Sponsored By:
The Barbara Delano Foundation
The Homeland Foundation
The David & Lucile Packard Foundation
The AVINA Foundation

Presented By:
WildAid
Hawaii Audubon Society
Pacific Fisheries Coalition

Jorge Eduardo Kotas * , Silvio dos Santos **, Venâncio Guedes de Azevedo **, José Heriberto Meneses de Lima *, José Dias Neto* and Celso Fernandes Lin *.

*IBAMA researchers
** REVIZEE researchers

e-mails : Jorge Eduardo Kotas, Silvio dos Santos, Venâncio Guedes de Azevedo, José Heriberto Meneses de Lima, José Dias Neto, and Celso Fernandes Lin.

Abstract

"Finning" is the main obstacle to shark conservation and management along Brazilian jurisditional waters. In 1998, the Brazilian Government through its Environmental Agency (IBAMA - Brazilian Institute for the Environment and Natural Renewable Resources) made a first effort to control "finning" by issuing a federal regulation (Portaria IBAMA n&nordm; 121 of August 24th, 1998), prohibiting shark finning by all vessels licensed to fish in Brazilian waters. In despite of the entry into force of this regulation, its enforcement has been proven to be difficult and probably will require international financial aid, trained personnel for sampling work along the main fishing harbours and the establishment of a national observer program. The enforcement would be based on a "National Management and Conservation Plan for Sharks".

Research efforts to better understand shark "by-catch" issues were initiated in 1998 by IBAMA and by the Ministry of Environment, through the Brazilian Program for the Assessment of Living Marine Resources in the Economic Exclusive Zone (REVIZEE), with observer coverage of 3 tuna longline fishing trips being conducted, in which information on fishing grounds, gear configuration, fishing operations, catch composition, blue shark biology, CPUE and shark survival rates were collected.

Brazilian ban on live "finning" of sharks

"Finning" is the main obstacle to shark conservation and management along Brazilian jurisditional waters. Although it is considered an illegal activity by the Brazilian Government through its environmental agency (IBAMA) and for the National Elasmobranch Society (SBELL) (Anonymous, 1992 a), finning is still a routine practiced aboard most national and foreign leased vessels.

In 1998, IBAMA made a first effort to control "finning", issuing a federal regulation law (Portaria IBAMA n&nordm; 121 of August 24th, 1998). The main points of this regulation are the following:

• Prohibit the use of gillnets (i.e., driftnets, anchored gillnets, etc.) larger than 2,5 km length
• Prohibit "finning"
• The amount of fins landed has to be proportional to the carcasses (i.e., fresh fins have to represent approximately 5 % of total carcass weight)

Despite the law's existence, enforcement is difficult and will require international financial aid, trained personnel for sampling work along the main fishing harbours and the establishment of a national observers' program. Enforcement would be based on a "National Management and Conservation Plan for Sharks", trying to reach the following goals:

• Adequate and updated dataset about shark landings, catches and fishing effort. Unfortunately, up to the present moment, the available data on sharks caught by different fishing gears (longlines, gillnets) is not broken down by species . It is common to find different shark species mixed in only one statistical category called simply "sharks". The use of a proper logbook form by fishing masters of all vessels operating in directed shark fisheries or in other fisheries where sharks are caught as by-catch, together with a good port sampling scheme, should be put into practice in order to collect reliable data on catch statistics for shark species. It is also important to have an adequate monitoring system to quantify the number of vessels and fishing gears operating in shark fisheries. The problem as regards the lack of information is so serious that. even the exact gillnet fleet size operating along the Brazilian coast is unknown.
• Fins and carcasses sampling work along the main fishing harbours. This point would be important to follow up the status of shark exploitation, through sampling activities for shark fin identification which will allow the estimation of weight and species composition of sharks caught and discarded at sea. It will also allow the managers to see trends in size, age composition and sex-ratio.
• Observers' cruises. In a similar way as it has being put into practice by other countries (Branstetter, 1996), it is crucial that IBAMA implement a shark observer program for monitoring "finning" activities, to confirm and augment the information provided through mandatory submission of logbooks, identifying shark species, collecting biological samples, as well as information on vessel and gear characteristics. An observer program, initially directed to cover fishing operations by foreign flagged leased vessels, would be the plan's "cornerstone" and the most expensive part. It will require adequate selected and trained professionals, like oceanographers, biologists and fishing engineers, to accomplish the wide range of research activities to be carried out as part of the observer program.
• Longline research cruises. Very little is known about the spatial-temporal distribution of sharks and the way that the biological-oceanographic relationships could help fishing masters to minimize shark "bycatches" in longline fisheries. IBAMA has research vessels that could be adapted for monofilament longline research cruises. With the use of minilogs and hook timers it would be possible to have an insight into shark stratification throughout the water column and also would allow tag-release, biological sampling and selectivity experiments directed to sharks. This project would need an external financial aid (figure 13).

