210 A comparison of catches of swordfi sh, ature, fi shing depth, number of hooks between fl oats, bait) can signifi cantly Xiphias gladius, and other pelagic species from affect the catch rates and species com- Canadian longline gear confi gured with alternating position of the catches. With swordfi sh fi shing, usually three to fi ve hooks are monofi lament and multifi lament nylon gangions attached between fl oats and lightsticks are attached intermittently to some Heath H. Stone of the gangions above the bait to at- tract swordfi sh or their potential prey Biological Station species. The gear is set during the ear- Fisheries and Oceans Canada 531 Brandy Cove Road ly evening, allowed to soak overnight St. Andrews, New Brunswick, E5B 2L9 Canada for 6–12 hours and retrieved at day- E-mail address: [email protected] break. The length of the fl oat lines de- termines the depth of the backline, and along with the length of the gangions, Langille K. Dixon distance between buoys and speed at P.O. Box 144 which the backline is set (i.e. the gear Woods Harbour tends to sink more at slower setting Nova Scotia B0W 2E0, Canada speeds) determine the actual depth the baits will fi sh. In the Canadian sword- fi sh fi shery, baits are often fi shed at depths of 12 m or less in the upper wa- ter column to take advantage of the di- urnal feeding migrations of swordfi sh The Canadian large pelagic longline tal shelf, where large females (mean and their movement into near surface fi shery extends from Georges Bank round weight ~120 kg) were targeted waters at night (Carey and Robison, south of Nova Scotia to the Flemish as they swam or “basked” in surface 1981). Cap, east of Newfoundland, and oper- waters during the day. This fi shery oc- In the early 1960s, the fi rst fl oating ates from May through November, curred primarily during July and Au- longlines used modifi ed halibut bottom when swordfi sh (Xiphias gladius), the gust, and required calm, clear weather longline gear buoyed by a variety of ob- main species targeted, migrate into to visually detect individual fi sh (Beck- jects (Beckett1). Both the backline and and adjacent to the Canadian EEZ. ett1). During the early to mid 1960s, gangions were made of tarred multi- Fishing effort progresses from west to the Canadian fl eet rapidly converted fi lament nylon and the gangions were east and back again and from offshore to surface longline gear which proved spliced directly to the backline. Mono- to inshore along the edge of the conti- to be far more effi cient than harpoon- fi lament nylon was fi rst used by Ca- nental shelf (Stone and Porter, 1999) ing. Not only were daily catches much nadian fi shermen in the late 1960s, following swordfi sh movements asso- higher, but vessels could operate dur- when a short (~38 cm) mono leader ciated with seasonal warming trends ing inclement weather (unsuitable for was attached between the tarred mul- of surface water temperature, and harpooning) and fi sh farther offshore tifi lament nylon segment of the gan- a northward movement of the edge as waters cooled over the continental gion and the hook. In the late 1970s of the Gulf Stream (Beckett, 1974). shelf. As a result, the fi shing season (following an eight year closure of the In winter, swordfi sh are confi ned to extended, the fi shing area expanded, Canadian fi shery when it was illegal to warmer waters associated with the catch rates increased, and the average land swordfi sh in Canadian ports ow- Gulf Stream outside the Canadian EEZ weight of fi sh declined because both ing to perceived high levels of mercury and are not easily accessed by the Cana- male and female swordfi sh were cap- in swordfi sh meat), gangions consisted dian fl eet. In recent years, national tured (Caddy, 1976; Hurley and Iles, of an upper tarred multifi lament sec- swordfi sh quotas for the Canadian fi sh- 1981; Beckett1). tion with a clip for attaching it to the ery (established by the International Pelagic longline gear adopted for use Commission for the Conservation of by Canadian fi shermen is similar to Atlantic Tunas) have been reached by that used in the New England fi shery early fall. (Berkeley et al., 1981) and consists of 1 Beckett, J. S. 1971. Canadian sword- Pelagic longlining was fi rst intro- a continuous backline up to 64 km fi sh longline fi shery. Int. Comm. Conserv. duced as a method for fi shing swordfi sh long, supported in the water column Atl. Tunas. SCRS Report 80/71/36, 14 p. in Canadian Atlantic waters in 1962, by styrofoam fl oats with up to 2000 International Commission for the Conser- having been stimulated by reports of