National Research Institute of Fisheries Science, Japan 2. Integrative Oceanography Division, Scripps Institution of Oceanography, USA

Transcription

1 Distribution and Population Dynamics of Japanese Sardine, Anchovy and Chub Mackerel in the Kuroshio/Oyashio System: Seeking for Mechanistic Responses to Regime Shifts Akihiko Yatsu 1, Hiroshi Kubota 1, Akinori Takasuka 1, Motomitsu Takahashi 2, Norio Yamashita 1, Hiroshi Nishida 1, Chikako Watanabe 1, and Yoshioki Oozeki 1 1 National Research Institute of Fisheries Science, Japan 2 Integrative Oceanography Division, Scripps Institution of Oceanography, USA

2 Recent Distribution of Japanese Sardine, Anchovy, Mackerels in the Northwestern Pacific Sardine (Low Stock) Anchovy (High Stock) Chub mackerel Distribution =Feeding gr. Spawning ground Distribution =Feeding ground =Spawning ground Distribution Spawning ground Feeding ground 3 species share common feeding ground and to some extent spawning ground Anchovy spawning and feeding grounds are overlapping

3 Japanese Catch of Japanese Sardine, Anchovy, Mackerels during Catch in ton (Sardine) 7,, 6,, 5,, 4,, 3,, 2,, 1,, Sardine Anc hovy Mackerels Re gime s hift Mackerels: chub mackerel + spotted mackerel 2,, 1,5, 1,, 5, Catch in ton (Anchovy, Mackerels) Regime shift years: after Yasunaka and Hanawa (22) excl. 1998/99 Alternation of 3 species in a decadal scale is probably related to climatic regime shifts

4 Kuroshio Locations of Spawning Ground of Japanese Sardine during 196s-9s Estimated from the Egg Census Survey (Hiramoto, 1996) Expand beyond Kuroshio during high stock period, but not to KOTZ

5 Egg Distribution of Japanese Anchovy (Zenitani and Kimura, 1997) KOTZ Kuroshio Expand to KOTZ during high stock period, but not south of Kuroshio

6 Latitude 緯度 (N) (N) = 5 = 1 = 2 = 5 マイワシ Sardine Year カタクチイワシ Anchovy Driftnet CPUE at 155E during June, , by Hokkaido University Latitude 緯度 (N) (N) = 5 = 1 = 2 = 5 マサバ Chub mackerel Year 西暦 (19+) Latitude 緯度 (N) (N) = 5 = 1 = 2 = Year (19+) 西暦 Driftnet monitoring sites at 155E Adult distribution expand to open ocean during high stock period, in the 3 species

7 Basic Biology Japanese sardine Japanese anchovy Chub mackerel Life span about 7 yr about 3 yr 7 yr or more Max size BL 25 cm 14 cm 4 cm Fist maturity age (year) 1 (Low Stock) or 3 (High Stock) 1 2 (Low Stock) or 3 (High Stock) Fist maturity BL 17 cm 6 cm 3 cm Spawning season winter spring-autumn spring Spawning area southern Honshu - Kyushu (expand to open ocean beyond Kuroshio in the High Stock period ) northern Honshu - Kyushu (expand to open ocean in KOTZ in the High Stock period) central Honshu - Kyushu Prey phytoplankton (Diatom) and zooplankton (Calanus, Oncaea, Corycaeus, Paracalanus) zooplankton (Oncaea, Microsetella, Corycaeus, Eucalanus, Paracalanus, Oithona) zooplankton (Neocalanus, Eucalanus, Krill), anchovy, squid, salps

8 Correlation Coefficient (r) Map between Winter SST and LNRR of Japanese Sardine (Yatsu et al., 25) : positive r : negative r KESA LNRR= Ricker curve OYSL: Oyashio (1st br.) Southern Limit OYSL PDO Recruitment (1^6) 35, 3, 25, 2, 15, 1, 5, ln (Recruitment Residuals) SSB (1t)

9 Correlation Coefficient (r) Map between Winter SST and LNRR of Chub Mackerel (Yatsu et al., 25) : positive r : negative r LNRR= Ricker curve ln (Recruitment Residuals) Principal spawning grounds Recruitment (million) 25, 2, 15, 1, 5, 85 Chub mackerel , 2, 3, 4, SSB (1t)

