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Global fishery resources have been declining for decades, leading some fisheries to collapse. Although the decline is partly due to man-made chemical contamination, causal chemicals have been identified in only a few cases. We conducted consecutive 3-year investigations of embryonic mortality in Taihu Lake, China, including heavily contaminated northern areas, including Zhushan (ZS), Meiliang (ML), and Gonghu (GH), and the less polluted southeastern Suzhou (SZ). In 2016, 65.8% of crucian carp (Carassius carassius) embryos collected from ZS died before hatching, a substantially higher mortality rate than those observed in ML (21.7%), GH (15.2%), and SZ (2.2%). In 2017, the embryonic mortality rates were 38.8% in ZS, 1.3% in ML, 6.9% in GH, and 3.5% in SZ, and these rates strongly correlated with the concentrations of tris(1,3-dichloro-2-propyl)phosphate (TDCIPP): 104.2, 1.8, 4.6, and 4.1 ng/g lipid weight (lw) in embryos from ZS, ML, GH, and SZ, respectively. In 2018, embryonic mortality decreased to 4.0% in ZS and 1.2% in GH, consistent with decreases in embryonic TDCIPP concentrations to 17.1 and 1.5 ng/g lw, respectively. Moreover, the TDCIPP concentrations in dead embryos (70.5−216.8 ng/g lw) were much higher than those in live embryos (1.2−10.5 ng/g lw). Embryonic mortality was also observed in well-controlled laboratory experiments in which wild crucian carp were exposed to TDCIPP at concentrations similar to those measured in embryos collected from Taihu Lake, thus confirming TDCIPP as a causal factor in mass crucian carp embryo mortality in Taihu Lake. TDCIPP thus poses a threat to the sustainability of fisheries worldwide, given the high worldwide production volume of this chemical and its embryonic lethal toxicity.

In this Letter, the velocity structures and the extension behavior of localized turbulent bands in channel flows are measured by particle image velocimetry in a plane parallel to the walls and are analyzed by comparing with direct numerical simulations at low Reynolds numbers. It is illustrated that the convection velocity of the band head (band’s downstream end) is not determined by the formation and propagation of low-speed streaks but by a high-speed “hat” shaped region near the band head. This “hat” region travels downstream obliquely like a solitary wave and leaves newly generated low-speed streaks to travel slowly in the spanwise direction, leading to the head extension of turbulent bands.

In this Letter, it is revealed that the convection velocity of a localized wave packet in two-dimensional plane-Poiseuille flow is determined by the solitary wave at the centerline of a vortex dipole, which is evinced by subtracting the base flow from the mean flow. The fluctuation component propagates obeying the local dispersion relation of the mean flow and oscillates with a global frequency selected by the upstream marginal absolute instability and, hence, is a traveling wave mode. The vortex dipole provides an unstable region for the fluctuation waves to grow up, and the Reynolds stress of the fluctuation waves leads to streaming components enhancing the vortex dipole. By applying localized initial disturbances, a nonzero wave-packet density is achieved at the threshold state, suggesting a first-order transition.