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Kenai River Rainbow Trout: Why They’re So Big

Kenai River rainbow trout
Here is a 30.5 x 18 caught by the author in late August right after the king spawn slowed down. © John Anderson

Kenai River Rainbow Trout: Why They’re So Big
Article By Jeremy Anderson

Kenai Mega Girth: Healthy salmon returns equals big fat rainbow trout

There may not be another river in the world that produces a large, girthy, native trout population like the Kenai River. We can thank four species of salmon that annually return to the Kenai and provide a massive amount of food. Weight Watchers would not approve of the non-stop buffet that our native rainbow trout enjoy when salmon are in the river, but these trout’s health is a direct reflection on how the salmon fishery and river habitat are doing.

When all the factors align, Kenai River rainbow trout add 25% to 35% to their body weight by the end of fall. When you see a girthy trout in the 15- to 20-plus-inch range, it looks like a football, with a small head and an enormous mid-section. When you catch such a fish in the 28- to 30-inch range, it could be up to 15 pounds. There are 20- to 30-pound rainbow trout in the river and on occasion one gets landed.

Why the Kenai is a unique drainage

The Kenai River watershed is vast and glacially fed by the Harding Ice Field and Snow River. It stretches 89 miles across the Kenai Peninsula from Kenai Lake to Cook Inlet and passes through Skilak Lake in between. Both lakes act as food banks, filtering systems, and winter residences for resident trout and juvenile salmon. Kenai trout are very migratory and throughout the season they move up and down the drainage trying to find the next sweet feeding spot. When the food supply is plentiful the trout will stay put, but if it drops off then these hunters will look for a more fruitful option somewhere else in the drainage, possibly miles away.

Kenai River trout
A 22.5-inch length by 15.5-inch girth Kenai rainbow caught by Mike Byas in late September 2018. © Mike Byas

Many tributaries flow into the Kenai and serve as additional salmon spawning grounds. Almost all of the headwater streams are still in their original, pristine state, which provides natural habitat salmon need for reproduction. Chinook, sockeye, pink, and coho salmon spawn in the Kenai and its tributaries each year, and with four species of salmon there is at least some spawning occurring for roughly eight months out of the year, someplace in the drainage.

The food cycle: what do Kenai River rainbow trout eat and throughout the year?

These rainbows eat a lot of salmon eggs and flesh, which is the major reason they hold the heavyweight belt in Alaska. New spawning salmon provide a fresh surplus of protein many months of the year. There are also old eggs and flesh that get caught up in snags, shorelines, and on the bottom of the river that trout feed on months after the spawn has ended. There are other food sources for trout during certain times of the year, including salmon smolts, leeches, lampreys, and bugs. Rarely will you see trout on the Kenai rising to catch a meal because most of the food they target is subsurface.

We see the fattest rainbows when one feeding season transitions to the next with a consistent supply of food. A lull in food supply causes trout growth to plateau. When we see consecutive good feeding seasons, we watch these rainbows continue to grow at a rapid rate, not only in length but in girth.

Kenai River Rainbow Trout
Rainbows like this that Zach caught were seen daily in the fall peak trout season in 2018 due to a great food supply. © Alaska Drift Away Fishing

In the summer of 2014, the trout were very healthy and strong due to a mild winter and great mid-summer food supply. The salmon spawns lined up that year as fall kicked in, especially the pink spawn, and we watched the ‘bows get fatter by the day. By mid-September the trout were so full, we saw a few slower fishing days, which we call a glut. When the spawn slowed down, the fishing picked up as our beads weren’t competing as much with real food. This created the perfect storm for catching big, fat ‘bows. There was no flood that year and the water level dropped slowly over the winter, so the river held food well. The cycle came full circle and in June 2015, big, fat rainbows were found throughout the river.

Spring

Ideally, trout would like to have multiple food sources at this time. They are spawning or recovering from the major efforts of spawning between April and early June and they are HUNGRY! Kenai ‘bows would prefer the ease of leftover food as the water rises, but when that isn’t plentiful, they will chase things that swim such as smolts. The water temperatures are warming up, which helps trout be more active as well.

Since rainbow trout spawn in the shallows during spring, they are very vulnerable and easy targets then. This is a very critical time for our trout population. Trout stress easier this time of year when caught, resulting in a higher mortality rate and messing with their ability to spawn. Once these trout stage up to spawn, avoid the shallows. Let the rainbows reproduce and pick another Alaska activity to enjoy during this time.

