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← Theoretical 1

Q48 — Sockeye Salmon — Life Stages and Chukchi Population Age Structure

Theoretical 1 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Ecology

Sockeye salmon (Oncorhynchus nerka) spends its initial life stage in rivers, then migrates to the ocean (more favorable feeding conditions), before returning to rivers to breed — changing body color at each stage. Its distribution spans the east coast of Eurasia, west coast of North America, and the north Pacific. The Chukchi Peninsula population, the northernmost, has complex age groups within breeding schools, longer marine lifespan, a predominance of early-maturing females, and a predominance of males in older age groups.

Figure showing sockeye salmon coloring at four life stages: river phase, ocean phase, breeding male, and breeding female. Figure. Peculiarities of sockeye salmon coloring at different stages of life. 1 — river phase (newborn period), 2 — ocean phase, 3 — male during the breeding season, 4 — female during the breeding season.

Using the information and images, determine whether the following statements are true or false:

A. The complex age composition of the sockeye salmon's Chukchi populations is directed to neutralize the potential impact of less favorable conditions during the river life stage.
B. In the Chukchi sockeye salmon populations, color changes at different stages of life lead to a predominance of males in the older age groups of breeding schools.
C. The complex age composition of the sockeye salmon's Chukchi populations may have conferred a selective advantage to the population by minimizing the impact of less favorable conditions during the river life stage.
D. Sockeye salmon entering rivers from the ocean is characterized by sexual dimorphism, while the salmon living in the ocean do not have it.
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Question reproduced from IBO 2022, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)