Cod Reproductive Success and Climate-Hydrographic Processes

FIGURE 18.8 Interannual variability in reproductive volume (water with salinity 11 psu and oxygen concentration 2 ml/1) in the main cod spawning areas in the eastern Baltic Sea (Plikshs et al., 1993 ICES, 2004b). 

6 SPRAT AND HERRING REPRODUCTIVE SUCCESS AND CLIMATE-HYDROGRAPHIC PROCESSES 

Sprat recruitment has been shown to be driven by climate-induced temperature changes during the years 1955-2005 (MacKenzie and Koster, 2004 MacKenzie et al., 2008). MacKenzie and Koster (2004) found a positive correlation between recruitment and the average water column temperature in May (Fig. 18.9). In an exploratory analysis relating recruitment to monthly depth-specific temperatures, Baumann et al. (2006) observed significant temperature-recruitment correlations between March and July in mid-water 

FIGURE 18.9 Relationship between May temperature at 45-65 m in the Bornholm Basin and sprat recruitment in Subdivisions 22-32 (MacKenzie et al., 2008). The dots are year classes 1973-1999 and the numbers represent year classes since 2000. The regression line (dotted) and 95% confidence limits (dashed) only includes the years 1973-1999 (MacKenzie and Koster, 2004). 

The effect of the physical environment on growth of the major Baltic fish stocks is mainly indirect, working via food availability as well as intra- and interspecific competition. All three major fish stocks displayed pronounced changes in growth during the last three decades (Fig. 18.10). 

---