Use of geographic information systems, spatial and environment-based models to study ecology and fishery of the veined squid (Loligo forbesi Steenstrup 1856) in Scottish waters
This PhD studies the ecology and fishery of the veined squid Loligo forbesi in Scottish waters by making use of different spatial and statistics tools, such as Geographic Information System (GIS), Generalised Additive Models (GAMs) and Geostatistics. The PhD thesis is divided in 6 chapters, arranged in a sequential order driven by the hypothesis and question which have arisen throughout the study. Chapter 1 aims to provide a general introduction of the objectives, state of the art and techniques utilised along all this work. Chapter 2 reports the use of Geographical Information Systems (GISs) to study squid resources in the North East Atlantic. Long-term monthly average Landings Per Unit of Effort (LPUE) series are mapped against SST, SBT, SSS, SBS and Depth to reveal plausible spatio-temporal relationships between oceanographic conditions and squid abundance. Hypotheses about the squid distribution and abundance in relation to environment, habitat selection and spatial migration are suggested. Chapter 3 reports a GAM application to describing intra-annual and inter-annual variation in squid abundance in Scottish waters is also reported. Geostatistical tools were applied in chapter 4 to model spatial patterns in squid abundance in Scottish waters to explore spatial heterogeneity and distribution. Spherical and gaussian model variograms and neighbourhood analysis were made. Results provide enough evidence to indicate that there are differences between the east and the west coast of Scotland. Chapter 5 reports a two-stage model to study distribution and abundance by a Binomial and Gamma sequential approach. GAMs and Regression trees on two stages were utilised using all the available environmental variables. These non-parametric modelling was used to forecast probability of presence and abundance of 1994 by a environmental data set. Finally, chapter 6 comprises the conclusions of the work, particularly from a point of view of the ecology of the squid.