North Atlantic cod recovery under climate change and exploitation pressure, a non-linear approach

• Main Author: Sguotti, Camilla
• Other Authors: Möllmann, Christian (Prof. Dr.)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky 2019
• Subjects: populations dynamics; non-linear dynamics; management; 570 Biowissenschaften; Biologie; 42.03 Methoden und Techniken der Biologie; 42.94 Meeresbiologie; 42.97 Ökologie: Sonstiges; ecology; Meeresökologie; fisheries science; ddc:570; atlantic cod; Gadus morhua; North Atlantic
• Online Access: http://nbn-resolving.de/urn:nbn:de:gbv:18-96110; https://ediss.sub.uni-hamburg.de/handle/ediss/8070

Deteriorated marine ecosystems are the results of the impact of a multitude of human pressures, such as fisheries exploitation and human-induced climate change, and have pushed the introduction of comprehensive policies to manage the resources. These policies are built on the ecosystem based management framework. Measures to recover depleted stocks in order to guarantee sustainable fisheries in the future and safe and productive fish populations have been introduced. However, after many years of management, many stocks such as Atlantic cod (Gadus morhua), are still depleted and far from safe biological limits, suggesting the presence of complex stock dynamics, and posing doubts on their recovery potential. Over my PhD, using data from 20 Atlantic cod stocks distributed all over the North Atlantic, I have evaluated the recovery potential of Atlantic cod stocks under climate change and exploitation pressure, and whether the recovery could be hindered by discontinuous dynamics. Applying a range of non-linear methods, I show that cod stocks present discontinuous and catastrophic dynamics hindering their recovery and resulting in lower productivity under climate change. Moreover, I uncover these dynamics not only in biomass but also in population processes such as recruitment. I demonstrate that catastrophic transitions have occurred and that, most of the stocks present very low resilience and are currently in a low and unsafe biomass state far from historical levels. Temperature increase, a proxy for ecosystem changes, and unsustainable exploitation are the drivers of these shifts and therefore under climate change, the recovery of the stocks seems unlikely. Moreover, recruitment is highlighted as one of the fundamental processes to achieve a population rebounding, but it is also negatively (on average) influenced by climate change. These results are fundamental from a management perspective because: i) they reveal non-linear discontinuous dynamics that are difficult to uncover but necessary to incorporate into ...