Task: Question Answering
Input (English): Passage: The wide variety of birds in Basse Casamance was noted by early explorers. While Basse Casamance National Park and Kalissaye Avifaunal Reserve have not been open for years due to the Casamance Conflict, Carabane has been found to be very conducive to ornithological observation. A study in 1998 discovered the following species on the island: African darter (Anhinga rufa), Goliath heron (Ardea goliath), palm-nut vulture (Gypohierax angolensis), black-tailed godwit (Limosa limosa), whimbrel (Numenius phaeopus), Eurasian curlew (Numenius arquata), Caspian tern (Sterna caspia), blue-spotted wood-dove (Turtur afer), red-eyed dove (Streptopelia semitorquata), white-rumped swift (Apus caffer), woodland kingfisher (Halcyon senegalensis), grey-backed camaroptera (Camaroptera brachyura), red-bellied paradise-flycatcher (Terpsiphone rufiventer), pied crow (Corvus albus), black-rumped waxbill (Estrilda troglodytres) and yellow-fronted canary (Serinus mozambicus).Fish are plentiful in the waters surrounding the island, where one may encounter trevallies (Carangidae), Giant African threadfins (Polydactylus quadrifilis), great barracudas (Sphyraena barracuda), or African red snappers (Lutjanus agennes). The mangroves are home to many crustaceans such as southern pink shrimp (Farfantepenaeus notialis), sand fiddler crabs (Uca pugilator), and molluscs. The shellfish population consists mostly of mangrove oysters (Crassostrea gasar), which cling to uncovered mangrove roots at low tide. The red-headed agama and monitor lizard make up the reptilian population of the island.
The sandbar of Carabane has very few mammals other than pets, although the French first noted the presence of monkeys in 1835. In 1870, other settlers noted with disgust that the natives often ate monkeys and dogs. In the early 21st century, bottlenose dolphins (Tursiops truncatus) are commonly sighted off the island. The lack of tourism because of the civil unrest has benefited biodiversity. In this way, the nearby Basse Casamance National Park, which has been closed for years, has seen a remarkable return of Nile crocodiles (Crocodylus niloticus), Senegalese manatees (Trichechus senegalensis), and breeding birds.On an island called Ilha dos Mosquitos (Portuguese for "Mosquito Island"), the natives and their visitors continue to protect themselves with mosquito nets and Shea butter. They must also protect themselves from other, smaller insects which are no less troublesome: black flies (Simulium). 
Question: What animal is commonly sighted in the 21st century off the island where monkeys were noted in 1835?
Output (English): bottlenose dolphins.