Effects of fishing, market price, and climate on two South American clam species

Abstract

Coastal shellfish are being threatened by several drivers acting at multiple temporal and spatial scales, including fishing, climate, and globalization of markets. We evaluated largescale and long-term combined effects of fishing, climate, and economic variables on 2 congeneric clams that inhabit sandy beaches of the Pacific (Mesodesma donacium) and the Atlantic (M. mactroides) in South America. Bioeconomic and climatic variables, such as coastal sea surface temperature anomalies (SSTA) and broad-scale climatic indices (Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation), were related to variations in clam populations in a differential way according to latitude and oceanographic features. For M. donacium, the nature and sign of the relationships between landings and explanatory predictors markedly differed between bioclimatic units. El Niño Southern Oscillation events negatively affected landings in Peru and northern Chile, whereas landings increased in southern Chile and showed a positive correlation with increasing SSTA, suggesting a positive effect at the southernmost edge of the species distribution. Long-term trends in the abundance of M. mactroides were related to fishing intensity and SSTA. As anticipated by basic economic theory, deficit of supply relative to demand, exacerbated by very low harvesting costs, pushed the price up and has driven these clam species to levels close to extinction (anthropogenic Allee effect). The lack of response of the stocks to long-term closures suggests that these systems exceeded critical thresholds (tipping points). Information on early warnings of tipping points is needed to help manage coastal shellfisheries that are increasingly threatened by long-lasting and large-scale stressors.

Social-Ecological Collapse: TURF Governance in the Context of Highly Variable Resources in Chile

“…In cases such as this, where biomass fluctuations are the norm, it seems that the cost of maintaining effective governance systems may be higher than the benefits over time, leading inexorably to SES collapse. Even though mass mortalities have been described for this resource (Riascos et al 2009), and suggestions have been made that this may have swamped existing management measures (Ortega et al 2012), this was not the case for M. donacium in Tongoy Bay. Although the population was decimated in Coquimbo with the ENSO in 1997-1998, the population in Tongoy was not affected.…”

“…Among the resources managed through the AMERB system in Chile is the surf clam, known as "macha." Fluctuations in landings of surf clams are a common feature of these fisheries worldwide (McLachlan et al 1996), making the sustainability of this fishery difficult to achieve (Ortega et al 2012). This variability reflects fluctuations in the population size, which is related to highly variable levels of recruitment and mortality de Alava 1995, McLachlan et al 1996).…”

Impacts of Climate Variability on Latin American Small-scale Fisheries

“…In the southwestern Atlantic Ocean, long-term trends in abundance of the yellow clam (Mesodesma mactroides) were negatively affected by a combined effect of increasing SSTA and fishing intensity (Ortega et al 2012). SSTA was positively correlated with AMO variations and both indices were inversely correlated with yellow clam abundance (Fig.…”

“…Indeed, a recent evaluation of the surf clam (Mesodesma donacium) in the Pacific (distribution range from 5ºS to 42º S) suggested that warm ENSO (El Niño) events negatively affected landings in Peru and northern Chile (Fig. 1A), but favored landings in southern Chile (southernmost edge of the species distribution), showing a positive correlation with increasing sea surface temperature anomalies (SSTA; Ortega et al 2012). Particularly in Peruvian beaches, the strong 1982/1983 and 1997/1998 El Niño events caused mass mortalities of surf clam (Arntz et al 1987).…”

A comparative appraisal of the resilience of marine social-ecological systems to mass mortalities of bivalves

“…Various causes have been identified for MMB outbreaks, including: high sea temperatures and heat waves (Cheney et al 2000, Ortega et al 2012, Rodrigues et al 2015; changes in salinity (Xiao et al 2005), turbidity, and pH; high primary production (Cheney et al 2000, Mydlarz et al 2006; eutrophic waters (Friedman and Hedrick 1991); invasive species as competitors or predators (Matsuyama 1999, McKindsey et al 2007; pathogens (Elston et al 1987); and density-dependent factors (Brazeiro andDefeo 1999, Xiao et al 2005).…”