Observer cruises

Longline fishing grounds

During 1998, tuna longliners based at Itajaí (State of Santa Catarina in the South region of Brasil) were monitored through scientifc observers. Three fishing trips were observed during the periods March/April, June/July, and September/October. A total fishing effort of 33,650 hooks and 34 sets was performed. This values represented 1 % of the average annual fishing effort from the national fleet in southern Brazil. For the 34 sets which were observed, 24 were located within the Brazilian EEZ and 10 in international waters. The mean number of hooks/set used during the first, second and third cruises were 1030, 992 and 950 respectively. The fishing area (between 27&nordm;30'- 34&nordm;30'S Latitude and 52&nordm;00'- 36&nordm;00'W Longitude) (figure 1) corresponds mainly to the occidental margin of the sub-tropical convergence, an oceanographic phenomenon related to the encounter of Brazil and Malvinas currents (Castello & Habiaga, 1988). The sea bed includes the continental slope, abyssal plains and oceanic elevations. Within this peculiar oceanic-epipelagic fishing grounds, swordfish (Xiphias gladius), tuna species (Thunnus obesus, Thunnus albacares, Thunnus alalunga) and sharks (mainly Prionace glauca) used to be caught, between March and November, with monofilament longline used by national vessels based either at Itajaí or at Santos harbours,. High swordfish concentrations which are found in this area during winter are associated with trophic migrations of the species due to the high abundance of squid (Haimovici, Perez, 1990; Arfelli, 1996). Blue shark concentrations and movements probably follow a similar pattern, added to its reproductive behaviour.

Monofilament longline vessels and gears

The observers were placed aboard longliners based at Itajaí. All the vessels were equipped with the monofilament longline and used squid (Illex argentinus) as bait together with a one way light stick attached to each branch line (table 3). These vessels could stay up to 30 days at sea and are a good representative sample of the longliners operating throughout the southern Brazilian EEZ.

The monofilament longline is used primarily for targeting swordfish (Xiphias gladius), but other pelagic species such as pelagic sharks (mainly Prionace glauca) and tuna fish (Thunnus albacares, T. alalunga, T. obesus), are also caught. When this fishing modality was introduced in 1994 in Santos and in 1996 in Itajaí, the fleet initially targeted swordfish, avoiding areas of higher shark densities. In this case, the hook was directly connected to the nylon gangion, allowing sharks to bite off the line and escape. However, with the increasing interest in shark fins for the Asiatic market, steel wires began to be used in the gangions edge, connected to the hook and not allowing sharks to escape.

Nowadays, the monofilament longline with steel wire in the gangions is the most common type of gear used by oceanic vessels in southern Brazil, due its easier operation and safety compared to the traditional multifilament system.

The monofilament longline system used by national vessels is composed of a nylon mainline where gangions are fixed. Buoys and radio-buoys are attached to this single structure (table 4 and figure 14). The mainline used is 4 mm diameter, and its total length ranges between 25,6 and 35 nautical miles (47 to 66 km). Buoys are attached to the mainline by a nylon cable with a snap. The distance between buoys ranges from 200 to 300 m length. Along it, 4 to 5 gangions are snapped to the mainline, equidistant 40 to 60 m respectively.

