Question 3: Discuss Excellence

Practises Navigation over long distances

Masu salmon (Oncorhynchus masou) are native to north-east Asia. Like all salmon they home very well, coming back to breed in the stream they hatched in, apparently because as young fish they imprinted on chemicals in that stream. In the river the females release eggs and the males swim over them releasing sperm, which is spawning; many adults die afterwards, and neither the fertilised eggs nor the young get any parental care. The paper’s photos show the fish just hatched, very young, as young fish heading downstream to the sea, and as adults heading back upstream.

Discuss how the homing behaviour of the salmon ensures their success as a species.

The 2023 paper, page 8 ↗ Marking schedule, page 4 ↗

Work it out

Try it on paper first. Stuck? Take one hint at a time.

1 Start from the explain answer: why is getting back to the very same stream so important for the young?
Eggs laid in the stream that raised the parent land where spawning sites and conditions suit masu salmon, so they are most likely to hatch and grow. A salmon that strayed could spawn where its young would die, or find no mates at all.
2 And for the species?
With every adult from a stream returning to it together, eggs are fertilised in huge numbers, and each stream’s population keeps renewing itself, so the species persists.
3 What is the masu salmon’s reproductive strategy, and why does it fit?
An r-strategy: huge numbers of eggs and sperm, then no parental care, and many adults die after spawning. Every stage has heavy losses, eggs eaten, fry starving, young caught on the way to sea, adults lost on the way back, so only vast numbers let enough complete the cycle.
4 Why is that a success rather than a waste?
Predators are swamped and cannot eat them all, so enough young reach maturity to replace their parents. That keeps the population size and its genetic diversity, which is reproductive success for the species.

Answer Homing to the same stream matters because eggs laid where the parent was raised land where spawning sites and conditions suit masu salmon, so they are most likely to hatch and grow; a straying salmon might spawn where its young die, or find no mates. With every adult from a stream returning together, eggs are fertilised in huge numbers and each stream’s population renews itself, so the species persists. The masu salmon is an r-strategist: vast numbers of eggs and sperm, no parental care, and many adults die after spawning. Losses are heavy at every stage, eggs eaten, fry starving, young caught on the way to sea and adults lost on the way back, but predators are swamped by the numbers, so enough young reach maturity to replace their parents. That keeps the population size and genetic diversity, which is the species’ reproductive success.

What the marker wanted

Achieved The describe points: homing and its advantage, navigation, the taxis, no parental care, many eggs, spawning in the same river, r-strategy.
Merit Those explained: how homing and navigation work and what they gain, and the advantages of many young and of spawning in the same river.
Excellence Discusses two things. First, why getting back to the very stream it hatched in matters so much to the young salmon and the species. Second, the r-strategy with no parental care, applied to masu salmon, and why it works as a way to reproduce. One gives E7, both E8.

One answer, N0 to E8. Excellence points come last: one gives E7, both give E8.

In our words, from NZQA’s 2023 marking schedule.

Common mistake

Explaining the advantages of each behaviour in general terms, not for the masu salmon, and not showing how they work together. NZQA’s 2023 report says that is where Merit answers stopped.

How did it go?

Got it moves it further out. Review brings it back tomorrow.