1. Sockeye salmon (Oncorhynchus nerka) spend the first years of their lives in the freshwater lakes of Alaska before migrating to marine waters. Their first months in marine waters are spent foraging and growing near the shore line. They then move to offshore regions of the North Pacific Ocean for 2 to 3 years.

The graph shows fork length frequency of juvenile O. nerka caught during their first months in marine waters in autumn 2008 and ocean age one O. nerka caught 15 months later during winter 2009 in the North Pacific Ocean.

(a) Identify the most frequent fork length for O. nerka caught during autumn 2008 and winter 2009.

Autumn 2008:

Winter 2009:

(b) Distinguish between the fork lengths of O. nerka in autumn 2008 and winter 2009.

(c) Suggest a reason for the variation in fork length of ocean age one O. nerka.


Protein content in O. nerka was measured to evaluate possible differences during their first 15 months at sea. The graph shows the relationship between fork length and total protein content per O. nerka caught during autumn 2008 and winter 2009.

(d) (i) Compare the protein content for O. nerka caught during autumn 2008 and winter 2009.

(ii) Outline the difficulty in predicting the age of O. nerka from fork length.

(e) Using the data, suggest one reason for the relationship between protein content and fork length.

(f) Scientists measured mercury levels in different fish. The table shows the results.

(i) Compare the results shown in the table for monkfish and shark.

(ii) Suggest additional information that would be helpful in evaluating these data.

(g) State which type of fish shows the most variation.




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