The ecological role and trophic relationships of seasonal cohorts of the Patagonian Squid (Doryteuthis gahi) in the marine ecosystem of the Falkland Islands

263 pages

Squids are a diverse and ecologically important group of marine organisms that play crucial roles in marine food webs and ecosystem functioning. Understanding the ecology and trophic dynamics of squid species is essential for comprehending the structure and functioning of marine ecosystems. This PhD thesis presents a comprehensive investigation into the trophic dynamics and ecological significance of Doryteuthis gahi, a squid species found around the Falkland Islands. The study encompasses three main research approaches: stomach content analysis, stable isotope analysis and Ecopath modelling. By synthesizing the main findings from these studies, a holistic understanding of the species' feeding habits, trophic position and ecosystem-level impacts can be achieved. The first study, employing stomach content analysis, revealed distinct diet compositions of D. gahi during different seasons and years. Notably, the diet shifted in prey preference from small crustaceans to fish and squid during ontogeny. The autumn-spawning cohort preyed more upon euphausiids whereas the spring-spawning cohort, having their feeding period mainly in austral-winter months, preyed more upon squid, fish and chaetognaths. A comparison with a dataset from 2001 showed an increased presence of Munida gregaria in the diet of D. gahi in 2020 compared to 2001. [...]

The Beauchene Fishing Company Ltd. is to thank for the sponsorship and funding of this PhD post. The Fisheries Department of the Falkland Islands is to thank for the funding acquisition, partly sponsoring and the provisioning of the necessary infrastructure for this PhD project

Peer reviewed