State the depth at which the maximum number of species per trawl were caught.

Compare the abundance of fish between the early period (1977 to 1989) and the late period (1997 to 2002).

Suggest one reason for the difference in the abundance of fish at depths down to 2000 m between the early period and the late period.

Discuss the evidence in these data for a decline in the biodiversity of fish between the early period and the late period.

State two types of interactions that are most likely to occur among deep-water fish.

1. ..................................................................

2. ..................................................................

Outline the concept of maximum sustainable yield in the conservation of fish stocks.

1550 (m) (accept answers in the range of 1450 (m) to 1650 (m))

both show decrease in abundance as depth increases;
both show similar/low abundance at depths greater than 3000 (m); (accept values in range 2500 (m) to 3000 (m))
for depths less than 2500 (m) the abundance is (much) greater in the early period than in the late period; (accept values in range 2000 (m) to 2500 (m))
the highest abundance occurs in the late period (although) this is isolated;

overfishing / pollution / change in sea temperature / change in food sources

no evidence that there are fewer species;
difficult to compare as more trawls in the early period /early period of longer duration than late period;
diversity may have increased from (around) 2000 (m) to 4000 (m) / outliers for greater species diversity are all late period;
not enough details about time of year/duration of trawls; (accept any other valid argument)
Do not accept answers stating only “not enough data”.

competition and predatory/predation (both needed)

is the maximum number of fishes of a species that can be caught/harvested without causing a population decline / still allowing a population to regenerate;
corresponds to the turning point of a population growth curve;
below that point yield is lower and population grows / above that point yield and population will decline;
used to determine fishing quotas;
difficulty in estimating populations;

Many candidates found interpretation of the graphical data about trawling challenging. Candidates frequently only gave enough to be awarded part credit. For (a) most candidates gave the correct answer.

Many candidates found interpretation of the graphical data about trawling challenging. Candidates frequently only gave enough to be awarded part credit. Most could compare the abundance values in (b) but many related to incorrect depth ranges.

Many candidates found interpretation of the graphical data about trawling challenging. Candidates frequently only gave enough to be awarded part credit. Could not suggest one valid reason for the difference.

Many candidates found interpretation of the graphical data about trawling challenging. Candidates frequently only gave enough to be awarded part credit. Many candidates stated that there was no evidence for the decline in biodiversity, but very few could back up their statement using the data correctly, some overlooking that the data were showing fish abundance, or others restated the wording of the question.

Many candidates found interpretation of the graphical data about trawling challenging. Candidates frequently only gave enough to be awarded part credit. There was a mixture of answers for (d), many containing only one valid element.

Many candidates found interpretation of the graphical data about trawling challenging. Candidates frequently only gave enough to be awarded part credit. Most candidates could define the concept correctly in (e), but add difficulty to gain a second mark.