The gangion structure (figure 15) is very simple and measures between 13 to 20 m total length. It is composed of 12 to 19 m monofilament nylon cable of 1.8 mm diameter, attached to the mainline by a snap with a swivel. On the other end, 1 m braided steel wire, with a plastic cover and measuring 2 mm of diameter is connected to the hook (swordfish 9/0). One or two lightsticks (4 inches in length) were fixed near the hook or 1 m opposite to it. The lightsticks, when kept in ice, can be reused for a second longline set. A second leaded swivel is fixed on the nylon cable 9.40 m below the snap, allowing sharks to swim freely without snaring the gangion and at the same time keeping the line stretched. The connection between the nylon and the steel wire is made with two hangers protected with plastic covering.

The plastic buoys are rigid, of 30 cm diameter and snapped to the mainline by a 10 - 20 m nylon cable with 3.6 mm diameter. The total number of buoys used per set ranged between 200 and 260. Radio-buoys were also used to search the longline gear through the GPS - PLOTTER (5 to 6 radio-buoys attached to the mainline after 40 - 43 plastic buoys). 2 signal-buoys are also used, one in the middle and the other at the longline end, due the problem with ship traffic.

The longline depth operation is reached by the use of the "line-setter" with "beeper" and varying the length of the buoy cable. Not all Brazilian longliners use this hydraulic device. In this case, fishing masters vary the buoy cable length and the gangion number between buoys.

Considering only the maximum cable buoy plus gangion length, the longline would be operating at 40 m depth . The depth could be greater due to the "catenaria" formed by the line-setter (photos 1 to 7).

Longline operation

Table 5 shows a resume of the longline operations for the 3 observers cruises considered. Sharks usually are recovered alive, and the animals used to be brought to the deck through the use of grapples, hooks and harpoon, depending on shark size and resistance. On the deck, or even along the vessel's edge, the animals are immediately sacrificed. They suffer a deep cut over the head causing intensive hemorrhage and are finally paralyzed by the insertion of a steel wire through the neural arch. After this "procedure" sharks are beheaded, gutted and the fins extracted, with carcasses chilled with crushed ice in the holds.

Catch composition

During the 3 observer cruises taken, 1247 elasmobranchs (68.9 %) and 563 teleosts (31.1 %) were caught. The blue shark represented 50.4 % of the total catch, hammerhead sharks (8.2 %), night shark (6.2 %) and shortfin mako (4 %) respectively. Other carcharhinids like C. obscurus and C. longimanus represented only 0.1 % . Bony fishes were mainly represented by the swordfish, with 13.5 % of the total catch, followed by yellowfin (9.1 %), albacore (6.7 %), bigeye (1.6 %) and white marlin (0.3 %) (figure 16 and 17).

Blue shark distribution related to sea water temperature

For the period October/97 to October/98, trends in monthly blue shark CPUE (number of fish/100 hooks), obtained through observer cruises and logbooks from longliners based in Itajaí and Navegantes were analysed in relation to the average surface sea-water temperatures for the same period (figures 2 and 3). Best yields (i.e., between 4.5 and 4.9 sharks/100 hooks) were observed in May and June, with the surface sea-water temperatures between 21.9 and 21.1&nordm;C respectively. Conversely, the highest temperature values in January and February, i.e., 26.8 and 27.7 &nordm;C respectively, corresponded to CPUE values of only 0.92 and 1.42 sharks/100 hooks. Hazin (1993), analyzing blue shark CPUE data from southern Brazilian longliners during the period 1986 - 1988, also found higher values for the period April-June and lower values between October-December. In the same area, Anonymous (1998 b) have reported best CPUE values in July, i.e., 4.87 and 3.05 sharks/100 hooks, between 25 to 40 m depth with temperatures ranging from 17 to 22&nordm;C respectively.

Blue shark catch estimate in southern Brazil

The previous monthly CPUE values obtained (sharks/hooks) were used to estimate the annual number of blue sharks caught by longliners in southern Brazil.

The average annual CPUE obtained for the considered period in southern Brazil was 2 blue sharks/100 hooks. This value was similar to values of CPUE obtained in the same area by the research vessel "Atlantico Sul" (i.e., mean value of 2.5 blue sharks/100 hooks), which also used a monofilament longline of 21 km mainline, 195 to 565 gangions of 13 m length with 3 m iron cables at the end, and depth operation range between 25 to 150 m (Anonymous, 1998 b).

