The Fate ofSpondylusStocks (Bivalvia: Spondylidae) in Ecuador: Is Recovery Likely?

Abstract

The bivalve genus Spondylus, with its large and magnificent shells, has played an important cultural and economic role in coastal Ecuador that reaches back to Valdivian and Incan times. At least 2 of the 3 occurring species lately faced exploitation rates that the populations could not sustain, and a fishing ban for Spondylus calcifer and Spondylus princeps was announced in October 2009. The objective of this study is to evaluate the recovery potential of the stocks that are still present. We analyzed the reproductive cycle of 5. calcifer in the area of Ayangue (Santa Elena Province), and its relation to temperature and food abundance. In addition, we calculated fecundity values for the two threatened species. Our results show that S. calcifer in Ayangue reproduces year-round, although with a peak in October to December, when temperature is low and chlorophyll concentration is high. The total fecundity increases with soft body mass and is significantly higher in S. calcifer than in S. princeps. The individual fecundity levels in our study range from 2.2–8.3 million eggs in S. princeps, and from 2.9–35 million eggs in S. calcifer, which is in the range of better studied oyster and scallop species. With the latest observations on current densities of both species, we conclude that these have long fallen below the reproduction thresholds for other broadcast spawning invertebrates, and possibly for positive net recruitment rates. Because broadcast spawners are susceptible to mate limitation (which is the dominant cause of Allee effects in aquatic invertebrates), the reproductive asynchrony we found in Spondylus populations in Ecuador further increases the significance of potential depensatory mechanisms and of nearest neighbor distance.