| Date | May 2012 | Marks available | 1 | Reference code | 12M.2.SL.TZ1.1 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Suggest | Question number | 1 | Adapted from | N/A |
Question
Bottlenose dolphins (Tursiops truncatus) inhabit almost all tropical and temperate oceans between 45°N and 45°S. Over a two-year period, aerial surveys were carried out to investigate the seasonal distribution of these animals along the mid-Atlantic and eastern coastal waters of the USA. Sightings were recorded using a global positioning system (GPS) while flying parallel to the coast approximately 500 m offshore. The diagram below shows a map of the section of coast surveyed. The bar graph shows the seasonal data for summer and winter at the corresponding latitudes (°N). A total of 5431 bottlenose dolphins were sighted during these surveys.
State the largest number of dolphins counted in a single summer survey.
Compare the distribution of dolphins in summer and winter.
Suggest one reason for the differences in distribution.
Markscheme
150 (allow answers in the range 140–160)
more evenly distributed in summer than in winter (across latitudes);
many near Cape Hatteras/35.0/2–35.4/6°N in winter/more than in summer;
more dolphins overall in the survey area in winter than in summer;
wider summer range / reaches 36.6 and 34.2°N/ less far N and S in winter;
unimodal distribution in winter versus bimodal in summer / OWTTE;
seasonal variation in food supply/prey/predators/water temperatures;
migration to find food/prey/warmer water/mates;
migrating dolphins rest/congregate near Cape Hatteras/35.2 – 35.4°N;
Cape Hatteras/35.2 – 35.4°N may be a mating area in the winter;
seasonal variation in human activity / valid example;
more food/warm water between mainland and Cape Hatteras in winter;
Examiners report
Most answers were correct, although some gave the highest overall number in winter.
Many candidates recognized the more even distribution of dolphins in summer than in winter and that more dolphins congregated near Cape Hatteras in winter than in summer. Some candidates just quoted data. Instead of saying “many” dolphins they would state a number and let the reader interpret the meaning.
By far, the most common answer identified seasonal variation in food supply or water temperature. Some candidates did not earn the mark because they had no reference to season. In 1(b) candidates had been asked to compare the distribution of dolphins in summer and winter and in 1(c) they were asked to suggest one reason for the differences in distribution. It was expected that some reference to seasonality would accompany any answer in 1(c).
