Romanov: Bycatch in the tLina purse seine fisheries of the western Indian Ocean 



99 



Elcii^atis hipinnulata (0.195 t/10.314 t), common dolphin- 

 fish. Coryphaena hippiirus (0.191 1/10.098 t), triggerfish of 

 the genus Canthidermis (0.137 t/7.277 t), sharks of the ge- 

 nus Carcliarhinits (O.n.'i t/9.28cS t), wahoo. Acaiithocyhi- 

 uni solandri (0.031 t/1.621 t), billfishes of the genera AUik- 

 aira and Tetrapturus (0.019 t/1.008 t), and mackerel scad, 

 Decapterus macarclliis (0.0093 t/0.491 kg). One capture 

 of a sea turtle (unknown species) was recorded (Tables 

 4 and 6). 



All types of schools 



Considering all school types in the aggregate, skipjack, yel- 

 lowfin, and bigeye tuna prevailed in the catch — Sf/r , 429r, 

 and 4'?; by weight, respectively (Table 5). Albacore repre- 

 sented a mere 0.2'7(, frigate tuna 0.9%, and kawakawa, 

 Etithyninis affinls. less than 0.1%. Nontuna bycatch 

 accounted for less than 3'^f of the catch. 



On the average, there was 0.518 ±0.099 t of nontuna by- 

 catch caught per positive set, or 27.127 ±8.869 t per 1000 t 

 of target species (Fig. 3). Bycatch levels by species (groups) 

 are given in Table 6. 



Discussion 



The lowest fish bycatch in the WIO tuna purse-seine fish- 

 ery was taken from free schools (mainly carcharhinid 

 sharks and Mobulidae rays) (Figs. 3 and 4, Tables 4 and 

 6). Bycatch of fishes was highest and most diverse from 

 catches on log-associated schools. Rainbow runner, common 

 dolphinfish. triggerfish. carcharhinid sharks, wahoo, bill- 

 fishes, and mackerel scad were predominant. Whale-asso- 

 ciated schools were characterized by an intermediate level 

 of bycatch (mainly carcharhinid and lamnid sharks) (Figs. 

 3 and 4, Tables 4 and 6 1. 



It is interesting to compare the bycatch rates obtained 

 in this study with those published for other regions. The 

 principal bycatch fishes in the Pacific (Bailey et al., 1996; 

 Hall, 1996, 1998; Anonymous, 1997) are the same as those 

 presented here. Bycatch levels are known to vary consid- 

 erably by year, area, fleet (Bailey et al, 1996; Hall, 1996; 

 Anon., 1997), and school type; this variability hampered 

 direct comparisons of the results from the present study 

 with those from published data. However, for the purpose 

 of comparison, I pooled my estimates by gi'oups in accor- 

 dance with the published data (Bailey et al., 1996; Hall, 

 1996, 1998; Anonymous, 1997). Bycatch levels per set and 

 per 1000 t of target species for various regions of the Pa- 

 cific and my estimates for the Indian Ocean are on the 

 same order of magnitude for most groups in similar types 

 of associations (Figs. 5 and 6). 



I also attempted to estimate the unrecorded bycatch by 

 the purse-seine fleets of the principal fishing nations of 

 the WIO by a comparison of fishing tactics. The Soviet fleet 

 in the WIO made an equal proportion of sets on free-swim- 

 ming schools and on log-associated schools during the year 

 (Table 2). Seasonally they switched effort from sets on 

 free-swimming schools to those on log-associated schools 

 (Fig. 7, A and B).The fishing practices of French and Span- 



ish tuna seiners showed similar seasonality until the niid- 

 1990s (Anonymous;'"'"' 1*^ Planet;'^'" Moron'-'). 



The fishing tactics of the Japanese (Hallier;^'' Okamoto 

 and Miyabe-') and Mauritian (Norungee et al.;-- No,.yn. 

 gee and Lim Shung-') purse-seine fleets differed consider- 

 ably from that described above. Japanese and Mauritian 

 vessels made sets on log-associated schools all year round, 

 with single instances of sets on other schools types. 



Only two school types (log schools and free schools) have 

 been described by Hallier;-" Hallier;-^ Parajua Aranda;^'' 



'Anonymous. 1992. Report of the workshop on stock assess- 

 ment of yellowfin tuna in the Indian Ocean, Colombo, Sri 

 Lanka. 7-12 October 1991, 90 p. |IPTP/91/GEN/20.| FAG, 

 Viale delle Termc di Caracalla, 00100, Rome, Italy. 



