Christiansen & Nygaard evaluate SPiCT for Greenland halibut in NAFO Division 1A Uummannaq; final SPiCT model configuration accepted to provide advice
Evaluation of surplus production modelling in continuous time (SPiCT) for Greenland halibut in NAFO Division 1A Uummannaq
Northwest Atlantic Fisheries Organization
www.nafo.int Serial No. N7744
NAFO SCR Doc. 26/024
SCIENTIFIC COUNCIL MEETING –JUNE 2026 Evaluation of surplus production modelling in continuous time (SPiCT) for Greenland halibut in NAFO Division 1A Uummannaq Henrik Christiansen1, Rasmus Nygaard1 1Greenland Institute of Natural Resources, Box 570, 3900 Nuuk, Greenland 2026-06-04 CHRISTIANSEN, H., & NYGAARD, R., 2026. Commercial data from the Greenland halibut fishery in Uummannaq fjord. NAFO Scientific Council Research Document, SCR Doc. 26/024: 1-16. Abstract The Greenland halibut stock in NAFO Division 1A Uummannaq has previously been qualitatively assessed using index-based information. First attempts to provide analytical assessments with surplus production models were made since 2024. Here, sensitivity analyses are presented, i.e., an evaluation of several runs with surplus production models in continuous time (SPiCT) where input priors for r and B/K were varied while other model setup parameters were held constant. In addition, variations of truncated input catch time series were evaluated. These model evaluations were discussed in plenary and indicate a level of robustness in parameter estimates that provide an improved quantitative perception of the state of the stock compared to the previous qualitative assessment. A final model configuration is presented, which was accepted during the 2026 Scientific Council June meeting to provide advice. Introduction The inshore Greenland halibut stocks in NAFO Division 1A have been separated from the offshore Greenland halibut stock in Subarea 0+1 in 1994. The latter is assessed using a stochastic surplus production model in continuous time (SPiCT) as developed by Berg & Pedersen (2016) since 2024 (Nogueira et al., 2024). Advice for the inshore stocks in Division 1A has previously been provided without analytical assessment model, using index-based information only. Caution must be taken when applying surplus production models for these inshore Greenland halibut stocks as they are believed to rely on recruitment from the offshore stock. However, application of a SPiCT model may at least provide quantitative estimates of the exploitable biomass status and thus enable the application of the NAFO precautionary approach (PA) framework. An important consideration is then how sensitive the model reacts to the specification of different priors in terms of growth rate (r) and the initial state of the biomass of the stock in relation to its carrying capacity (B/K). Furthermore, if input time series vary in length, it should be explored whether this affects model results. Here, several (>30) model runs are evaluated and compared to investigate model sensitivity and develop an appropriate model configuration for the assessment of the Greenland halibut stock in Division 1A inshore Uummannaq.
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