Sustainable aquaculture and aquatic resources management

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A Review on Reservoir System and Its Ecology in Indian Perspective

Published on 31/5/2017

Abstract

Rural populations often depend on small reservoirs for their water supply. These are not natural aquatic system but are designed to serve specific purposes and provide the means to utilize water in a variety of useful and efficient ways. Water from these sources is not only utilized for drinking purposes, but also for commercial and industrial use. Though reservoirs are constructed, they are considered as an intermediate between a river and a lake. Thus limnological characteristics of this hybrid system have been of great interest to ecologists and researchers. Several limnological attributes regarding water quality, plankton abundance, fish population are been discussed in this review article. Ecological studies on global and Indian perspective are the major highlight of this review. A few modeling approaches are also discussed which are commonly used globally to preserve and manage the pristine aquatic nature of this hybrid ecosystem.

A Tanganyikan cichlid Neolamprologus mustax selectively exploits territories of another cichlid Variabilichromis moorii due to its inter-individual variation in aggression

Published on 30/4/2017

Abstract

Animals in a population consistently differ from one another in behavioural types over time and this difference can affect intra- and interspecific relationships. However, empirical studies about roles of behavioural individual variation in interspecific interactions are scarce. Here, we provide evidence that inter-individual variation of a cichlid in aggression affects access to its territory by a heterospecific cichlid. In Lake Tanganyika, a zoobenthivorous cichlid Neolamprologus mustax (Nm) is admitted into territories of an algivorous Variabilichromis moorii (Vm) to prey on benthic invertebrates, while other zoobenthivorous fishes are chased from the territories. We conducted an experiment in which caged Nm fish were exposed twice to each Vm fish in natural habitats. Results indicated repeatable individual variations in Vm aggression towards Nm. Moreover, diving observations indicated that Nm fish frequently used some of Vm territories inside their own territories, but rarely or never used others. This uneven use of Vm territories by the Nm fish was negatively correlated with individual variations in Vm aggression. We conclude that the preferential access of Nm to Vm territory is gained by Nm’s recognising more tolerant Vm fish or discriminating among sites for their territories.

Short-Term Response of a Downstream Marine System to the Partial Opening of a Tidal-River Causeway

Published on 30/4/2017

Abstract

The spillway gates of the Petitcodiac Causeway, a hydraulic structure ~35 km upstream of the mouth of the Petitcodiac River in New Brunswick, Canada, were permanently opened in April 2010. The short-term effect opening the spillway gates had on downstream intertidal mudflats of the upper Bay of Fundy was investigated. Specifically, a multivariate before-after-control-impact design was used to determine if opening the spillway gates affected the invertebrate community (crustaceans, polychaetes, and molluscs), abiotic sediment conditions (sediment water content, mean particle size, penetrability, and depth of the apparent redox potential discontinuity), or resource availability (sediment chlorophyll a concentration and organic matter content) of five intertidal mudflats (two impacted sites, three reference sites) spanning Chignecto Bay, the northern arm of the upper Bay of Fundy, up to 5 months post-opening. No biologically or statistically meaningful differences were detected between impacted and reference sites for any of the measured variables. This suggests that opening the causeway did not have a quantifiable impact on these intertidal mudflats, at least within half a year of the opening. This is likely a result of the macrotidal nature of the Bay of Fundy that overwhelmed any immediate changes to hydrodynamics that occurred after the opening of the causeway gates.

Behavioral and reproductive effects of bird-borne data logger attachment on Brown Pelicans ( Pelecanus occidentalis ) on three temporal scales

