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Graphical abstract Highlights • C. bellicosus has a latitudinal gradient in genetic diversity and effective population size. • There is asymmetric northward flow of propagules in this crab metapopulation. • Southern populations are sources, northern populations are sinks. • Northward larval dispersal during spawning explains the genetic structure. • Current fisheries management does not recognize the metapopulation structure. Abstract Management of commercial fisheries resources is commonly done assuming that populations are spatially homogeneous throughout their geographic range. However, uneven gene flow can result in gradients of genetic diversity that can affect population dynamics and management reference points and may contribute to overfishing. We examined whether the brown swimming crab, Callinectes bellicosus , fished along 1200 km on the coast of Sonora (Mexico) is a homogeneous population. Based on previous empirical evidence of differences in phenology, we hypothesized that C. bellicosus has a metapopulation structure which needs to be included in management tools. We conducted a genetic study of C. bellicosus taken at seven sites along the coast of Sonora and obtained their microsatellite genotypes. Recent gene flow, as well as the role of each site as source or sink, were investigated. We found a latitudinal gradient in genetic diversity and identified sites along the coast acting as sources or sinks of migrants. Central sites act as sources, while northern sites are sinks; the main source of migrants was the southern-most site. A predominantly asymmetric metapopulation structure composed of local populations with moderate connectivity may be explained by larval dispersal in the northward oceanic current during the spawning period. Including migration rates between sites in a metapopulation dynamics model of C. bellicosus and considering that fishing and management decisions in source populations will impact neighboring populations located downstream can improve current management of this important commercial fishery. [ABSTRACT FROM AUTHOR]

Sex ratio and environmental influence on population growth rate of Callinectes bellicosus (Decapoda: Portunidae) in the Gulf of California. The brown swimming crab (Callinectes bellicosus) is an economically important species in the Gulf of California, and its fishing activity, held in Sonora from 1986, has been affected by a 20-year declining trend in its biomass. With the aim to understand the possible reasons of this species population changes along time, we estimated population growth rate (r) and sex ratio of C. bellicosus, and combined them with three parameters describing its habitat: sea temperature, wetland extension and habitat size in four areas along the coast of Sonora. For this, monthly mean sex ratio was estimated from crabs samples obtained from commercial catches during 1998-2002 and 2012; mean sea surface temperature for the spawning period (May-August) were derived from remote sensors for the same years; while wetland coverages were obtained from published reports, and habitat size was estimated as the fishing surface. For each area, r was estimated using a method developed for limited data situations using commercial landings (t) from 1986-2013. With data from the four areas, simple and multiple linear regression models were developed to ascertain theoretical sensitivities of r to variations in sex ratio and environmental parameters. A total of 24 556 crabs were sampled; males dominated (68.8%) over females during the study period and in all areas; a cluster analysis identified two groups according to sex ratio: a Northern group with zones 1 and 2, and a Southern group with zones 3 and 4. r values were different in all zones (P<0.001) as was sex ratio (P=0.037); no differences in temperature were identified within the study years (P>0.995). Both the estimated data and sensitivity analyses suggest the existence of a direct and positive dependence of r on the proportion of female crabs and wetland size. We hypothesize that excess fishing of females caused the declining biomass trend of the brown swimming crab in Sonora, and concluded on the convenience of implementing harvest refugia inside coastal wetlands to protect females during the spawning season. Rev. Biol. Trop. 64 (3): 1259-1271. Epub 2016 September 01. [ABSTRACT FROM AUTHOR]

The illegal trade in totoaba (Totoaba macdonaldi) is causing adverse social, ecological, and economic impacts. This illegal activity is accelerating the overexploitation of totoaba and pushing the critically endangered vaquita (Phocoena sinus) closer to extinction. Despite extensive efforts to recover vaquita populations, scant attention has been given to the totoaba trade as an independent issue. As a result, data on the totoaba trade are limited, which hampers robust analyses and development of effective interventions to reduce illegal harvesting. We used a previously developed framework specifically designed to examine dynamics of illegal markets and guide measures to mitigate illegal use of totoaba. This framework separates markets into 3 analytical levels: characterization of participating actors (e.g., fishers, intermediaries); examination of how actors interact within the market (e.g., organization of supply chains); and assessment of the overall market dynamics that result from these interactions (e.g., factors determining price and quantity). We reviewed existing literature (108 initial articles) and interviewed key market actors, academics, and nongovernmental organization experts (14) to obtain data for this framework. Our findings offer an overview of the totoaba illegal market operation, highlighting intervention points (e.g., customs agents) and areas where additional information is required to decrease information gaps (e.g., US local market). We describe the structure and complexity of this market, emphasizing the influential role of organized crime in shaping its dynamics (e.g., controlling prices paid to fishers and stockpiling). By providing a systematic and in‐depth understanding of the market operation, we aimed to establish a benchmark for effective interventions and future research aimed at reducing uncertainties. Our results provide a crucial step toward addressing this critical issue and can help facilitate development of effective strategies to combat the illegal totoaba trade and promote biodiversity conservation more broadly. [ABSTRACT FROM AUTHOR]

The importance of mucus produced by jellyfish species remains as understudied as their feeding behavior. Here, we study medusae under captivity, ascertain the role of mucus, and describe its feeding behavior. Between February and March 2019, live adult cannonball jellyfish, Stomolophus sp. 2, were collected in Las Guásimas Bay (Gulf of California, Mexico) and were offered fish eggs, mollusk "D" larvae, or Artemia nauplii in 4-day trials. Descriptions of feeding structures were provided for S. sp. 2. Digitata adhere food and scapulets fragment them, which, driven by water flow, pass via transport channels to the esophagus and the gastrovascular chamber where food is digested. Due to stress by handling, medusae produced mucus and water, lost feeding structures, and decreased in size. Based on our observations and a thorough literature review, we conclude that the production of mucus in S. sp. 2 plays several roles, facilitating capture and packing of prey, acting as a defense mechanism, and facilitating sexual reproduction; the latter improves the likelihood of a population persisting in the long run, because fertilized oocytes in mucus transform to planulae, settle, and transform into asexually reproducing polyps. Polyps live longer than the other life stages and are more resistant to adverse environmental conditions than the medusoid sexual stage. [ABSTRACT FROM AUTHOR]

Abstract: Constant harvest rate as a management strategy for the Pacific sardine (Sardinops caeruleus) fishery in the Gulf of California is supported by an analysis of variations in the catchability coefficient (q), stock abundance and commercial catch. Catchability was analyzed based on population length-structured data standard length (SL), expressed as CPUE, for 26 fishing seasons (1972–1973 to 1997–1998). We used a deterministic model of catchability to estimate the catchability-at-length assuming catchability depends on length and sardine behavior. Results demonstrated that catchability increases with sardine length, with low values for older sardines (sizes greater than 20.5cm SL), which are poorly represented in catches. Most changes in q-at-length values can be observed within the range of 12.5–15.0cm SL, which corresponded to first maturity and first capture lengths, respectively. Catchability-at-length pattern was represented for an exponential model with adjusted R 2 =0.94. Moreover, we observed an inverse power relationship between catchability and stock abundance with a slope value of β d =−0.58, which indicates the existence of hyperstability or density-dependent catchability. The strong fluctuations in biomass of the Pacific sardine, the pattern of hyperstability, and the current state of the sardine fishery defined to be harvested at the maximum allowable catch, are the rationale for recommending a constant harvest rate as management strategy, with a value of HR=0.29 and maintain the current minimum legal size of capture. [Copyright &y& Elsevier]