Vertical distribution of Baltic sprat larvae changes in
Vertical distribution of Baltic sprat larvae - changes in patterns of diel migration? 波羅的海黍鯡幼體的垂直分佈 -日週迴游模式的改變? Voss, R. , Schmidt, J. O. , and Schnack, D. 2007. Vertical distribution of Baltic sprat larvae: changes in patterns of diel migration? – ICES Journal of Marine Science, 64. Speaker: 高似嘉 1
Introduction 2
Sprattus sprattus- Classification • Actinopterygii 輻鰭魚綱 (條鰭魚) Clupeiformes 鯡形目 Clupeidae 鯡科 Sprattus 黍鯡屬 sprattus 黍鯡種 3
Cod Sprat Cod larvae Zooplankton Fish eggs Acartia紡錘類 Pseudocalanus 橈腳類 4
From the early 1980 s to the late 1990 s Pseudocalanus 橈腳類 Cod Acartia 紡錘類 Sprat 5
• Mechanisms influencing survival of sprat larvae are only poorly understood, at least partly because of missing knowledge of vertical distribution patterns of larvae, so hampering process-orientated research. 6
• Here, we investigated the vertical distribution and migration of sprat larvae and zooplankton in the Bornholm Basin, based on samples obtained from 1998 to 2002 and in 1989 to 1990. The purpose of the studies was to document the vertical distribution of sprat larvae and their potential prey. 7
Material and methods 8
1. Sampling and laboratory analysis • Vertically resolved sampling was conducted during seven spring cruises between May 1989 and June 2002 (Table 1) in the central part of the Bornholm Basin, central Baltic Sea (Figure 1). 9
vertically resolved zooplankton sampling in June 2002 sampling on all other dates 10
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Mesh size (larval fish) 335 um Mesh size(zooplankton) 50 um 5 m depth intervals MOCNESS borax-buffered formaldehyde– seawater solution (4% final concentration) laboratory analysis 12
Sprat larvae: ≥ 0. 1 mm Zooplankton: at least 500 individuals laboratory analysis 1. adult males and females 2. Species(Zooplankton) 3. Abundances 13
2. Data analysis • weighted mean depths (WMD) 加權平均深度 • WMD=(∑ni∙di) /∑ni (where ni is the abundance of individuals in depth stratum i with midpoint depth di. ) 14
Length groups • Sprat larvae were classified into three length groups • (2 to <5; 5 to <10; ≥ 10 mm) 15
Results 16
• 1. Ontogenetic migration • 2. Diurnal vertical migration • 3. Prey distribution 17
1. Ontogenetic migration 0 18
2. Diurnal vertical migration • Diurnal vertical migration was investigated for the largest size class of sprat larvae (≥ 10 mm), because this group is least restricted by limited swimming ability (Figures 3 and 4). 19
No significant day– night differences in vertical distribution 仔稚魚適 應溫暖且 低鹽的環 境 溫容 鹽 度氧 度 量 20
Significant day– night differences in vertical distribution 仔稚魚在白 天適應較低 溫及高鹽的 環境 溫容 鹽 度氧 度 量 21
3. Prey distribution • The SF of Acartia spp. biomass, the preferred prey for sprat larvae. 22
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Discussion 24
Vertical migration patterns • Larger larvae’s vertical aggregation of feeding larvae is often determined by a combined effect of food abundance and suitable light level. Light level is important because sprat larvae are visual predators. The main daily feeding period of sprat larvae is around midday. 25
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Prospective 27
• We propose further research into temperature and prey as potential drivers of behavioural change in larval Baltic sprat, because this might considerably impact larval survival probability and therefore recruitment. 28
Regime shift (物種組成轉移) From the early 1980 s to the late 1990 s Pseudocalanus Cod acartia Sprat 數值越高,溫度越高 NAO(北大西洋振盪) 30
Thanks for your attention 31
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