Chapter 5 - Absolute population estimates by sampling a unit of aquatic habitat.

Many of the methods described in this chapter have comparatively low efficiencies, so that the emphasis must be on the use of a unit of habitat, rather than on the absoluteness of the estimate. Sampling costs and difficulties frequently dictate the use of a low efficiency method that must be calibrated by a subsidiary study to obtain an efficiency conversion factor by which the results can be adjusted to give an absolute estimate. The choice of method is determined by the nature of the habitat, the size and mobility of the animals and the scale of the study. Marine studies frequently require larger, heavier more complex samplers than those needed for freshwaters, but similar methodological approaches are applicable. As the primary determinant of the method is the type of habitat, methods will be classified under the following headings: (1) Open water - inhabited by surface dwellers, swimming macrofauna and planktonic animals (2) Vegetation - animals living on or around submerged or floating plants and (3) bottom or benthic fauna - animals living on or in the substrate.

Methods for the study of the microfauna of inland or marine waters, which are not covered here, are introduced in works such as Edmondson & Winberg (1971), Baker & Wolff (1987), Pepper et al. (1995) and Ford (1993). In contrast to terrestrial habitats, major difficulties in making absolute estimates of the fauna lie in actually taking a sample of known size. As the problems of extraction, where this further operation is needed, are similar to those encountered with terrestrial samples these are discussed together in Chapter 6.

5.1. Open water 5.1.1. Nets 5.1.2. Pumps 5.1.3. Water sampling bottles 5.1.4. The Patalas-Schindler volume sampler 5.1.5. Particular methods for insects 5.2. Vegetation 5.2.1. Emergent vegetation 5.2.2. Submerged vegetation 5.2.3. Sampling floating vegetation 5.3. Bottom fauna 5.3.1. Hand net sampling of forest litter 5.3.2. Lifting stones 5.3.3. The Planting of removable portions of the substrate 5.3.4. Cylinders and boxes for delimiting an area 5.3.5. Trawls, bottom sledges and dredges 5.3.6. Grabs 5.3.7. Dendy inverting sampler 5.3.8. Box samplers and corers 5.3.9. Air-lift and suction devices 5.4. Poisons and anaesthetics used for sampling fish in rock pools and small ponds