Chinook salmon, also known as king salmon, are the largest of the Pacific salmon species. Their diet is crucial to their growth, survival, and overall impact on the ecosystems they inhabit. As anadromous fish, Chinook salmon have a complex life cycle, transitioning between freshwater and saltwater environments, each with its own unique food sources and dietary demands.
Life Cycle and Dietary Shifts
Chinook salmon begin their lives in freshwater streams and rivers. Young Chinook salmon, also known as juveniles or smolts, primarily feed on terrestrial and aquatic insects, amphipods, and other crustaceans. After one to two years in freshwater, the smolts migrate to the ocean, where their diet shifts to include a greater proportion of fish.
In the open ocean, Chinook salmon exhibit a preference for fish and squid, although the specific types of prey depend on their location and availability. They are considered less of a generalist compared to sockeye, pink, and chum salmon, which consume a more diverse array of invertebrates and fish.
Chinook Salmon in Lake Michigan
Chinook salmon have been a dominant predator in Lake Michigan for several decades. However, the food supply in Lake Michigan has changed significantly due to invasive species, nutrient reductions, and high numbers of predatory fish. This has led to increased competition for baitfish like alewife.
Consumption Rates Compared to Lake Trout
When considering the impact of Chinook salmon on the Lake Michigan ecosystem, it is essential to compare their consumption rates with other predatory fish, such as lake trout. Chinook salmon are characterized by a high growth rate and a short lifespan, typically spawning and dying at age 2.5 or 3.5, while lake trout can live much longer.
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On an annual basis, a Chinook salmon consumes more food than a lake trout of the same size, due to their faster growth rate, preference for warmer waters, and higher activity levels. A Chinook salmon consumes 42.5 lbs of food between age 0 and 3.5, while a lake trout consumes an average of 13 lbs annually from age 1 to 12. However, when considering the entire lifespan, a Chinook salmon consumes 147.7 lbs of food from age 0 to 3.5, while an average lake trout consumes 143.3 lbs of food between the time of stocking as a yearling into Lake Michigan and age 12.
Despite the longer lifespan of lake trout, Chinook salmon have a more significant impact on prey populations due to their higher consumption rate and shorter generation time. During the lifespan of a 12-year-old lake trout there will have been four generations of Chinook salmon.
Factors Influencing Consumption Rates
Several factors influence the consumption rates of Chinook salmon, including water temperature and growth rate.
- Temperature: Chinook salmon inhabit warmer waters than lake trout, with average summer temperatures ranging from 53.6 to 55.4°F. Higher temperatures increase metabolic costs, leading to higher consumption rates.
- Growth Rate: The primary driver of the difference in consumption rates between lake trout and Chinook salmon is the difference in growth rates between the two species. Chinook salmon grow substantially faster than lake trout, requiring more energy and food.
- Activity: Chinook salmon are more active than lake trout, travelling large distances and generally moving around more, requiring more energy.
Gross Growth Efficiency
Gross growth efficiency (GGE) is a measure of how efficiently a fish converts food consumption into growth. The GGE for a 3.5-year-old Chinook salmon is estimated to be 13.3%, while the GGE for a 12-year-old lake trout is 8.0%. This means that Chinook salmon are more efficient at converting food into growth than lake trout.
Diet Composition
Chinook salmon in Lake Michigan primarily feed on alewife. Lake trout tend to be opportunistic feeders and will take advantage of a variety of prey items, whereas Chinook salmon are more specialized preferring almost exclusively alewife as prey. Since about 2003, lake trout have been taking advantage of a relatively new prey source in Lake Michigan, the round goby. Preliminary comparisons indicate that there is a seasonal component to lake trout feeding whereby they consume larger numbers of round goby in the spring and increased dependence on alewife as the year progresses. Smelt and bloater have been abundant in the diets of lake trout in the past, but for the recent 5 years over 75% of lake trout diets have been comprised of alewife and round goby. Preliminary investigations indicate that in the spring (April to mid-June) alewife comprise between 7% to 20% of the diet of lake trout, and from mid-June to August alewife can represent from 50% to 80% of the diet.
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Management Implications
Understanding the diet and consumption rates of Chinook salmon is crucial for effective fisheries management. Fishery managers must make decisions in real time based on the best available scientific information. Bioenergetics models are used to estimate food consumption by Chinook salmon and lake trout, taking into account factors such as growth, temperature, diet, and energy density of prey.
Nutritional Value of Chinook Salmon
Chinook salmon is not only an important part of the ecosystem but also a valuable source of nutrition for humans. According to the American Heart Association, making oily fish like salmon a regular part of your diet can reduce your risk of stroke and heart disease. Wild caught California king salmon salmon is higher in Omega-3 fatty acids than previously thought.
Macronutrient Breakdown
A ½ fillet of chinook salmon (154g) contains 356 Calories. The macronutrient breakdown is 0% carbs, 54% fat, and 46% protein.
- Fat: 21g (26% DV)
- Saturated fats: 5g (25% DV)
- Monounsaturated fats: 9g
- Polyunsaturated fats: 4g
- Protein: 40g
Vitamins and Minerals
Chinook salmon is a good source of protein (71% of your Daily Value), potassium (17% of your Daily Value), and magnesium (45% of your Daily Value). It is also rich in several vitamins and minerals, including:
- Niacin: 15mg (97% DV)
- Phosphorus: 571mg (82% DV)
- Selenium: 72μg (131% DV)
- Vitamin B12: 4μg (184% DV)
- Vitamin B6: 1mg (55% DV)
- Vitamin A: 229μg (25% DV)
- Folate (B9): 54μg (13% DV)
- Riboflavin (B2): 0.2mg (18% DV)
- Thiamine: 0.1mg (6% DV)
- Copper: 0.1mg (9% DV)
- Iron: 1mg (18% DV)
- Magnesium: 188mg (45% DV)
- Potassium: 778mg (17% DV)
- Zinc: 1mg (8% DV)
- Calcium: 43mg (4% DV)
- Vitamin C: 6mg (7% DV)
Omega-3 Fatty Acids
Ocean-run salmon contain high levels of Omega-3 fatty acids which play a protective role against heart disease. Chinook salmon is a rich source of omega-3 fatty acids, including:
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- Docosahexaenoic Acid (DHA): 1g
- Eicosapentaenoic Acid (EPA): 2g
- Docosapentaenoic Acid (DPA): 0.5g
Comparison with Sockeye Salmon
Chinook salmon is richer in selenium, magnesium, and phosphorus, yet sockeye salmon is richer in vitamin B12, vitamin B6, vitamin B1, vitamin B5, and vitamin B2. Sockeye salmon's daily need coverage for vitamin B12 is 67% higher. Chinook salmon has 3 times more magnesium than sockeye salmon.
Potential Renal Acid Load (PRAL)
PRAL (Potential renal acid load) is calculated using a formula. On the PRAL scale the higher the positive value, the more is the acidifying effect on the body. The lower the negative value, the higher the alkalinity of the food.
Important Considerations
- Dietary cholesterol is not associated with an increased risk of coronary heart disease in healthy individuals.
- Saturated fat intake can raise total cholesterol and LDL (low-density lipoprotein) levels, leading to an increased risk of atherosclerosis.
- Data provided by FoodStruct.com should be considered and used as information only. Please consult your physician before beginning any diet.