Inferring past demographic changes in a critically endangered marine fish after fishery collapse

Abstract

Several worldwide marine fish stocks need to recover from collapse or overexploitation. However, the effects of a fishery collapse at the genetic level are still largely unknown, as is the extent of reduction in genetic diversity caused by fisheries and the consequences for extinction risk. Here we present a case study of totoaba, the first marine fish considered as critically endangered. We assessed 16 microsatellite loci to determine whether the demographic collapse of the species resulted in a loss of genetic diversity. Our data indicate that genetic diversity of totoaba is in the range of values observed for fish with similar biological traits without a documented fishery collapse. Contemporary demographic analysis indicated no loss of genetic diversity. Long-term genealogical analysis showed a substantial reduction in effective population size. However, the time and causal effects for population decline cannot be inferred because of the large uncertainty in estimates. Our results indicate that the totoaba in the Gulf of California has not suffered a measurable contemporary reduction in genetic diversity, and that genetic diversity is driven by long-term climatic events. Estimates of current effective size indicate that it is large enough that genetic factors may not be a major problem for conservation. We conclude that the recent fishery collapse of totoaba did not have sufficient consequences at the genetic level to increase the risk of extinction from genetic drift. However, selective effects of fishing on the adaptive potential in totoaba remain unclear.

Critically Endangered totoaba Totoaba macdonaldi: signs of recovery and potential threats after a population collapse

“…The lack of a monitoring program after the fishing ban in 1975 resulted in a lack of usable records and updated information, making it difficult to assess the current population status. Evidence from the present study and other studies (De-Anda-Montañez et al 2013, Valenzuela-Quiñonez et al 2014 indicates that totoaba maintain their known life history almost 40 yr after population collapse. The current distribution area of totoaba is in the range of its known historical distribution in the Gulf of California (Flanagan & Hendrickson 1976, Cisneros-Mata et al 1995.…”

“…To toaba still spawns in the Colorado River delta under anti-estuarine conditions (De-Anda-Montañez et al 2013), suggesting that the species does not exhibit estuarine-dependent behavior as previously established (Flanagan & Hendrickson 1976, Cisneros-Mata et al 1995, Valdez-Muñoz et al 2010, Bobadilla et al 2011, Valenzuela-Quiñonez et al 2011. The genetic diversity of totoaba is sufficient for long-term conservation and is similar to several healthy marine fish (Valenzuela-Quiñonez et al 2014), suggesting that the population collapse in the 20th century did not affect the overall general life history of totoaba. Hence, the threatened status of totoaba should be re-evaluated using this new information.…”

“…These data are necessary to confidently assess the totoaba population status (Valenzuela-Quiñonez et al 2011, 2014. Although, population recovery or stability of totoaba has been suggested, based on historical size structure, mortality rates, and genetic diversity (RosalesJuárez & Ramírez-González 1987, Román-Rodríguez & Hammann 1997, Valenzuela-Quiñonez et al 2014, the current population status is unknown (Márquez-Farías & Rosales-Juárez 2013, Valenzuela-Quiñonez et al 2014.…”

Nuevas características en distribución espacial, edad y crecimiento de la especie protegida Totoaba macdonaldi en el Golfo de California

“…Rowell et al (2008b) validate the relationship between temperature, water oxygen isotope composition (δ 18 O) and otolith δ 18 O. Other studies focus on the distribution of juveniles and its relationship with salinity (Valdez-Muñoz et al, 2010), the rate of rebound estimate for totoaba (r 2M = 0.055) (Márquez-Farías and Rosales-Juárez, 2013), and recently, genetic diversity and population dynamics (Valenzuela-Quiñonez et al, 2014, 2016. Nevertheless, some basic questions remain valid, such as which is the distribution, age structure and individual growth of this species today?…”

“…In recent years, totoaba poaching has increased because of the high price of its swimming bladder in the Asian market (Valenzuela-Quiñonez et al, 2014;Greenpeace East Asia, 2015). There is a growing social pressure demanding the government to withdraw the current permanent ban of the totoaba (Valenzuela-Quiñonez et al, 2011;García-De León, 2013).…”