Published on 31/3/2017

Abstract

Although the use of bird-borne data loggers has become widespread in avian field research, the effects of capture and transmitter attachment on behavior and demographic rates are not often measured. Tag- and capture-induced effects on individual behavior, survival and reproduction may limit extrapolation of transmitter data to wider populations. However, measuring individual responses to capture and tagging is a necessary step in developing research techniques that minimize negative effects. We measured the short-term behavioral effects of handling and GPS transmitter attachment on Brown Pelicans under both captive and field conditions, and followed tagged individuals through a full breeding season to assess whether capture and transmitter attachment increased rates of nest abandonment or breeding failure. We observed slight increases in preening among tagged individuals 0–2 h after capture relative to controls that had not been captured or tagged, with a corresponding reduction in time spent resting. One to three days post-capture, nesting behavior of tagged pelicans resembled that of neighbors that had not been captured or tagged. Eighty-eight percent of tagged breeders remained at the same nest location for more than 48 h after capture, attending nests and chicks for an average of 49 days, and 51% were assumed to successfully fledge young. Breeding success was driven primarily by variation in location; however, sex and handling time also influenced the probability of successful breeding in tagged pelicans, suggesting that individual characteristics and the capture process itself can confound the effects of capture and transmitter attachment. We conclude that pelicans fitted with GPS transmitters exhibit comparable behaviors to untagged individuals within a day of capture and that GPS tracking is a viable technique for studying behavior and demography in this species. We also identify measures to minimize post-capture nest abandonment rates in tracking studies, including minimizing handling time and covering nests during processing.

Mowing Submerged Macrophytes in Shallow Lakes with Alternative Stable States: Battling the Good Guys?

Published on 31/3/2017

Abstract

Submerged macrophytes play an important role in maintaining good water quality in shallow lakes. Yet extensive stands easily interfere with various services provided by these lakes, and harvesting is increasingly applied as a management measure. Because shallow lakes may possess alternative stable states over a wide range of environmental conditions, designing a successful mowing strategy is challenging, given the important role of macrophytes in stabilizing the clear water state. In this study, the integrated ecosystem model PCLake is used to explore the consequences of mowing, in terms of reducing nuisance and ecosystem stability, for a wide range of external nutrient loadings, mowing intensities and timings. Elodea is used as a model species. Additionally, we use PCLake to estimate how much phosphorus is removed with the harvested biomass, and evaluate the long-term effect of harvesting. Our model indicates that mowing can temporarily reduce nuisance caused by submerged plants in the first weeks after cutting, particularly when external nutrient loading is fairly low. The risk of instigating a regime shift can be tempered by mowing halfway the growing season when the resilience of the system is highest, as our model showed. Up to half of the phosphorus entering the system can potentially be removed along with the harvested biomass. As a result, prolonged mowing can prevent an oligo—to mesotrophic lake from becoming eutrophic to a certain extent, as our model shows that the critical nutrient loading, where the lake shifts to the turbid phytoplankton-dominated state, can be slightly increased.

Applicability of Perinereis aibuhitensis Grube for fish waste removal from fish cages in Sanggou Bay, P. R. China

Published on 31/3/2017

Abstract

The present study investigated the applicability of integrated polychaete-fish culture for fish waste removal to offset negative impact induced by organic benthic enrichment. A field study demonstrated that deposition rate was significantly higher underneath the fish farm than that in control area. The material settling under the farm was characterized by a high amount of fish feces (45%) and uneaten feed (27%). Both feeding rate (FR) and apparent digestibility rate (ADR) increased with decreasing body weight, as was indicated by significantly a higher rate observed for the groups containing smaller individuals in a lab study. The nutrient in fresh deposited material (De) was higher than that in sediments collected under the farm (Se), resulting in lower feces production but higher apparent digestibility rate for the De group as feeding rate was similar. Consequently, higher nutrient removal efficiency was observed in the De group. A mass balance approach indicated that approximately 400–500 individuals m−2 is required for removing all waste materials deposited underneath the fish farm, whereas abundance can be lower (about 300–350 individuals m−2) when only the fish waste needs to be removed. The results showed that a significant amount of waste had been accumulated in the fish cages in Sanggou Bay. The integration of fish with P. aibuhitensis seems promising for preventing organic pollution in the sediment and therefore is an effective strategy for mitigating negative effect of fish farms. Thus such integration can become a new IMTA (integrated multi-trophic aquaculture) model in Sanggou Bay.

