus that triggers the act of reproduction. The shortest days often represent the most favorable period for live visible reproduction.

The water temperature also acts on behavior, cooling after a fairly mild weather period triggers a great spawning activity on the river.

The characteristics of the spawning ground must correspond to the requirements of the salmonids: a clean pebble or gravel bottom of 2 to 8 cm in diameter, with good interstitial infiltration (which ensures the oxygenation essential for the good embryonic development of the buried eggs in the substrate), a current speed ranging from 40 to 80 cm / s under a water cover of 20 to 50 cm in general.

Underwater view of an Atlantic salmon spawning ground

On a profile along the river, the drop-off sites are often identified at the tail end (or hole) in the pre-raft area.

Sometimes but more rarely we can locate them at the head or entry of the wetlands, very regularly on areas where the water layer tightens both in height and in width.

This constriction induces an acceleration of the speed on which the female salmonid will lean during the cleaning and the digging of the spawning ground carried out with its caudal fin.

The fine particles in the substrate will then be evacuated by the force of the current downstream, towards a next pool.

Small trout will prefer areas close to the shore or under plant cover. Large trout and salmon can sometimes be satisfied with a central area on the watercourse. But they too prefer the reassuring areas of the banks, especially if the central bed is too open to the sky.

The female chooses the place of deposit, after a few surveys with her tail, she validates or not the site of the nest. Then begins cleaning the spawning ground in search of the best location. It then goes on to dig the nest which will be used for removal. The size of the spawning ground is proportional to the size of the female that created it.

A couple of trout on a large spawning ground

The female chooses her partner for mating, the pheromones attract with him other congeners who make up the cohort of dominated or peripheral males.

In general, couples are made up of individuals of close size. The male comes regularly to cross the female to stimulate her, sometimes comes to vibrate at her side. But in all cases, it ensures its role as a dominant male by inexorably chasing away the intrusive males to offer certain tranquility in the work to his partner and to agree on a couple of relationships.

Fario trout on their spawning grounds

The female is mature, she expels her eggs in the bottom of the spawning ground sheltered from currents. The male glued to it participates in reproduction by mixing its milt with the eggs in order to fertilize them. They act stiffened bodies and open jaws for a few seconds.

The sperm will have to fertilize the female’s oocytes in less than about 25 seconds to ensure the viability of the egg.

During the act of fertilization, it often happens that peripheral males (as well as sperm parr in the case of salmon) participate in turn following the dominant male.

At the end of the act, the female covers the eggs by “sweeping” the gravel and pebbles located on the upstream periphery.

Recovery work

Fertility is slightly different between the two species, around 2000 eggs per kilo for a trout, slightly less for a salmon. The eggs are large compared to other fish species, around 4mm for trout and 5mm for salmon, they are also more resistant.

The incubation period is also distinct, it is expressed in degrees x days. Hatching takes place at around 420 degrees x days for trout (either 42 days under 10 degrees water for example or 84 days under 5 degrees water), 480 degrees x days for salmon.

But life under gravel does not stop there!

And this point seems fundamental to me, too often forgotten by fishermen. Follows the period of resorption of the yolk sac, ventral pocket ensuring a reserve of food, which lasts 310 degrees x days for the trout and 410 degrees x days for the salmon. Before they reach the fry stage and are sufficiently mobile to leave the spawning area, they remain vulnerable and limited in their movement.

Free then of this ventral pocket which is absorbed, they start to swim in search of food and an adapted habitat.

This suggests that life under gravel and on the outskirts are important in terms of duration. As an example and for simulation, it is good to summarize in tables the stages and duration of spawning with spawning carried out on various dates