The humpback whale, Megaptera novaeangliae, is distributed in all oceans of the world. It is a highly migratory species, mating and calving in the tropics during winter and feeding in high-latitude waters during summer (Dawbin, Reference Dawbin and Norris1966). Information gathered from both observations of free-ranging animals and from stomach content analysis of animals killed during commercial whaling has indicated that humpbacks do not normally feed while on their tropical breeding grounds or during migration (Chittleborough, Reference Chittleborough1965; Dawbin, Reference Dawbin and Norris1966). Nevertheless, in the last 15 years, records of humpback whales displaying feeding behaviour outside the traditional high-latitude feeding grounds have been reported with some regularity. Evidence of feeding has been recorded for known breeding areas, such as Hawaii (Salden, Reference Salden1989), the Dominican Republic (Baraff et al., Reference Baraff, Clapham, Mattila and Bowman1991) and Mexico (Gendron & Urbán, Reference Gendron and Urbán1993). Mid-latitude feeding in the southern hemisphere has also been documented during migration southbound off South Africa (Best et al., Reference Best, Sekiguchi and Findlay1995) and northbound off Australia (Dawbin, Reference Dawbin and Norris1966). Stone et al. (Reference Stone, Katona and Tucker1987) suggested that humpback whales from the North Atlantic feed briefly and opportunistically at Bermuda (32°20′N) while migrating. Feeding during winter in mid-latitude waters outside of normal feeding or breeding habitats and migration corridors has also been described (Swingle et al., Reference Swingle, Barco, Picthford, McLellan and Pabst1993).

In the western South Atlantic, humpback whales breed off the coast of north-eastern Brazil. The species' most important reproductive ground in this area is the Abrolhos Bank (16°55′s 038°50′W) and its vicinity (Siciliano, Reference Siciliano1997; Martins et al., Reference Martins, Morete, Engel, Freitas, Secchi and Kinas2001). Sightings and strandings of humpbacks are also common along the coast of south-eastern Brazil, especially in Espírito Santo and Rio de Janeiro States. Nevertheless, humpback whales are rarely recorded in southern Brazil, probably due to their offshore distribution while migrating through this region (Siciliano et al., Reference Siciliano, Pizzorno and Barata1999). The aim of this short communication is to report the incidental catch of a humpback whale with evidence of recent feeding in southern Brazil, a mid-latitude area in the western South Atlantic Ocean.

On 4 April 2002, the carcass of a 7.27 m humpback whale was washed ashore at Capão da Canoa beach (29°45′38″S 50°00′43″W), Rio Grande do Sul, Brazil. The presence of this humpback whale in the coastal waters of Rio Grande do Sul is atypical, considering the species known migratory pattern and the scarcity of records in this region. Prior to this record there were only two other strandings of humpback whales in the northern Rio Grande do Sul since 1991 (GEMARS, unpublished data). Studies conducted in the Abrolhos breeding ground, north-eastern Brazil, indicate that humpbacks inhabit that region from June to January, with peaks between August and October (Siciliano, Reference Siciliano1997; Martins et al., Reference Martins, Morete, Engel, Freitas, Secchi and Kinas2001). Antarctic feeding activity extends from November to at least April (Stone & Hammer, Reference Stone and Hammer1988; Secchi et al., Reference Secchi, Dalla Rosa, Kinas, Santos, Zerbini, Bassoi and Moreno2001). Recent evidence indicates that the Antarctic Peninsula is not the summer feeding ground utilized by the humpback whales from Brazil (Stevick et al., Reference Stevick, Aguayo, Allen, Avila, Capella, Castro, Chater, Dalla Rosa, Engel, Félix, Flórez-González, Freitas, Haase, Llano, Lodi, Munoz, Olavarría, Secchi, Scheidat and Siciliano2004), and therefore a coastal migration is not to be expected (Siciliano et al., Reference Siciliano, Pizzorno and Barata1999). Photo-identification and satellite-tracking studies have suggested that humpback whales from Brazil may utilize waters off South Georgia and the South Sandwich Archipelago as feeding grounds and undertake offshore migrations to these waters (Stevick et al., Reference Stevick, Godoy, Mcosker, Engel and Allen2006; Zerbini et al., Reference Zerbini, Andriolo, Heide-Jørgensen, Pizzorno, Maia, Van Blaricom, DeMaster, Simões-Lopes, Moreira and Bethlem2006).

The animal was a female and its carcass was in a good condition. Whale lice of the species Cyamus boopis Lütken, 1870 were present in the whale's epidermis. In the sample analysed, juveniles, adult males and females, including pre-copulatory pairs and ovigerous females were present. Pieces of gill-nets were found around the whale's body, suggesting entanglement in fishing gear. Afterwards, the master of a commercial fishing vessel based in Tramandaí (29°58′s 50°07′W) informed us that one day prior to the whale's stranding, his gill-nets incidentally caught a whale off the same beach. The nets had been set to catch sharks at the isobath of 20 m, with a mesh size of 18 cm. The nets were at the surface and had a height of 12 m. According to the fishermen, the whale was already dead when the activities of retrieving the nets began.

