National Tuna Fishery Report 2001 – New Zealand
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National Tuna Fishery Report 2001 – New Zealand Talbot Murray & Lynda Griggs NIWA, Wellington Introduction New Zealand tuna fisheries are based on stocks that occur largely outside of the 200 nautical mile Exclusive Economic Zone (EEZ). In New Zealand waters tuna represent important and valuable seasonal fisheries (currently worth more than $NZ 20 million). No tuna species are included in the Quota Management System and only southern bluefin tuna (Thunnus maccoyii), managed by the Commission for the Conservation of Southern Bluefin Tuna (CCSBT), is subject to catch restrictions, with a 420 t competitive national catch limit. Other tuna species of commercial importance to New Zealand are albacore (T. alalunga), bigeye (T. obesus), skipjack (Katsuwonus pelamis) and yellowfin tuna (T. albacares). While billfish also comprise regular bycatch on tuna longlines, all billfish except swordfish (Xiphias gladius) must be released when caught by commercial fishers. Swordfish may not be targeted but can be landed by domestic fishers. This species has become increasingly important in the domestic tuna longline fishery as it has expanded and landings in the last few years have rapidly increased. In New Zealand, South Pacific albacore form the basis of a summer troll fishery, primarily on the west coasts of the North and South Island, with annual landings over the past 10 years averaging 4583 tonnes (maximum landing 6526 t in 1998). Albacore are also caught throughout the year by longline (usually ≤ 1000 t per year). Bigeye, the second most valuable tuna (per kg), are caught by longline around the northern half of the North Island throughout the spring – autumn period with landings averaging 174 t per year over the past 10 years (maximum landing 422 t in 2000). Skipjack are caught in small numbers by trolling with most of the catch by purse seine during summer months. Skipjack landings have averaged 4583 t per year over the past 10 years (maximum landing 9699 t in 2000). Southern bluefin tuna traditionally have been caught by handline and trolling during winter months off the West Coast of the South Island from small vessels. These methods are still occasionally used. Most southern bluefin tuna, however, are caught by medium to large (20–50 m) longline vessels in autumn – winter months. Southern bluefin catches, restricted to a national competitive catch limit of 420 t since 1989, have usually been below this limit with landings averaging 281 t per year over the past 10 years (maximum landing 529 t in 1990). Northern bluefin tuna, only recently recognised as contributing to tuna landings, have averaged 9 t per year over the past 10 years (maximum landing 21 t in 1999). Yellowfin tuna, caught in small numbers in the troll and purse seine fisheries, are generally a bycatch of longline sets targeting bigeye in summer months. Landings of yellowfin tuna have averaged 98 t per year over the past 10 years (maximum landing 198 t in 1996). Swordfish are a bycatch of longline sets targeting bigeye and southern bluefin tunas around both the North and South Islands. Swordfish landings have averaged 337 t per year over the past 10 years but have been increasing with increased longline effort, especially over the last few years (maximum landing 1004 t). Marlins, also a bycatch of longline fishing in northern New Zealand waters, can not be retained and must be released whether alive or dead. In addition to the tuna target species, several other valuable species together with commonly caught species of little or no value, are bycatch in the longline fishery. Species composition and estimates of longline bycatch are reported by Francis et al. (1999 and 2000). The longline bycatch of other fish species has also focused attention on the potential for impacts on a range of dependent or associated species, particularly those that are rare, have low fecundity or about which little is known. Similarly, for purse seine fishing in the EEZ a wide range of fish taxa (over 60 species) have been taken as bycatch in sets targeting skipjack tuna (Habib et al. 1982). Trolling and other tuna fishing methods do not appear to have an appreciable bycatch. The New Zealand Tuna Fleet A wide range of vessel types fish for tuna in the New Zealand EEZ. Of these, only those engaged in purse seining and some tuna longline vessels are purpose built tuna vessels. Most vessels engaged in tuna fisheries also operate in a range of other fisheries and employ a range of fishing methods. Trolling, purse seining and longlining are the main tuna fishing methods used in New Zealand although handline and pole-and-line are also used. Appendix 1 summarizes the number of vessels reporting tuna catches by gear