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BackgroundIn Yucatán State, southern México, as in many other parts of the world where tilapia has been introduced for aquaculture, the deficient application of management measures has led to the establishment of non-native parasites. The aims of this study were to describe the geographical distribution of protozoan and helminth parasites of farmed Nile tilapia Oreochromis niloticus (L.) throughout the Yucatán and to examine the potential statistical associations of the prevalence and mean abundance of these parasites with management and environmental variables.MethodsAll 29 Nile tilapia farms currently operating in Yucatán were surveyed. Maps were created to describe the geographical location of the parasites infecting Nile tilapia at each farm. We evaluated the statistical associations of management and environmental variables with the mean abundance values of each parasite species using a multivariate redundancy analysis (RDA) and generalized additive models (GAM). We also used Ripley’s K to determine whether there were significant clusters of the mean abundance of particular parasite species in specific regions of the Yucatán State.ResultsA total of 580 O. niloticus were examined, and 11 species of parasites were recorded. Cichlidogyrus sclerosus was the most frequent and abundant parasite at all 29 farms, whereas Gyrodactylus cichlidarum was found in 26 of the 29 farms. The RDA showed that the most important predictors were the concentration of nitrites and ammonium and the water exchange rate. The GAM showed the significant effect of the tank capacity, no use of quarantine area and no use of prophylactic treatments on the mean abundance of G. cichlidarum. The geographical distribution patterns of the mean abundance of most parasite species exhibited clustering near to the coast of Yucatán.ConclusionTwo groups of farms were distinguished: (i) farms with medium to high technology, where the most frequent and abundant parasite was G. cichlidarum, and (ii) farms with low technology, where the most frequent and abundant parasite was C. sclerosus. Good biosecurity practices such as the use of quarantine and prophylactic treatments prior to the introduction of infected Nile tilapia to the farms are recommended to avoid the establishment of parasites such as G. cichlidarum in farms.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1332-9) contains supplementary material, which is available to authorized users.

-Time-area closures have become a frequently used tool to control fishing effort and protect feeding and spawning areas. However, because time-area closure strata are mainly based on biological and ecological considerations, and do not accounts for fishermen's behavior-at-sea, this type of regulation tool may not entirely achieve its objectives. With the aim of comparing the impact of two different time-area regulations: (1) a moratorium on Fish Aggregating Devices (FAD) sets (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) and (2) a no-take area for surface fleets (2005)(2006)(2007)(2008)(2009)(2010) on the dynamics of the European (EU) tuna purse seine fleet operating in the eastern tropical Atlantic, several fishery indicators were evaluated through a Before-After, Control-Impact (BACI) approach. The results showed that prior to any regulation, the fleet used to be concentrated within the Gulf of Guinea area. During the first years of the moratorium on FAD (from November to January within a large region in the eastern Atlantic) there was a movement towards outside the protected area, increasing the total sets on FAD (restricted fishing activity). In general, this moratorium fulfilled its objectives; however, it was not respected during the last years of this regulation. The no-take time-area closure restricted all tuna catches for the surface fisheries but only in November and within a small area (i.e., the Picolo zone). As a result, there was an increase in activities on free schools outside the no-take area. Our findings suggest the use of some simple fishery indicators to understand fleet dynamics as a complement of ecological information before implementing new time area closures. Furthermore, since tunas are highly mobile species, anticipating the possible re-allocation of effort of purse seiners to adjacent areas in response to the spatial regulation is required to design different candidate time-area closures and to evaluate their effectiveness to protect juvenile tunas.

Within the Ecosystem-based fisheries management framework, we evaluated the changes over time in bycatch species of the European tuna purse-seine fishery operating in the eastern Atlantic Ocean. Bycatch data was collected during two scientific observer programs conducted in the late 1990s and in the late 2000s. Over these two time periods, we compared the temporal trends in bycatch species composition, the probability of occurrence of functional groups per fishing set, the spatio-temporal species richness and the potential impact on several species listed in the red list of the International Union for Conservation of Nature (IUCN). The analyses were performed separately on the two main fishing modes of the fleet, i.e. sets on free-swimming school sets and on fish aggregating devices (FADs). Owing data quality constraints, we did not estimate bycatch rates. Ours results showed that the species composition of sharks caught on FADs decreased over time. The total species richness was higher for FAD sets than for free-swimming school sets (87 vs. 61 species respectively), such difference is common between fishing modes worldwide.

Small‐scale fisheries' management is complex given its multigear, multispecies nature; despite this, fishing effort has usually been controlled by nominal units, ignoring changes in effective fishing effort. This study aimed to understand the adaptive strategies of small‐scale fishers in San Felipe, Yucatan, Mexico through an analysis of their fishing operations. Minor changes in trip numbers among three seasons were observed, but increases in fishing time, depth and travel costs from one season to another at the operational level were found. It was also evident that high value species at the beginning of the season were gradually replaced by low‐value finfish as the season progresses. The results provide insights for new adaptive management strategies according to fisher's adaptive responses. For instance, using boats or fishing trips as fishing effort units in Yucatan may not be the most appropriated unit for management, as fishers adapt their strategies at different levels.

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The community metrics chosen generally had robust statistically significant associations with both physicochemical and contaminant variables, which supports the ecological relevance of these parameters as indicators of aquatic environmental health. Within the study area, the shoal flounder and their parasites live in a polluted environment with relatively high levels of hydrocarbons and nitrate. Regarding nitrate, we emphasise that if uncontrolled sewage discharge continues in the southern Gulf of Mexico, hypoxic conditions similar to those caused by the Mississippi river can be expected in the near future.

BackgroundBecause agriculture and offshore oil extraction are significant economic activities in the southern Gulf of Mexico, high concentrations of nutrients and hydrocarbons are expected. As parasite communities are sensitive to environmental impacts, these contaminants should have an effect on metrics such as species richness, relative abundance and similarity. Consequently, these community metrics can be used as indicators of aquatic environmental health. Our objectives were to describe the parasite communities of the shoal flounder Syacium gunteri and to determine potential thresholds above which environmental contaminants become major controlling factors of parasite community metrics.MethodsThe study area included 33 sampling sites in the southern Gulf of Mexico, where benthic sediments, water and shoal flounder individuals were collected. Data on ecto- and endo-parasites from flounder and nutrients, contaminants and physicochemical variables from the water and sediments were obtained. The statistical associations of the parasite community metrics at the component and infracommunity levels and the environmental data were analysed using redundancy analysis (RDA).ResultsOverall, 203 shoal flounder were examined for parasites, recovering 13 metazoan parasite species, and 48 physicochemical (e.g. temperature, nutrients) and contaminant (e.g. hydrocarbons, heavy metals) variables were obtained. The larval stages of the cestode Oncomegas wageneri and the nematodes Pseudoterranova decipiens and Hysterothylacium sp. were numerically dominant at the component and infracommunity levels. The parasite community metrics had significant negative statistical associations with both nitrate and total PAHs. With the exception of these two chemicals, which exceeded the threshold effect levels (TELs), no other environmental variable exceeded the range considered safe for marine organisms.ConclusionsThe community metrics chosen generally had robust statistically significant associations with both physicochemical and contaminant variables, which supports the ecological relevance of these parameters as indicators of aquatic environmental health. Within the study area, the shoal flounder and their parasites live in a polluted environment with relatively high levels of hydrocarbons and nitrate. Regarding nitrate, we emphasise that if uncontrolled sewage discharge continues in the southern Gulf of Mexico, hypoxic conditions similar to those caused by the Mississippi river can be expected in the near future.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-014-0541-3) contains supplementary material, which is available to authorized users.