An Unusual Pulse in Recruitment of Two Reef Fishes in the Galápagos Islands Coincident with the 1997–1998 El Niño

Recruitment pulses of reef fishes can result in significant changes in both population and community structure of fishes on reefs (reviewed by Sale, 1991). These pulses can occur because of increased reproduction (Danilowicz, 1997), increased larval or juvenile Pulses of commercially valuable species can also be significant factors to consider for fishery management, as a pulse may be fished down over the following years or seasons (see Sissenwine, 1984 and references therein). Environmental factors can also have a substantial impact on recruitment pulses, and while pulses are frequently observed, they can be attributed only occasionally to a specific environmental event (e. This paper presents evidence of pulses in recruitment of two reef fishes in the Galápagos Islands that occurred coincident with a large-scale environmental perturbation, the 1997–1998 El Niño. The El Niño/Southern Oscillation (ENSO) phenomenon is the largest recurring global climatic perturbation, generally occurring every 3 to 7 yrs (Hansen, 1989). The Galápagos Islands are heavily affected by this phenomenon, where average sea surface temperatures can rise by more than 4°C throughout the archipelago and current patterns can change dramatically (Wyrtki et al. Wellington et al., in press). In normal years, the warm season in Galápagos (January– May) is dominated by the Panama Current from the north, while the cold season (June– December) is dominated by upwelling from the equatorial undercurrent from the west and the Humboldt Current from the south (Glynn and Wellington, 1983; Houvenaghel, 1984). During ENSO events, the influence of the Humboldt Current weakens drastically, upwelling ceases, the Panama Current penetrates further south for longer duration, and unusually warm water accumulates in the entire tropical eastern Pacific as the trade winds slacken (Wyrtki et al., 1976; Glynn and Wellington, 1983). Strong ENSO events can be devastating to marine ecosystems in the Galápagos as productivity drops in the warmer water (Chavez et al., 1999). Many organisms dependent on marine productivity suffer greatly increased mortality and reproductive failure, including corals, pinnipeds, marine iguanas, and sea birds Bustamante, unpub. data). Abundances of fishes also change during ENSO events (McCosker and Rosenblatt, 1984), and juvenile growth of some species declines (Meekan et al., 1999), but the magnitude of these changes is unknown. Recruitment failure in eastern Pacific fishes may be associated with ENSO events (Wellington and Victor, 1985; Lenarz et al. 1995). In contrast, in this study I document a dramatic increase in the abundance of subadult bumphead parrotfish (Scarus perrico) …