On the origin and phylogenetic position of Arctic charr ( Salvelinus alpinus complex, Salmonidae) from Lake Cherechen’ (middle Kolyma River basin): controversial genetic data

Published on 31/3/2017

Abstract

Within the Arctic charr complex (Salvelinus alpinus complex), many different populations and forms with disputable origin and systematic status have been described. Some of them, such as the charr from Lake Cherechen’ (middle Kolyma River basin), combine characters of different phylogenetic groups, representing a possible consequence of former hybridization. The data on 32 allozyme loci and on nucleotide sequences of 501-bp fragments of the mtDNA control region as well as of 899-bp fragments of exon 2 of the RAG1 gene were used for the analysis of the origin of Lake Cherechen’ charr and their phylogenetic relationships with other representatives of the Arctic charr lineage. As was shown previously, the dwarf and large forms of charr from this lake are morphologically similar to other charr populations from the upper Kolyma River, but bear the mtDNA haplotype of northern Dolly Varden Salvelinus malma malma, not of Taranets charr Salvelinus alpinus taranetzi. The analysis of the allozymes and RAG1 gene confirms the affinity of the Lake Cherechen’ charr to the Arctic charr lineage, but it is insufficient to unambiguously attribute them to the Eurasian or Taranets group. The presence of mtDNA of northern Dolly Varden in Lake Cherechen’ Arctic charr and the replacement of their native mtDNA are the result of the introgressive hybridization with S. m. malma. An alternative explanation connected with incomplete lineage sorting seems highly improbable. Our study confirms a postglacial secondary contact of the representatives of different phylogenetic groups of the S. alpinus-S. malma species complex in the Kolyma basin and in the area from Taimyr to Chukotka. It also indicates the need for more thorough analysis of the morphological and genetic diversity of charr from this region as well as caution in taxonomic decisions.

Analysis of DNA methylation level by methylation-sensitive amplification polymorphism in half smooth tongue sole ( Cynoglossus semilaevis ) subjected to salinity stress

Published on 31/3/2017

Abstract

Increasingly arisen environmental constraints may contribute to heritable phenotypic variation including methylation changes, which can help the animals with development, growth and survival. In this study, we assessed the DNA methylation levels in three tissues (gonad, kidney and gill) of half smooth tongue sole under the salinity stress. The methylation-sensitive amplification polymorphism (MSAP) technique was applied to illustrate the regulation of epigenetic mechanism in environmental stimuli. Fish were subjected to 15 salinity treatment for 7 and 60 days, respectively. A total of 11259 fragments were amplified with 8 pairs of selective primers. The levels of methylated DNA in different tissues of females and males without salinity stress were analyzed, which were 32.76% and 47.32% in gonad; 38.13% and 37.69% in kidney; 37.58% and 34.96% in gill, respectively. In addition, the significant difference was observed in gonad between females and males, indicating that discrepant regulation in gonadal development and differentiation may involve sex-related genes. Further analysis showed that total and hemi-methylation were significantly decreased under 15 salinity for 7 days, probably resulting in up-regulating salt-tolerance genes expression to adjust salt changing. With the adjustment for 60 days, total and hemi-methylation prominently went back to its normal levels to obtain equilibrium. Particularly, full methylation levels were steady along with salinity stress to maintain the stability of gene expression. Additionally, the data showed that gonads in females and gills in males were superior in adaptability. As a result, DNA methylation regulates tissue- specific epiloci, and may respond to salinity stress by regulating gene expression to maintain animal survival and activity.

Isolation and characterization of melanin pigment from yesso scallop Patinopecten yessoensis

Published on 31/3/2017

Abstract

Melanin is one of the essential compounds in the pigments of molluscan shells. However, the effects of melanin on color variations in molluscs are largely unknown. Our previous study suggests that Yesso scallop Patinopecten yessoensis might contain melanin pigment in the dark brown shell. We therefore isolated melanin from the pigmented shells using hydrochloric acid method, and characterized the types of melanin pigments by spectrophotometry. The purified melanin, which was verified by spectrophotometry scanning and HPLC analysis, showed the typical characteristics of melanin absorption spectra and HPLC chromatograms. The contents of pheomelanin and eumelanin in pigmented shells, which were determined by the linear standard curve of melanin at 405 nm and 350 nm absorbance, were 48.23 ± 1.350 and 157.65 ± 5.905 mg, respectively. The present results indicate that the brown-pigmented shells of scallops comprise approximately 76.6% of eumelanin and 23.4% of pheomelanin, which supports the presence of eumelanin-rich pigment in scallop shells. Therefore, the combination of hydrochloric acid extraction and spectrophotometric quantification is a rapid and efficient method to isolate and quantify melanin in shells. This will facilitate the melanin studies related to shell color polymorphism and the selective breeding of bivalves with different shell colors.

