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.

Conservation of the evolutionary legacy of endangered species is a key component for long-term persistence. Totoaba is a long-lived fish endemic to the Gulf of California and is considered critically endangered. There is currently a debate concerning its conservation status and whether it can be used as a fishery resource. Unfortunately, basic information on biological and genetic population structure of the species is lacking. We sampled 313 individuals and employed 16 microsatellite loci and 3 mitochondrial DNA markers (16S, 547 pb; COI, 619 pb; control region, 650 pb) to assess population structure and demography of totoaba in the Gulf of California, with samples from locations that encompass nearly all of its recognized geographic distribution. We could not reject a hypothesis of panmixia for totoaba, using nuclear or mitochondrial markers. Demographic analysis of mtDNA suggests a sudden population expansion model. The results have important implications for totoaba conservation because poaching is a significant conservation challenge and could have additive negative effects over the single population of totoaba in the Gulf of California.

Several characteristics of Totoaba macdonaldi Perciformes: Sciaenidae, including migratory movements along temperature gradients make it vulnerable to oxidative stress. Oxidative stress can also be associated with reproduction. The objectives of the present study were to examine oxidative stress indicators in liver of totoaba throughout the seasons (spring, autumn and winter), and the associated fluctuations in superficial sea temperature (SST, °C), as well as to evaluate possible variations between sexes and reproductive maturity stages. A total of 173 liver samples from totoaba captured in the Gulf of California, Mexico, were obtained from April 2010 to February 2013. Superoxide radical production (O2•−), lipid peroxidation (TBARS) levels, and activity of antioxidant enzymes; superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione S-transferase (GST) were quantified spectrophotometrically. Generalized linear models (GLM) were used to determine which factors contribute to explain O2•− production and TBARS levels. The significant predictive variables were the seasons, which were significant in all applied models, as well as SOD and CAT activities. In general, enzyme activity was higher in immature totoaba; this was not seasonally modified. Low temperatures in winter were associated with high O2•− production and TBARS levels, particularly in totoaba that are not yet reproductively mature. Seasonal changes in sea surface temperature did not affect the oxidative stress indicators in mature totoaba (both males and females); this suggests that mature totoaba are less sensitive to temperature changes from an oxidative stress perspective.

The accurate definition of population units (stocks) and local adaptation are the cornerstones of fishery management. Unfortunately, this knowledge is unknown mainly for abalone species in the Northeast Pacific, where stocks have failed to recover. The pink abalone (Haliotis corrugata) is a fishing resource on the western coast of the Baja California Peninsula (BCP) and is currently catalogued as diminished with a recovery trending pattern. This research determined if the biological units matched the administrative and stock assessment units along the west coast of the BCP and the implications for fishery management. To test this hypothesis, a double digest restriction site-associated DNA sequencing approach was used to generate 1 733 neutral and 6 putative outlier loci for population genomic analysis. Neutral markers detected a smooth partition in two regional groups, the southern (San Juanico, La Bocana, Bahía Asunción, Puerto Escondido, Punta Eugenia, and Natividad Island) and northern regions (Cedros Island, Faro San José, San Jerónimo Island, and Guadalupe Island). Putative outlier loci indicated evident differentiation of those groups. The population subdivision at 28° latitude with both marker types was related to a biogeographic boundary. Results did not support the current administrative zones of pink abalone fisheries and contrasted with genetic homogeneity reports in the region.

The description of the movements and habitat preference of marine fishes is essential to understand their biology and in the evaluation of commercially exploited species and the conservation of endangered ones. In this regard, little is known about the movements of the totoaba (Totoaba macdonaldi), despite its being listed as critically endangered and having been a relevant fishery resource in the past century in Mexico. Totoaba is a fish species endemic to the Gulf of California characterized by late maturation, prolonged life and annual reproduction. Totoaba has maintained its known historical distribution range, although its movements and habitat occupancy in the water column have remained poorly understood. The present study describes, for the first time and at a daily fine scale, the vertical movements and habitat preferences of the totoaba in the Upper Gulf of California. Pop-up satellite archival tags (PSATs) were used to record depth and temperature at 4-minute intervals. Ten individuals were caught and tagged in May 2016 in the Upper Gulf of California and Colorado River Delta Biosphere Reserve. All PSATs were either prematurely released or lost. Data derived from two recovered tags that saved data for 43 and 75 tracking days, respectively, were analysed. The results showed that tagged fishes moved southward to the vicinity of Angel de la Guarda Island; these are consistent with spatial displacement patterns reported in the literature, with a linear displacement of 223 km from deployment to pop-up sites. Fish spent 47% of the time within a depth range of 25–35 m. Depth increased to 70 m for one fish in early summer (late June). The preferred temperature of fishes ranged between 21–23°C. A generalized linear model revealed that vertical movement was influenced by temperature. The vertical displacement of the totoaba shows a diurnal variation that may be associated with the distribution of its prey. Further work is needed to test this hypothesis with a larger number of organisms.