ON THE CATCH COMPOSITION AND WEIGHT-LENGTH RELATIONSHIP OF TUNAS , BILLFISHES AND SHARKS OF NORTH BRAZIL

The tuna longline fishery in the southwestern equatorial Atlantic, based in Brazilian ports, began using leased Japanese tuna longliners in 1956. This activity ceased in 1964 due to political and economical circumstances and reinitiated in 1983 (Hazin et al., 1990). Information on the fishery, catch composition and biology of the tunas, billfishes and sharks inhabiting the equatorial Atlantic and waters adjacent to North Brazil are lacking. The tuna fishery has not been yet developed in this area and recently, a fishing company based in the city of Belém carried out cruises in the equatorial Atlantic in order to evaluate the potential of this fishery in the region. This study is a short contribution to the knowledge of the species captured in waters adjacent to the North Brazilian coast. Its main objective is to describe the catch composition and the length-weight relationship of tunas, billfishes and sharks landed in Belém – Pa. This is the first study of the basic biology of the tunas, billfishes and sharks in North Brazil. A total of 10 research cruises were carried out in cooperation with a fishing company located at Belém during the period November 2000 to September 2002 along the North coast of Brazil between 0630 ́N to 0330 ́S and 04930 ́W to 02930 ́W (Fig. 1) under the scope of Project PROTUNA (Development of technologies for the exploitation of pelagics in North Brazil). The gear used was the longline described in Figure 2.

The tuna longline fishery in the southwestern equatorial Atlantic, based in Brazilian ports, began using leased Japanese tuna longliners in 1956.This activity ceased in 1964 due to political and economical circumstances and reinitiated in 1983 (Hazin et al., 1990).
Information on the fishery, catch composition and biology of the tunas, billfishes and sharks inhabiting the equatorial Atlantic and waters adjacent to North Brazil are lacking.The tuna fishery has not been yet developed in this area and recently, a fishing company based in the city of Belém carried out cruises in the equatorial Atlantic in order to evaluate the potential of this fishery in the region.
This study is a short contribution to the knowledge of the species captured in waters adjacent to the North Brazilian coast.Its main objective is to describe the catch composition and the length-weight relationship of tunas, billfishes and sharks landed in Belém -Pa.This is the first study of the basic biology of the tunas, billfishes and sharks in North Brazil.

Longitude
Swordfish (Xiphias gladius) is responsible for 43% of the total catch (percentage in weight) (Table 2).The yellowfin tuna (Thunnus albacares) and the bigeye tuna (Thunnus obesus) are also well represented (24 and 16% of the catch in weight, respectively).Sharks (including at least 5 species) and 4 other species of billfishes comprised only 6 and 8% by weight, respectively.From 1983 to 1997, in Northeast Brazil, sharks (mainly the blue sharks and Carcharhinus sharks) dominated the catches representing 54% of the total catch (Hazin et al., 2000).From 1998, as in North Brazil, the fishery in this region targeted mainly the swordfish, and sharks were captured as by-catch (Santana, 2001).
The mean lengths of specimens of each species of tunas and billfishes were similar for each trimester, but in the case of the swordfish, white marlin, blue marlin and sailfish, differences between trimesters were noted (Table 3).For the swordfish, smaller individuals were found mainly towards the end of the year (4 th trimester).For the northeast Brazil, minimum size was reported during the third trimester of the year (Hazin, 2000).Twenty eight percent of all swordfish landed in North Brazil were composed of individuals smaller than the minimum size of capture established by ICCAT (The International Commission for the Conservation of Atlantic Tunas), i.e. 125 cm LJFL with 15% of tolerance or 119 cm LWFL with 0% of tolerance.For the fishery based on the northeast Brazil, around 2.7% of the captured individuals were smaller than the minimum size established (Marques, 2001).However this percentage may vary according to the sampling methodology: data obtained from sampling in the landing sites showed a higher percent of smaller individuals (probably due to the facility of storage for sampling) than the reported from the exportation spreadsheets, which showed larger individuals (probably due to the higher market value of the larger individuals).Individuals as large as 280 cm UJFL were also found in Northeast and Southern Brazil (Amorim et al., 1998;Marques, 2000).For the white marlin, blue marlin and sailfish, larger individuals were mainly reported in the second trimester.
Among the most abundant shark species landed in North Brazil, 47% of C. maou was under the length of first maturity (180-190 cm TL, 151 cm FL approximately; Lessa et al. 1999).Lessa et al., (1999) and Amorim et al. (1998) also reported a large amount of juveniles in the south-eastern Atlantic, suggesting that this area may be used as nursery for the species.In North Brazil, however, although mean lengths are smaller than the reported in Northeast Brazil, maximum size reported in the region (300 cm TL) is superior than the registered in the Northeast (250 cm TL). C. falciformis, showed significant differences in the mean length among samples caught in the trimesters of the year.The largest individuals were reported in the second trimester (Table 4).The relationship between body length and weight if of great importance in fishery biology not only for the estimates of biomass obtained from analytical models but also the parameter b of the relationship has also an important biological meaning, indication the rate of weight gain relative to growth (Gulland, 1983;Frota et al., 2004).Length-weight relationship for some tuna and sharks is available for the northeast and central Brazilian coast (Hazin et al., 1990;Lessa et al., 1999;Frota et al., 2004).Weightlength relationship (TW x FL for sharks and tunas and TW x UJFL for billfishes) is shown in Table 5.
Concluding, it was verified that swordfish dominated the catch (by weight), followed by the yellowfin and bigeye tunas the tunas showed little seasonality in size, but the bill fishes and sharks presented a marked seasonal size variation almost half of the exemplars of Carcharhimus maou captured was under the first maturity length.

Fig. 1 .
Fig. 1.Individual sets of the research cruises carried out in North Brazil from 2001 to 2002.

Fig. 2 .
Fig. 2. The longline used for the tuna fishery in North Brazil.

Table 1 .
Species recorded in the long line fishery carried out in North Brazil

Table 2 -
Proportion in weight of tunas, billfishes and sharks captured in North Brazil.

Table 3 .
Minimum, mean and maximum fork length of tunas and upper jaw -fork length (m) of billfishes captured in North Brazil.(n = number of observations; std = standard deviation).

Table 4 .
Minimum, mean and maximum fork length (m) of sharks captured in North Brazil.(n = number of observations; std = standard deviation).

Table 5 .
Weight-length relationship of tunas, billfishes and sharks captured in North Brazil.