DUDE: Some years, kokanee are pretty small, but in other years out of the same fishery, the kokes are much bigger. Is there an explanation?
KOKANEE: Yes. The correct answer takes in many considerations. Better sit down, as this might take some time to lay out for you.
DUDE: Done.
KOKANEE: I want you to know that if I give away too much information, I might lose my spawning rights.
DUDE: All the more reason to pay attention.
KOKANEE: Size is first approached from an available food concept. And one needs to focus on the available food supply for a single kokanee. If you have just one large bucket of food for just one kokanee, that koke will be well fed. However, if all you have is one bucket of food for a thousand kokanee, then, with not much food to go around, no one is getting fat or big.
DUDE: OK -- number of fish and an available food supply – got it.
KOKANEE: You have only the start of it. Let’s talk about birth control.
DUDE: You are not going to play political football on me, are you?
KOKANEE: Would you rather catch a bunch of small kokanee or a few less of much larger kokanee?
DUDE: It’s obvious.
KOKANEE: Kokanee are not an endangered species. We are very successful at spawning, hatching, and generally have lower fry mortality than most salmon species. But if the spawning habitat is cut off from spawning kokes, then cutting off that habitat acts as birth control.
DUDE: Oh. Fewer fish for the same food supply equals bigger fish.
KOKANEE: For many excellent kokanee lakes, there are several spawning creeks coming into the main body of water. Placing weirs in the creeks so the kokes are not able to reach their spawning grounds effectively cuts down the population.
DUDE: So for the fisheries folks, it’s “to weir or not to weir – that is the question.”
KOKANEE: And their task is not quite that simple either. Science can make better predictions if there are fewer variables. And always keep in mind that science and politics don’t mix. To be considered are also the factors that affect the food supply itself. If the food supply has been constant over several years, then manipulating spawning grounds gives a more reliable result. Calculations are made based on the number of fish desired as a ratio to the reliable food source necessary to sustain that fish population.
DUDE: So you are saying if many variations affect the food supply, it becomes more challenging to use weirs as a means of birth control.
KOKANEE: Exactly. And many fish and game folks are thrown blame based on factors they cannot control.
DUDE: So what are some of the factors that affect the food supply?
KOKANEE: The pH of the water and the water temperature are the first to be considered. In chemistry, pH is a numeric scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. Recall that the primary food for kokanee is plankton, more specifically zooplankton. Kokanee's favorite food is the zooplankton called Daphnia. Kokanee fry devour copepods, a smaller zooplankton. Zooplankton can move about in the water column and are not dependent upon wind and wave action to go on an adventure. Zooplanktons eat their share of the phytoplankton. Phytoplankton needs sunlight to produce the carbohydrates that the zooplankton rely on. If the pH of the water is too acidic, the beneficial green algae cannot survive. Algae, like other plants, utilize light to photosynthesize food for growth. Low temperatures slow algae growth. During the day, photosynthesis takes place due to the presence of sunlight. Algae draw carbon dioxide from the water to utilize during photosynthesis, promoting cell growth. Removal of carbon dioxide from the water raises the pH levels, as a result of the reduction in carbonate and bicarbonate levels of water, since they are used to replenish the lost carbon dioxide. At night, no photosynthesis takes place, so algae stop taking in carbon dioxide from water and go into a respiratory stage. During this respiratory stage, algae consume oxygen that was produced during photosynthesis and release carbon dioxide into the water. This increased production of carbon dioxide decreases the pH levels in the water at night.
DUDE: There’s more?
KOKANEE: Algae are a very welcome part of a lake’s ecosystem. They form the base of the food chain and are thus vital. They provide a source of food, energy, and shelter for the zooplankton, fish, and other aquatic organisms. Algae also play a strong role in the ability of an ecosystem to absorb nutrients and heavy metals.
DUDE: Temperature?
KOKANEE: If the water is too cold, green algae cannot sustain growth. This is the situation in the cold months of late fall, all of winter, and early spring. If the winter produces abundant snow in the high country feeding a lake, the rate at which that snowpack melts and flows to the lake determines, in part, how fast a lake will warm up after winter. Remember too that in winter the angle of the sun to a lake is lower than when the days get longer in spring and summer. Water has a great capacity to absorb infrared radiation (from sunlight) and to retain that gained heat. And sunlight drives the growth of green algae. So, snowpack inflows and the angle of the sun on the lake work together to make the lake’s temperature what it is.
