NATURAL TROUT REDDS IN WINTER

One of my favourite winter activities is walking along the river in search of new fishing spots for the season ahead. It is also a valuable opportunity to observe the condition of the water and the river environment. With water levels generally lower at this time of year, the banks are much easier to explore. We can follow the river in search of natural trout redds, the areas of clean gravel where fish lay their eggs, which provide us with a useful indication of the health of the local fish population.

Unfortunately, winter can feel like an ordeal for freshwater anglers. The fishing season is closed, yet the rivers look magnificent. All we can do is look back on the excitement of the previous year, dream about the fish we might catch next season and perhaps set off in search of new fishing spots. Along the way, we also have the chance to see how this year’s natural spawning is progressing.

That is exactly why, on a sunny Sunday in December, my friend and colleague Marco and I headed to the Adige for a survey.

Our first stop

We began at a traditional spawning site in Zone B, managed by the Associazione Pescatori dilettanti Vallagarina, which we monitor every year.  Unfortunately, the level of the Adige was slightly higher than expected because of water releases from the Mori dam. As a result, we spotted only around ten redds, all in the most open and shallow areas. The relatively small number may also reflect a trend we have observed in recent years. Trout appear to be spawning later, possibly because of increasingly high temperatures during the autumn and winter months and the wider effects of climate change. 

We therefore decided to travel farther north, upstream of the dam. I had noticed that the river flow was lower there and the conditions seemed more suitable for searching for spawning areas, including some outside the usual, well-known locations.

Searching the riverbank

As soon as we reached the bank of the Adige, we began walking and carefully scanning the shallows along the water’s edge. We were looking for the characteristic patches of lighter-coloured gravel that reveal the presence of a redd.

As we walked, we chatted about how beautiful the river looked that day and how wonderful it would have been to fish it in those conditions.

Eventually, we reached our first group of redds. There were around ten of them, all concentrated within a fifty-metre stretch of river.

This spawning site seemed to be shared by both inexperienced fish and a few seasoned veterans. You can immediately recognise the work of trout spawning for the first time. They often choose sections of the bank that may later be left exposed when the water level fluctuates.

The more experienced fish, on the other hand, seem to know exactly where to lay their eggs so that the redds remain safely covered by water. To our delight, we found one particularly large redd, approximately one metre in diameter, suggesting that a sizeable trout had spawned there.

We climbed down onto the riverbed to try to take a few photographs, but unfortunately our efforts came to nothing. The light was poor and some of the redds had already been left exposed by the changing water level. We decided to put the camera away and continue our search.

Life beneath the stones

We also took the opportunity to turn over a few stones and examine the river’s benthic life.

We found numerous empty caddisfly cases, a few freshwater shrimps and some Baetis larvae. It was nothing extraordinary and, to be honest, I had expected to find more. Nevertheless, considering the time of year and the very cold water, we could hardly complain.

We also watched a few mayflies being gently carried along by the current. Sadly, they drifted downstream undisturbed, with no sign of a fish rising to take them.

We then moved farther downstream, where the water begins to deepen and the riverbed is normally difficult to see. Thanks to the exceptionally low water level, however, we were able to identify a few more isolated redds.

One last attempt

To complete our survey, we decided to explore upstream of the area we had examined during the afternoon.

Here, the river flows through a fast riffle that is usually deep enough to conceal the bottom completely. I know, however, that some of the largest fish in this part of the river choose this spot to spawn. It is quiet, undisturbed and, most importantly, protected by a consistently substantial depth of water.

That afternoon, the river level was ideal for spotting any redds that might have been present. Unfortunately, we arrived too late. With the sun already beginning to set, there was no longer enough light to see the riverbed clearly.

A living river

At the end of our survey, we were able to confirm that the river is alive and that natural reproduction is taking place, particularly in the traditional spawning areas where fish have historically laid their eggs.

We did not find a particularly large number of redds. This could suggest that the fish population is smaller than in previous seasons or that it may be declining.

However, we must also consider the pattern observed over the past few years. Trout, especially marble trout, appear to be delaying their spawning, probably because of the unusually high water and air temperatures recorded during the autumn and the first part of winter.

It would therefore be useful to return to the same areas after a few weeks. If the situation remained unchanged, the limited number of redds might indicate a relatively small fish population. If new redds appeared, however, it could be a sign that the trout’s spawning habits are changing in response to environmental conditions.

Lorenzo Casetti