About Population-Level-Assessments

In the data-poor situations common to bycatch populations, ecological risk assessment (ERA) provides a framework for estimating the vulnerability and stock status of bycatch populations, and evaluating potential consequences of fisheries management actions [1]. This process is categorised as ‘population-level assessment’ (PLA) in the context of the BMIS.

Risk-based PLA considers population-level attributes such as abundance and population structure (sex, age and size composition), as well as other variables such as life history traits and threats (including fishing pressure), to evaluate risks to bycatch populations. Risk analysis can be used to prioritize data collection, scientific assessment, and management action [2]. It enables the implementation of an ecosystem approach to fisheries management, so that both bycatch and target populations are managed sustainably.

Various methods may be employed for evaluating risk, including productivity susceptibility analysis (PSA), demographic analysis and stock assessments. They vary from purely qualitative in nature, through semi-quantitative to fully quantitative. Qualitative risk assessments are useful for assessing large numbers of species for which biological data are scarce by providing the relative risks of species to prioritize research and management [2]. In contrast, quantitative assessments require more data and are usually applied to a more restricted group of species [2]. There is overlap among the methods (e.g. 3) and some bycatch studies may utilise a range of risk analysis techniques. For example, Hobday et al (2011) created an ‘Ecological Risk Assessment for the Effects of Fishing’ (ERAEF) framework which involves a hierarchical approach that moves from a comprehensive but largely qualitative analysis of risk at Level 1, through a more focused and semi-quantitative approach at Level 2, to a highly focused and fully quantitative “model-based” approach at Level 3 [4].

The three methods listed above are described separately in this section, as are abundance indices, the simplest measure of relative abundance. The ‘risk analysis – open category’ catches those references that don’t easily fit other categories. What constitutes a bycatch species ‘population’ is defined on a study by study basis, on one or more attributes e.g., geographical region or life stage.


  1. Cortés E, Brooks EN, Shertzer KW (2015) Risk assessment of cartilaginous fish populations. ICES J Mar Sci 72:1057–1068. doi: 10.1093/icesjms/fsu157
  2. Arrizabalaga H, de Bruyn P, Diaz GA, et al (2011) Productivity and susceptibility analysis for species caught in Atlantic tuna fisheries. Aquat Living Resour 24:1–12. doi: 10.1051/alr/2011007
  3. NIWA (2016) Pacific-wide sustainability risk assessment of bigeye thresher shark (Alopias superciliosus) - Prepared for the WCPFC. Wellington New Zealand
  4. Hobday AJ, Smith ADM, Stobutzki IC, et al (2011) Ecological risk assessment for the effects of fishing. Fisheries Research 108:372–384. doi: 10.1016/j.fishres.2011.01.013