SCRS/2008/178 NOMINAL CPUE FOR THE CANADIAN SWORDFISH LONGLINE FISHERY 1988-2007 S. Smith and J. D. Neilson SUMMARY An update is presented of the nominal catch rate series and fishery distributions for swordfish from the Canadian pelagic longline fishery in 2007. In 2006 and 2007, the fishery distributions generally remained consistent. Areas of effort concentration included the Northeast Peak of Georges Bank and the western edge of the Grand Banks. Fishermen continued to avoid areas of high swordfish catches in 2007 in order to conserve swordfish quota to pursue other tuna fisheries. In 2006, nominal catch rates had declined to a level not observed since 2001 and recovered slightly in 2007. Recent catch rates may be confounded by a changing fishing strategy by the pelagic longline fleet, which avoids concentrations of swordfish in pursuit of other tunas. KEYWORDS: pelagic fisheries, tunas
1.0 INTRODUCTION The North Atlantic swordfish resource was assessed in 2006 by the International Commission for the Conservation of Atlantic Tunas, utilizing catch rate data up to and including 2005 (Anon, 2007). This paper provides an update of the nominal catch rate series and fishing summary for swordfish from the Canadian pelagic longline fishery in 2007. 2.0 DESCRIPTION OF THE FISHERY The Canadian longline fishery typically operates from Georges Bank to the Flemish Cap when swordfish migrate into and adjacent to the Canadian Fishing Zone. Generally, the pelagic longline fishery occurs along the edge of the Gulf Stream and south of the Scotian Shelf in May and June, and then shifts to the edge of the continental shelf (Georges Bank, Scotian Shelf, and Grand Banks) from July through November (Fig. 1). In 2006 and 2007, fishery distribution generally remained typical, although more sets were made to the East of the Grand Banks in 2007 than in 2006. In general, fewer vessels now travel to the Grand Banks off Newfoundland since they can catch their portion of the quota in waters closer to their home port (Fig. 2). Prior to the inception of Individual Transferable Quotas (ITQ s) in 2002, pelagic longliners targeted other tunas (albacore, bigeye and yellowfin) early and late in the season, before and after the swordfish quota was caught. Under the ITQ system, longliners direct for swordfish or use the individual swordfish quota for bycatch to target the other tunas. This has resulted in a longer fishing season for swordfish than in previous years, ending in December, rather than September. During an informal telephone survey with industry representatives, it was determined that, as noted in Paul and Neilson (2007), fishermen continued to avoid areas of high swordfish catches to conserve swordfish quota and allow for the pursuing of tuna fisheries. Both harpoon and longline fleet representatives indicated that there was no apparent change in the size of swordfish from 2007, and the overall condition remained very good. 3.0 RESULTS AND CONCLUSIONS The nominal CPUE index values for swordfish caught in the Canadian pelagic longline fishery followed a steady decline from the highest point in the series in 1990 to the lowest point in 1996. Since then, the CPUE increased to the second highest level in the series in 2005. In 2006, nominal catch rates declined to a level not observed since 2001 but increased slightly in 2007 (Fig. 3). The decline in catch rates in 2006 was in contrast to anecdotal reports from the swordfish harpoon fleet (which typically catches larger swordfish basking near the surface). The harpoon fishery reported exceptionally good catch rates in 2006 and again in 2007. The increasing trend in catch rates since the historic low in 1996 is indicative of an increase in the relative abundance of swordfish since that time. Fleet representatives have noted that the decline in CPUE in 2006 is the result of an effort to avoid swordfish in order to increase tuna catches. This trend continued in 2007. The nominal catch rate series presented here has not yet been standardized as presented in Paul et al. (2007), therefore, we do not yet know the impact of standardization on this index.
4.0 LITERATURE CITED ANON. 2007. Report of the 2006 ICCAT Swordfish Stock Assessment Session. Col. Vol. Sci. Pap. ICCAT, 60(6): 1787-1896. PAUL, S.D. and J.D. Neilson. 2007. Updated sex- and age-specific CPUE from the Canadian swordfish longline fishery, 1988-2005. Col. Vol. Sci. Pap. ICCAT, 60(6): 1914-1942.
Figure 1. Distribution of Canadian swordfish catches by pelagic longline from May to October, 2007.
2006 50 45 40 65 60 55 50 45 40 Figure 2. Distribution of Canadian pelagic longline sets, 2006 (top) and 2007 (bottom).
Number of swordfish/total hooks *1000 16 14 12 10 8 6 4 2 0 Nominal swordfish LL CPUE 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 Figure 3. Nominal CPUE index (number of fish per 1000 hooks) from the Canadian pelagic longline fishery, 1988-2007.