Assessing conservation risks to populations of an anadromous Arctic salmonid, the northern Dolly Varden ( Salvelinus malma malma ), via estimates of effective and census population sizes and approximate Bayesian computation

Published on 31/3/2017

Abstract

Census population size (N c ) is crucial to the development of resource management strategies, however, monitoring the effective population size (N e ) of managed populations has proliferated because of this parameter’s relationship to the short-term impacts of genetic stochasticity and long-term population viability. Thus, having a sound understanding of both N c and N e , including population connectivity, provides valuable insights into both the demographic and genetic risks to extinction. Here, we assessed microsatellite DNA variation in four (of five known) anadromous northern Dolly Varden (NDV, Salvelinus malma malma) populations from Canada’s western Arctic region, to estimate N e using both temporal-based and single-sample estimators and to test for associations between N e and N c . We also employed approximate Bayesian computation (ABC) to evaluate several evolutionary scenarios that have potentially shaped contemporary population structure in this species, focusing particularly on population size and connectivity. We found evidence for moderate to large contemporary and historical N e , suggesting that short- and long-term extinction risks are low for these populations. Estimates of contemporary and long-term N e were variable within and among populations and overall estimates could not be reliably linked with N c or available spawning habitat. The overall estimate of N e /N c , was 0.152 and ranged from 0.024 to 0.442 when including errors around the estimate of N e and N c . Finally, ABC analyses suggest that NDV had a common origin followed by divergence in isolation while maintaining large effective sizes, but also that these populations were bottlenecked in the past, likely the result of post-glacial colonization processes. These results corroborate indications of limited gene flow at present, indicating independent demographic and evolutionary trajectories that imply NDV is best managed on a per-river-population basis. Overall, the results of this study further our general understanding of N e , N e /N c and demographic independence in NDV, and provide a comprehensive and quantitative assessment of the potential genetic and demographic risk status of Arctic anadromous salmonids, including baselines for future monitoring.

The Need for Social Ethics in Interdisciplinary Environmental Science Graduate Programs: Results from a Nation-Wide Survey in the United States

Published on 31/3/2017

Abstract

Professionals in environmental fields engage with complex problems that involve stakeholders with different values, different forms of knowledge, and contentious decisions. There is increasing recognition of the need to train graduate students in interdisciplinary environmental science programs (IESPs) in these issues, which we refer to as “social ethics.” A literature review revealed topics and skills that should be included in such training, as well as potential challenges and barriers. From this review, we developed an online survey, which we administered to faculty from 81 United States colleges and universities offering IESPs (480 surveys were completed). Respondents overwhelmingly agreed that IESPs should address values in applying science to policy and management decisions. They also agreed that programs should engage students with issues related to norms of scientific practice. Agreement was slightly less strong that IESPs should train students in skills related to managing value conflicts among different stakeholders. The primary challenges to incorporating social ethics into the curriculum were related to the lack of materials and expertise for delivery, though challenges such as ethics being marginalized in relation to environmental science content were also prominent. Challenges related to students’ interest in ethics were considered less problematic. Respondents believed that social ethics are most effectively delivered when incorporated into existing courses, and they preferred case studies or problem-based learning for delivery. Student competence is generally not assessed, and respondents recognized a need for both curricular materials and assessment tools.

