704 



Fishery Bulletin 97(3), 1999 



The data 



The shrimp fishery in Kuwait consists of two sec- 

 tors: industrial trawlers and dhow trawlers (for a 

 review see Mathews and Samuel, 1991; Mathews, 

 1994; Ye et al., 1996 1. The main species caught are P. 

 semisiilcatus, Metapenaeus affinis, and Parapenae- 

 opsis stylifera. Penaeus semisulcatus dominates in 

 the central and southern waters, and the other two 

 species are mainly distributed in northern waters. 

 The dhow boats trawl in relatively shallow waters, 

 and their catches are auctioned at local fish markets 

 (Abdul-Ghaffar and Al-Ghunaim, 1994; Ye et al., 

 1996). Species composition of the dhow catch varies 

 with changes in fishing grounds and with seasonal 

 migration. The monthly percentages of P. semisu- 

 lcatus in the dhow landings change greatly within a 

 season, for example, from 29.6 to 87.1% in 1993-94. 

 Owing to the difficulty in collecting reliable effort 

 data from the dhow sector, effort is usually standard- 

 ized in relation to that of the industrial sector in re- 

 porting Kuwait's shrimp fishery statistics. The dhow 

 effort is thus calculated by dividing the total catch of 

 combined species of the dhow sector by the CPUE of 

 combined species from the industry sector (Mathews, 

 1994), which ignores the change in target species. 

 The catchability off! semisulcatus under such a stan- 

 dardized effort would change simply because of the 

 variation in target species. 



The industry sector comprises three companies: 

 United Fisheries of Kuwait (UFK), Bubiyan Fishing 

 Company, and National Fishing Company. The 

 shrimp catch landed by UFK is mainly exported. 

 Fishing operations of the UFK fleet are mainly in 

 the southern and central Kuwait waters, where P. 

 semisulcatus dominates (Siddeek et al., 1989); this 

 occurs because P. semisulcatus is individually larger 

 and much more valuable in international markets 

 than the other two species (Siddeek et al., 1989; Ye 

 et al., 1996). Consequently, the percentage of P. 

 semisulcatus in the UFK catch remains relatively less 

 variable within a season, for example between 59.5% 

 and 84.5% in the 1993-94 season (Ye et al., 1996). 



Seasonal landing data from the dhow boats were 

 recorded every five days (Mohammed et al., 1996); 

 however, industrial fleets reported their catches and 

 fishing effort monthly. To estimate monthly varia- 

 tions in catchability, we assumed a uniform distri- 

 bution of the industrial catch within any month and 

 added this to dhow catches for that month. This ob- 

 scured the within-month variation in catch. The dhow 

 landings constituted about 53% of the total P. 

 semisulcatus landings in the 1994—95 and 1995-96 

 seasons (Ye et al., 1996); therefore such an assump- 

 tion would not affect the estimates of monthly 



catchability significantly. In our study, catchability 

 was assumed to be constant within a month, and the 

 fishing effort data of the P. semisulcatus fishery were 

 standardized by using the entire industrial shrimping 

 fleet catch rates, as is customary (GuUand, 1983; 

 Mohammed et al., 1996). The total catch, fishing ef- 

 fort, and abundance index are shown in Table 1. 



Catchability by the UFK fleet is relatively stable 

 within a fishing season. From Equations 1 and 3, 

 CPUE = qN. CPUE can be an indicator of variation 

 in stock abundance only when catchability q is con- 

 stant. Figure 1 shows q estimates calculated by sim- 

 ply dividing UFK CPUE data (Siddeek et al., 1989) 

 by the shrimp stock abundance, represented by catch 



