Guidelines for sampling fish in inland waters
The book is addressed mainly to Fishery Biologists but it is hoped that Fishing Gear Technologists also can acquire some basic knowledge of sampling problems and procedures which, in turn, can result in improved design of gears. To successfully utilize these guidelines the reader should be acquainted with the general biology of fishes, with limnology and elementary statistics. Preferably he should have some knowledge of fishing gear.
The scope of these guidelines is limited to various techniques for capturing and observing fish at all stages of life. It is confined to inland waters, but a wide range of habitats in which fish can be sampled is recognized. Some of these techniques do not differ from those used in commercial or artisanal fisheries, but for sampling they should be used with understanding of the intricate relationships between fish and the gears in operation. The statistical aspects of sampling form an important part of this understanding. The other part is that related to construction and mode of operation of a gear. The reader should be able to choose a gear, or a set of devices, most suitable for his sampling programme out of those described here, although the guidelines do not offer detailed information on the construction of the gears.
In most cases, a gear technologist, or an expert on electric fishing or acoustic methods, should be at least consulted, and sometimes involved in planning and performing research with the selected gear.
Neither the text nor the references cover all sampling techniques and problems related to the design of sampling procedures. Lagler (1971) distinguished several categories of methods of fish capture in two groups: (i) Handling, which includes removal of water, use of chemicals, spearing, netting and electric fishing; and (ii) Sensing, i.e., watching and using photography, television, acoustic methods, etc., all techniques by means of which fish can be located and even counted. The ingenuity of researchers has been far more diverse than the scope of these guidelines. These guidelines cannot replace actual research experience; nor can reading the chapters below and the literature referred to substitute for operational experience in fish sampling