Evaluate the methods used to estimate populations of marine organisms.

Sampling does not count every organism so may not be a true estimate

Highly mobile marine animals unevenly distributed so difficult to estimate population size

Transects/quadrats used to estimate populations of stationary organisms

Useful on rocky shores/beaches/intertidal zones/reef

Estimation of mobile larval stages of stationary organisms/coral more difficult

Capture-mark-release-recapture useful for mobile animals in restricted environments (Vice versa)

Example of organism can estimate by this technique

Drawback of technique

Echolocation/sonar used to estimate the population size of fish that form shoals

Echolocation cannot distinguish between species (Accept other valid limitation)

The age structure of «commercially» caught fish can be used to estimate population size

Restricted-age fish «as bycatch» dumped before landing so biased estimates
OR
Depends on accuracy/honesty of those catching fish

This seemed to be the lowest scoring of the longer response questions at the end of each option. Candidates found this question very difficult, not knowing how to approach it. They did not seem to have the content knowledge required nor did they know how to ‘evaluate’ the methods used to estimate population size. Many did nothing more than describe a few steps in the capture-mark-release-recapture technique. Others mentioned the general difficulty of collecting data of populations in the ocean. Some mentioned echolocation/sonar with some evaluation as well as the use of the age structure of fished populations, but very few were able to achieve all 6 marks.