Recruitment of Baltic cod and sprat stocks: identification of critical life stages and incorporation of environmental variability into stock-recruitment relationships

Abstract

SUMMARY:The recruitment processes of Baltic cod and sprat were analysed and critical periods were identified by addressing the major impact factors on individual early life history stages separately and relating observed abundance data between successive stages. For cod, recruitment appeared to be dependent on egg survival, with low oxygen concentration in dwelling depths and predation by clupeids as the major causes for egg mortality. Surviving egg production and larval abundance were weakly correlated, whereas larval abundance was significantly related to year class strength. This indicated that the period between the late egg and the early larval stage is critical for cod recruitment. A potential variable identified to affect this life stage was prey availability for larvae. For sprat, early and late egg stage production as well as late egg stage production and larval abundance were significantly related. However, year class strength was largely independent of larval abundance. Thus, the period between the late larval and early juvenile stage appeared to be critical for sprat recruitment. Potential variables identified to affect this life stage were ambient temperature and wind stress. Environmental factors showing statistically significant covariance with the survival of one of these critical life stages were incorporated into stock-recruitment models for individual spawning areas separately and for the Central Baltic combined.

On the edge of death: Rates of decline and lower thresholds of biochemical condition in food-deprived fish larvae and juveniles

“…There is a substantial body of literature that indicates limiting prey levels are a source of larval mortality and a factor affecting recruitment success. In the Baltic Sea, empirical and model results indicate prey limitation controls survival of cod larvae (Köster et al, 2003). In a recent study, Huwer et al (in press) utilized sRD measurements to identify Baltic cod larvae in poor nutritional condition within areas having low concentration of the preferred prey, Pseudocalanus acuspes.…”

The influence of temperature on the development of Baltic Sea sprat (Sprattus sprattus) eggs and yolk sac larvae

“…The early ontogenetic stages, i.e. eggs and larvae, are strongly influenced by abiotic factors such as temperature, salinity, oxygen or wind forcing (Grauman and Yula 1989;Blaxter 1992;Köster et al 2003). Temperature plays a central role due to its importance in controlling physiological processes (Blaxter 1992;Fuiman 2002).…”

Available Information for Estimating Reproductive Potential of Northwest Atlantic Groundfish Stocks

“…Recent research challenging these assumptions, however, demonstrates that stock-recruitment relationships can be significantly improved by use of SRP indices that consider stock demography, spawner quality and environmental variability (Marshall et al, 1998;Scott et al, 1999;Köster et al, 2001;Murawski et al, 2001;Begg and Marteinsdottir, 2002). These studies also demonstrate that considerable amounts of data relevant to spawner-recruitment studies are available, which are not utilized in standard stock assessments (Ulltang, 1998;Trippel, 1999;Köster et al, 2003;Marshall et al, 2003).…”