• Academic publication

Sampling frequency, duration and the Southern Oscillation influence the ability of long-term studies to detect sudden change

Hewitt JE, Bulmer R, Stephenson F, and SF Thrush. April 2021. Global Change Biology 27:2213–2224.


Monitoring design criteria generally focus on number of data points, sampling frequency and duration, often derived from previous information on species seasonal and multi-year temporal patterns.  Our study questioned whether the timing of any impacts relative to Southern Oscillation would also be important. We imposed a series of simulated reductions on macrofaunal abundance data collected regularly over 29 years from two sites, using species selected for observed differences in temporal dynamics.  We found both within-year sampling frequency and the timing of the imposed reduction relative to the Southern Oscillation Index affected detection ability.  The latter result, while apparently demonstrating a confounding influence on monitoring, offers the opportunity to improve our ability to detect and interpret analyses of monitoring data, and thus our ability to make recommendations to managers.


  • When an impact occurs in time relative to the Southern Oscillation affects the ability of the monitoring programme to detect the impact
  • The sampling frequency of monitoring programmes of macrofaunal species needs to be greater than one or two times per year in order to detect even large changes
  • SOI indices and species temporal patterns need to be included in monitoring analyses to improve detection
  • Management should consider El Nino and La Nina when consenting



SOI, climate patterns, tipping points, monitoring design, monitoring analysis