Considering the average annual fishing effort (hook number) used by the national longline fleet in southern Brazil during the period 1990 - 1994 of 3,415,916 hooks (Anonymous, 1998 a) and the mean CPUE value of 2 blue sharks/100 hooks, the average blue shark number caught per year in southern Brazil by the national fleet was calculated:

# avg blue sharks/year = (2*3415916)/100 = 68318 sharks.

Blue shark CPUE during observer cruises

The blue shark was the most important shark species caught throughout the 3 longline cruises observed (figure 4). Best yields were found during the first and second cruises (autumn-winter) with mean CPUE values of 34.1 and 40.6 sharks/1000 hooks respectively. The CPUE declined dramatically to only 3.4 sharks/1000 hooks for the third cruise, probably because it was carried out in most coastal waters with low blue shark abundance. Amorim (1992), analyzing blue shark catches taken by Brazilian longliners during the period 1971 to 1988 in southern Brasil, also registered the highest catches between May and July and low values from December to January. This trend probably reflects the seasonal fluctuation in blue shark abundance with adult male concentrations in autumn-winter in southern Brazil.

Considering the blue shark CPUE geographical distribution per block of 1o x 1o in the first cruise (figure 5), high values were observed around submarine elevations, i.e., CPUE values of 98 and 43 blue sharks/1000 hooks in blocks 2936/3 and 3140/1 respectively. One of these submarine elevations, called "Rio Grande" would be an oceanic highly productive area, concentrating marine life (i.e., sharks, turtles, tuna). Also observed was a decrease in blue shark abundance from oceanic to coastal areas, i.e., from 36 sharks/1000 hooks in the block 3044/3 to only 1 shark/1000 hooks in block 3350/3. For the second cruise, high CPUE values, between 36 - 73.6 sharks/1000 hooks were found along the continental slope and oceanic basin (figure 6). The third cruise was marked by low blue shark CPUE values, i.e., ranging from 1.05 to 12.6 sharks/1000 hooks with most of the sets concentrated along the continental slope .

Blue shark size composition during observer cruises

During the first cruise (March-April/98), 138 male blue sharks were measured, between 200 and 285 cm total length. Only 8 females were caught, ranging from 215 to 272 cm total length (figure 7). The sex ratio of males to females was 18:1. Most of the males were adults, with sperm in the seminal vesicle and calcified clasper. Females were also mature, i.e., 2 sharks were in a pre-ovulatorium stage with enlarged uterus and 6 had fecundated eggs inside the uterus and embryos in different developmental stages. During this cruise the mean size was 245 cm. For the second cruise (June-July/98), 181 male blue sharks were measured, ranging from 168 to 281 cm total length (figure 8). The mean size was 227 cm. Male sharks sampled had claspers in different reproductive stages. Below 200 cm, most of the males were considered immature because their claspers were non-calcified (figure 9). Biological sampling aboard showed that 2/3 of the males were mature or in a maturing process, with sperm in their vesicles. Eight females were also measured, between 225 and 262 cm total length. At least 4 females were pregnant, with embryos between 25 and 39.5 cm total length. The sex ratio of males to females was 23:1. Amorim (1992) also observed that for the second and third quarters the length distributions were mainly composed of male blue sharks. In the third cruise (September-October/98), which occurred in coastal waters, i.e., near the shelf border and slope, only 12 males were sampled, between 108 and 272 cm total length. Eight of these males, with sizes over 216 cm, presented calcified clasper. Eleven females were sampled, ranging from 195 to 248 cm total length. Two pregnant females were also observed, with total lengths of 246 and 248 cm, and embryos in size between 34 and 48 cm. Although the number of blue sharks caught was smaller compared with the two previous cruises, the sex-ratio was 1:1. Amorim (1992) considered that the mating season for this species occurs between November and April, matching with this equivalent sex-ratio.