Antioxidant response of ridgetail white prawn Exopalaemon carinicauda to harmful dinoflagellate Prorocentrum minimum exposure and its histological change

Published on 31/3/2017

Abstract

The dinoflagellate Prorocentrum minimum, one of the most widespread red tide causing species, affects marine aquaculture and ecosystems worldwide. In this study, ridgetail white prawn Exopalaemon carinicauda were exposed to P. minimum cells (5 × 104 cells mL−1) to investigate its harmful effects on the shrimp. Antioxidant activities and histological changes were used as indicators of health status of the shrimp. In 72 hours, the mortality of E. carinicauda was not affected, but its antioxidant response and histology were statistically different from those of control. Elevated superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities and depressed catalase (CAT) activity were observed in gill; while increased SOD, glutathione S-transferase (GST), CAT activities and modulated GPX activity were observed in hepatopancreas. Thus, antioxidant activities in gill and hepatopancreas seem to respond differentially to harmful alga exposure. Increased malondialdehyde (MDA) content in early a few hours indicates the damage of the antioxidant defense system. Although MDA content recovered to a low level thereafter, a series of histological abnormalities including accumulation or infiltration of hemocytes, tissue lesions and necrosis were discovered in gill and hepatopancreas. Exposure to P. minimum induced sublethal effects on E. carinicauda, including temporary oxidative damage and histological injury.

Oceanographic drivers of population differentiation in Indo-Pacific bottlenose ( Tursiops aduncus ) and humpback ( Sousa spp.) dolphins of the northern Bay of Bengal

Published on 31/3/2017

Abstract

The Bay of Bengal is one of the most productive ecosystems in the northern Indian Ocean and it harbours a rich community of cetaceans, including Indo-Pacific bottlenose (Tursiops aduncus) and humpback (Sousa spp.) dolphins. The taxonomy of these genera has been controversial, but within the Indian Ocean both seem to be divided into phylogenetically discrete units that range from the east to the west. Within the Sousa genus, S. plumbea is distributed in the western Indian Ocean while S. chinensis is distributed in the eastern Indian and western Pacific Ocean. T. aduncus has a discontinuous distribution throughout the Indo-Pacific Ocean and two different phylogenetic units are known to exist, one along the eastern African coast and another one in the eastern Indian and west Pacific Ocean. In this study we investigate the phylogeography of Indo-Pacific humpback and bottlenose dolphins in the northern Bay of Bengal. We sequenced the mitochondrial DNA control region for 17 bottlenose and 15 humpback dolphins and compared the results with previously published sequences within each genus. In both cases, we found that Bangladesh dolphins are genetically different from neighbouring populations. While the Bangladesh T. aduncus seem to be more closely related to the African T. aduncus form than the Pacific form, Sousa spp. seem to be more closely related to individuals from Australia. The genetic uniqueness of these populations has important evolutionary implications, due to their isolation, coastal distribution in a geographic cul-de-sac characterized by an extreme infusion, redistribution and recycling of biological productivity, and conservation implications since their survival is threatened in particular by fatal interactions with fisheries. We suggest that the particular and extreme oceanographic conditions found in the Bay of Bengal may be driving speciation in these dolphins and other marine megafauna.

Population structure and persistence of Pacific herring following the Great Tohoku earthquake

Published on 31/3/2017

Abstract

We evaluated the effect of the Great Tohoku earthquake, which occurred on March 11, 2011 in Japan, on the genetic diversity and population structure of Pacific herring (Clupea pallasii). Pacific herring (n = 4466) were collected between 2003 and 2014 through more than 20 sampling events during spawning periods at nine spawning sites throughout the Pacific herring distribution range in Japan. We measured them and genotyped 3784 fish at five microsatellite loci. Following the tsunami, the sea-spawning population at the center of the affected area was almost extirpated and was replaced by a genetically distinct lagoon-spawning population from an adjacent brackish lake. However, the pattern of gene flow was stable for populations, with unique admixture proportions in local populations despite the high gene flow (F ST = 0.0184). Our results indicate that Pacific herring in Japan spawn in a range of salinities and exchange genes between local populations regardless of the spawning ecotypes. We hypothesize that the combination of constant gene flow between local populations from straying of spawners and spawning fidelity creates weak but significantly differentiated stable population structure. This process can allow restoration of the genetic characteristics of damaged populations over many generations and can thereby promote the long-term viability of marine fishes that have high gene flow.

