We examined spatial and temporal differences in growth patterns of young-of-the-year (YoY) sprat Sprattus sprattus synchronously sampled in October 2002 from 4 different regions of the Baltic Sea (western, central, eastern, northeastern Baltic). The microstructure of the sagittal otoliths of 427 individuals from 64 sampling sites were analysed to determine the day of first feeding (DFF) and the growth history of YoY survivors. DFF distributions differed markedly between Baltic areas, with a shift to later mean DFFs and narrower distributions from west to northeast. This was consistent with the shift in mean seasonal spawning effort of Baltic sprat, derived from long-term observations (1973 to 2002) of sprat egg abundance in these areas. Otolith growth trajectories (i.e. increment width-at-age) had a characteristic shape related to sampling area and, more importantly, to the time of the year at which the individual started feeding (DFF). During the larval stage, individuals from the northeastern area and those born later in the year had higher growth rates than their earlier born conspecifics, while the pattern was reversed during the juvenile stage. Weekly means of satellitebased sea-surface temperature were used to approximate the potential temperature history of YoY survivors, which significantly influenced the shape of the otolith growth trajectory. We conclude that different DFFs and therefore different temperature histories were primarily responsible for the largescale spatial growth variability between newly recruited Baltic YoY sprat in 2002.KEY WORDS: Young-of-the-year sprat · Otolith microstructure analysis · Satellite data · Sea-surface temperature · Growth patterns · Day of first feeding · Egg abundance
Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 317: [225][226][227][228][229][230][231][232][233][234][235][236] 2006 throughout the larval and early juvenile stages of sprat . Because survival in the field is often coupled with growth (Houde 1989), a better understanding of the processes that influence growth patterns in larval and juvenile Baltic sprat is desirable. However, an inherent limitation of growth studies on larvae and early juveniles is that 'average' patterns do not reflect the small fraction of individuals that will eventually emerge as survivors of these stages (Sharp 1987). It is thus meaningful to obtain samples from successful sprat recruits and investigate their growth histories, which can later be compared to individuals sampled earlier from the population.Growth histories of sprat survivors are best inferred from otolith microstructure analysis of newly recruited, young-of-the-year (YoY) or 0-group sprat because, until their first winter, sprat are known to form readily discernible, daily increments that correspond in width to daily somatic growth rates and allow a direct backcalculation until the day of first feeding (DFF) (Baumann et al. in press). In sprat, DFFs comprise the best available proxy for hatch date, beca...
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