Environmental and stock effects on spatial distribution and abundance of mature cod Gadus morhua

Identification of environmental and stock effects that influence the spatial distribution and abundance of a spawning stock is necessary for understanding stock and recruitment processes, but data on such effects are rare. We examined environmental (depth, temperature), locational (latitude, longitude), and stock (length, age) effects on the distribution and abundance of mature and spawning cod Gadus morhua in Icelandic waters. Generalized additive models (GAMs) were used to test the effects of these covariates on data collected from historic groundfish surveys (1985 to 1999) around the onset of spawning. Mature cod were present in waters all around Iceland, with persistent concentrations in any given year (indicative of regional spawning components) off the southwest, southeast, and north coasts. Depth, temperature and, more importantly, location were significant covariates affecting both the relative abundance of mature cod and the spatial distribution of spawning cod. Incorporating the effects of these covariates and their underlying relationships into stock and recruitment processes will provide insight into the mechanisms involved in population structuring of cod in Icelandic waters.