Seabird bycatch in the Brazilian pelagic longline fishery and a review of capture rates in the southwestern Atlantic Ocean

Abstract

The southwestern Atlantic Ocean is an important foraging ground throughout the year for several albatross and petrel species. Longline fishing fleets in the region currently pose the main threat for this group of seabirds at sea, and conservation measures are urgently required. We present information on bycatch rates of seabirds in the Brazilian domestic pelagic longline fishery from 2001 to 2007, and review bycatch rates reported for the demersal and pelagic longline fisheries in the southwestern Atlantic Ocean. Overall seabird capture rate for the Brazilian pelagic longline fleet during 63 cruises (656 sets and 788 446 hooks) was 0.229 birds per 1000 hooks, varying from 0 to 0.542 according to season. Capture rates were higher between June and November (cold season) and affected mainly the black-browed albatross Thalassarche melanophris (55% of birds captured), the white-chinned petrel Procellaria aequinoctialis, the spectacled petrel Procellaria conspicillata and the Atlantic yellow-nosed albatross Thalassarche chlororhynchos. Capture rates previously reported in the SW Atlantic varied from 0 to 5.03 birds per 1000 hooks, with those reports based on logbooks or fishermen interviews tending to underestimate capture rates, whereas those based on small numbers of hooks or short time periods tend to greatly overestimate rates in both pelagic and demersal longline fisheries. Previous studies have played an important role in delimiting the seabird bycatch problem, forming a baseline for mitigation actions and serving as a guide for improvements in data collection. However, data collected by onboard seabird-dedicated observers are more reliable, provide a greater range of information relating to bycatch, and form a baseline for more robust analysis and addressing further questions. The current study highlights the stochastic nature of seabird fatalities in longline fisheries and the need for extensive sampling to obtain realistic estimates of capture rates covering different years, seasons, vessels, and the range of fishing gear and practices.

Requisite improvements to the estimation of seabird by‐catch in pelagic longline fisheries

“…It is not clear whether this estimate is any more accurate than a previous estimate for ICCAT fisheries, particularly bearing in mind that < 50% of birds killed during line setting may be retrieved in the haul (Brothers et al, 2010). Nevertheless, a key message from Yeh et al, supported by earlier reviews highlighting the 100-1000 s of birds estimated or suspected to be killed in numerous other fisheries (Bugoni et al, 2008;Anderson et al, 2011), is that independent observer programmes for by-catch still need substantial expansion and improvement. Only then will they be sufficient for comprehensive by-catch assessments, and adequate monitoring of vessel compliance and the effectiveness of recommended by-catch mitigation at ocean basin scales.…”

“…Furthermore, it is worth considering to what extent the Taiwanese observers were able to faithfully report the number of birds killed, given their responsibilities for recording multiple operational variables and all catch, in addition to all by-catch and general bird observation. Indeed, in their review of seabird by-catch rates in the southwest Atlantic, Bugoni et al (2008) point out that the most reliable information on by-catch is obtained by having dedicated seabird observers. The reality is that by-catch observation focused only on 5% of overall effort is inadequate even for frequently-bycaught species, given the large spatial and seasonal heterogeneity in by-catch rates.…”

Sex-biased incidental mortality of albatrosses and petrels in longline fisheries: differential distributions at sea or differential access to baits mediated by sexual size dimorphism?

“…Vessels were targeting tuna (Thunnus spp. ), sharks (mainly Blue Shark Prionace glauca) and Swordfish (Xiphias gladius) through a range of hook-and-line and pelagic longline fishing methods as described by Bugoni et al (2008c). This fleet operates in deep waters over the continental shelf and in offshore waters in southern Brazil throughout the year (Mayer and Andrade 2005) in the region under the influence of the Subtropical Convergence (Garcia 1998 (Fig.…”

Recoveries of juvenile Giant Petrels in regions of ocean productivity: potential implications for population change

“…The Humboldt (HUMB, or Peruvian), Benguelan (BENG) and Falkland (FKLD, also known as the Malvinas) biomes provide local and visiting predator aggregations with spatially abundant zooplankton, fish and squid resources (Shannon 1985, Croxall and Wood 2002, Thomas et al 2004, Thiel et al 2007). Some upwelling biomes are important winter fishing grounds for humans (e.g., BRAZ, Bugoni et al 2008) and cephalopod feeding Procellariiform species, such as blackbrowed albatrosses and white-chinned petrels (e.g., BENG, Abrams 1983; BRAZ, Olmas 2002). While no stomach contents or stable isotope analyses are available to gain insights into the diet of these birds recovered from coastal biomes during winter it is known that mixed age-groups and sexes of both Giant Petrels are known feed on live fish and squid during winter (Hunter 1985, Harper 1987, Hunter and Brooke 1992.…”