Linkages between coastal and open ocean habitats of Pacific salmon and small pelagics in the Northwestern and central Pacific

Transcription

1 Linkages between coastal and open ocean habitats of Pacific salmon and small pelagics in the Northwestern and central Pacific Akihiko Yatsu* and Masahide Kaeriyama** * National Research Institute of Fisheries Science ** Hokkaido Tokai University Distribution, migration and population dynamics Their inter-annual and inter-decadal variations Possible factors causing these variations

2 Migration of Japanese stocks of chum salmon Nursery (Summer & Fall) Feeding & Growth (Spring & Summer) 3-5 years Wintering (Winter) Nursery (Spring) Wintering (Winter) Transition Zone

3 Cluster analysis of return rates during of Japanese stocks of chum salmon by hatching area (Saito, 2) 2+3: NE Hokkaido Distance 5+7: Pacific coast of Honshu

4 SST of coastal area and return rates of Japanese stocks of chum salmon by hatching area during (Saito, 2) SST (Mar-Jul) Area of preferable SST anomaly (Nov-Jul) ln (Return rate) of Areas 5+7 (Pacific Honshu) ln (Return rate) of Areas 2+3 (Hokkaido) Year class

5 Body size of juvenile chum salmon released and return rate in the Hokkaido stocks Return rate (R, %) Return rate is probably a function of body size and SST conditions; hence of early survival R=4.56BW-.11 (r=.864, F=46.93, P<.1) Body weight (W, g)

6 Carrying capacity K: Replacement level in the Ricker curve without fishing N(2) N(4) K N K ( t+ 1) = = an ln( a) b ( t) exp( bn( t) ) K in year y : determined by two parameters, a & b,as estimated from the past 2years data from year y N(t+1) N(1) N(5) N(3) N(t)

7 Changes in total carrying capacity (K) of sockeye, chum, and pink salmon in the North Pacific Ocean C arrying capacity (K, m illio n fis h ) and r=.743, the Aleutian (F=85.23, P<.1) Low Pressure Index (ALPI) r=.81 (F=133.6, P<.1) Year class K ALPI ALPI PI ALPI: Beamish et al. (1997)

8 Correlation coefficient (r) between ALPI and SST (1-degree block) Jan-Mar :Positive r :Negative r Apr-Jun

9 72 Chum salmon growth and residual of K r=.96 (F=342.5, P<.1) FL (mm) FL (mm) (K-Biomass)/K (%) Low Residual Carrying Capacity High High Density Effect Low RCC (%) FL: mean fork length of age-4 adult returning to 11 rivers in Hokkaido Biomass: average of past 2 years from year of K calculation

10 Salmon dynamics Return rate < coastal environment (SST and presumably, zooplankton and predators) < ALPI Return rate < juvenile body size at release from hatcheries Growth < Density-dependent < Residuals of K K < Subarctic ecosystems <ALPI Biomass < Early survival, K and human impacts (hatchery, fishing) WSA Gyre is a passage for Japanese chum salmon, but its importance relative to other areas remains unresolved

11 Japanese catch of Japanese sardine, anchovy and mackerels during Sardine catch (t) 5,, Sardine 4,, Anchovy Mackerels 3,, 2,, 1,, ,, 1,5, 1,, 5, Anchovy & mackerel catch (t) Mackerels: chub mackerel + spotted mackerel

12 Distribution and migration of Japanese sardine and California sardine Transition Zone

13 Egg distribution of Japanese sardine High stock periods: Spawning grounds extend across Kuroshio current Line: Kuroshio axis Low stock periods: Spawning grounds confined within inshore areas

14 CPUE (No./1Tans) 25, 2, 15, 1, 5, 155 E Anchovy Sardine CPUE of Japanese sardine and anchovy by research gillnet surveys along 155º E, 17º E and 175º E in June-July during CPUE (No./1Tans) 4, 3, 2, 1, E Anchovy Sardine Data from Hokkaido University gillnet monitoring surveys

15 Distribution and migration of Japanese sardine and California sardine Transition Zone

16 Correlation coefficient (r) map between winter SST and LNRR of Japanese sardine : positive r : negative r Kuroshio Extension (KE) LNRR= ln (Recruitment Residuals) Ricker curve Recruitment (1^6) 35, 3, 25, 2, 15, 1, 5, SSB (1t)

17 Extended Ricker model of Japanese sardine ln (RPS) = ln (Recruitment/SSB) = a -bssb + ckest + d ln RPS Observed Model r2= SSB: spawning stock biomass KEST: winter SST of Kuroshio Extension

18 Correlation map between spring SeaWiFS Chl-a and Japanese sardine LNRR Saito (unpublished)

19 Japanese sardine catch: APLI or overfishing? California sardine Japanese sardine Catch (ton) Japanese sardine 5,, ALPI anomaly 4,, 3,, 2,, 1,, ALPI (3-year running mean) California sardine catch data: McFarlane et al. (22)

20 Fishing effect and growth of Japanese sardine SSB (1 t) 1, 1, 1, 1 Fishing control 1 Actual F=.5 actual F after 1997, using observed RPS values Mean body weight (g) Biomass (1t) Age Age 1 Age 2 Age 3 Age 4 Age 5 Biomass Densitydependent growth

21 Japanese sardine dynamics Reproductive success (RPS) < SSB (density effects) + SST of Kuroshio Extension + unknown factors RPS < primary production of TZ and presumably by zooplankton spp composition, timing of blooming, etc. Biomass accumulation = SSB x RPS x Growth x Survival (after recruit) intensive fishing may prevent stock recovery Growth < density effect WSA Gyre is one of feeding grounds, but only when it is abundant Importance of WSAG relative to Transition Zone (TZ) remains unknown Kuroshio Extension and TZ are hot areas for RPS

22 Conclusions Japanese stocks of chum salmon and small pelagic fishes migrate between coastal water and open ocean, and between subarctic and transition zone. These stocks undergo decadal and annual variations in their abundance (and distribution of small pelagics). Population dynamics include both natural environment and human effects - e.g., fishing and stock enhancement. WSA Gyre is a passage for Japanese chum salmon, and feeding ground for Japanese sardine only when it is abundant; but effects of biological transport between WSA and ESA, and between WSA and TZ was unanswered. Ecosystems are OPEN; for modeling, these large-scale migrations and dynamics must be considered in order to obtain total picture for gyre-coastal systems.

23 SST of coastal area and return rates of Japanese stocks of chum salmon by hatching area during (Saito, 2) SST anomaly (Nov-Jul) Area of preferable SST (Apr-Jul) ln (Return rate) of Areas 5+7 (Pacific Honshu) ln (Return rate) of Areas 2+3 (Hokkaido) Year class