DUDE: Let me see if I can apply this. Fishing in the early spring for kokes can be frustrating because the water is too cold and there is little food for the kokanee to eat, making them less active.
KOKANEE: Right. The type and amount of dissolved nutrients also affect algae growth. The most important one is the amount of phosphorus available and dissolved in the water. Less phosphorus, less algae.
DUDE: How do the dissolved nutrients get into the lake?
KOKANEE: You really have to think in terms of the entire watershed that comes into the lake. When the watershed has wildfires, nutrients are released that are washed downstream and wind up in the lakes. Heavy storms can cause significant erosion in upstream water paths. Rapid snowmelt can do the same. While some of the nutrients are already dissolved in the water flowing downstream, sediments that enter the lakes will take time to dissolve, becoming part of that lake’s ecosystem. So you can see that there are a lot of factors. In the old days, runoff from agriculture produced too much phosphates and other gunk into reservoirs.
DUDE: What other factors affect size?
KOKANEE: Manipulation of the natural food supply has sometimes produced huge kokes with disastrous long-term effects. Many years ago, Mysis shrimp were introduced into the Flathead Lake watershed in Montana. The Mysis managed to migrate downstream into Flathead Lake. The sole purpose was to be an enhanced food supply for the resident kokanee in the upstream lakes. The goal was to create large kokanee. Mysis shrimp pack a lot more protein than processing plankton. It is sorta like the difference between steak and salad. At least that was the theory.
DUDE: Let me guess. Things did not go as planned?
KOKANEE: Not even close. Glad you are sitting down. Remember, phytoplankton is the primary food source of the zooplankton, which in turn is the main food source for kokanee. Phytoplankton needs sunlight, so in most waters, phytoplankton distribution is limited to about the top 30 feet of the water column. Once the sunlight that penetrates the water column falls below about 10%, phytoplankton cannot achieve photosynthesis. Zooplankton migrate up the water column to feed in the evening because they avoid light. They descend the water column in the morning.
DUDE: OK so far. So I guess zooplankton are like lawnmowers -- consuming the green algae and keeping it in check. But what do the Mysis shrimp eat?
KOKANEE: They eat the zooplankton that the kokanee depend on. In fact, the Mysis way is to devour all of the Daphnia. Kinda like water Vikings. Mysis are vast consumers of the Daphnia and easily out-compete kokanee for that food source. The remaining zooplanktons, such as the copepods, are much smaller and less efficient at keeping the algae in check, and are much less of a nutritious food source for the kokanee. It has been thought that Mysis consumes more than six times the zooplankton as the kokanee do.
DUDE: Why don’t the kokanee eat the Mysis?
KOKANEE: In case you had not noticed, when kokanee emerge as fry, they are tiny. Mysis being 1–2 centimeters would be more than a mouthful. And the Mysis are eating the food that the kokanee fry and fingerlings need. No food, no survival. The two-year-old kokanee don’t eat them. With less and less available food, kokanee become size-challenged. Of course, there was a temporary exception over in Wallowa Lake in Northeast Oregon. Mysis were introduced, and the chain reaction started. But somehow the adults managed to develop a taste for Mysis, and as a result grew to record sizes. But when these monster kokes were caught or spawned, the kokanee fishery collapsed. And putting huge numbers of kokanee fingerlings into that lake made no difference.
DUDE: So the kokes that did survive had their main food source removed until the Daphnia could get re-established. And with less food, smaller kokes.
KOKANEE: And, another factor is the presence of predator fish that feed on kokanee. Generally, these predator fish, such as lake trout and larger rainbows, hang out at the lower part of the water column, and that is where the Mysis hang out during the day. These predator fish love Mysis and grow fat and large on the bounty. As a result, their numbers increase dramatically. And in turn, more predator fish feed on the kokanee population, reducing and in some cases devastating the kokanee population.
DUDE: So the kokanee never get a chance to get very big.
KOKANEE: Exactly. A double whammy.
DUDE: How long can it take to get things back in balance?
KOKANEE: 20 to 25 years. Some lakes never recover.
DUDE: I’ve got a feeling you can tell me more.
KOKANEE: So you are paying attention. Yes, there are more factors.
Next Month, the Conclusion of Interview with a Kokanee!