baited hooks suspended on gangions vation of Atlantic Tunas, 8 Corazon de Maria, 28002 Madrid, Spain. incidental swordfi sh catches by foreign spaced at regular intervals (Fig. 1). Al- longliners targeting tuna or laminid though the general design of pelagic sharks (Beckett1). Prior to 1962, har- longline gear is relatively simple, op- pooning was the principal method used erating characteristics (including area, Manuscript accepted 22 August 2000. to capture swordfi sh on the continen- month and time of set, surface temper- Fish. Bull. 99:210–216 (2001). NOTE Stone and Dixon: A comparison of catches of Xiphias gladius and other pelagic species with longline gear 211 backline and a lower monofi lament leader to which the hook was attached. The mono- fi lament leader made up one half (~1.8 m) of the overall length of the gangion (~3.6 m) and was considered to yield bet- ter catch rates because it was assumed to be less visible to swordfi sh and other pe- lagic species. This innovation also effec- tively reduced shark damage to the gear because only the monofi lament leader had to be replaced if it was bitten off. In the late 1980s, fi shermen began to use mono- fi lament nylon for both sections of the gan- gion and for the backline on the assump- tion that this would further improve catch rates by decreasing overall visibility of the gear. Canadian pelagic longline fi shermen have been using monofi lament gangions Figure 1 for over a decade now and generally agree Schematic diagram illustrating typical Canadian pelagic longline gear con- over its ability to outperform the older fi guration. (Note: this confi guration differs slightly from the one used in our tarred multifi lament nylon gangions in experiment.) terms of swordfi sh catchability, although this theory has never been tested scien- tifi cally. In this note, the results of a col- laborative science and industry study involving the Cana- the length of the set (i.e. up to 64 km). Generally, 20 sec- dian Department of Fisheries and Oceans and the Nova tions of gear were deployed for most sets (one section=72 Scotia Swordfi shermen’s Association are presented. Our hooks and 23 buoys), yielding a total of 1440 hooks per set study was designed to compare the catchability of sword- (for sets 4–10), although there was some variation in hook fi sh and other pelagic species on commercial longline gear number for the fi rst three sets (set 1: 1008 hooks; sets 2–3: confi gured with alternate monofi lament and tarred mul- 1656 hooks). Although the 1:1 ratio of gangion types was tifi lament nylon gangions. It was based on the premise not maintained in some gear sections owing to gear dam- that some species can avoid capture on the tarred multi- age and subsequent replacement, the overall ratio for the fi lament gangions which are thicker, darker, and possibly entire set remained at 1:1. more “visible” than the monofi lament nylon gangions. Monofi lament gangions consisted of two 3.6-m sections of 400-lb test, 2-mm diameter monofi lament nylon at- tached together with stainless steel crimps, with the lower Materials and methods section or leader attached to a no. 9 Mustad J-hook (Fig. 3). Multifi lament gangions had a 3.6-m upper section of The study was conducted aboard the 19-m fi shing vessel tarred braided nylon (400 lb test, 5-mm diameter), and a Nova Blue from 22 July to 2 August 1999, along the edge lower 3.6-m monofi lament leader (400-lb test, 2-mm diam- of Georges Bank (depth to bottom: 360–1400 m) from Cor- eter) to which a no. 9 Mustad J-hook was attached. There- sair Canyon to the Northeast Peak (Fig. 2). This area is fore, the lower section (leader) of both gangion types was closed annually to commercial longlining operations from monofi lament nylon and the upper section varied between 1 January to 1 August to reduce bycatches of bluefi n tuna multifi lament and monofi lament nylon material. With this and small swordfi sh. Therefore, no other vessels were fi sh- confi guration, only the leader section had to be replaced ing in this closed area at the time this experiment was if damaged by sharks. Each leader also had three lumi- conducted. The gear was deployed each evening between nous green beads and one in 20 had a green lightstick at- 1800–2300 h in surface waters following the 20–22°C iso- tached 1 m above the hook (Fig. 3). When the gear were therm from south to north, allowed to soak overnight, set, gangions were clipped onto a monofi lament backline and hauled back from north to south beginning at day- (730 lb test) at intervals of 36 m after baiting the hooks break (~0600 h) the following morning.