Fishing gear modifications to reduce elasmobranch mortality in pelagic and bottom longline fisheries off Northeast Brazil
Published source details
Afonso A.S., Hazin F.H.V., Carvalho F., Pacheco J.C., Hazin H., Kerstetter D.W., Murie D. & Burgess G.H. (2011) Fishing gear modifications to reduce elasmobranch mortality in pelagic and bottom longline fisheries off Northeast Brazil. Fisheries Research, 108, 336-343
Published source details Afonso A.S., Hazin F.H.V., Carvalho F., Pacheco J.C., Hazin H., Kerstetter D.W., Murie D. & Burgess G.H. (2011) Fishing gear modifications to reduce elasmobranch mortality in pelagic and bottom longline fisheries off Northeast Brazil. Fisheries Research, 108, 336-343
This study is summarised as evidence for the following.
Deploy fishing gear at selected depths to avoid unwanted speciesAction Link
Use a different hook typeAction Link
Deploy fishing gear at selected depths to avoid unwanted species
A replicated, paired, controlled study in 2004-2005 in 608 shallow, coastal water sites in the West Atlantic Ocean off Recife, Brazil (Afonso et al. 2011) found that longline hooks deployed in the water column (pelagic) caught fewer sharks and rays (Elasmobranchii) of three of eight species, compared to hooks set close to the seabed (demersal). Fewer numbers were caught on pelagic hooks than demersal for the three most captured species: southern stingray Dasyatis Americana (pelagic: 0.5 fish/1,000 hooks, demersal: 3.3 fish/1,000 hooks; n=43); blacknose shark Carcharhinus acronotus (pelagic: 0.8 fish/1,000 hooks, demersal: 2.9 fish/1,000 hooks; n=41); and nurse shark Ginglymostoma cirratum (pelagic: 0.1 fish/1,000 hooks, demersal: 1.2 fish/1,000 hooks; n=14). A further five species were caught infrequently on pelagic hooks only (tiger shark, Galeocerdo cuvier, manta ray, Manta birostris, bull shark, Carcharhinus leucas, scalloped hammerhead, Sphyrna lewini, blacktip shark, Carcharhinus limbatus). Catch rates were so low they were not significantly different between pelagic and demersal hooks (pelagic: 0.1–0.4 fish/1,000 hooks, demersal: 0 fish/1,000 hooks; n=11). In September 2004 to August 2005, a total of 384 longline sets with 100 J-shaped hooks each were deployed, half close to the seabed and the other half suspended in mid-water, in depths of 8–14 m, 1–3 km from the coast. Hooks were baited with moray-eel Gymnothorax sp.. Sixty-two sharks and 46 rays were caught in total.
Use a different hook type
A replicated, controlled study in 2004–2005 of one area of seabed and one mid-water area in the Atlantic Ocean, off Brazil (Afonso et al. 2011) found that using a circle hook type instead of a conventional J-type hook in a longline finfish fishery did not reduce the capture of unwanted sharks and rays (elasmobranchs), but did reduce the capture mortality of some species. For pelagic longlines, incidental catch rates were similar between the circle and conventional J hook for six of 10 shark species (circle: 0.3–1.8, J hook: 0.3–2.1 catch/unit effort), however, they were higher for four (circle: 2.3–6.4, J hook: 0.8–2.6 catch/unit effort). Total fishing mortality rates of three species were lower on circle hooks (22–27%) than J hooks (67–80%) and, although survival was typically higher on circle hooks for the other seven species, they were not statistically different (0–100% on both hook types). For demersal longlines, there were also no differences in catch rates between hook types for eight shark and ray species (circle: 0.2–1.4, J hook: 0.0–1.3 ind/1,000 hooks), and fishing mortality of two shark species was lower on circle hooks (0–23%) than J hooks (50–74%). See original paper for species individual data. Between August 2004 and April 2007 two hook experiments were carried out with pelagic and bottom set longlines. A total of 224 pelagic longline sets (7,800 hooks, moray-eel Gymnothorax spp. bait) were deployed off Recife (8–14 m depth, 1–3 km from the coast) with alternate sets of circle hooks (size 18/0, 0° offset) and conventional J hooks (size 9/0, 10° offset). Twelve demersal longline sets (650 hooks, skipjack tuna Katsuwonus pelamis bait) were deployed off Natal at 40–70 m depths. Hook types (circle and J hooks as before) were alternated in equal numbers for each set.