Investigating spatio-temporal change in spawning activity by Atlantic mackerel between 1977 and 1998 using generalized additive models

Long-term, seasonal and spatial patterns in spawning activity of Atlantic mackerel (Scomber scombrus) along the continental shelf west of Europe were investigated. Stage I egg densities from all eight available international, triennial surveys (1977, 1980, 1983, 1986, 1989, 1992, 1995 and 1998) were modelled using generalized additive models. The data showed that seasonal and spatial patterns of spawning activity varied inter-annually. Total annual egg production peaked in 1989 with minima in 1983 and 1998. Further examination of these trends (1977-1998) showed that the intensity of spawning activity has shifted location, declining in the south and rising in the north. There was no direct link between stage I egg densities and sea surface temperature, although the rate of temperature increase along the shelf edge was strongly related to the total annual egg production by the mackerel. (C) 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.