Literature in this category examines threats to bycatch species from human activities, including fisheries [e.g. 1], and looks for patterns in these interactions.
Studies considering bycatch threats often analyse interactions between fisheries and bycatch species, and identify aspects to target for threat mitigation. These aspects may include spatial areas in which bycatch threats are greatest (‘hotspots’) [e.g. 2]. Some studies prioritise actions to reduce identified threats [e.g. 3]. Papers may discuss threats in terms of percentages of populations affected, such as how many seabirds are killed in longline fisheries each year [e.g. 4]. Oliver et al. (2015) address broad-scale patterns of elasmobranch bycatch in commercial longline, trawl, purse- seine and gillnet fisheries and Bugoni et al. (2008) explore seabird bycatch rates in the south-western Atlantic Ocean.
Quantitative studies of bycatch rates may also analyse population trends, but these fit better in categories under ‘Population Level Assessment’, such as ‘Abundance Indices ’.
Simple analyses of bycatch interaction rates reveal, for example, how many sea turtles or seabirds are caught per 1000 hooks. More complex analyses are required to derive abundance indices, to account for variation in fishing method, spatial effects, and other factors.
The two categories can be illustrated using a simple example. From 1990 to 1995 a fishing vessel targeted swordfish, but from 1996-2000, the same vessel switched to targeting tuna. In the earlier time period, the vessel was fishing at a shallower depth than in the later time period and hence caught more turtles per thousand hooks. The bycatch interaction rates were higher in the early period due to the different fishing methods, but the raw data do not provide a picture of turtle abundance for the period 1990-2000. To estimate a continuous index of turtle abundance, these data can be used in models that take account of the different fishing methods.
- Wallace BP, Kot CY, DiMatteo AD, et al (2013) Impacts of fisheries bycatch on marine turtle populations worldwide: toward conservation and research priorities. Ecosphere 4:art40. doi: 10.1890/ES12-00388.1
- Fossette S, Witt MJ, Miller P, et al (2014) Pan-Atlantic analysis of the overlap of a highly migratory species, the leatherback turtle, with pelagic longline fisheries. Proceedings of the Royal Society of London B: Biological Sciences 281:20133065. doi: 10.1098/rspb.2013.3065
- ACAP (2014) Prioritising ACAP Conservation Actions - Update and Report to MoP5. ACAP Seabird Bycatch Working Group, Punta del Este, Uruguay
- Croxall JP, Butchart SHM, Lascelles B, et al (2012) Seabird conservation status, threats and priority actions: a global assessment. Bird Conservation International 22:1–34. doi: 10.1017/S0959270912000020
- Bugoni, L., Mancini, P.L., Monteiro, D.S., Nascimento, L., and Neves, T.S. 2008. Seabird bycatch in the Brazilian pelagic longline fishery and a review of capture rates in the southwestern Atlantic Ocean. Endang Species Res 5: 137–147. doi:doi: 10.3354/esr00115.
- Oliver, S., Braccini, M., Newman, S.J., and Harvey, E.S. 2015. Global patterns in the bycatch of sharks and rays. Marine Policy 54: 86–97. doi:10.1016/j.marpol.2014.12.017.