10 KOTZ: Key Area for Recruitment KOTZ Population numbers 1.E+16 1.E+15 1.E+14 1.E+13 1.E+12 1.E+11 1.E+1 1.E+9 1.E+8 1.E Year class Sardine Egg Yolk-sac larvae Feeding larvae Recruit Watanabe et al. (1995) Recruitment (1 million) Recruitment Index Sardine , Pre-recruitment Index Recruitment (1 million) Chub mackerel Recruitment Index ,, 1,, 1,, 1, 1, 1, 1 Pre-recruitment Index Early survival is mainly determined after the feeding larvae distributing in KOTZ

11 Prey Composition (in No.) of Juvenile Sardine and Anchovy in KOTZ (May, 1997; Kubota et al., unpublished) Phytoplankton Oncaea spp. Corycaeus spp. 6.2% Sardine 4.9% 8.1% Small Calanoida (PL < 1mm) Paracalanus spp. Calanus spp. Large Calanoida (PL < 1mm) Unidentified plankton Other large copepod Other small copepod Anchovy 7.6% 2.6% 5.% 3.% Oncaea spp. 75% 76% Cladocera N=12, SL= mm N=5, SL= mm Cladocera and some copepods were common prey Large Calanoida (PL < 1mm)

12 Growth Rate Comparison between Simultaneously Collected Sardine (Gms) and Anchovy (Gma) in KOTZ (Takahashi et al., PICES XIII 24) 1. 1 Gms = Gma (n=5, r=.84, P =.78) Sardine Anchovy Gms (mm d -1 ) ( ) Poor prey Gma (mm d -1 ) Direct effect of temperature on early growth and, hence early survival if prey is sufficient in KOTZ

13 Optimal Growth Temperature Hypothesis (Takasuka et al., PICES XIII 24, submitted) Growth rate (mm day 1 ) Anchovy Sardine Anchovy collapse Sardine flourish Temperature shift Anchovy flourish Sardine collapse 16.2ºC 22.ºC Sea surface temperature ( C) Different optimum SSTs for early growth were detected in sardine and anchovy collected from various areas and years in the NW Pacific, leading to a plausible hypothesis of regime shift

14 Early Growth of Chub Mackerel in KOTZ and Recruitment-per-Spawners (RPS) during (Yamashita et al., unpublished) 1 23(n=32) 2 24 Fork length (mm) (n=27) 25(n=77) RPS (Number/kg) (RPS is Tentative value) Age (day) Early growth may also be a key for survival of juveniles of chub mackerel --- needs more data Growth Rate(mm/day)

15 Prey Composition of Skipjack Tuna (24) (Watanabe et al., unpublished) April-May 24 June-August 24 June-August 24 Kuroshio Kuroshio KOTZ Number (%) Fishes Amphipods Fishes Decapods Misc Fishes Squids Weight (%) Misc Anchovy Frequency (%) Amphipods Squids Anchovy Amphipods Anchovy SKJ heavily prey upon anchovy larvae and adults in recent years

16 Skipjack Catch (1968) May Skipjack Recruitment Anomaly in the Western North Pacific (Inagake et al., 25, Enyo News 116) June More arrival of SKJ since the 198's but anchovy larvae is less vulnerable to SKJ than sardine and chub mackerel, due to expanded spawning area to KOTZ

17 Nursery Spawning Migration and Interaction Sardine Anchovy Chub mackerel Wintering Skipjack Feeding Winter KOTZ Kuroshio Spring Predation by skipjack (Kuroshio: Winter, KOTZ: Spring) Predation of anchovy by chub mackerel (Kuroshio & KOTZ: Spring) Competition for small copepods between sardine and anchovy (KOTZ) Less vulnerability of anchovy larvae to skipjack (Kuroshio: Winter)

18 Ecosystem Connectivity and Regime Shifts (Bakun and Broad (eds) 22, Climate and Fisheries) Sardine Anchovy FIGURE 4. Ecosystem Connectivity. Reproductively isolated local populations may be indirectly connected via a shared resource (i.e., bottom-up connectivity ) or a shared predator or fishery (i.e., top-down connectivity ). Climatic shifts may affect any of these ecosystem levels.

19 Summary: Implications of Temperature and Food Web for the 3 Species in KOTZ SST Vertical mixing and strength Oyashio - bottom-up Stratification - timing of spring bloom ZP species/size compositions Growth and survival of larvae Contact to skipjack (and squids); higher mortality when SST is high - top-down Food web Direct consumption of anchovy by chub mackerel Possible competition for small copepods between sardine and anchovy Less vulnerability of anchovy larvae to skipjack Unanswered question: Evolution of different life-histories, particularly between sardine and anchovy