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

Abstract

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.

Iridium profiles and delivery across the Cretaceous/Paleogene boundary

“…Traditional sediment mixing models are advection-diffusion models, where the 167 record of a sedimentary event is distributed within a mixed layer characterized by a 168 mixing coefficient (which can be modeled identically to a diffusion coefficient) and 169 advected by burrows into layers of sediments that are older than the event (Guinasso and 170 Schink, 1975). model with depth-dependent eddy diffusivity of Tanaka and Franks (2008) to model Ir 173 anomaly shapes across the K/Pg boundary. They used the mixing model to explain the 174 observed Ir anomaly shape at North Pacific DSDP Site 577B, Shatsky Rise (their Fig.…”

Sequence and localization of an ultraviolet (sws1) opsin in the retina of the Japanese sardine Sardinops melanostictus (Teleostei: Clupeiformes)

“…With respect to their spawning season, another hypothesis for the biological function of UV vision in S. melanostictus could be proposed. In the north-western Pacific, E. japonicus spawns throughout the year with a peak from April to September, while S. melanostictus spawns during a much shorter period of February to April (Aoki & Murayama, 1993;Takasuka et al, 2008;Tanaka & Franks, 2008;Gnyubkina et al, 2013). Spawning is mainly associated with water temperature; S. melanostictus spawns when the sea surface is cooler whereas E. japonicus spawns when the sea surface is warmer (Takasuka et al, 2008).…”

The Principles of Buoyancy in Marine Fish Eggs and Their Vertical Distributions across the World Oceans

“…The above model has been further developed by several authors to account for density stratification in the upper layer and for depth-dependent eddy diffusivity coefficient, K ( z ), and for non-stationary conditions [ 30 , 57 – 59 ]. For example, an important modification of the original simplified model is that depth-dependent K ( z ) in combination with a homogeneous mixed layer can results in displacement of the maximum egg concentration from the surface to levels deeper down in the mixed layer [ 60 , 61 ], which was also confirmed by their observations.…”