Spatial patterns of the temporal dynamics of three gadoid species along the Norwegian Skagerrak coast

Abstract

Time series from an extensive research survey of juveniles of cod Gadus rnorhua, p~lia~k Pollachius pollachius and whiting Merlangius rnerlangus sampled from 1919 to 1994 at 38 stations along the Norwegian Skagerrak coast were investigated. Spatial and temporal analyses were per- formed to study the spatial pattern of the temporal dynamics of the 3 fish species. Spatially consistent variations were detected in abundance, year-to-year fluctuation as well as in periodicity. The spatial heterogeneity occurred at a mesoscale (differences hetween fjords) and at a local scale (differences hetween stations within a fjord) for the 3 gadoids. However, the magnitude of the spatial heterogene- ity differed hetween species. Cod and whiting, which were more abundant in sheltered areas, showed higher spatial variahility than pollack, which was more abundant in exposed locations. In this way, the spatial pattern of abundance appeared to be linked to the scale of variability oi the species. AJl3 spe- cies exhibit periodic fluctuations of 2 to 2.5 yr in their optimal habitats, which probably resulted from intrinsic interactions in age-structured populations, such as density-dependent competition and canni- balism. In addition, all the species exhibited long-term trends possibly due to extrinsic forces, such as environmental changes or anthropogenic influences.