Occurrences of whale shark ( Rhincodon typus Smith , 1828 ) in the Saint Peter and Saint Paul archipelago ,

The Saint Peter and Saint Paul Archipelago in the central tropical Atlantic, is an important ground of whale sharks that are commonly sighted throughout the year close to the fishing boats in the adjacencies of the islands. In sightings reported between February 2000 and November 2005, the lengths of the individuals ranged between 1.8 to 14.0 m. The causes of these concentrations in the archipelago are still unclear, once there are no upwellings and plankton concentrations for feeding, and no reproductive activities were reported. Nevertheless, they could be associated to the spawning period of the abundant flying fishes, mainly in the first semester, when sightings were more frequent.


Introduction
The whale shark, Rhincondon typus is the biggest fish of the world, inhabiting all tropical and subtropical oceans, with records of them in warm tropical waters, except in the Mediterranean (Compagno, 1984;Colman, 1997).Although whale sharks have a wide distribution, knowledge of its biology and ecology still limited (Jones and Kaly, 1995).In general, occurrences of whale sharks are sporadic and unexpected, which can be associated with the limited knowledge of its ecology (Colman, 1997).
Due to the strategic position of the Saint Peter and Saint Paul Archipelago (SPSPA) between the two hemispheres, and the Atlantic and African continents, the archipelago is an important concentration ground of migratory species such as tunas, billfishes, turtles, dolphins, and the whale sharks.It is one of the smallest, most isolated groups of oceanic islands in the world.The rocky islands are particularly interesting from the population biology and biogeographical perspectives because of their very small size and isolation.They are uniquely influenced by both the superficial Southern Equatorial Current flowing eastward, and the Equatorial Undercurrent flowing westward.The area has been visited by scientific expeditions 27 th 2000 was estimated comparing the fish to the length of the fishing boat since the whale shark remained for 10 minutes by the side of the boat.Most sightings were made in the morning (25), and in the afternoon (16).In January 2004, four sharks were seen at night, one of them remained for 360 minutes beside the boat.Sighting times ranged between 1 to 360 minutes, with no correlation between the moon phase (χ 2 ; p < 0.001).Sex determination of all individuals was not possible due to most of the sightings being made from the fishing boats and not from underwater observations.In the SPSPA, the whale shark did not present a clear period of occurrence, but the sightings were more common mainly during the first semester (Figure 3).
Twenty three sightings were reported at buoy 1, eighteen at buoy 2 where fishing boats are commonly moored and ten were not described (Figure 4).Only two sightings were recorded on the east side, and on one occasion very close to the rocks.Probably the sightings of June 18 th , 19 th and 20 th , 2000, were of the same individual of 8 m TL.The same situation may have occurred with the sighting recorded on March 27 th and 28 th ,2002, both for individuals of 5 m TL.Two whale sharks presented some remarkable characteristics, one shark (5 m TL) had the top of the caudal fin cutted, and another shark (8 m TL) did not present the first dorsal fin.Both were photographed.
since 1799 when the inhospitable nature and inaccessibility of the archipelago prevented detailed biological studies.However, since the establishment of a scientific research station by the Brazilian Navy, in July 1998, researchers have been able to visit the island periodically and continually.
Records of whale shark in the SPSPA were reported by Edwards and Lubbock (1982), Gadig (1994), and Rangel (1998).Since the beginning of scientific research in the SPSPA in 1998, whale sharks have been frequently sighted around the islands.
The aim of this study is to compile the existing data of sightings of the whale sharks recorded in the SPSPA, localize the sighting points, estimate the lengths of individuals, and observe the sighting frequency throughout the year.

Material and Methods
The Saint Peter and Saint Paul Archipelago is a very small group of rocky islands located on the mid-Atlantic Ridge, just north of the Equator (00° 55' N and 29° 21'W), 1,000 km from the Brazilian coast, and 1,890 km from Senegal, Africa (Figure 1).Data were obtained between February 2000 and November 2005, from recorded registers, besides interviews and information provided by fishermen and researchers that utilized the scientific station.Total length was obtained by visual estimate, or using a tape measure when appropriate.A χ 2 text was used to compare sightings with moon phase.

Results
In the present study, 54 observations of whale shark were made in the SPSPA (Table 1).Total length ranged from 1.8 to 14 m, although precise lengths were collected only on one occasion with a metric cable, in June 2001 (Figure 2).The maximum length of 14 m on March

Discussion
The movements of the whale sharks can be related to productivity and invertebrate egg deposition (Compagno, 1984;Colman, 1997), commonly associated with turbulence around oceanic islands, as in the SPSPA.Gunn et al. (1992) pointed out the association between whale sharks and tunas in the Coral Sea, where the sharks concentrate for predation upon the lantern fishes during the reproduction period of these fishes.In the case of SPSPA, shoals of yellow fin tuna (Thunnus albacares), concentrate around the islands from October onwards, to feed upon the flying fish (Cypselurus cyanopterus) that reproduce in the area mainly between December and March (Lessa et al., 1998;Lessa et al., 1999;Vaske-Jr, et al., 2003;Vaske Jr. et al., 2005).Although no filter feeding activity has been reported during sightings.Eggs and larvae of flying fish are the most abundant planktonic item in the adjacencies of the SPSPA that could be the main food item for whale sharks in this period.
The SPSPA does not present upwellings or high primary productivity in the adjacencies (Travassos et al., 1999) that could explain the concentrations of whale sharks as observed by Arnborn and Papastravrou (1988) in the Galapagos Islands.Thus, if the whale shark utilizes the SPSPA for feeding, it is probable that the more frequent sightings in the first semester could be associated with the greater abundance of eggs and larvae of the flying fish.No reproductive activities were reported or observed, so the whale shark could also utilize the archipelago as a resting point on their migratory routes in the Atlantic, which remain unknown.
The sighting time was variable, which means that sharks are not annoyed with the presence of the boats; on the contrary, they may even be attracted by the boats.
Future studies are necessary for knowledge on the whale shark in the SPSPA, including telemetry as used by Eckert and Stewart (2001) to elucidate the migratory routes, and observe if the individuals of the SPSPA come from another point in the oceans, or if they are part of a resident population.

Figure 2 .
Figure 2. Length distribution of whale sharks sighted in the Saint Peter and Saint Paul Archipelago between February 2000 and November 2005.*Undefined.

Table 1 .
Whale shark occurrences in Saint Peter and Saint Paul Archipelago.