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

Abstract

In an effort to increase purse seine fishing efficiency for tropical tunas, over 30,000 drifting Fish Aggregating Devices (dFADs) are deployed every year by fishers in the Western and Central Pacific Ocean (WCPO). The use of dFADs also impacts ecosystems, in particular through marine pollution and dFAD beaching. This paper presents the first estimate of dFAD beaching events in the WCPO (>1300 in 2016–2017) and their distribution. Lagrangian simulations of virtual dFADs, released subject to contrasting deployment distributions, help us determine the relative importance of operational versus environmental drivers of dFADs drifting to beaching areas. The highest levels of beaching, occurring on Papua New Guinea and Solomon Islands, are likely a result of the prevailing westward oceanic circulation and subsequent local processes driving dFADs towards land. Similarly, high beaching rates in Tuvalu appear to be due to the general circulation of the WCPO. In contrast, beaching in Kiribati Gilbert Islands appear to be more strongly related to dFAD deployment strategy. These findings indicate that reducing beaching events via changes in deployment locations may be difficult. As such, management approaches combining dFAD deployment limits, the use of biodegradable dFADs, recoveries at-sea close to sensitive areas and/or beached dFAD removal should be considered.

Spatial management can significantly reduce dFAD beachings in Indian and Atlantic Ocean tropical tuna purse seine fisheries

“…Our estimates of dFAD beaching rates after 2013 are higher than those estimated in the western central Pacific (Escalle et al 2019) and in previous examinations in the IO and AO (Maufroy et al 2015; Zudaire et al 2018). Escalle et al (2019) examined an area of the Pacific characterized principally by many small island chains, perhaps explaining lower beaching rates with respect to the continental land masses of the IO and AO. In the IO and AO, Maufroy et al (2015) examined the period prior to 2013 for which we also find lower beaching rates.…”

“…In the IO and AO, Maufroy et al (2015) examined the period prior to 2013 for which we also find lower beaching rates. Zudaire et al (2018) were principally concerned with the more-limited area of the Seychelles Archipelago, which is composed of a large set of small islands similar to the area examined by Escalle et al (2019) in the western central Pacific, and they considered a somewhat more restrictive definition of beaching.…”

“…An initial examination of French dFAD spatiotemporal use in the tropical Indian Ocean (IO) and Atlantic Ocean (AO) over the period 2007-2011 indicated that ~10% of deployed dFADs ended up beached (Maufroy et al 2015), highlighting the potential for considerable impacts on fragile coastal habitats due to these events. A similar examination in the Western and Central Pacific Ocean found that ~6% of all trajectories were likely to have beached over a two year period (2016-2017; Escalle et al 2019). However, given the significant differences in bathymetry and circulation between the western and central Pacific Ocean , IO and AO, and the more than four-fold increase in the number of dFADs deployed by purse seiners in the IO and AO since 2011 (Katara et al 2018;Floch et al 2019), the extent to which existing literature applies to current patterns of dFAD use is an important open question.…”

Beaching patterns of plastic debris along the Indian Ocean rim

“…Connectivity matrices (such as used by e.g. Escalle et al, 2019) showing the percentage of beached particles originating from different countries confirm this. For high beaching probability, particles that beach in specific countries mainly originate from that same country (Figure 5e, high percentages along the diagonal).…”

Spatial management can significantly reduce dFAD beachings in Indian and Atlantic Ocean tropical tuna purse seine fisheries

“…An initial examination of French dFAD spatiotemporal use in the tropical Indian Ocean (IO) and Atlantic Ocean (AO) over the period 2007-2011 indicated that ~10% of deployed dFADs ended up beached (Maufroy et al 2015), highlighting the potential for considerable impacts on fragile coastal habitats due to these events. A similar examination in the Western and Central Pacific Ocean found that ~6% of all trajectories were likely to have beached over a two year period Escalle et al 2019). However, given the significant differences in bathymetry and circulation between the western and central Pacific Ocean , IO and AO, and the more than four-fold increase in the number of dFADs deployed by purse seiners in the IO and AO since 2011 (Katara et al 2018;Floch et al 2019), the extent to which existing literature applies to current patterns of dFAD use is an important open question.…”