“…For instance, multi-stage design is very common in the monitoring of fish populations, whereby fish are caught at different sampling sites, all or a high proportion of the fish in that catch are measured for length, but only a sub-sample of the measured fish are aged. Comparisons of different sub-sampling designs for collecting and studying the distribution of a particular trait, such as age composition of a populations (Kimura, 1977; Pennington, Burmeister & Hjellvik, 2002; Chih, 2009; Hulson, Hanselman & Shotwell, 2016), have been more thoroughly studied in fisheries science than in other ecology fields (Kosmelj, Cedilnik & Kalan, 2001; Stafford et al, 2006; Smith et al, 2011; Brown et al, 2013). Thus, the sampling design to gather data on population abundance (stage 1) is paramount in ecological research, but also the sub-sampling design to gather data on traits-structure in the population (stage 2 or 3) can have a major impact on the population estimates, which will be used as reference points for assessment and management.…”