Anna: Atlantic salmon become increasingly willing to migrate to the spawning grounds with time in the Autumn. Migration to the spawning grounds is the opposite of fallbacks. You may e.g. look up this paper by D. Tetzlaff, C. Soulsby, A. F. Youngson, C. Gibbins, P. J. Bacon, I. A. Malcolm, and S. Langan (2005) Variability in stream discharge and temperature: a preliminary assessment of the implications for juvenile and spawning Atlantic salmon. Hydrol. Earth Syst. Sci., 9, 193-208.

Thus, it may be helpful to release the fish closer to spawning time when they physiologically are more motivated to migrate.

Thank you Bror!

I agree that is would be better to transport them closer to spawningtime but there is a fear to lose some of the genetic diversity in the population if the ones in the early run dont get transported up. To let them wait below the first power plant would mean months of just searching for a way up? Is there a risk they would give up and move back to the lake? Searching for a way passed the power plant is also quite hard and we see injury's on the fish from jumping in concrete and so on so longer time below there would probably cause more injurys. Also the fishingpressure is quite intense in that area.

Do you think there is a way to keep them up in the river once they are released? Electricity barrier? Or could it help to drive them further up and give them a chance to move downstream a bit without falling behind the powerplant? 

I will look up the paper!

Tack så mycket!

Anna;

If possible, I would keep them in a net pen in still water until closer to spawning. I do not think their motivation for migration will decrease. On the contrary, it will increase. 

That would be interesting to test.

Thank you!

You are trying to enhance the salmon production by transplanting salmon and thus want the transported salmon to stay above the dams? Or do you have some other recearch objectives? Transporting salmon further upstream will most likely reduce the proportion of fish moving downstream. And, as Bror already mentioned, transporting and releasing fish later in the season will have the same effect. But some fish will probably move downstream anyway, that is just normal salmon behaviour.

Couple of years ago, we transported 6 radio-tagged adult salmon 80 km upstream above two hydroelectric dams to a tributary river. Transportation took place two months before the spawning, on August 23. After release the fish moved only upstream and they all stayed in the tributary river over the spawning season.

You may be interested in this also:

Conference Paper Restoring the Atlantic salmon stock of the River Tuloma - a ...

Thanks Petri!

We have looked at migration behaviours at  different times, early in the season (may-june) and late (aug-sept). The management in the river transport fish to sustain the wild population (there are no fishways). I would like to see if there is any measure we could do to diminish the losses of fish in the early run. We dont see the same fallbackrate in the late run, propably because they are highly motivated and more mature. If they were to not open the trap until august, the early fish would have to wait below the trap (first powerstation) for about 3 months...Would they do that or turn back to the lake?

Thanks for the paper!

How much stress the fish experience in the trapping and handling will influence the fallback rates.  The more the fish are stressed the more likely the flight fright response will be engaged and for fish the quickest way to flee is back downstream.  Thus minimize potential stessors as much as possible such as trap and handle during low light levels.  Minimize noise that will startle the fish.  Consider using mild anestetics or water conditioners (such as salt) during transport to minimize stress. Use water to water transfers.  The time of day for releases may decrease fallback, try at dusk or dawn.  Consider holding in a net pen at the release site for acclimation after transport and then release by opening a door to the net pen so they exit volitionally.  If the action is translocation the fish may still fallback downstream  because the water they are being introduced into is foreign to them.  I worked on a translocation project of American shad from the conneticut and Hudson Rivers into the upper Susquehanna 30years ago.  It didn't work and all fish immediately migrated downstream until death or they reached the ocean because they new it was not their natal waters.

Although its kept at a minimum, they do encounter a lot of stress, no question about it but handling is the same over the whole season and its only in the early group we see the high fallback rates.

Net pen would be interesting to try as well as a release point further up.

Thanks Eric!

Anna, we sometimes have to move Chinook Salmon around barriers, such as the intake for a hatchery.  When we are concerned with fallbacks, we will either hold them in a hatchery raceway until they are close to spawning and/or put up a weir to prevent them from moving back downstream.  The weir works well but is not feasible in streams in which you cannot wade to install the weir.  Also, it will block migration of all fish that are not small enough to pass through the bars of the weir.  We usually only have the weir in place for less than two months.  In the case of moving the salmon past a hatchery, the weir is also useful for keeping carcasses off of the hatchery water intake.

Thanks Timothy!

This is a big river and part from stoping all migration for a time i guess a weir would get blocked up with material from the river pretty fast? When you hold the fish in the raceway, do you have any problems with fungi or other parasites?

