Seabird interactions with the deepwater bottom-longline fleet

In New Zealand waters, bottom longlining is conducted by vessels with diverse characteristics, both physical (e.g., vessel size) and operational (e.g., manual lining versus using autoline systems). Typically, bottom-longline fisheries are considered in two groups: inshore fisheries, involving small vessels deploying hand-baited hooks and targeting a mix of species including snapper (Pagrus auratus), bluenose (Hyperoglyphe antarctica), and hapuku/bass (Polyprion oxygeneios, P. americanus), and large deepwater vessels that use auto-line systems, typically operate at considerable distances offshore and target ling (Genypterus blacodes) (e.g., Ramm 2010, 2012, Pierre et al. 2013). Nevertheless, an additional component of the bottom-longline fishing fleet comprises middle-sized vessels that often operate in deeper water, and target species such as ling, bluenose, ribaldo (Mora moro) and sea perch (Helicolenus spp.).

Fishing operations using bottom longlines catch seabirds due to the birds’ propensity to forage on baits, fish processing waste, and fish retrieved during hauling. Factors such as slow longline sink rates, the incidental discharge of bait scraps during auto-baiting, and discarding of used baits on hauling exacerbate this bycatch risk. At the same time, there are effective methods available to reduce seabird bycatch risk in bottom-longline fishing operations, including the use of streamer (tori) lines, line weighting, and discharge retention (Bull 2007, Lokkeborg 2011).

Amongst bottom-longline vessels in New Zealand waters, both the highest risk to seabirds and the greatest uncertainty in risk estimation have been linked to vessels less than 34 m in length that target species other than snapper or bluenose (Richard & Abraham 2013c). Within this sector of the bottom-longline fleet, seabirds of particular conservation concern that have been reported caught are Chatham albatross (Thalassarche eremita), Salvin’s albatross (T. salvini), black petrel (Procellaria parkinsoni) and flesh-footed shearwater (Puffinus carneipes) (Richard & Abraham 2013c). Vessels less than 34 m in length that target bluenose reflect the next highest risk to seabirds, followed by larger vessels (i.e., greater than 34 m length). Seabirds associated with the risks by these other vessel groups include eight species of albatross, and also black petrel and flesh-footed shearwater (Richard & Abraham 2013c).

Here, we report on the Department of Conservation’s (DOC) Conservation Services Programme (CSP) project MIT2013-03. The aim of this project was to characterise bottom-longline fishing activity by middle-sized and large vessels operating in deeper water in relation to seabird captures. Also included in this study was the identification of factors associated with high seabird bycatch risk of these middle-sized vessels.