579 



Abstract — Information on the sea- 

 sonal abundance and distribution of 

 whale sharks {Rhincodon typiist is 

 largely unknown throughout range of 

 the species. Between 1989 and 1998, 

 three spatially and temporally inten- 

 sive aerial surveys were conducted 

 by the National Marine Fisheries 

 Service, Mississippi Laboratories 

 that provided information on sea- 

 sonality, distribution, and aggrega- 

 tions of whale sharks in the northern 

 Gulf of Mexico. Transects totaling 

 89.369 km were surveyed over the 

 course of the study and a total of 1 19 

 whale sharks were counted during 81 

 sighting events. There was no sta- 

 tistical difference in the sightings 

 per unit of effort (SPUE) of whale 

 sharks between the eastern and 

 western continental slope waters of 

 the Gulf of Mexico. In the continen- 

 tal slope waters of the eastern Gulf 

 of Mexico, whale sharks were more 

 abundant during the summer than 

 in the winter. In the western Gulf 

 of Mexico, whale shark SPUE was 

 significantly greater in the summer 

 than during the fall or winter; there 

 was no significant difference between 

 summer and spring. There was also no 

 significant difference in whale shark 

 SPUE among spring, fall, and winter 

 in the western Gulf of Mexico. Aggre- 

 gations of whale sharks were seen 

 only during the winter and summer, 

 and there were significantly more 

 individuals per aggregation during 

 the summer. The largest aggregation 

 of whale sharks observed during the 

 study consisted of 23 individuals. 



Abundance and distribution of whale sharks 

 (Rhincodon typus) in the northern Gulf of Mexico 



Carolyn M. Burks 



William B. Driggers III (contact author) 



Keith D. Mullin 



National Oceanic and Atmospheric Administration 



National Marine Fisheries Service 



Southeast Fisheries Science Center 



Mississippi Laboratories 



P,0 Drawer 1207 



Pascagoula, Mississippi 39568 



Email address for W, B, Driggers: William, Driggersiainoaa gov 



Manuscript submitted 8 January 2005 

 to the Scientific Editor's Office. 

 Manuscript approved for publication 

 13 January 2006 by the Scientific Editor. 



Fish. Bull. 104:579-584 (2006). 



Whale sharks {Rhincodon typus) are 

 distributed in all tropical and subtrop- 

 ical marine waters of the world, with 

 the exception of the Mediterranean 

 Sea (Compagno, 1984). This species 

 is considered vulnerable to extinction 

 according to the World Conservation 

 Union (lUCN)' partly because of a 

 lack of information pertaining to its 

 life history. Although the seasonality 

 of whale sharks has been examined 

 in two geographically discrete areas 

 (Taylor, 1996; Duffy, 2002), no infor- 

 mation exists for the seasonal distri- 

 bution or relative seasonal abundance 

 of this species over a broad spatial 

 scale. The paucity of such information 

 is probably attributable to logistical 

 difficulties associated with collecting 

 required data or to the expense of sur- 

 veying large areas. 



Whale sharks aggregate in areas 

 of high biological productivity, and 

 seasonal abundance of whale sharks 

 could result from increased localized 

 prey abundance. Whale sharks feed 

 on a variety of organisms including 

 invertebrates and teleosts (Com- 

 pagno, 1984). Unlike basking iCe- 

 torhiniis ?naxi}')nis} and megamouth 

 {Megachasma pelagios) sharks, which 

 passively filter prey from the water 

 column, whale sharks are capable of 

 suction filter feeding (Colman, 1997). 

 Although this feeding strategy en- 

 ables whale sharks to capture a wider 

 range of prey in terms of size, mo- 

 bility, and diversity than other filter 

 feeding elasmobranchs, this feeding 

 strategy requires dense aggregations 



of prey in order for whale sharks to 

 meet their energetic demands (Com- 

 pagno, 1984). Feeding aggregations 

 of whale sharks have been reported 

 in the Atlantic, Indian, and Pacific 

 Oceans and specifically in the wa- 

 ters off Belize, Western Australia, 

 the Galapagos Islands, Mexico, New 

 Zealand, and Thailand (Taylor, 1996; 

 Clark and Nelson, 1997; Colman. 

 1997; Eckert and Stewart, 2001; Hey- 

 man et al., 2001; Wilson et al., 2001; 

 Duffy, 2002). 



The whale shark was first described 

 in 1828 from a type specimen col- 

 lected off the coast of South Africa 

 (Penrith, 1972). The first record of 

 a whale shark in the western North 

 Atlantic Ocean was not reported until 

 1902 and it was 1937 before this spe- 

 cies was documented in the Gulf of 

 Mexico (Gudger, 1939; Baughman and 

 Springer, 1950; Breuer, 1954). Since 

 1937 several authors have reported 

 sightings of whale sharks in the Gulf 

 of Mexico (Gudger, 1939, 1941; Baugh- 

 man, 1947, 1950, 1955; Gunter and 

 Knapp, 1951; Breuer, 1954; Springer, 

 1957; Clark and von Schmidt, 1965; 

 Hoffman et al., 1981; Hoffmayer et 

 al., 2005). However, these reports are 

 restricted to spatially discrete areas, 

 and most are primarily anecdotal and 

 largely based on isolated observations 

 of few individuals. In the present 

 study we report the seasonality, rela- 



1 The World Conservation Union. 2005. 

 http://www.redlist.org [accessed 5 Janu- 

 ary, 2006]. 



