Action: Use shark liver oil to reduce seabird bycatch
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- Two replicated and controlled trials found reductions in the number of seabirds following boats, or diving for baits, when shark liver oil was dripped behind the boats. Other oils had no effect.
- A third replicated and controlled trial in found no differences in the number of seabirds following a bait-laying boat with shark liver oil.
Seabirds may be predated by large fish such as sharks and so may show avoid the smell of them. Dripping shark liver oil whilst setting lines may, therefore, reduce bycatch.
Supporting evidence from individual studies
A replicated, controlled experiment off the coast off north-east New Zealand (Pierre & Norden 2005) found that the number of dives made by seabirds in pursuit of pilchard baits behind a longline fishing vessel was dramatically lower (< 5 birds/min) when small quantities of shark liver oil were dripped onto the water behind the vessel than during control trials using vegetable oil (always > 30 birds/min) or sea water (20-40 birds/min). Diving birds were mainly flesh-footed shearwaters Puffinus carneipes, but also Buller's shearwaters Puffinus bulleri and white-faced storm petrels Pelagodroma marina.
One replicated, controlled experiment off Kaikoura, South Island, New Zealand, in 2005 (Norden & Pierre 2007) found no significant differences in the number of seabirds following a bait-laying boat when it was dripping shark liver oil (both commercially available and made by fishermen) behind the boat, compared to control conditions. However, a second trial in April 2006 off Hauraki Gulf, North Island, New Zealand found the number of seabirds following a bait-laying boat decreased significantly faster if fisherman-produced shark liver oil was dripped behind the boat, compared to controls dripping seawater. Other fish oils (anchovy, pollock and commercially available shark liver oil) did not have a significant impact on the number of following birds. However, all oils except for anchovy did significantly reduce the number of dives made by seabirds.