Summer

In early summer, Kenai ‘bows begin to migrate. There is some minimal salmon spawning this time of year and the Kenai will get some eggs or flesh out of the deal, but it’s usually not a substantial amount. From mid-June through early August, sockeye fishermen fillet their fish and then discard the carcasses and eggs into the river. This is the most important factor for our rainbow trout to grow big and fat during the summer season. These trout have become accustomed to this part of the Kenai River food cycle, and have an excellent sense of smell. They are often waiting just below the fillet stations where people throw carcasses back into the river.

Cleaning tables and fillet zones are found on almost every mile of the Kenai River. If someone who lives on the river has a cleaning table, there is a decent chance they are also filleting fish from the ocean and other rivers as well, contributing even more food to the system. This happens from early June through fall.

Kenai River anglers
Many people fish for red salmon in June, July, and early August. The fish they clean can create an unnatural, but welcome supply of mid-summer food for trout. © Alaska Drift Away Fishing

Fall

In a typical year, this is when Kenai rainbows get the most opportunity for food with four species of salmon spawning. Mid-August through November is the absolute best time to fish for trophy rainbows on the Kenai River because it coincides with the majority of the salmon spawn. Kenai River rainbow trout first target the massive amount of eggs rolling down river. Once the salmon start to die off, the trout transition to eating flesh.

Most kings on the Kenai start to spawn in mid-August, and the king spawn continues for several weeks. Depending on the year, it is a river-wide spawn stretching between Cooper Landing and Soldotna, potentially producing an amazing amount of food. This time of year can really give trout a boost in their food supply so they can continue to grow and stay healthy. If king salmon spawning numbers are low, then the rainbow trout will not grow as much and will struggle to maintain their weight, which has occurred in recent years.

The pink spawn can be river-wide, begins in mid-August, and is different depending on the year. On odd years, low numbers of pinks return to spawn and you will find them in only a few small pockets throughout the river prior to sockeye spawning. On even years, aka a “pink year,” the pink spawn on the Kenai River is much larger, and the rainbow trout gorge themselves from mid-August through the end of September. There can be between one- and two million pinks and they spawn throughout the entire river off gravel bars, the bottom of islands, and even in the deeper, medium-paced water. Even year pink spawns will produce fatter trout than any other time.

The sockeye spawn in our system in late August through September and it can be enormous. On non-pink years, this is the bulk of trout’s food for September. Sockeye spawn in slower waters near Kenai and Skilak lakes where the rainbow trout have a chance to eat a lot without expending too much energy. These eggs are smaller than king eggs, but what they lack in size they can make up for in numbers.

Silver salmon spawn in two separate fall runs that stretch longer than any of the other species. The runs start in late August and run through November. These fish like to spawn on or just off the shallow gravel bars throughout most of the Kenai River. The second spawn comes at an important time of year for Kenai River rainbow trout because it provides another chance at fresh eggs and flesh before winter kicks in.

Winter

There is a small, winter run of silvers that will spawn into February or early March. This is the only new food that is provided in the winter. The other source of food is leftover eggs and flesh from the previous season’s salmon. The trout also chase things that swim at this time of year, but that does take more energy than sitting in a winter feeding lane. With colder water, the trout’s metabolism is slowed, too.

Winter is a very sensitive time of year to target the rainbow trout due to colder temperatures. If it is cold enough for the eyelets on your rod to freeze, then there is potential to damage the gills of a fish when it is pulled out of the water. The trout will try to breath, the cold air hits its gills, and you can severely hurt or even kill the fish.

Other factors that affect Kenai trout

Water Level Changes

The bottom line is that water level change is one of the most critical factors in a trout’s food supply. If the river rises and drops slowly, food will be available for a longer period of time. Slow rises in water will flush more food into the food lanes that was previously stored for safe keeping, such as carcasses on the bank. Quick and drastic changes in water levels, like flooding, will wash away food quickly and trout won’t have what they need to continue to grow at the “Kenai Rate.”

In the fall of 2017, there were low numbers of salmon spawning and significant flooding on the Kenai. We did have some great trout fishing and found some fatties, but the limited amount of food went quick that year. Most of the trout never got the chance to pack on the pounds, so they came into the winter at a disadvantage. We saw the repercussions of that when we saw skinny to average-sized fish in early summer of 2018.

Habitat and Erosion

Having good bank habitat is critical for juvenile salmon and trout. When riverbank structure erodes, young-fish habitat disappears. In recently years, people have replaced wooden docks with metal grates, which help vegetation grow with more access to the sun and rainwater. Rebuilding banks with root wads, rocks, gravel, and cable has helped prevent bank erosion. Erosion is something that the people of the Kenai River have been working on since the issue started and the results have been good. There are still areas that need to be restored and protected from erosion, both on public and private property.

