A numerical modelling investigation of jellyfish transport and swimming behavior in Killary Harbour using a coastal hydrodynamic model

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.

Funder

Irish Research Council

Publisher

NUI Galway

Rights

Attribution-NonCommercial-NoDerivs 3.0 Ireland
CC BY-NC-ND 3.0 IE

cbn

Collections

University of Galway Theses (PhD Theses)