Regional connectivity and spatial densities of drifting fish aggregating devices, simulated from fishing events in the Western and Central Pacific Ocean

Abstract

The increased use of drifting Fish Aggregating Devices (dFADs) by tuna purse seine fleets in recent years has supported considerable catches of these species. A greater understanding of the spatiotemporal dynamics of these objects as they drift with ocean currents is critical for understanding historical changes in fishing power, spatial management, and examining the effect of ambient dFAD density on catch and effort. Here, dFAD dynamics were estimated for all floating object sets made by purse seiners in the Western and Central Pacific Ocean during 2016 and 2017. The drift trajectories of these floating objects prior to the observed fishing events were estimated by seeding virtual Lagrangian particles within a state-of-the-art hydrodynamics model, and simulating their movements backwards in time. Resulting trajectory distributions are similar to observed dFAD trajectories from the same period. The approach provides spatial density estimates in areas where observed dFAD data are incomplete, particularly in the exclusive economic zone (EEZ) of Howland and Baker Islands, and certain high seas areas. We provide estimates of inter-EEZ connectivity of dFADs, which highlight the fact that dFADs set upon in small EEZs such as Nauru and Howland and Baker Islands are likely to have drifted from neighbouring EEZs less than one month prior to fishing. dFADs typically transited multiple EEZs, with a median of 4 and a maximum of 14, when assuming a drift-time of six months. Moreover, between 4 and 22% of dFAD sets made in the WCPO were estimated to have originated from the Eastern Pacific Ocean, depending on drift-time. We examine our results in the context of the improved management and assessment of dFAD fisheries, providing a methodology to estimated relative dFAD density over historical periods to support analyses of catch and effort. The sensitivity of these estimates to hydrodynamic models, including the proposed SKIM doppler radar altimetry method, is discussed.

Environmental versus operational drivers of drifting FAD beaching in the Western and Central Pacific Ocean

“…While dFADs do have various designs in the WCPO, this information regarding dFAD design was not available for observed dFADs used in this study. Sensitivity analyses of potential beaching, through simulation of assumed varying appendage depth, could be undertaken to examine this uncertainty in more detail 39 .…”

Multiple spawning events promote increased larval dispersal of a predatory fish in a western boundary current

“…The paths of each particle were interpolated using 5‐min steps based upon the daily velocity fields from the ROMS model output. Each particle included a small Brownian motion walk function of 100 m 2 s −1 which added natural variation to the movement of each particle and ensured no two particles followed the exact same path (Scutt Phillips, Escalle, Pilling, Sen Gupta, & Van Sebille, 2019; Van Sebille et al, 2018). This means on top of particle advection from modelled velocities, particles were advected with a velocity scaled by the diffusion coefficient in a random direction.…”

“…Symbols show the release location for the forwards (triangles) and backwards (circles) simulations. The dotted line represents the boundaries of the regional oceanographic model which provided the velocity estimates used in the simulations (Kerry et al, 2016) natural variation to the movement of each particle and ensured no two particles followed the exact same path (Scutt Phillips, Escalle, Pilling, Sen Gupta, & Van Sebille, 2019;Van Sebille et al, 2018). This means on top of particle advection from modelled velocities, particles were advected with a velocity scaled by the diffusion coefficient in a random direction.…”

Plastics pollution as waste colonialism in Te Moananui

“…Non-Indigenous scientists recommend Moananui peoples use FADS to increase their commercial catches (Bell et al, 2015). It is now estimated that between 30-65,000 FADS are floating around in the Western and Central parts of Te Moananui (Phillips et al, 2019) and many of these are washing up on beaches, damaging coral reefs, and potentially altering the distribution of tuna (Richardson et al, 2017;Leal et al, 2019;Phillips et al, 2019).…”