Kenai River trout
Jacque caught this 25 x 19 back in 2016, the true meaning of football. © Alaska Drift Away Fishing

Fishermen and Boats

Each fisherman makes many personal decisions out on the water, and the consequences of those decisions create an impact. Here are a few things to think about while fishing for salmon. Only catch what you can eat and practice good catch-and-release techniques, so more salmon can spawn. Also, if you hook a salmon while trout fishing, get it in quick or break it off so it can return to spawn. Sport angler decisions definitely have an impact on final salmon spawning numbers.

 

Kenai River sockeye salmon
Happy anglers will bring home delicious sockeye salmon to eat and the carcasses will provide sustenance for the river and its trout. © Alaska Drift Away Fishing

Here are a few things to think about while rainbow trout fishing. Be considerate when taking photos so you don’t hurt the fish when releasing it. If you are going to shore with a nice fish, ferry across slowly and take your time to get a proper grip on the fish, but don’t squeeze them too hard. The trout will fare better. Also, power-lapping a spot will push the rainbow trout into non-ideal feeding spots which can be detrimental to their health. Finally, treat all trout like big ones. Young trout grow fast and proper handling is critical for the next generation of fatties.

Boats (yes, jets as well) running over spawning grounds in shallow water can each kill 20% to 40% of the eggs in the gravel. These are salmon and trout eggs. Now imagine if 10 boats go over the same spot. Navigate carefully and keep your boat in the deep channel when under power so we can protect our spawning beds and keep those eggs incubating in the gravel.

Kenai salmon carcass
Salmon flesh is food. © Alaska Drift Away Fishing

Vast and Dramatic Ocean

There are many ocean factors that have a huge impact in how our Kenai River rainbow trout are going to fare because salmon spend the majority of their lifetime in the ocean. If average to above-average salmon runs make it to the Kenai River, then we get a high percentage of fat rainbow trout. If the salmon returns are low in a particular year, then the trout won’t pack on the girth that the Kenai is known for.

King salmon eggs
King salmon eggs that came out of a trout’s mouth after being caught in August 2018. © Alaska Drift Away Fishing

Our oceans are always changing. Pacific Decadal Oscillation (PDO) is an ocean factor that affects salmon returns. It is a 20- to 30-year cycle in the Pacific Ocean that affects surface water temperatures. This changes the biological productivity for Alaska and the west coast of Canada and the Unites States by shifting cool and warm water currents. An overall rise in ocean water temperatures is another negative factor in recent years as salmon thrive in cooler water temperatures. Both the PDO shift and overall water temperature changes affect the salmon’s food supply in the ocean.

A few other factors contributing to what makes it back to the river are diverse fishing activities that take place in the ocean. Illegal fishing boats in international waters are being found on a more regular basis with masses of salmon on board. The ocean pollock fishery, one of the world’s largest fisheries, has a history of a bycatching a large number of king salmon, potentially reducing the Kenai king numbers that return to spawn. Overfishing salmon in the ocean locally can be detrimental to in-river returns as well.

Kenai River rainbow trout: tying it all together

Measuring fish
A 28-inch rainbow with a big girth that James caught on October 2nd after a great pink salmon spawn. This fish took a bead imitating an old egg. © Jeff Murray

Regarding the Kenai, we have an amazing, native rainbow trout fishery unlike any other in the world. When we see consecutive good feeding seasons, we watch Kenai River rainbow trout grow at an amazing rate in both length and girth. Remember all the variables that contribute to the growth of big, fat trout and think about it when you are making your game plan for the day. Rainbow trout health is a huge indicator of salmon populations, river habitat health, and people’s fishing actions.

As we embark into the future, we must put the fish first. Careful management of our local salmon runs will result in better salmon returns. Strong salmon returns make for happy sport anglers, commercial fishermen, and great trout fishing. Look up organizations like Fish for the Future or the Kenai River Sportfishing Association if you want to get involved. Everyone plays a part in the outcome of our fisheries and we need to make decisions today that will help us tomorrow. My son loves fishing and I hope he will have the same opportunities to fish the Kenai River as we have today.

 

Jeremy Anderson is a contributing writer for Fish Alaska and co-owner of Alaska Drift Away Fishing. His passion for the Kenai River, sharing fishing with others, and educating anglers, is what keeps him on the water. You can find out more about Jeremy and trout fishing on their website.

This article originally appeared in the August/September 2019 issue of Fish Alaska as Kenai Mega Girth: Healthy Salmon Returns = Big Fat Trout.

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