State the largest number of dolphins counted in a single survey.

Calculate the mean number of dolphins counted per survey for the winter season.

Compare the data for the dolphin populations in winter and summer.

Compare the distribution of dolphins in summer and winter.

Suggest one reason for the differences in distribution.

Outline the relationship between body mass and LCT_w for male dolphins.

Suggest one reason for the high LCT_w measured for the female dolphin.

Evaluate the hypothesis that water temperature determines the range and distribution of bottlenose dolphins in the wild.

Explain how an increase in water temperature due to global warming could affect the distribution of bottlenose dolphins along the eastern coast of the USA.

2200 (allow answers in the range 2175–2225)

800 (allow answers in the range 750–850)

more surveys in summer / fewer in winter;
larger average/biggest number sighted (per survey) in winter / converse;
larger total number of dolphins (from adding up all surveys) in summer;
variation in both seasons / overlap in numbers between summer and winter;
Do not accept answers relating to distribution.
Do not accept answers stating that the dolphin population is higher in winter.

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;

male dolphin with the lowest body mass has the highest LCT_w;
with larger dolphins/above 180/185/187 kg no change in LCT_w with body mass;
weak negative correlation / as mass increases LCT_w drops / vice versa;
uncertainty due to small amount of data;

Accept any of the following points about the female:
older so (possibly) has a lower metabolic rate / other result of age;
higher surface area to volume ratio (than male);
less active than males so releasing less metabolic heat;
less insulation due to subcutaneous fat/adipose tissue;
suckling / pregnant / part of mass was fetus;

supported as water temperature affects metabolic rate;
supported as dolphins will avoid areas with water below their LCT_w;
water temperature is unlikely to be a factor for bigger males;
wide (latitude) range in summer suggests temperature does not determine range;
few animals / only one female / only narrow range of latitudes investigated;
data may not be reliable since the study was conducted in captivity;

may migrate/move range further north;
migrate to area with cooler/suitable water temperature;
ocean currents may change;
most productive waters/food supply may be further north;
distribution more spread out (due to warmer waters in more areas);

The unusual circular form of the graph made it more difficult to read off the value for the largest number of dolphins in a single survey and only about two thirds of candidates did this carefully enough to earn the mark.

There was quite a lot to do here; three values had to be read from the graph and then a mean value calculated. Again about two thirds of candidates scored the mark.  

There were plenty of valid comparisons for candidates to make and most scored two marks. Some candidates failed to understand that the results are merely sightings of dolphins and not total population counts; they therefore incorrectly implied that the population size varied considerably during each season.

Candidates found this question more challenging and in some cases it was clear that they had not studied the data carefully enough. As in all compare questions, the answer should make genuine comparisons and not describe the two things separately, in this case the winter and summer distributions. Some candidates did not understand that a population is a number of organisms and a distribution is where those organisms live. 

A huge variety of suggestions for the difference between the summer and winter differences was given by candidates and many of these answers were considered valid. The answer could have been based either on possible differences in dolphin behaviour between summer and winter for example breeding, or possible differences in the environment such as water temperature.  

Answers were in many cases weaker than expected. Most candidates stated that as mass increased, the LCT_w of make dolphins decreased, which earned one mark. The difficulty came in earning the second mark. The mark scheme gives a variety of other points that can be made, for example that the individual dolphin with the lowest mass had the highest LCT_w or that above 187kg there does not seem to be much if any further decrease in LCT_w. Many candidates seemed to realize that to get the second mark they needed to give more than the negative correlation but then merely restated the correlation in different phraseology.

Any possible reason for the high LCT_w in females was accepted, though not simply that she was older –some reason for higher LCT_w in an older female was required.

Candidates found this question hard and the examining team had some sympathy with them as there isn‟t very much basis in the data for evaluation of the hypothesis. The most effective answers concentrated on the graph of mass against LCT_w as this shows that the metabolic rate of dolphins will have to increase if dolphins are in cold water. Some candidates realized this, but few then went on to comment on the small sample size or the fact that this data was obtained with dolphins in captivity and that in the wild there could be a different trend.

This was expected to be an easy and high scoring question, but many candidates struggled with it and revealed gaps in their understanding of the data given earlier in the question. It is important to read all of the text in a data-based question, as it places the data in context and often gives information without which the data cannot be understood properly. In many cases candidates based their answer on faulty understanding. For example, a surprisingly large number decided that Cape Hatteras was on the equator and that to find cooler water dolphins could move north or south. No detailed geographical knowledge was needed to score two marks, but geographical misunderstandings did not help. The answer expected in advance by the examining team was that the dolphins population would move north in response to global warming to find cooler water. It was given be a minority, but other valid answers were accepted.