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 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 ) Actinopterygii 輻鰭魚綱 ( 條鰭魚 ) Clupeiformes 鯡形目 Clupeiformes 鯡形目 Clupeidae 鯡科 Clupeidae 鯡科 Sprattus 黍鯡屬 Sprattus 黍鯡屬 sprattus 黍鯡種 sprattus 黍鯡種 3

Cod Acartia 紡錘類 Sprat 4 Zooplankton Fish eggs Pseudocalanus 橈腳類 Cod larvae

From the early 1980s to the late 1990s 5 Pseudocalanus 橈腳類 Acartia 紡錘類 Cod Sprat

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. 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 The purpose of the studies was to document the vertical distribution of sprat larvae and their potential prey. 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 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). 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

10 vertically resolved zooplankton sampling in June 2002 sampling on all other dates

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12 MOCNESS Mesh size (larval fish) 335 um Mesh size(zooplankton) 50um 5m depth intervals borax-buffered formaldehyde– seawater solution (4% final concentration) laboratory analysis

13 laboratory analysis Sprat larvae: ≥0.1mm Zooplankton: at least 500 individuals 1.adult males and females 2.Species(Zooplankton) 3.Abundances

2.Data analysis weighted mean depths (WMD) weighted mean depths (WMD) 加權平均深度 加權平均深度 WMD=(∑ni∙di) /∑ni 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 Sprat larvae were classified into three length groups (2 to <5; 5 to <10; ≥10 mm) (2 to <5; 5 to <10; ≥10 mm) 15

Results 16

1.Ontogenetic migration 1.Ontogenetic migration 2.Diurnal vertical migration 2.Diurnal vertical migration 3.Prey distribution 3.Prey distribution 17

1.Ontogenetic migration 18 0

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). 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

20 No significant day– night differences in vertical distribution 仔稚魚適 應溫暖且 低鹽的環 境

21 Significant day– night differences in vertical distribution 仔稚魚在白 天適應較低 溫及高鹽的 環境

3.Prey distribution The SF of Acartia spp. biomass, the preferred prey for sprat larvae. 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. 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. 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

延伸 29

Regime shift ( 物種組成轉移 ) 30 Pseudocalanus acartiaCodSprat NAO( 北大西洋振盪 ) From the early 1980s to the late 1990s 數值越高，溫度越高

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