Seabird mortality associated with ice trawlers in the Patagonian shelf: effect of discards on the occurrence of interactions with fishing gear

Abstract

This study investigated the level of seabird mortality caused by the domestic trawl fleet (freshies) for hake (among other less important targets) operating in waters off central Patagonia (37-481S), analyzing the effect of environmental and operational variability on the level of seabird interactions. With a total of 135 vessels, the fleet is one of the largest in Argentina. Specifically tasked seabird observers were placed onboard trawlers during the summer and winter seasons of the years 2006 and 2007. The type and number of seabird interactions (i.e. contacts with fishing gear) were recorded during shooting and hauling operations, covering 72 days of observation and 328 trawls. Black-browed albatrosses, white-chinned petrels Procellaria aequinoctialis, southern giant petrels Marconectes giganteus and southern royal albatrosses Diomedea epomophora were the most abundant species interacting with trawlers. Confirmed mortalities of black-browed and southern royal albatrosses were the result of collisions and entanglement with the warp cable while birds were scavenging. The estimated total mortality rate was 0.017 birds h À1 and 0.105 birds per vessel per day. The intensity of interactions (in terms of the number of contacts per unit time) was largely explained by the distribution of the fishing effort. Seasonality and the incidence of discards were the strongest factors explaining the occurrence of seabird interactions. The total annual mortality in the trawl fleet under investigation was roughly estimated to be from several hundred to over a thousand albatrosses. However, these figures should be considered preliminary due to the limited spatial and temporal coverage of data and the fact that estimations were based on a low number of observed mortalities. The implementation of a strategic discard management may significantly reduce the number of seabird mortalities from collisions with warp cables or improve the effectiveness of other complementary mitigation methods. Urgent implementation of mitigation measures is needed in this fleet to reduce the mortality of albatrosses and petrels along the Patagonian shelf.

Marine debris ingestion by albatrosses in the southwest Atlantic Ocean

“…On the other hand, plastic also tends to accumulate over the shelf-break and continental shelf areas of the southwest Atlantic because of the density of fishing vessels, the main source of marine debris for seabirds in the region Quintana 2003, 2008), and the occurrence of numerous oceanographic fronts (Acha et al 2004). This may at least partially explain the greater frequency of plastic in royal albatrosses, which forage extensively over the continental shelf and shelf-slope (Nicholls et al 2002;Jiménez et al 2014) and interact with large number of fishing vessels, including trawlers, longliners and others, mainly off Uruguay and Argentina (Favero et al 2011;Jiménez et al 2014). However, it is also probable that some of birds sampled in our study had retained plastic particles in their ventriculus from the Pacific Ocean.…”

“…Given their small breeding populations and low productivity, great albatrosses are likely to be the species most affected by pelagic longline fisheries in the southwest Atlantic Ocean (Jiménez et al 2012), with royal albatrosses probably also killed in small numbers by trawlers (Favero et al 2011). Recently, high levels of bycatch in the pelagic longline fishery were reported for both royal albatross species in Uruguayan and adjacent waters (Jiménez et al 2014).…”

Demographic parameters of black-browed albatrosses Thalassarche melanophris from the Falkland Islands

“…and petrels Procellaria spp. are also known to be affected (e.g., Bugoni et al 2008;Jiménez et al 2009;Favero et al 2010).…”

“…The combined estimates for (adult-plumaged) albatross mortality along the Patagonian shelf and shelf break maybe of the order of ca. 5,000 individuals per year (from Neves and Olmos 1997;Yorio and Caille 1999;Olmos et al 2000;Favero et al 2003;Reid et al 2004;Reid and Edwards 2005;Crofts 2006;Gandini and Frere 2006;González-Zevallos and Yorio 2006;Laich et al 2006;Moreno et al 2006;Sullivan et al 2006b;González-Zevallos et al 2007;Otley et al 2007;Bugoni et al 2008;Moreno et al 2008;Sancho 2009;Jiménez et al 2009Jiménez et al , 2010Favero et al 2010). Even if we assume that the true mortality is twice as high as the above estimate (which is not unreasonable) and is entirely of birds from the local population, fisheries-related mortality would affect less than 1% of the birds from the Falklands.…”

Industry-based development of effective new seabird mitigation devices in the southern Australian trawl fisheries

“…Attention originally focused on seabird interactions with longline fisheries (Brothers 1991, Weimerskirch et al 1997, Nel et al 2002, Tuck et al 2003; however, trawl fisheries are also known to cause substantial seabird mortalities (Sullivan et al 2006b, Moore & Zydelis 2008, Watkins et al 2008, Favero et al 2011, González-Zevallos et al 2011. Seabirds have wide-ranging foraging distributions, are longlived, with low fecundity and a late age-at-maturity (Warham 1990), which are all characteristics that make their populations vulnerable to any additional mortality.…”