Blue shark size composition - landings from longliners based at Itajai

Data on weight of individual carcasses of blue sharks landed from longliners in Itajaí harbour between January 1997 and December 1998 were recovered from log commercial sheets of fishing companies. These weights (kg), were converted to total length (cm) through the length-weigth relationships obtained in the present study, allowing the analysis of blue shark size composition during the considered period. A total of 19,183 blue shark carcasses were weighed, i.e., 7882 and 11,301 individuals in 1997 and 1998 respectively. A similar exploitation pattern was observed for the two years considered (figure 10) . Longliners caught blue sharks from 115 cm to 382 cm converted total length, but more frequently within 200 and 270 cm total length. A mean size of approximately 227 cm was found. Amorim (op. cit) reported for longliners based at Santos - SP, during the period 1971 - 1988, that blue sharks caught had total lengths between 200 and 300 cm. However, comparing the mean size of both localities between these different periods (figure 11), a decline of 14 cm in total length of sharks is observed. This considerable decline could be explained by the increasing fishing pressure over the blue shark stock(s) in the South Atlantic, not only caused by national fleets but also by foreign high seas vessels. The historical decline in the mean size could be a first indication of overfishing.

Comparing the monthly trends in minimum size obtained for the years 1997/98, the lowest values occurred from June to August (end of autumn-winter), a probable recruitment period. Amorim (1992) apud Amorim et al. (1998), reported that since 1990, longliners from Santos were catching smaller blue sharks in southermost areas between June and August, with a size range between 80.5 and 109.4 cm total length (approximately age of 6 months) .

Blue shark morphometry (males)

Morphometric relationships were also studied for male blue sharks due to the need to convert different shark measures to total length (figure 12). Linearized relationships were calculated:

The length measurements were taken in cm.

Another relationship found for male blue sharks was between the carcass weight (CW) and the whole weight (TW). It was defined as,

(CW) = -0.46 + 0.99 Ln(TW) (n = 181; R2 = 0.9412)

weight was measured in grams.

Length-weight relationships for male blue sharks

A length-weight relation of the type Y = aXb , was calculated for male blue sharks:

TW = 0.0008 (TL)3.27 (R2 = 0.90 ; n = 181)

Where:
TW = Total weight
TL = Total length

The following relationship between carcass weight (CW) and carcass length (CL), was also estimated for male blue sharks:

CW = 0.0084 (CL)3.05 (R2 = 0.89 ; n = 181)

Shark survival

Data collected during the observer cruises also allowed the study of sharks' condition, i.e., if they arrived alive or dead on deck during longline recovery operations. The animal was considered alive if it showed relative activity like biting, nictitant eyelid and gill motion. The shark was dead if no activity was detected, even with external stimulus . Table 01 presents the results of these observations. From a total of 508 sharks of different species observed, 88 % arrived still alive on deck and were immediately sacrified by crewmen. The highest survival rate was detected for the blue shark (97 %), followed by shortfin mako (78 %), night shark (69.8 %) and the smooth hammerhead shark (53 %). Other sharks showed insignificant sample numbers and were not considered (n < 30). more intensive work in this field is recommended, because it probably would be a key factor for the adoption of conservation measures to reduce the incidental catches of sharks in longline fisheries by high seas fleets and at the same time would allow to conduct tag-release studies.

Shark fins

During the observers cruises, finning activities were registered (Table 02). The type of fin cut off from sharks was related to the species involved and crew. For the first cruise carried out in March-April and June-July/98, with the same crewmen, first and second dorsals, pectorals, pelvics, and the anal and inferior lobes of the caudal fin were extracted from Prionace glauca, Carcharhinus signatus, Sphyrna lewini, Sphyrna zygaena, Carcharhinus longimanus and Carcharhinus obscurus. In the case of shortfin mako (I. oxyrhinchus), only the first dorsal, pectorals and the inferior lobe of the caudal fin were extracted (the second dorsal and pelvic fins were only used when the fish was an adult). During the third cruise (September-October/98), with another longline vessel and crew, the finning pattern was different. In this case, only the first dorsal, pectorals and inferior lobe of the caudal fin were extracted from Sphyrna zygaena, Sphyrna lewini, Isurus oxyrinchus, Prionace glauca, Carcharhinus signatus and Carcharhinus obscurus.

Blue shark comprised 94 % and 76% of the fins extracted during the first and second cruises respectively. The total number of shark fins extracted from different species were 3659 and 4508. For the third cruise the smooth hammerhead comprised 38 % of the fins, with a total of 421 shark fins of different species extracted.

