Using Figure 6(c), identify a food chain in the St Lawrence River ecosystem that has five trophic levels.

Using Figure 7, state the St Lawrence beluga whale population in 1920 and 1940.

1920:

1940:

Calculate the percent decrease in beluga whale numbers from 1920 to 1940.

With reference to Figure 8, explain why the beluga whale is more at risk from toxic pollutants, such as heavy metals and persistent organic pollutants (POPs), than most other organisms in its food web.

Suggest why the St Lawrence River beluga whale population has not recovered despite being given protected status in 1983.

Response should indicate the flow of energy from phytoplankton to beluga whale (e.g. using arrows in the correct direction or words indicating what is eating what).
For beluga whale accept either beluga or whale.
Do not accept a food chain that includes sun/light.

1920: accept 6000–6300;
1940: 2000.

Both responses required for [1].

 $$\begin{gathered} \left(\frac{\left(6000 - 2000\right)}{6000} \times 100 =\right) 66.7 \%/67 \% ; \\ \left(\frac{\left(6300 - 2000\right)}{6300} \times 100 =\right) 68.2 \%/68 \% \end{gathered}$$

Accept answers between 66.67 % and 68.25 %. Also accept 66.6 recurring.
Accept answers between –66.67 % and –68.25 % (as it is a percentage decrease).
Units are not required.
Only the final answer is required for [1].
Do not accept 66 %/66.6 % (incorrect rounding).

these are persistent toxins that build up in the fatty tissues (and beluga whales have 40–50 % body fat);
they are at the top of the food chain (biomagnification along the food chain);
bioaccumulation over a long life span;
increasing concentration of pollutants (bioaccumulation) within the species consumed by the whale;
persistent pollutants accumulate along the food chain due to decrease of biomass and energy;
eat benthic feeders, which assimilate toxins by scavenging corpses of marine organisms;

Do not accept just the terms ‘biomagnification/bioaccumulation’.

isolation is leading to genetic diversity loss and lowered resistance to disease;
small population size may affect reproductive rate / low genetic diversity may affect the reproductive rate;
slow development / late to reach sexual maturity / produce only a low number of offspring;
pollutants bioaccumulating in fatty tissues interfere with successful reproduction;
high levels of pollutants still found in their habitat, impacting their ability to reproduce effectively / industrial effluent discharges may kill/harm whales / pollutants could adversely affect food supply of the whale;
shipping causes separation of mother from calf (increasing number of calf deaths);
ships/human activities produce noise that interferes with feeding behaviour/reproduction in whales;
water temperatures rising, moving outside tolerance of beluga whale food source, reducing food availability;
invasive species may reduce food available for beluga whale;
despite being protected, may get caught in commercial fishing nets and drown;
may be killed in collisions with boats, as the St Lawrence River is an important shipping route;
commercial fishing removing food source / competition for food with commercial fisheries;
there may be illegal hunting of beluga whales.

Do not accept only ‘threat of pollution / hunting / due to sport fishing / K-selected species and therefore slow to recover’.