Reducing bycatch in the South African pelagic longline fishery: the utility of different approaches to fisheries closures

Abstract

Seabirds, turtles and sharks are often of conservation concern because they are frequently bycatch in fisheries. Fisheries managers shifting from a target species focus to an ecosystembased approach are being required to consider the impact of fisheries on non-target species. There are a range of complementary management tools that help reduce bycatch, such as gear restrictions, temporal restrictions, and bycatch reduction devices. One management approach that is increasingly being considered is fisheries closures. We tested the utility of 3 closure approaches for the improved protection of bycatch species in the South African pelagic longline fishery. As there was some variation where and when different groups of bycatch species were caught, we found that temporary spatial closures were the most effective strategy for both protecting bycatch and minimizing the cost to fishers. This is logical because having mobile closures in space and time provides more flexibility than permanent spatial closures or seasonal closures. However these benefits need to be traded off against the costs and problems of implementing temporary spatial closures. Of the 2 sub-optimal strategies, we discovered that seasonal closures are significantly less effective than spatial closures.

Why study bycatch? An introduction to the Theme Section on fisheries bycatch

“…The papers in this Theme Section are no exception to the trend reported above, with 10 studies on sea turtles (Alfaro Shigueto et al 2008, Braun-McNeill et al 2008, Crognale et al 2008, Gardner et al 2008, Gless et al 2008, Grantham et al 2008, Howell et al 2008, Peckham et al 2008, Southwood et al 2008, and Tomás et al 2008, 7 studies on birds (Anderson et al 2008, Benjamins et al 2008, Bugoni et al 2008, Gilman et al 2008, Grantham et al 2008, and Zador et al 2008b, and 5 studies on marine mammals (Brotons et al 2008, Chilvers 2008, Karamanlidis et al 2008and Scheidat et al 2008. Even without consideration of the number of species in each taxon, the distribution of research effort presented here is clearly skewed (though this may in part be due to elevated awareness of Endangered Species Research and this issue in the sea turtle research community).…”

“…A multi-species example from this Theme Section is the study by Grantham et al (2008), in which multiple bycatch taxa (birds, sea turtles, and sharks) were considered in deciding which of 3 approaches to bycatch reduction was most effective. The approaches that were compared included region-wide temporal closures, small-scale spatial closures, and small-scale temporal closures.…”

Conserving migratory and nomadic species

“…While here we consider only a static conservation network, a dynamic conservation scheme, where the sites for conservation action track the movements and population dynamics of species across time, could limit the area under conservation action at any one time and may be appropriate where threats are also dynamic (Bengtsson et al 2003;Costello & Polasky 2004;Grantham et al 2008). …”

“…This thesis directly addresses the first two of these, evaluating current practice and designing new approaches to both. There are currently only a few examples of conservation planning specific to migratory or nomadic species (Martin et al 2007;Grantham et al 2008;Klaassen et al 2008;Sawyer et al 2009;Sheehy et al 2011;Singh & Milner-Gulland 2011;Iwamura et al 2013) though the theoretical framework for dealing with these issues is improving rapidly (Hodgson et al 2009;Hole et al 2011).…”

“…Conservation planners have rarely included animal movements when prioritizing actions, instead focusing on how to incorporate costs (Naidoo et al 2006), feasibility (Knight et al 2011;Tulloch et al 2014), uncertainty in data (Carvalho et al 2011;Tulloch et al 2013), future threats (Game et al 2008), and multiple options for conservation action (Reyers et al 2012). Recent emphasis on the importance of incorporating spatial and temporal dynamics into the planning process (Grantham et al 2008;Lourival et al 2011) has led to some attention being focused on this issue (e.g. Runge et al 2014), with several recent studies incorporating the movements of migratory species into conservation planning (Martin et al 2007;Iwamura et al 2014).…”