type, size (GRT) and year. Foreign licensed tuna fishing, primarily for southern bluefin tuna, has been declining since the late 1980s and no foreign licensed vessels have operated in the New Zealand EEZ since 1995–96. At the same time domestic tuna fishing has expanded through the increased use of longline for both southern bluefin and bigeye tunas. A few (usually 5 vessels) Japanese longliners on charter to a New Zealand company have fished each year since 1988–89 except 1990–91 (3 vessels) and 1995–96 (no vessels). Figure 1. Total number of tuna New Zealand vessels (including chartered vessels) by fishing method. longline 1000 troll pole-&-line purse seine 100 10 No. vessels fishing No. 1 1988 1990 1992 1994 1996 1998 2000 Year Most vessels fishing for tuna target albacore by trolling (Fig. 1), the number of vessels trolling has remained relatively constant at 200 to 300 vessels in each of the last several years. The number of vessels longlining has steadily increased since 1990 to 115 vessels, most of these target bigeye tuna. Most of the skipjack catch is taken by 6 medium-sized purse seiners, this fleet has remained virtually unchanged until the entry of a large super seiner in 2000, at least two more super seiners are entering the New Zealand fleet in 2001. Although up to 11 2 boats report using pole-and-line the number of vessels using this method has been variable and this method accounts for only small amounts of catch. Total Tuna and Swordfish Catches The largest annual landings by species are from the summer surface fisheries for albacore (troll fishery) and skipjack tuna (purse seine fishery). Figure 2 shows that skipjack landings during the late 1980s to mid 1990s were variable, ranging from 1000 to 5000 t, since the mid 1990s, however, skipjack landings have increased from 4000 to 10 000 t in 2000. Albacore landings have been variable ranging from 2000 to about 7000 t Figure 2. Domestic landings (tonnes wholeweight) of albacore and skipjack tuna by year from LFR reports. 10000 9000 ALB 8000 SKJ 7000 6000 5000 4000 3000 Landings, tonnes Landings, 2000 1000 0 1985 1990 1995 2000 Year The annual landings of species caught primarily by longline are shown in Figure 3. Prior to 1990 most tuna longlining was by 3–5 Japanese vessels operating under charter, primarily targeting southern bluefin tuna, with catches of bigeye, yellowfin and swordfish made primarily at the end of the season. Landings for these species (except yellowfin tuna) have increased due to the expansion of the domestic longline fishery starting in 1990. Figure 3. Domestic landings (tonnes wholeweight) of bigeye, southern bluefin, northern bluefin, and yellowfin tunas and swordfish by year from LFR reports. 1100 BIG NTU STN YFN 1000 SWO 900 800 700 600 500 400 300 Landings, tonnes 200 100 0 1985 1990 1995 2000 Year 3 The landings in Figure 3 are typically by longliners targeting either southern bluefin or bigeye tunas. Bigeye catches prior to 1996 were typically less than 100 t, however, since 1997 landings rapidly to about 400 t. Yellowfin tuna landings are low, prior to 1994 they were similar to those of bigeye (less than 100 t) but since 1994 have ranged from 100 to 200 t. Southern bluefin tuna catches limited by a national competitive quota of 420 t since 1989. SBT catches since then have usually been well below this level but the quota was exceeded in 4 of the past 15 years. In cases where the quota has been exceeded, the domestic allocation has been reduced so that New Zealand catches do not exceed the quota on average. In recent years landings of northern bluefin tuna have increased to about 20 t, this increase in landings is due to the recently acquired ability to distinguish southern and northern bluefin tunas. One of the most striking features of Figure 3 is the dramatic increase of swordfish, prior to 1995 landings were typically less than 100 t. However, while targeting of any billfish is prohibited, the increase in effort has seen the swordfish catch and landings increase dramatically to about 1000 t. Provisional Estimates of Catch by Gear Type New Zealand tuna fishers are required to report catches of tuna when it is caught as number of fish for each operation, with weight reported for each landing. The catch in weight is provided to the fisher when landed to a licensed fish receiver. Since a mixture of fishing methods can be and often are used on a fishing trip, landed weight does not distinguish catch by gear type. Catch by method therefore can not readily be estimated unless the weight can be related to the CPUE and scaled to the landings or unless information as to when specific methods are used is available to partition landings data. This later approach is used in this paper to provide provisional estimates of catch in weight by gear type.