Transport of eggs and larvae:
numerical experiments for  Japanese sardine and Japanese anchovy 

 

How do larval mortalities of sardine & ancovy
related to their environment ?

Particle-tracking experiment
for sardine larvae

Japanese sardine (Sardinops melanostictus) and Japanese anchovy (Engraulis japonicus) show the out of phase stock fluctuations synchronous to multidecadal ocean/climate regimes: sardine generally increase in cold periods and anchovy increase in warm periods (this cycle of these western Pacific species is same as the similar species in the eastern Pacific but the responses to the temperature are opposite). Although previous studies found significant relationships between the recruitment rates and ocean/climate indices, detailed examination is needed because these indices do not necessarily represent environments of larvae, which generally are transported by the strong jet of the Kuroshio from coastal waters to the offshore area of the Kuroshio Extension.

Fig. 1. Landing fluctuations of Japanese sardine (Mt) and
Japanese anchovy (10 x Mt)  (Courtesy of Dr. Yatsu)

Numerical particle-tracking experiments using high-resolution OGCM outputs

Numerical particle-tracking experiments were conducted using temperature and velocity fields calculated by OGCM For Earth Simulator (OFES) and observed egg distribution provided by Fisheries Research Agency of Japan.

Mt

Anchovy

Sardine

Japanese anchovy

Japanese sardine

Fig. 2. A SST snapshot by OFES. The spawning area of sardine and anchovy is demarcated by red line; subareas within spawning and destination areas are also shown with blue dashed lines (a curve indicate the axis of the Kuroshio and its extension)

Environmental temperature experienced by sardine and anchovy larvae

Fig. 3. Egg-density weighted environmental temperature for sardine (upper) and anchovy (lower), from 1979 to 2004.

anchovy

sardine

Sardine larvae experienced basically colder temperature than 20°C, except for the period from late 1980’s to early 1990’s, when the stock abundance was high (see Fig.1). Prominent warming (caused by a drastic warming in this area) was recognized in 1988, when the stock collapse began. The environment for anchovy larvae was relatively warm, but became colder with the increasing stock abundance after 1990’s.

Relationship between environmental temperature and the recruitment rate

Recruitment rate variability of sardine was negatively correlated to (Lagrangian) environmental temperature (especially for those spawned in the western inshore area of Japan). Anchovy recruitment variability was well explained by the spawning stock biomass (density effect) and a quadratic function of temperature with an optimum temperature of 21.2°C. Thus, difference in temperature responses (and also habitat areas and seasons) between the sardine and anchovy are suggested to be important factors in controlling the dramatic out- of-phase fluctuations of these species.

anchovy

sardine

ln (RPS)

Regression

ln (RPS)

Regression

Fig. 4.

Time series of the recruitment rates: estimation from the observation (ln (RPS), solid lines) and regressions (lines with marks).


RPS: Recruiter per spawner

References

  1. Itoh, S., T. Saruwatari, H. Nishikawa, I. Yasuda, K. Komatsu, A. Tsuda, T. Setou, and M. Shimizu: Environmental variability and growth histories of larval Japanese sardine (Sardinops melanostictus) and Japanese anchovy (Engraulis japonicus) near the frontal area of the Kuroshio, Fish. Oceanogr., 20, 114–124, 2011 [Abstract].

  2. Itoh, S., I. Yasuda, H,. Nishikawa, H. Sasaki, and Y. Sasai: Transport and environmental temperature variability of eggs and larvae of the Japanese anchovy (Engraulis japonicus) and Japanese sardine (Sardinops melanostictus) in the western North Pacific estimated via numerical particle-tracking experiments, Fish. Oceanogr. 18, 118-133, 2009 [Abstract]

  3. Itoh, S. and S. Kimura: Transport and survival of larvae of pelagic fishes in Kuroshio system region estimated with Lagrangian drifters, Fish. Sci., 73, 1295-1308, 2007 [Abstract]

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