• Anonymous. 1994a. Report of the expert consultation on 

 Indian Ocean tunas, .5th session. Mahe, Seychelles, 4-8 Octo- 

 ber 199.3, 32 p. IIPTP/94/GEN/22.1 FAO. Viale delle Terme di 

 Caracalla. 00100, Rome, Italy. 



' Anonymous. 1994b. National report of Spain. In Proceed- 

 ings of the expert consultation on Indian Ocean tunas, 4-8 

 October. 1993 (J. D. Ardill. ed. i. p. 44-47. IPTP Coll. Vol. 8., 

 TWS/93/1/14. FAO. Viale delle Terme di Caracalla. 00100, 

 Rome. Italy. 



' Pianet. R. 1994a. Purse seine fishery trends in the western 

 Indian Ocean from data collected in Victoria (Seychelles), 

 1984-1992. //( Proceedings of the expert consultation on 

 Indian Ocean tunas, 4-8 October, 1993 (J. D. Ardill. ed.). p. 

 41-44. IPTP Coll. Vol. 8.. TWS/93/1/13. FAO. Viale delle 

 Terme di Caracalla, 00100. Rome. Italy. 



' Pianet. R. 1994b. National report of France. //! Proceedings of 

 the expert consultation on Indian Ocean tunas. 4-8 October. 1993 

 (J.D.Ai-dill,ed.i.p.48-.52. IPTP Coll. Vol. 8.TWS/93/1/16. FAO, 

 Viale delle Terme di Caracalla, 00100, Rome. Italy 



' Moron. J. 1996. National report of Spain. In Proceedings 

 of the expert consultation on Indian Ocean tunas. 6th session, 

 Colombo. Sri Lanka. 2.5-29 September. 1995 (A. A. Anagnuzzi, 

 K. A. Stobberup, N. J. Webb, eds. I, p. 63-69. IPTP Coll. Vol. 9. 

 FAO, Viale delle Terme di Caracalla, 00100, Rome, Italy 



' Hallier. J.-P. 1991. Tuna fishing on log associated schools in 

 the Western Indian Ocean: an aggregation behaviour. /;; IPTP 

 Coll. Vol. Work. Doc, Vol. 4. p. 325-342 [TWS/90/66.1 FAO, 

 Viale delle Terme di Caracalla. 00100. Rome. Italy. 



Okamoto. H., and N. Miyabe. 1996. Review of Japanese tuna 

 fisheries in the Indian Ocean. In Proceedings of the expert 

 consultation on Indian Ocean tunas. 6th session, Colombo. Sri 

 Lanka. 25-29 September. 1995 (A. A. Anagnuzzi, K. A. Stobb- 

 erup, N.J. Webb, eds.), p. 15-21. IPTP Coll. Vol. 9. FAO, Viale 

 delle Terme di Caracalla, 00100, Rome, Italy 



' Norungee, D., A. Venkatasami, and C. Lim Shung. 1994. 

 Catch and landing statistics of the Mauritian tuna fisheries 

 (1987-1992) and an analysis of the skipjack tuna catch of 

 the Mauritian purse seine fishery (1987-1993). In Proceed- 

 ings of the expert consultation on Indian Ocean tunas. 5th ses- 

 sion. Mahe. Seychelles. 4-8 October. 1993 (J. D. Ai'dill. ed.), 

 p. 266-273. IPTP Coll. Vol, 8. TWS/93/4/5. FAO. Viale delle 

 Terme di Caracalla. 00100. Rome. Italy. 



' Norungee. D.. and C. Lim Shung. 1996. Analysis of the purse 

 seine fishery of Mauritius, 1990-1994, and comparison of catch 

 rate and species composition of catches of Mauritian purse 

 seiners to those of French fleet. In Proceedings of the expert 

 consultation on Indian Ocean tunas, 6th session, Colombo, Sri 

 Lanka. 25-29 September, 1995 (A. A. Anagnuzzi, K. A. Stobb- 

 erup. N.J. Webb. eds.). p. 1.5-21. IPTP Coll. Vol. 9. FAO. Viale 

 delle Terme di Caracalla, 00100. Rome. Italy 

 Hallier. J.-P 1994. Purse seine fishery on floating objects: 

 What kind of fishing effort? Wliat kind of abundance indices? In 



continued 



