The fin whale Balaenoptera physalus (Linnaeus, 1758), is the second-largest whale; the average length of fin whales in the Northern Hemisphere is 22 m for males and 24 m for females (^{Gamble, 1985}).The body is elongated and slender, brownish-gray in the dorsal portion and paler in the ventral area (^{Notarbartolo-Di-Sciara et al., 2003}). This whale has a characteristic asymmetric color in the anterior-ventral portion, being white/ cream in the right lower jaw, whereas the left portion is black/dark. The dorsal fin is tall and bigger in size compared with other Balaenopterids; it is located at the third body portion, portion, with white cream a V grey-light shape pattern (called chevron) which extends over the dorsal portion and flanks behind the head (^{Notarbartolo-Di-Sciara et al., 2003}; ^{Perrin, 2018}). The species has a cosmopolitan distribution occurring principally in temperate and cold waters (^{Rice, 1998}). Currently, three subspecies are recognized. The species also has a V grey-light two in the Southern Hemisphere, and B. p. physalus in the Northern Hemisphere (^{Committee-on-Taxonomy, 2018}). Similar to all other large whales, the fin whale was profusely hunted during the 20th century, resulting in a drastic reduction of their populations. This species is considered internationally as an Endangered species (^{Reilly et al., 2013}), and is subject to special protection in Mexico (^{SEMARNAT, 2010}). Additionally, the International Whaling Commission (IWC) issued a moratorium on commercial hunting of this species, and was listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (^{UNEP-WCMC, 2018}).

The Mexican Caribbean is recognized as one of the principal Mexican marine eco-regions (^{Lara-Lara et al., 2008}; ^{Niño-Torres et al., 2015}). Currently, for the Mexican Caribbean, there are reported 18 aquatic mammal species (^{Niño-Torres et al., 2015}), none of them, a Rorcual species (Balaenopteridae Gray, 1864).

As part of the activities of the Comisión Nacional de Áreas Naturales Protegidas (CONANP) and the Marine Mammal Stranding Network of Quintana Roo (RVMMEQR), a stranded alive whale was aided on August 2, 2018, near to the fishermen’s camp beach (21° 31´31.03” N; 86° 48´11.26” W, fig. 1a) at the northern section of the Isla Contoy National Park. The stranded animal was an adult fin whale, B. physalus, of ~ 18 m in length. Species identification was based on the form of the dorsal fin, the chevron, and the right lower jaw coloration (“white-lip”) characteristic of this species (^{Notarbartolo-Di-Sciara et al., 2003}; ^{Perrin, 2018}) (fig. 1b-c). After some maneuvers, the fin whale was towed to deep waters and released. Sex was not determined.

Stranding records are of outstanding importance, especially when they concern species that are difficult to observe in the wild. The stranded event reported here represents the first record of a fin whale B. physalus in the Mexican Caribbean, and the second for the Western Caribbean Sea (^{Ramos et al., 2016}). The first case was reported in Belize on the April 28, 1986, in which a single adult female stranded alive near to Placencia (^{Sanders et al., 1997}; ^{Ramos et al., 2016}). Other fin whales records in the Caribbean Sea have been reported in Venezuela at Margarita Island and Paraguana Peninsula on August 1953 and February-May 1959 (^{Agudo, 1995}; ^{Romero et al., 2001}), and Colombia (^{Muñoz-Hincapié et al., 1998}). Live groups of this species have been documented in Puerto Rico (^{Mignucci-Giannoni, 1998}).

Figures 1a-c a) Location of region in the Mexican Caribbean, where the stranded whale Balaenoptera physalus (Linnaeus, 1758) was found, at the fishermen’s camp beach; b) Detail of the dorsal fin; c) Chevron and right lower jaw coloration in the stranded whale (Photography by: Caribbean Connection Cia.). 

We should highlight that this stranding event occurred during the summer season (August), which is unexpected. ^{Gamble (1985)} described that the breeding season for western North Atlantic fin whales takes place in Florida, Gulf of Mexico, and the Caribbean Sea waters during the winter, whereas they spend spring and summer at higher latitudes (north) at their feeding grounds. An interesting hypothesis is that this individual could belong to the Southern population. Unfortunately, it wasn't possible to take DNA samples to determine its place of origin.

This stranding event represents an important record of the marine mammal species richness in the Mexican Caribbean, increasing the number of confirmed species from 18 (^{Niño-Torres et al., 2015}) to Characterizing the species occurrence, abundance, and distribution is relevant to create and implement adequate management and conservation plans (^{Ramos et al., 2016}), that help to preserve the natural resources and biodiversity. In the Mexican Caribbean ~98% of the marine ecosystems are protected under different categories of “natural protected areas.”