Techniques for surveying exploited species - Conservation and Sustainable Use - page 46

Analysis type Field application Key advantages Key disadvantages

Complete census Eliminates statistical uncertainty Very rarely possible

Plot and All Minimises statistical uncertainty Only effective for abundant, static species /

plotless (no model error) objects

sampling Block plots Easily applied at small scales Inefficient at large scales

Strip plots Less effort wasted travelling between Not effective when travel impairs observation

plots—provides wider coverage

Plotless samples Can reduce required survey time Assumes random distribution of

individuals (very rarely justified)

Distance sampling All Not biased by heterogeneous detection Requires substantial sighting rate to

probabilities yield good precision of estimates

Points Useful when travel impairs observation Yields low coverage at large spatial scales

Lines Less effort wasted travelling between Difficult where terrain hinders travel

points—provides wider coverage

Trapping webs Brings the benefits of distance sampling Very intense trapping effort required;

to species that cannot easily be seen biased by high rates of movement

Mark-recapture All Can be applied to species that are Often biased by heterogeneous capture

difficult to observe; can provide probabilities; requires a substantial

supplementary information on proportion of the population to be

survival and productivity rates observed; sampled area often hard to define