Seabird avoidance measures for small Alaskan longline vessels
The incidental mortality of seabirds in longline fisheries is an international marine conservation problem. Although estimates of worldwide totals are lacking, hundreds of thousands of seabirds are probably taken in longline fisheries annually. In the Alaskan groundfish longline fisheries, incidental seabird mortality averaged 13,540 birds per year from 1993 to 2003, peaking at 26,000 seabirds in 1998. Procellariiform (or "tubenose") seabirds, a category that includes albatross species, were the most commonly caught (69%). The short-tailed albatross, an endangered species under the US Endangered Species Act (ESA), is the focus of regulatory and conservation attention in the Alaskan longline fisheries. The U.S. Fish and Wildlife Service's Biological Opinion specifies that short-tailed albatross takes exceeding six within a 2-year period (four in the groundfish fishery and two in the Pacific halibut fishery) would trigger reinitiation of a Section 7 consultation in these respective fisheries, and consequently interrupt or close Alaska's $250 million (ex-vessel value) demersal longline fisheries (USFWS 2003). In 2001, the North Pacific Fishery Management Council (Council) took final action on seabird avoidance measures required in the Alaska longline fisheries for groundfish and Pacific halibut. Streamer lines (also called tori or bird scaring lines) are central to the majority of these regulatory measures, based on recommendations from a collaborative industry-agency-academic research effort conducted in 1999 and 2000, which demonstrated that these lines nearly eliminated incidental seabird mortality. The research, however, focused exclusively on vessels over 55 ft LOA fishing with fixed gear (where individual gangions are permanently attached to the groundline), and the Council recognized that the recommended seabird avoidance measures may not be appropriate for some small vessels (55 ft and less) and for some gear types. Consequently, a separate set of regulations was established for vessels 55 ft and less, and large vessels using snap-on gear (where individual gangions are clipped on or off with snaps as the gear is deployed or retrieved). Given the lack of information on appropriate measures for these two categories of Alaska longline vessels, the Council also strongly encouraged the advancement of a cooperative research program to develop seabird bycatch mitigation measures for small vessels and all vessels using snap-on gear. The research reported herein stems from this directive. This study was conducted from May to June 2002 on eight vessels ranging from >26 to 55 ft in length. Two vessels were salmon trollers with infrastructure (mast, poles, and rigging) deploying snap-on gear, three vessels were combination vessels with infrastructure deploying fixed gear, and three vessels were bowpickers with no infrastructure deploying snap-on gear. Addressing the effectiveness of seabird avoidance measures required characterizing two variables: (1) the "2-m access window," or the distance astern that longline hooks were accessible to surface foraging Alaska seabirds, which generally dive no deeper than 2 m; and (2) the distance astern that streamer lines were maintained aloft, because it is this aerial extent that deters birds from the sinking hooks. The 2-m access window was measured using two complementary techniques (bottle lines and time-depth recorders) under typical fishing conditions, and during experimental trials in which both vessel speed and weight added to the groundline varied. The performance of currently required mitigation techniques was tested to determine practical performance standards, and alternative materials and deployment approaches were also tested (e.g., streamer lines made of lighter material, weights added to increase streamer line drag, and height of streamer line attachment to the vessel). For trollers and bowpickers using snap-on gear, the mean distances behind the vessel at which snap-on gear. This 90-m access window exceeded the mean for fixed gear set by large vessels (68 m) and was more in the range of that measured for large auto-bait freezer/longline vessels fishing cod in the Bering Sea (66–107 m). Large vessels (>55 ft) fishing groundfish are currently required to deploy streamer lines in pairs and to meet performance standards based on vessel length (40 m if vessel length is 55–100 ft, 60 m if vessel length is ≥100 ft). These results suggest that gear type and vessel setting speed are more important than vessel length in determining risk to seabirds. We conclude that the current requirement of a single streamer line with no mandatory material or performance standards for this vessel category (≥26–55 ft setting fixed gear and with mast, boom, and rigging) is unlikely to provide sufficient protection to seabirds, should longline fishing overlap with seabirds. We note that testimony to the Council has also emphasized that many of the vessels, for which this study is relevant, fish exclusively or primarily in inside waters, where tubenose seabirds are believed to be rare. During all this work with small vessels in Alaska’s inside waters, no Procellariiform seabirds were sighted nor were any types of seabirds observed interacting with longline gear, further supporting the view that small vessels fishing in inside waters may pose only minimal risk to seabirds.