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Dissertation zugänglich unter
Length back-calculation and growth patterns of juvenile Baltic sprat (Sprattis sprattus L.)
Längenrückberechnung und Wachstumsmuster juveniler Ostseesprotten (Sprattus sprattus L.)
Günther, Claudia Charlotte
Dokument 1.pdf (2.807 KB)
Freie Schlagwörter (Englisch):
biology , fishery science , growth , otoliths , sprat
Temming, Axel (Prof. Dr.))
Tag der mündlichen Prüfung:
Kurzfassung auf Englisch:
The present thesis investigated the recruitment-relevant post-larval and juvenile life-stages in Baltic sprat by examining individual age and growth patterns recorded in otolith microstructures.
Length back-calculation on the basis of daily otolith micro-increments is an important tool to investigate mechanisms influencing mortality in a yearly cohort. A new length back-calculation method, the Metamorphosis Inflection Point (MIP) method, was developed taking into account a non-linear ratio between fish length and otolith length on an individual basis. A change in the relationship between fish length and otolith length co-occurred with the otolith length when maximal increment widths were deposited on the otolith and with the mean fish length when the increase in body height was maximal during the development. This coincidence of three changing morphometric features formed the back-bone of the new back-calculation algorithm. Length growth in young sprat features two peaks, one smaller in the larval and one larger in the early juvenile stage. The MIP algorithm assigned the minimum in length growth to the maximum in otolith growth at metamorphosis. Compared to the results of the linear biological intercept method, higher length growth rates were found during the larval and the juvenile stage.
In an experiment, length, dry and wet mass and otolith growth during the early juvenile stage was examined under ad libitum conditions at different constant temperatures in the laboratory. The main goals were to investigate length and otolith growth under ad libitum feeding conditions between 16°C and 22°C and to quantify the amount of food consumed under ad libitum conditions. Juveniles were found to require ten times more food than post-metamorphic sprat. Optimal otolith growth in relation to temperature was described with a quadratic function. Results of the experiment were used to reconstruct feeding conditions from increment patterns of wild caught juvenile sprat from the Western Baltic Sea in 2003 and 2007. Assuming somatic and otolith growth are mainly influenced by three factors, size, temperature and food ingestion, one factor can be estimated when two are known. Hence, by calibrating the effect of temperature on otolith growth under ad libitum feeding at a fixed size in the laboratory, feeding conditions were inferred from otoliths of wild-caught sprat at the same size using daily surface temperatures measured in the Kiel Bight. In 2007, sub-optimal feeding conditions during the early juvenile life-stage of Young-of-the-Year survivors were found in contrast to optimal feeding conditions for the majority of Young-of-the-Year survivors in 2003. However, individuals that experienced peak temperatures of the season during the early juvenile stage suffered un-favourable feeding conditions, irrespectively of the year. These individuals were born early in the season. Thus, results confirm that summer born individuals had an advantage over spring born individuals. High temperatures in the early juvenile stage of spring born sprat elevate the metabolic rate and thus the amount of food needed to grow optimal.
The difference in growth performance of early and late born sprat leaded to the question which specific meteorological conditions influence the seasonal location of the main spawning time and hence the survival rates and subsequent recruitment. By analysing age and length growth of juvenile sprat from different years in the Western Baltic Sea, high water temperatures in spring and low summer water temperatures were found to cause a broad window of survival including spring and summer born individuals and a low mean length growth rate. In contrast, low spring water temperatures combined with high summer water temperatures were observed in a year with a late and narrow window of survival which was accompanied by a high mean length growth rate. Low growth rates occurred in a year with low recruitment, while high growth rates appeared in a year with high recruitment. The influence of spring and summer water temperature on recruitment was further investigated using yearly hydro-acoustic estimates of 0-group sprat for the Western Baltic Sea and surface temperatures between 1999 and 2010. A highly significant correlation was found between the abundance of juvenile sprat in autumn and the ratio between minimum and maximum water temperatures of the year. It was concluded that a cold spring will delay spawning and/or egg development and hence shift the main growth phase of larvae later into the summer season, where these larvae can benefit from high temperatures, while juveniles can experience optimal conditions after the peak temperatures of the year.