Anna, the streams that we work on are at low levels in the late summer/early fall when Chinook Salmon spawn, so debris is not an issue.  As for holding the salmon, fungus is usually not a problem but it can usually be easily treated/prevented with formalin and/or hydrogen peroxide treatments.  As for other diseases and/or parasites, they probably don't pick up anything new while they are being held - they generally have what they brought with them from the ocean.  Any parasites that have are unlikely to cause a problem.  The only disease that is likely to cause a problem for our salmon is bacterial kidney disease, which can increase prespawn mortality.  It's rare that we give antibiotics to salmon that will be released but, depending on the stream and whether we think that BKD is going to be a problem (it rarely is a problem in nature), we may give them a shot of erythromycin or azithromycin to improve their chances of survival to spawn.  But if there is a chance that these salmon might be harvested by anyone, we can't give them any antibiotics.

Tim

Thanks Timothy!

Hi Anna, that is a tough question. While doing radio telemetry studies on steelhead trout, Chinook salmon, and coho salmon, we found that some fish would 'fall back' after tagging, and some exhibited upstream movements one day, and downstream movements the other day. Steelhead were the worst, they seemed to go up or down in a random manner, but all fish (and species) we tagged ultimately swam upstream to spawning areas. One question I have is how fast is the water they are being released in? If the stream or river is fast, they may tend to swim downstream due to affects from handling and transport.

Hi Michael!

The river has a mean annual discharge at the outlet of 160 m3/s, with a mean annual high of 690 m3/s. During my study (2 yrs) we had between 70 and 250 m3/s in the area of release. There is maybe a slight tendency for fish to move downstream at higher discharges but not a very strong one. It is only in the early run we see this. 

Is there a report or a paper on your telemetry study i could read?

Cheers!

Could handling effects be inducing "fall backs"? Even in unimpeded river we found that some adult sea trout and Atlantic salmon that had just been tagged and released would drop back downstream from where they were netted for a short period before resuming upstream migration.

I definitely think handling affects the fish and some will probably move downstream due to that but in this study we treated all fish the same way but we have 50% fallbacks in the early group (june/july) and only about 10% in the late. Maybe early fish can “afford” to get a bit confused and have enough time to search around for a familiar spot whereas the late are more sexually mature and just more triggered by the river flow

There might be something in that, I found that early migrants were generally slower whereas later migrants showed a more concerted migration and were much faster.

That is what i found too. The early ones moved slower, possibly in the least costly way in regards of energy consumption. 

Dear Anna;

My experience is that the closer to spawning time, the more willing Atlantic salmon are to migrate. You may remember (Jonsson et al. 2007) showing how time of upstream migration to the spawning grounds was related to water flow in the river. The more water in summer and early autumn, the earlier the fish ascended the river. But (1) migration stopped at very high discharges and (2) large fish needed more water to ascend upstream than smaller ones (see also Jonsson et al. 1990). Furthermore, Tetzlaff et al. (2008) reported that number of Atlantic salmon entering the Girnok Burn, Scotland on a given day was related to patterns of discharge over the preceding part of the arrival period. In wetter years, fish entry to the stream usually starts relatively early and continues throughout the pre-spawning period. In contrast, dry years may result in fish entry being delayed. Thus, Atlantic salmon appears more motivated to migrate towards the spawning grounds late than early in the season. I have similar experience from upstream migration of anadromous brown trout (Jonsson & Jonsson 2002). Thus, my hypothesis is that fallbacks can be reduced by delaying the upstream migration of the fish. This assumes, however, that the the fish migrated downstream as smolts from the area of the river where you would like them to return. Also, I would expect that fallbacks would be more common at extremely low and extremely high river discharges than at intermediate flows. It would be interesting if you have material to test this hypothesis.

References

Jonsson, B., Jonsson, N. Hansen, L.P. (2007) Factors affecting river entry of adult Atlantic salmon in a small river. -  Journal of Fish Biology 71: 943-956.

Jonson, N. Jonsson, B. (2002) Migration of anadromous brown trout in a Norwegian river. - Freshwater Biology 47: 1391-1401.

 Jonsson, N,, Jonsosn, B. Hansen, L.P. (1990) Partial segregation in the timing of migration of Atlantic salmon of different ages. - Animal Behaviour 40: 313-321.

Tetzlaff, D., Gibbins, C., Bacon, P.J., Youngson, A.F., Soulsby, C. (2008) Influence of hydrological regimes on the pre-spawning entry of Atlantic salmon (Salmo salar L.) into an upland river. - River Research and Applications 24: 528-542.

Thanks Bror!

The paper is on print now and i can hopefully upload it soon. We did see an effect of discharge, higher discharge on the day of release increased the risk of becoming a fallback. What is hard to explain though is that the fish fell back, on average,  1 week after realase.

/Anna

Congratulation with the paper

Do you think that the fish fell back were exhausted and fell back because of the flow?

Bror