In 1998, crewmen received US$12.00/kg of blue shark fins landed in Itajaí harbour. In the case of the scalloped hammerhead it could reach US$ 45.00/kg. Nowadays, shipowners receive 50 % of the fins profits. The national fleet crewmen do not throw away shark carcasses because Brazilian fishing companies sell shark carcasses for the national market.

Discussion

Although it is still unclear, there seems to be an interaction between blue shark concentrations and sea-water temperatures in southern Brazil. There are several pieces of evidences relating blue shark abundance and distribuition with sea-water temperature. Stevens (1992) observed Japanese longliners directed to Thunnus maccoyii in southeast Australia avoiding areas of blue shark concentrations with northern currents between 15 to 16&nordm; C . Strasburg (1958) realized that blue sharks in tropical waters were caught at greater depths than in temperate waters. Although Gubanov and Grigor‡ev (1975) believe that the vertical and horizontal distribution of blue sharks is related to sea-water temperature, Carey and Scharold (1990) observed wide temperature (7 to 28&nordm; C) and depth (from surface to 620 m) ranges for this species.

In southern Brazil, the blue shark CPUE peaks, composed of male concentrations, are also related to its migratory strategy, which means that they are found at a shallower depth in the water column during the period April - June, increasing its catchability by the monofilament longliners. Anonymous (1998 b) found best CPUE values in southern Brazil, i.e., between 4.9 and 3.05 sharks/100 hooks, in a depth range of 25 to 40 m and 17&nordm; to 22&nordm; C temperature. Amorim et al. (1989) also observed that male blue shark catches are predominant between autumn and the beginig of winter in southern Brazil. Hazin (op. cit) related blue shark vertical and horizontal distribution to its physiological condition, i.e., sexual stage. He also observed in a different area, i.e., offshore northeast Brazil, temperature preferences for females (14 to 20&nordm;C) and males (13 to 17&nordm; C) and a male vertical migration to the top of the thermocline between July and December, increasing its catchability. In this area females would be more vulnerable to longline between February and July when sea-water surface temperatures are higher. He also found a positive correlation between female blue shark CPUE and sea-water surface temperature, but negative for males. The subtropical convergence presents a thermal gradient between 14 to 18&nordm; C, and the squid Illex argentinus is strongly associated with this oceanographic phenomenon (Anonymous, 1998 b). Big adult squid concentrations occurr between July and September in southern Brazil, and the presence of squid paralarvs (1,9 mm size), indicate the existence of a spawning area during springtime. This suggest a strong relationship between the distribution of Illex argentinus and the abundance of Prionace glauca.

Along the Brazilian EEZ, other CPUE values were also found for the blue shark. Evangelista et al . (1998) in northeast Brazil, during April-May 1997, obtained an average blue shark CPUE of 0.1 shark/100 hooks. Hazin et al. (1990) found in the same area, for the period July 1986 to December 1992, a mean value of 0.4 sharks/100 hooks, ranging between 0.5 to 0.7 sharks/100 hooks. He also found that east of 35&nordm; W longitude, the average CPUE value was 0.5 shark/100 hooks.

Blue shark CPUE values were also found in different world areas. Stevens (1992), for Japanese longliners operating in southeast Australia, detected an annual average of 1 shark/100 hooks for the period 1988 - 90. He also found values between 1.3 and 5.4 sharks/100 hooks for Korean and Japanese longliners operating along New Zealand waters between 1980 to 1989. In the north Atlantic, CPUE values averaged between 0.3 and 7 sharks/100 hooks (Murray, 1953, Sivasubramanian, 1963, Casey and Hoenig, 1977). Strasburg (1958) found a high blue shark concentration , i.e., 6.3 sharks/100 hooks between Cape Hatteras and Cape Cod. In the equatorial Pacific, Nakano (1994) found a mean CPUE value of 0.4 shark/100 hook. For the north Pacific CPUE blue shark values ranged between 0.3 and 2.8 sharks/100 hooks and exceptionally 8.3 sharks/100 hooks (Shomura and Otsu, 1956; Strasburg, op. cit.; Sivasubramanian, op.cit; Williams, 1977; Nakano, op.cit.).

