Local variability, human factor or vague procedure? Searching for the reasons of excessive mortality in free living aquatic insects, resulting from biological monitoring

During the analysis of the biomonitoring data of Polish watercourses, it was found that the vast majority of aquatic insects (83–95% of more than 8.8 million individuals collected between 2012 and 2019) die unnecessarily during sampling, as a result of the sub-sampling procedure. Great, in some cases 30-fold differences in the mortality of insects, including those belonging to protected taxa, were observed between the samples analyzed by various regional laboratories. The most important reason for these differences appears to be factors that can be collectively referred to as the ‘human factor’, related to removing insects from the sphere of ethical protection, makes their killing an activity ethically neutral. This kind of attitude, which does not attach any importance to the life and suffering of insects interacts with the lack of precise requirements for the sampling equipment used. Those factors seem to be the most important in explaining the causes of excessive mortality of aquatic insects during sampling and the huge differences between laboratories. Principal component analysis and the analysis of variability measures showed that ecological differences between sampling sites can only be considered as a secondary determinant. Implications for insect conservation Improperly planned and conducted monitoring procedures, through excessive mortality of free-living aquatic insects, have or may have a negative impact on the environment and biodiversity. Therefore, it seems very important to promote alternative solutions that reduce such mortality in biological monitoring, such as: non-lethal methods of animal sampling, the use of pre-sampling areas to estimate the density of animals before sampling and estimation of the maximum abundance of a sample necessary for a reliable estimate of taxonomic richness using rarefaction.