Tropical Shearwater population stability at Reunion Island, despite light pollution

Published on 31/3/2017

Abstract

Seabirds are exposed to numerous threats at sea and on land, and they are among the most endangered birds worldwide. Procellariids are attracted by artificial light, and this causes massive fallout at various places of the world. In Reunion Island, Tropical Shearwaters Puffinus bailloni are heavily impacted by light pollution. To assess the population trends of this species, we conducted two large-scale acoustic surveys across the island (in 1996/1997 and in 2013/2015) and analysed the numbers of birds attracted by lights and rescued by the local wildlife rescue center between 1996 and 2015. We detected 220 colonies in 2013/2015, including 124 colonies previously surveyed in 1996/97 and 96 newly discovered colonies. The average vocal activity recorded at colonies was similar during the two surveys suggesting no marked change in population size. Some 13,200 Tropical Shearwaters were found grounded since 1996 due to light attraction, of which 88 % were successfully released. The number of reported grounded birds increased 19-fold between 1996 and 2015. This increase was due to a combination of factors that are difficult to disentangle: (1) increasing public awareness; (2) increasing light pollution; and (3) the absence of population collapse. Indeed, both acoustic surveys and the number of rescued birds indicate that the Tropical Shearwater population of Reunion Island did not decline between 1996/1997 and 2013/2015. We suggest that the rescue campaigns conducted annually strongly contributed to this stability. Thus, we recommend maintaining the rescue operations, but also to reduce light pollution.

First record of three African trichodinids (Ciliophora: Peritrichida) in cultured Nile tilapia ( Oreochromis niloticus ) in Saudi Arabia with re-evaluation of their host specificity

Published on 31/3/2017

Abstract

Saudi Arabia has a developing aquaculture industry that farms primarily tilapia. Although trichodinids are presumably the most usually encountered protozoan parasites in these cultured fish, they have rarely been studied in this context, and there is no data on the species that might infect cultured tilapia in Saudi Arabia. The present study was therefore carried out as a general survey to investigate the occurrence and identify the species of trichodinids that can infect cultured tilapia (Oreochromis niloticus) in Saudi Arabia. A total of 500 tilapia fish were collected from fish farms in Riyadh city and examined in order to determine the species of trichodinids present in the positive specimens. Three species of trichodinids (Trichodina maritinkae, T. centrostrigeata and T. frenata) were isolated and described as new records in Saudi Arabia. These trichodinids were found simultaneously in the same fish with overall prevalence of 20% (100/500). The identification and characterization of these three species are documented based on Riyadh specimens, for the first time. Additionally, the present paper confirms the existence of T. frenata for the second time globally and establishes this trichodinid as a new parasite for O. niloticus. T. maritinkae is highly specific to clariids, and previously, it has not been reported from any fish species other than clariids. The present work also confirmed that T. centrostrigeata can also infest cichlid fish. The list of host records of these species is expanded and their host specificity re-evaluated based on the results of this study in addition to the previously published data. We conclude that there is a need for further study of the impacts of these Trichodina spp. on Saudi Arabian fishery sector.

Nearshore fish community responses to large scale dam removal: implications for watershed restoration and fish management

Published on 23/3/2017

Abstract

The nearshore is a critical zone for northeast Pacific Ocean fish communities, including ecologically and culturally important salmon species. The largest dam removal in the world was recently completed on the Elwha River, with the goal of restoring fisheries and ecosystems to the watershed. The nearshore Elwha fish community was monitored monthly from January 2008 to November 2015 before, during and after dam removal. As of September 2015, approximately 2.6 million m3 of sediment material had increased the area of the Elwha delta to over 150 ha. Newly formed nearshore habitats were quickly colonized by fish communities during the dam removal period but the communities were similar in total species richness and Shannon diversity before and after dam removal, and were similar to a nearby reference site (Salt Creek estuary). Select fish species, including ESA-listed Pacific salmon and trout Oncorhynchus spp., and eulachon Thaleichthys pacificus, and non-native, American shad (Alosa sapidissima), appeared quickly in these new habitats. Hatchery releases of Chinook, O. tshawytscha, coho, O. kisutch, and steelhead, O. mykiss (over 3 million total fish annually to the lower river), dominated the Elwha estuary catch from April through August of each year before, during, and after dam removal. Chum salmon catch rate, size, and duration of estuary occupancy declined during and after dam removal. Overall catches of chum salmon fry prior to, during, and after dam removal were significantly negatively correlated with Chinook salmon catches but significantly, and positively, correlated with coho salmon. When assessed at the Elwha estuary separately, chum abundance was significantly positively correlated with Chinook, coho, and steelhead abundance. These patterns indicate overlap, and likely interaction between these respective groups of hatchery and wild fish. Continued hatchery releases may therefore further challenge chum salmon recovery and should be considered when planning for watershed recovery.

