Fig 1.
Study area and location of cod trawl hauls.
The map (made with Natural Earth) shows ICES Subdivisions (SDs, separated by solid black lines), and the ICES statistical rectangles (thin dotted lines). Bathymetry is shown in shades of blue. The Eastern Baltic cod stock occurs in the area covered by SDs 25–32 (SD 31, covering the Bothnian Bay, is not shown).
Fig 2.
(a) Commercial landings in the ICES Subdivisions (SDs) 25–29 (excluding SD 28.1). The black line is the ratio of landings in the northern SDs (SD 27–29) to the total landings (SDs 25–29, excluding SD 28.1). (b) Commercial landings in SDs 28.1 (Gulf of Riga), SD 30 (Gulf of Finland) and SD 32 (Bothnian Sea). Landings in SD 31 are not presented because of the very small amount.
Table 1.
Intercept (A), linear coefficient (β)and estimated degrees of freedom of smoothing terms are shown for all the models. The deviance explained (dev.expl), the generalized cross validation (GCV) and genuine cross validation (gCV) scores are also indicated for each model. All the terms of each model are significant (p-value < 0.001).
Fig 3.
(a) effect of spatial location. (b) spatial effect of cod population size. (c) interactive effects of salinity and oxygen. (d) effect of depth. (e) effect of the reproductive volume. (f) estimated variance-to-mean relationship (solid line, slope equals to 268). The circles are averaged squared residuals in each category (e.g. 0 < E(Y) < 2, 2 < E(Y) < 4 and so on).
Fig 4.
Predictions of cod spatio-temporal population distribution at different population levels.
(a) 1970–1972 (hindcast), (b) 1982–1984, (c) 1986–1988, (d) 1991–1992, (e) 2006–2007. (f) Baltic cod population size (ages 3+). Red and blue colors indicate high and low predicted CPUEs, respectively.
Fig 5.
Minimum area containing 95% of the estimated cod abundance by year.
Fig 6.
Indicator of the recent spatial development of the cod population.
Time series of cod commercial landings (proportion of landings in SDs 25–26 caught in SD 26; data from ICES stock assessment working group reports), cod commercial landings per unit of effort (LPUE in kg landed/hour, ratio SD 26 / SD 25; data from the Scientific, Technical and Economic Committee for Fisheries of the European Commission) and survey catch per unit of effort (CPUE in kg/h, ratio SD 26 / SD 25; data from ICES DATRAS database).