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The early run fish are now spawning with the majority of trout still a way off yet. Read on for what to look for and avoid on this, the last weekend of the season.
This weekend marks the end of the Trout Season on the rivers of Victoria. As expected the early fish have started to spawn in the past 10 days with the vast majority not yet on the job. Despite the politics going on at the moment between those who want the closed season extended and those who do not, there is an underlying common desire shared by most of us. That is the protection of any trout already spawning.
Spawning is the name for trout reproduction. The process of female trout laying eggs and male trout fertilizing the eggs is spawning. Many factors influence the place where a trout may spawn. They include:
- Stream bottom (usually gravel)
- Water depth (between 6-24 inches)
- Water velocity
- Stream cover (trees, bushes, logs, etc.)
Brown trout in our district spawn during late May, June and early July, depositing their eggs in saucer-shaped nests called redds, which are dug by the female in the clean gravel lining the bottom of streams. The redd is created by the female fish while lying on its side and rapidly beating its tail in an up-and-down motion, allowing the current to move the gravel slightly downstream See Photos 2 and 3. When she is finished building the redd, she then lays her eggs and the male fertilizes them. Usually one but up to two males can sometimes fertilise the eggs.
The female travels upstream and begins to dig another pit. She does this so that the gravel from the new pit will be carried downstream and thus cover the eggs she laid in the redd. The female moves to the upstream edge of the redd, again beating its tail on the stream bottom, burying the eggs in gravel. After spawning is completed, the eggs are abandoned. The eggs incubate through the winter, hatch during late winter, and the tiny fry emerge from the gravel some six weeks later on average. This whole process is, of course, temperature dependent. With a constant water temperature of 10 degrees Celsius hatching occurs in 41 days. The number of eggs produced depends on fish size. An 8-inch mature brown trout may spawn 200 eggs, while a 10-pound female might spawn over 8,000 eggs. Males usually become sexually mature at two years of age and females at three.
After the eggs are fertilised they begin developing. The first stage of development is the eye. A yolk sac, that provides nutrients to the small fish, then develops. These small fish are called 'sac fry'. When the yolk sac is absorbed the small fish make their way out of the riverbed gravel. The incubation time as mentioned earlier depends on water temperature with the warmer the water the faster the development.
It is very important that water flows through the gravel to allow oxygen to make its way to the eggs. Sediment can interfere with this process. Some of the natural causes of sediment are fires (Gippsland several years ago) and mudslides. Man-made causes include overgrazing, poorly designed roads and digging near stream beds.
When you factor in all of the possible limiting factors on trout spawning successfully you soon see that the odds are really stacked against them. So what can we do? Well we can firstly not target these fish during this vulnerable time. We fish for sport and their is little sporting value in catching a fish that is too concerned with sex to worry about self preservation. Secondly we can avoid walking on these redds and adding to the mortality rate. These early spawning fish should be allowed to go about it in peace.
Watching trout spawn can be one of the most interesting experiences a fly fisher can ever have. Getting close to a large fish on the gravel is exciting even to the most experienced of anglers and it really is a privilege to be able to watch it . We would recommend that next time you are out on the river that you take a look. Leave the rod in the car, take a sandwich and a camera and enjoy the show. It is something special that we should all protect for when all is said and done it is the future of our fishery.