Incidental catches of humpbacks have been reported from various regions of the world, although the impact of this mortality at a population level has been uncertain (Clapham & Mead, Reference Clapham and Mead1999). In Brazil, incidental catches of humpback whales were previously recorded mainly from the south-eastern coast (Barros, Reference Barros1991; Siciliano, Reference Siciliano1994; Pizzorno et al., Reference Pizzorno, Brito, Dorneles, Azevedo and Gurgel1998; Freitas Netto & Barbosa, Reference Freitas Netto and Barbosa2003). The scarcity of records of interactions between humpbacks and fisheries on the southern coast of Brazil is probably a consequence of the species offshore distribution in this area. On the other hand, the occurrence of entanglement of southern right whales (Eubalaena australis), a coastal species during the breeding season, seems to be fairly common in southern Brazil (Greig et al., Reference Greig, Secchi, Zerbini and Dalla-Rosa2001).

The humpback whale calves are 3.96 to 4.57 m in length at birth (Clapham et al., Reference Clapham, Wetmore, Smith and Mead1999). Most calves remain with the mother for about one year, when they are approximately 8–10 m, and may start feeding independently at six months of age (Clapham & Mead, Reference Clapham and Mead1999; Clapham et al., Reference Clapham, Wetmore, Smith and Mead1999). In this manner, the length of this animal (7.27 m) suggests that it was probably about to complete its first year and would normally still be in association with its mother.

Investigation of the stomach contents revealed that the whale had ingested large amounts of food. The predominant prey item identified was the small shrimp Acetes americanus (Decapoda: Sergestidae). Acetes americanus is a small pelagic species (~1.0 cm) that occurs from Central America (Puerto Rico, Panama) to southern Brazil (Rio Grande do Sul). This species is widely distributed throughout the continental shelf of Brazil, occurring up to 40 m deep, and is probably associated with tropical waters (D'Incao & Martins, Reference D'Incao and Martins2000). Planktonic larvae of unidentified species of Brachyura were also present. The diet of humpback whales in the southern hemisphere is constituted primarily by euphasiids, with Euphausia superba representing the main food item (Clapham & Mead, Reference Clapham and Mead1999). Humpback whales have been reported to feed on localized concentrations of other euphausiid species during migration off Australia (Dawbin, Reference Dawbin and Norris1966) and South Africa (Best et al., Reference Best, Sekiguchi and Findlay1995) and amphipods off South Africa (Best et al., Reference Best, Sekiguchi and Findlay1995). The present report adds the shrimp Acetes americanus as a new prey species for the humpback whale in the southern hemisphere.

The estimated mean time passage of the food from the fore-stomach to the fundic chamber of another balaenopterid, the fin whale (Balaenoptera physalus), is 3–6 hours (Vikingsson, Reference Víkingsson1997). Assuming that this rate is similar in the humpback whale, it is suggested that this whale was feeding at least in the last ten hours prior to its death. Applying the average swimming speed recorded by Zerbini et al. (Reference Zerbini, Andriolo, Heide-Jørgensen, Pizzorno, Maia, Van Blaricom, DeMaster, Simões-Lopes, Moreira and Bethlem2006) for a humpback whale from the western South Atlantic coast (92 km d⁻¹), it may be affirmed that the feeding area was in a mean distance of 20.7 nautical miles (38.3 km) from the entanglement site, still within the limits of the Rio Grande do Sul coast.

The present record demonstrates that humpbacks may occasionally undertake feeding behaviour in mid-latitude waters of the western South Atlantic Ocean. Hassel et al. (Reference Hassel, Venturotti, Magalhaes, Cuenca, Siciliano and Marques2003) reported on possible feeding behaviour by the dwarf minke whale (Balaenoptera acutorostrata), during the summer in Rio de Janeiro, south-eastern Brazil. The Bryde's whale (B. edeni) has been observed preying on Brazilian sardines (Sardinella brasiliensis) along São Paulo and Rio de Janeiro State coasts (22–24°S) (Siciliano et al., Reference Siciliano, Santos, Vicente, Alvarenga, Zampirolli, Brito, Azevedo and Pizzorno2004), while the stomachs of two stranded Bryde's whales from Rio de Janeiro presented a large amount of A. americanus (Siciliano et al., Reference Siciliano, Santos, Vicente, Alvarenga, Zampirolli, Brito, Azevedo and Pizzorno2004). Therefore, it is possible that the productive waters of the southern and south-eastern Brazilian coast may occasionally be used by baleen whales, as an opportunistic feeding zone, and that the shrimp A. americanus could play an important role in the feeding of these species.