Reviews in Fish Biology and Fisheries

Published on 23/3/2017

Distribution, ecology, and status of the white shark, Carcharodon carcharias, in the Mediterranean Sea

Published on 23/3/2017

Abstract

The occurrence of the white shark, Carcharodon carcharias, in the Mediterranean Sea has been reported since the Middle Ages (476–1453). Several studies have documented its presence in various areas of the basin, but no comprehensive review of the distribution and status of this species is available for the area. We compiled a total of 628 white shark records from 476 to 2015. Data suggests that the white shark is more common in the western Mediterranean Sea, especially in the Adriatic Sea and in the Sicilian Channel and is more frequently observed during summer months. However, analysis using night-time satellite imagery showed the existence of an anthropogenic bias in the distribution of white sharks. All size classes have been recorded in the region. However, the highest occurrence of young of the year has been recorded in the Sicilian Channel, in the Adriatic Sea and in the Aegean Sea, in summer, suggesting these areas might serve as nursery grounds. In the Mediterranean Sea, the white shark exhibits a broad diet. The most common prey found include small cetaceans (Tursiops truncatus, Stenella coeruleoalba), tuna (Thunnus spp.), swordfish (Xiphias gladius) and loggerhead sea turtle (Caretta caretta). A total of 53 white shark records refer to interactions between sharks and humans that resulted in a detrimental impact on humans, which include 42 bites and 11 reports of the presence of human remains in the stomach of captured animals. Analysis of the temporal variation in mean total lengths of white sharks found a decreasing trend from 1913 to 2012. The decreasing length of white sharks suggests this species might be declining in the Mediterranean Sea.

Asymmetric hybridization and introgression between sibling species of the pufferfish Takifugu that have undergone explosive speciation

Published on 22/3/2017

Abstract

Pufferfishes belonging to the genus Takifugu are a prominent example of recent adaptive radiations of marine fishes. Using amplified fragment length polymorphism (AFLP) and mitochondrial DNA (mtDNA) markers, the genetic characteristics of natural hybrids between two sibling species, Takifugu snyderi and Takifugu stictonotus, were investigated to gain insights into the role of hybridization in rapid diversification. Numerous early generations of hybrids (131 F1 hybrids and 18 first-generation backcrosses) were screened by Bayesian assignment procedures from samples collected at three sites off the Pacific coast of eastern Honshu, Japan (Ibaraki: 36°21′N, 140°37′E; Fukushima: 37°03′N, 141°03′E; Iwate: 40°02′N, 141°59′E), during 2012–2014. Analysis of mtDNA indicated that hybridization is highly directional, as the majority of the F1 hybrids (75.6%) were offspring between T. stictonotus females and T. snyderi males. Among the 18 backcrosses, 17 were toward T. snyderi and one was toward T. stictonotus. Two of 118 individuals classified as genetically pure T. snyderi based on AFLP markers were affected by mtDNA introgression from T. stictonotus. These results suggest that interspecific gene flow has been highly asymmetrical toward T. snyderi, which may partly explain the marked difference in intraspecific genetic diversity between the two species. The proportion of F1 hybrids in the Ibaraki and Fukushima areas is exceptionally high compared with that of other marine fishes, indicating the need for continuous monitoring of hybridization and its impact on integrity of each parental species under the changing marine environment.

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