A modeling framework to meta-analyse discard survival experiments illustrated by Nephrops norvegicus in European demersal trawl fisheries

Good knowledge of discard survival in commercial or recreational fisheries is key in enabling more accurate stock assessments and supporting evidence-based regulatory measures; however, estimating discard survival is challenging. To improve the estimation of survival rate at regional scales and to identify key drivers, we present here a meta-regression (MR) framework that considers differences in experimental design, quality and context specificity between individual studies. First, studies are filtered through a systematic critical review to exclude results considered too uncertain or potentially biased. Discard survival rates are then corrected to limit estimation method bias, and associated uncertainty is included as a weighting. The MR is finally applied under a hierarchical mixed-effects framework to account for the nested structure of the data and correct for experimentally induced mortality bias. We illustrate how the MR can address methodological and analytical limitations in discard survival studies using Norway lobster (Nephrops norvegicus) discarded from European demersal trawl fisheries. While some effects were already identified from single studies, such as the temperature change, the MR highlighted other effects not perceptible at a regional scale, varying more at the scale of the fishing operation, such as tow duration, but also related to the size of experimental subjects and physiology. This flexible framework has applicability to other species or contexts. The case study provided insights to make recommendations for future survival studies to improve the predictive potential of this type of MR, such as the importance of following standardized protocols and analyses, and to report data at the finest resolution.