Characterisation of smaller vessel deepwater bottom-longline operations

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MIT2013-03 Characterisation of smaller vessel deepwater bottom-longline operations (PDF, 4,780K)

Summary

Amongst bottom longline fisheries, the highest risk to seabirds and the greatest uncertainty in risk estimation have been linked to vessels less than 34 m in overall length that do not target snapper or bluenose. In this project, we characterised, with respect to seabird capture, bottom longline fishing activity executed by these vessels operating in deeper water. We also identified the reasons for the high seabird bycatch risk identified amongst these vessels, and the high uncertainties associated with that risk. 

Using the Ministry for Primary Industries' data, we confirmed that the bottom longline fleet could be effectively characterised using three size-based vessel strata. Further, the number of hooks is broadly correlated with vessel sizes. Small vessels (< 20 m in overall length) mostly target snapper, set less than 5,000 hooks per day, and less than 500,000 hooks per year. Large vessels (> 34 m) primarily target ling, set more than 10,000 hooks per day, and more than 2,000,000 hooks per year. Between these groups, medium-sized vessels target a range of species, including ling, bluenose, hapuku, school shark, and ribaldo, set less than 10,000 hooks per day and around 500,000 hooks per year. 

Amongst this focal group of medium-sized vessels, government fisheries observers have never covered more than 5% of hooks. Amongst medium-sized bottom longline vessels, seabirds most commonly reported caught by fishers from the 2008/09 to the 2012/13 fishing years were white-chinned petrel, sooty shearwater, Salvin's albatross, grey petrel, Westland petrel, and Chatham albatross. These species also dominate the limited observer records of seabird captures. There is considerable diversity in the operations and gear types used by medium-sized bottom longline vessels, including the use of both integrated-weight line and external weighting approaches, J hooks and circle hooks, manual baiting and autoline systems, and monofilament and tarred rope backbones. 

The nature and extent of seabird bycatch reduction approaches deployed amongst medium-sized longline vessels is not well understood given the paucity of observer information. However, the available information is sufficient to broadly characterise factors exacerbating seabird bycatch risks. These include the discharge of fish waste during hauling, inconsistent use of streamer lines and that streamer lines used are of poor construction, the use of line-weighting regimes that expose baited hooks to foraging seabirds for extended periods and distances astern vessels, and day-setting. Significant information gaps remain. However, the combination of knowledge available on fishing activities undertaken by bottom longline vessels 20–34 m in length, and mitigation measures relevant to these fisheries, is sufficient to provide for the reduction of seabird bycatch risks but needs to be supported with improved information collection across amongst this vessel group.

Publication information

Pierre, J.P., Thompson, F.N., and Cleal, J. 2014. Seabird interactions with the deepwater bottom longline fleet. Report prepared by Dragonfly Science for the New Zealand Department of Conservation, Wellington. 36p.