Acoustic Surveys of Abundance and Distribution of the Japanese Sardine Sardinops melanostictus in the SpawningGrounds off Southern Kyushu, Japan.

Aoki, Ichiro; Inagaki, Tadashi

doi:10.2331/suisan.59.1727

Cited by 4 publications

(4 citation statements)

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“…Acoustic surveys in our study region (Aoki and Inagaki, 1993) and other observations (Nakai et al. , 1955; Aoki and Murayama, 1993) showed the sardine school to be in the depth range of 10–50 m, with a spawning peak around 20–30 m. Spawning was assumed to occur in the model at 2100 h each evening (Morimoto, 1993) when 10 000 eggs were introduced into the model with a Gaussian vertical distribution centered at 25 m depth, with a standard deviation of 5 m vertically.…”

Section: Vertical Mixing Modelmentioning

confidence: 72%

“…The axis, or adjacent region, of the Kuroshio Current, a water mass in which the Japanese sardine was intensively spawning, was found by the combined use of (1) acoustics (Aoki and Inagaki, 1993; Aoki and Murayama, 1993) to detect and monitor the adult fish schools, (2) gill nets and angling gear to capture adult sardine to examine their physiological maturity (Aoki and Murayama, 1993), and (3) surface and oblique hauls of plankton nets to detect newly spawned eggs. Sampling began in the daytime of February 26 and continued until 2300 h of February 28, when a spawning water mass was found.…”

Section: Methodsmentioning

confidence: 99%

“…The number of eggs per sample was converted into a ‘concentration,’ that is, number of eggs per 100 m 3 of water. During our sampling every 6 h over 4 days, the adult sardine school was always identifiable in the acoustic data (Aoki and Inagaki, 1993; Aoki and Murayama, 1993).…”

Section: Methodsmentioning

confidence: 99%

“…The path of Kuroshio in early March of 1991 is drawn as a belt delimited by a pair of curved lines (after data from the Japan Coast Guard, 1991), flowing from south to northeastward. adult sardine school was always identifiable in the acoustic data (Aoki and Inagaki, 1993;Aoki and Murayama, 1993). Before or after each egg sampling, a CTD (Neil Brown Mark III) cast was done; 19 casts were used for our analysis (Fig.…”

Section: Field Observationsmentioning

confidence: 99%

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Vertical distributions of Japanese sardine (Sardinops melanostictus) eggs: comparison of observations and a wind‐forced Lagrangian mixing model

Tanaka

Franks

2008

Fisheries Oceanography

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To understand how Japanese sardine eggs vertically disperse in water, we acquired a series of depthresolved samples of eggs while tracking a drogued buoy to follow the water mass in which the eggs were spawned. This survey was conducted in early March of 1991, when the sardine population was abundant and actively spawning in the Pacific off Kyushu. Buoyancy of the eggs was estimated by measuring the specific gravity, and was 1-4 · 10 )3 less than that of the water in which they were spawned, giving a rising speed of 1-2 mm s )1 . In an attempt to diagnose the dynamics underlying the observed vertical profiles of the eggs, a one-dimensional egg distribution model incorporating the egg rising speed and wind-and depth-dependent vertical diffusivity was formulated. Observed eggs were mainly in the surface mixed layer, and their vertical distribution changed with wind-induced surface mixing: during strong winds, the eggs were distributed relatively evenly over the upper 60-75 m, whereas during weak winds and shallow pycnocline, the eggs formed a subsurface peak around 25 m depth. The model accurately reproduced these variations in the vertical distributions of eggs, suggesting that the gradients of egg concentration are sensitive to the strength of wind and the structure of underlying hydrography. Further tests with the model showed the importance of positive buoyancy: neutrally buoyant eggs formed subsurface maxima below the food-rich euphotic zone. The balance of vertical mixing and floating, which allows the eggs to remain in the euphotic zone but away from the near-surface waters, may be an adaptation to minimize surface-enhanced predation, while allowing the eggs to hatch in the food-rich euphotic zone.

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Section: Vertical Mixing Modelmentioning

confidence: 72%