A numerical modelling investigation of jellyfish transport and swimming behavior in Killary Harbour using a coastal hydrodynamic model
Date
2024-01-24Author
Sayeed, Md Ashkar Bin
Metadata
Show full item recordUsage
This item's downloads: 33 (view details)
Abstract
The occurrence of jellyfish in coastal areas, particularly in large numbers or swarms,
can pose a significant threat to tourism and aquaculture. They can sting swimmers
and bathers, become entangled in fishing nets, and harm and/or kill farmed fish.
There have been many records of fish kills and large associated economic losses
reported globally. Despite their threat, there is still quite a limited understanding of
the mechanisms of jellyfish transport and swarming. While jellyfish primarily drift
passively on the ocean’s currents, they also have the ability to swim with and against
currents. However, their swimming behaviours are poorly understood, and the
effects of their swimming on their total transport are relatively unknown. In this
research, a jellyfish transport model was developed and used to investigate jellyfish
transport in Killary Harbour, a fjord on the west coast of Ireland. Killary was chosen
as a case study site as it has experienced damage and mass kills of farmed fish by
jellyfish in recent years.
A 3D baroclinic hydrodynamic model of Killary Harbour was developed using the
Environmental Fluid Dynamics Code (EFDC) and was coupled with a Lagrangian
particle-tracking module to simulate the transport of jellyfish. The particle-tracking
model was developed to produce three different jellyfish transport models
incorporating different transport mechanisms (1) passive drifting only, (2) passive
drifting and diel vertical migration and (3) passive drifting, diel vertical migration,
and horizontal swimming. Jellyfish transport predictions were compared with
recorded movements of tagged jellies within the fjord. Tagged jelly movements
were detected by 8 GPS receivers placed along the banks of the fjord. The
percentage of the available number of modelled particles within each detector’s
range was determined temporally and compared with the GPS observations.
The jellyfish modelled as passively drifting particles agreed relatively well with the
observed jellyfish positions in the short term, but longer term, results were mixed.
The diel vertical migration (DVM) model offers a new approach to investigating
jellyfish DVM behaviour in coastal waters through the use of a constant migration limiting threshold depth and synchronised movement with passive drift. Although
this resulted in some improvements in performance over the passive drift model,
the results were varied. Finally, in the horizontal swimming model, swimming
behaviours were incorporated through a set of swim rules that govern horizontal
swimming rates and times, while vertical swimming is implemented according to
the DVM strategy. The main factors influencing jellyfish transport in this model were
found to be swim speed and swim direction. The motility of jellyfish, combined with
tidal and wind-driven currents, in the model can indeed cause particles to be
transported in a similar manner to the observed jellyfish. However, the results also
suggest that individual variations in jellyfish, such as size and development, may play
a role in their transport. Overall, these investigations provide valuable insights into
understanding jellyfish transport mechanisms and their relative contributions to
their total transport.