Zooplankton in a whale shark (Rhincodon typus) feeding area of Bahía de los Ángeles (Gulf of California)

Abstract

Bahía de los Ángeles (BLA) is highly influenced by oceanographic processes that occur in Canal de Ballenas, favoring primary and secondary production inside the bay. Zooplankton is an important item in the diet of the whale shark (Rhincodon typus). The whale shark supports BLAs eco-tourism industry. El Rincón (southern BLA) is a preferential feeding area of the whale shark. Zooplankton surface samples were collected at twelve locations in El Rincón in September, November, and December, 2009. Eleven phyla were identified, belonging to both meroplankton and holoplankton. In September the meroplankton fraction was 62.6% of the total abundance, in November it only accounted for 8.6%, and in December it accounted for 14%. This suggests that the breeding season of fish and invertebrates was prior to the September sampling. Copepods, which are the preferred prey for immature whale sharks, always had the largest fraction of the holoplankton. Copepods had relatively low levels of abundance at all sampled locations (<10,000 ind m-3 ) in September and December. Their largest abundance was in November (up to >50,000 ind m-3 ), with an average of 73.8% of totalzooplankton abundance. Whale sharks were sighted feeding in November, at sites with large abundance ofzooplankton, especially Acartia spp. Whale sharks were not sighted when Acartia was absent. Data in the literature and in this work supports the perception that high abundance of Acartia may be the determining factor for the congregation of whale sharks in El Rincón.