Trends in blue shark CPUE values can also reflect trends in fishing strategy or stock health. Amorim (1992) analysed shark CPUE from longliners based at Santos, which also operated in southern Brazil during the period 1983 to 1988, and observed that the mean annual blue shark CPUE reached maximum values between 6 and 11 sharks/100 hooks, when longliners used the traditional Japanese multifilament system. Conversely, with the introduction of the monofilament longline since 1994, the CPUE dropped to an average value of 2 sharks/100 hooks in 1997-98. This phenomenon could be explained by the rising fishing effort over blue sharks since the 1980s, or changes in the fishing gear depth operation .

Global estimates of blue shark catches based on CPUE and fishing effort data were previously made by many researchers. Stevens (1992) considering a mean world blue shark CPUE from Japanese longliners of 0.1 shark/100 hooks, estimated a global catch of 433,447 blue sharks , which means approximately 13000 t. , with an average individual weight of 30 kg. Bonfil (1994), considering a world longline fishing effort of 750 million hooks and a CPUE of 0.5 shark/hook, estimated 4 million blue sharks caught as "by-catch". He also considered that approximately 6.2 to 6.5 million blue sharks are caught each year by high seas fleets.

Results from the sampling activities carried out in Brazilian waters by observers indicated that the national monofilament longliners based in Itajaí and operating in southern Brazil used to catch blue sharks from 108 cm to 285 cm total length, with an average of 227 cm. The catches are represented mainly by mature males sizes over 200 cm, this sex being more vulnerable to the national longliners fleet in this area during the first and second quarters of the year. Amorim (op.cit) and Amorim (1992) also detected the same phenomenon in the same area , with the multifilament and monofilament longliners from Santos. It is yet unknown why the females are caught in lower number than males. This phenomenon could be explained by the fact that blue sharks have spatial and temporal sexual segregation or even behavioural segregation (i.e., during gestation, females would feed less actively than males) (Gubanov & Gregoriev, 1975; Pratt, 1979; Strasburg, 1958). In Northeast Brazilian waters, females occurred at lower depths than males during the first semester of the year, with the influence of highest sea-water temperatures. Conversely, during the second semester, males were more abundant in surface waters, with the lowest sea-water temperatures (Hazin, 1993). This depth stratification affects the vulnerability of the sexual group.

Several authors studied blue shark morphometry and length-weight relationships in different areas. Stevens (1975), for the north Atlantic found the regression, Fork length = 11.27 + 0.78 (Total length). Amorim et al. (1996), calculated for blue sharks caught by Brazilian longliners based in Santos, Pectoral - caudal length = 0.45 (Total length)1.03 . Hazin (1993), along the Brazilian northeast EEZ, studied several morphometric relationships for male blue sharks, i.e.:

Fork length = 11.27 + 0.78 (Total length) (R2 = 0.94; n = 73)
Precaudal length = 3.92 + 0.74 (Total length) (R2 = 0.95 ; n = 72)
Interdorsal space = -4.24 + 0.22 (Total length) (R2 = 0.86 ; n = 73)

Cramer et al. (1997), sampling blue sharks aboard North American longliners obtained the following relationship:

Total weight = 3.18 * 10-6 (Furcal length)3.1313 [weight (kg); length (cm)]

Amorim et al. (1996) found another length-weight relationships for blue sharks caught by Santos longliners:

Carcass weight = 2.81 * 10-5 (Total length)2.52 [weight (kg); length (cm)]

Anonymous (1998 b), during several longline research cruises in southern Brazil, found evidences of allometric growth for males and isometric for females. The length-weight relationship obtained for males was,

Y = 0.0022 X2 - 0.5435 X + 40.817 (n = 93 ; R2= 0.9126)

Acknowledgements

We would like to thank the Hawaii Audubon Society, WildAid and the Western Pacific Fisheries Coalition for the invitation and financial support to participate in the Shark 2000 Conference. Many thanks also to IBAMA, the Ministry of Environment, and the REVIZEE Program, for the opportunity to work together in the study of sharks. Finally we would like to thank our colleagues from CEPSUL (Research and Fishery Extension Center of the Southeast-South Region), especially Mr. Jorge Almeida de Albuquerque, who always gave us support on our shark projects.

References

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