9:15 AM - 9:30 AM
[AOS15-02] Estimating the transport and settlement distribution of abalone larvae in the Otsuchi bay using high-resolution particle tracking model
Keywords:Particle tracking, Otsuchi bay, abalone larvae
Abalone is an important fishery resource in the Sanriku coast. In the present study the dispersal and settlement of abalone larvae in the Otsuchi bay was investigated using a three-dimensional particle tracking system driven by a state-of-the-art high resolution ocean circulation model. The velocity field was simulated by the multi-level nested version of COCO (an ocean general circulation model developed at AORI, University of Tokyo) driven by climatological forcing. The horizontal grid spacing of the inner-most domain focusing the Otsuchi bay is approximately 14 m, in which complex geometry of the bay boundary includes artificial objects such as an embankment are resolved.
The particles that represent eggs and larvae of abalone were continuously released in 5 minutes interval from 20 spawning points located along the 10 m bathymetry contour. The trajectory of each particle was integrated by summation of advection by three-dimensional velocity field, vertical turbulent dispersion represented by random-walk, the Stokes drift estimated from a drifting buoy, and settling velocity of abalone eggs/larvae observed in still water. The modeled larvae particle is supposed to acquire the ability to settle on ground suitable for survival (i.e., habitat of coralline algae) in 4 days after the release, while the particles that failed to settlement in 14 days die and removed from the calculation. The integration was performed from Jul. 1st to Oct. 30th and total 4,216,320 particles were released.
The simulated distribution of settlement is consistent with our knowledge from observation, particularly at the northeast bank of the bay. The settlement distribution map shows that the mound near the southern tip at the bay mouth is a hot-spot of abalone settlement, which has not been confirmed in reality yet. It also exhibits substantial settlement along the southern coast outside the bay, that implies the possibility of connectivity of abalone over the bays in the Sanriku coast within a few generations.
In the present simulation the effect of Stokes drift caused by swell directing from the bay mouth to interior was not significant since the modeled particles were not suspended near the surface for long time. On the other hand, tidal current might play important role for abalone settlement since the number of particles successfully settled inside the bay was doubled in an experiment where the velocity field was 24-hour averaged.
The particles that represent eggs and larvae of abalone were continuously released in 5 minutes interval from 20 spawning points located along the 10 m bathymetry contour. The trajectory of each particle was integrated by summation of advection by three-dimensional velocity field, vertical turbulent dispersion represented by random-walk, the Stokes drift estimated from a drifting buoy, and settling velocity of abalone eggs/larvae observed in still water. The modeled larvae particle is supposed to acquire the ability to settle on ground suitable for survival (i.e., habitat of coralline algae) in 4 days after the release, while the particles that failed to settlement in 14 days die and removed from the calculation. The integration was performed from Jul. 1st to Oct. 30th and total 4,216,320 particles were released.
The simulated distribution of settlement is consistent with our knowledge from observation, particularly at the northeast bank of the bay. The settlement distribution map shows that the mound near the southern tip at the bay mouth is a hot-spot of abalone settlement, which has not been confirmed in reality yet. It also exhibits substantial settlement along the southern coast outside the bay, that implies the possibility of connectivity of abalone over the bays in the Sanriku coast within a few generations.
In the present simulation the effect of Stokes drift caused by swell directing from the bay mouth to interior was not significant since the modeled particles were not suspended near the surface for long time. On the other hand, tidal current might play important role for abalone settlement since the number of particles successfully settled inside the bay was doubled in an experiment where the velocity field was 24-hour averaged.