Using Multivariate Autoregressive State-Space Models to Examine Stocks of Greenland Halibut in the North Atlantic

• Main Author: Úbeda Quesada, Julio
• Other Authors: Sánchez-Lizaso, José Luis, Nogueira Gassent, Adriana, Universidad de Alicante. Departamento de Ciencias del Mar y Biología Aplicada
• Format: Master Thesis
• Language: English
• Published: 2021
• Subjects: Population structure; Greenland halibut; Multivariate Autoregressive State-Space models; North Atlantic Ocean; Sustainable fisheries management; Zoología; Barents Sea; Canada; Greenland; East Greenland; Faroes; Iceland; North Atlantic
• Online Access: http://hdl.handle.net/10045/117002

To manage a fishery effectively, and implement worthwhile fisheries regimes and conservation plans, it is highly important recognizing the stock structure of an exploited species. Greenland halibut is managed in the North Atlantic as four separated offshore stocks. Here I work with three of those stocks, the Northeast Canada - West Greenland (NWAS), the East Greenland, Iceland and Faroes waters (WNS) and the Barents Sea (NAS) to examine if the existing management boundaries should be maintained or should be reconsidered. For that I have combined abundance time-series from bottom trawl surveys from 4 different countries from 1996 to 2019, and I have mathematically formulated 13 different hypotheses about the population structure of Greenland halibut with Multivariate Autoregressive State-Space (MARSS) models. These hypotheses were based on the literature and biology of the GHL, at two different depth zones (shallow < 400 m; deep > 400 m) and for 3 length ranges (9-29 cm, juveniles; 30-60 cm maturing; > 61cm adults). Finally, for each hypotheses, I run the models with different levels of parameters complexity, and with and without covariates (NAO index and commercial catches) to evaluate relationships with climate and commercial catches. The best fit model included five different trajectories without the effect of the covariates: (1) One overall trajectory for NWAS; (2) East Greenland north; (3) East Greenland south (juveniles, maturing, and adults deep) - West Iceland (juveniles, and maturing deep); (4) West Iceland adults deep - West Iceland (juveniles, maturing and adults shallow) - East Iceland (juveniles, maturing and adults shallow) - East Iceland adults deep; and (5) East Iceland (juveniles and maturing deep) – All NAS. The results of the best fit model suggest that the assessment of Greenland halibut in the North Atlantic should be treated carefully, flagging out the WNS, which seems to be a mix of different populations.