Contamination of water bodies by inorganic mercury (Hg[II]) used in placer mining of gold deposits in the Madre de Dios Department, Perú, contributes to the bioaccumulation of methylmercury (MeHg) in fish tissue....Contamination of water bodies by inorganic mercury (Hg[II]) used in placer mining of gold deposits in the Madre de Dios Department, Perú, contributes to the bioaccumulation of methylmercury (MeHg) in fish tissue. We measured MeHg and total Hg (THg) concentrations (mg/kg wet weight [ww] tissue) of thirteen fish species from the Tambopata River, Perú, and the connected oxbow lake Tres Chimbadas. We also used stable isotope analysis (δ15N and δ13C) to estimate trophic positions of fishes. Average MeHg concentrations of fish species ranged from 0.042 mg/kg ww (Satanoperca jurupari) to 0.463 mg/kg ww (Hoplias malabaricus) in the main channel and from 0.090 mg/kg ww (Parauchenipterus sp.) to 1.282 mg/kg ww (Pimelodina flavipinnis) in the lake. Spearman rank correlation indicated that trophic position had no influence on MeHg concentrations of species in the main channel, but in the lake, trophic positions of species were positively associated with MeHg. Migrations of the pimelodid catfish surveyed from the main channel are well documented. Because little gold mining occurs at our study site, fishes from the main channel may be bioaccumulating MeHg from areas where mining is widespread. Fish species that reside in the lake are relatively sedentary and migration is limited by the brief period of floodplain inundation and the long, narrow corridor that connects the lake to the main channel;lake sediments are therefore the likely source for MeHg bioaccumulation. Five out of the eight fish species surveyed from the main channel and two out of the five species from the lake had MeHg levels higher than United States Environmental Protection Agency fish tissue criterion for human consumption.展开更多
Many curves have been proposed and debated to model individual growth of marine invertebrates. Broadly, they fall into two classes, first order (e.g. von Bertalanffy) and sigmoidal (e.g. Gompertz). We provide an innov...Many curves have been proposed and debated to model individual growth of marine invertebrates. Broadly, they fall into two classes, first order (e.g. von Bertalanffy) and sigmoidal (e.g. Gompertz). We provide an innovative approach which demonstrates that the growth curves are not mutually exclusive but that either may arise from a simple three-stage growth model with two steps (k<sub>1 </sub>and k<sub>2</sub>) depending on the ratio of the growth parameters . The new approach predicts sigmoidal growth when is close to 1, but if either growth from stage A to stage B or B to C is fast relative to the other, the slower of the two steps becomes the growth limiting step and the model reduces to first order growth. The resulting curves indicate that there is a substantial difference in the estimated size at time t during the period of active growth. This novel two-step rate model generates a growth surface that allows for changes in the rate parameters over time as reflected in the new parameter n(t) = k<sub>1</sub>(t) - k<sub>2</sub>(t). The added degree of freedom brings about individual growth trajectories across the growth surface that is not easily mapped using conventional growth modeling techniques. This two (or more) stage growth model yields a growth surface that allows for a wide range of growth trajectories, accommodating staged growth, growth lags, as well as indeterminate growth and can help resolve debates as to which growth curves should be used to model animal growth. This flexibility can improve estimates of growth parameters used in population models influencing model outcomes and ultimately management decisions.=展开更多
West Nile virus,a mosquito-vectored flavivirus of the Japanese encephalitis serogroup,was first detected in North America following an epizootic in the New York City area in 1999.In the intervening 11 years since the ...West Nile virus,a mosquito-vectored flavivirus of the Japanese encephalitis serogroup,was first detected in North America following an epizootic in the New York City area in 1999.In the intervening 11 years since the arrival of the virus in North America,it has crossed the contiguous USA,entered the Canadian provinces bordering the USA,and has been reported in the Caribbean islands,Mexico,Central America and,more recently,South America.West Nile virus has been reported in over 300 species of birds in the USA and has caused the deaths of thousands of birds,local population declines of some avian species,the clinical illness and deaths of thousands of domestic horses,and the clinical disease in over 30000 Americans and the deaths of over 1000.Prior to the emergence of West Nile virus in North America,St.Louis encephalitis virus and Dengue virus were the only other known mosquito-transmitted flaviviruses in North America capable of causing human disease.This review will discuss the North American experience with mosquito-borne flavivirus prior to the arrival of West Nile virus,the entry and spread of West Nile virus in North America,effects on wild bird populations,genetic changes in the virus,and the current state of West Nile virus transmission.展开更多
文摘Contamination of water bodies by inorganic mercury (Hg[II]) used in placer mining of gold deposits in the Madre de Dios Department, Perú, contributes to the bioaccumulation of methylmercury (MeHg) in fish tissue. We measured MeHg and total Hg (THg) concentrations (mg/kg wet weight [ww] tissue) of thirteen fish species from the Tambopata River, Perú, and the connected oxbow lake Tres Chimbadas. We also used stable isotope analysis (δ15N and δ13C) to estimate trophic positions of fishes. Average MeHg concentrations of fish species ranged from 0.042 mg/kg ww (Satanoperca jurupari) to 0.463 mg/kg ww (Hoplias malabaricus) in the main channel and from 0.090 mg/kg ww (Parauchenipterus sp.) to 1.282 mg/kg ww (Pimelodina flavipinnis) in the lake. Spearman rank correlation indicated that trophic position had no influence on MeHg concentrations of species in the main channel, but in the lake, trophic positions of species were positively associated with MeHg. Migrations of the pimelodid catfish surveyed from the main channel are well documented. Because little gold mining occurs at our study site, fishes from the main channel may be bioaccumulating MeHg from areas where mining is widespread. Fish species that reside in the lake are relatively sedentary and migration is limited by the brief period of floodplain inundation and the long, narrow corridor that connects the lake to the main channel;lake sediments are therefore the likely source for MeHg bioaccumulation. Five out of the eight fish species surveyed from the main channel and two out of the five species from the lake had MeHg levels higher than United States Environmental Protection Agency fish tissue criterion for human consumption.
文摘Many curves have been proposed and debated to model individual growth of marine invertebrates. Broadly, they fall into two classes, first order (e.g. von Bertalanffy) and sigmoidal (e.g. Gompertz). We provide an innovative approach which demonstrates that the growth curves are not mutually exclusive but that either may arise from a simple three-stage growth model with two steps (k<sub>1 </sub>and k<sub>2</sub>) depending on the ratio of the growth parameters . The new approach predicts sigmoidal growth when is close to 1, but if either growth from stage A to stage B or B to C is fast relative to the other, the slower of the two steps becomes the growth limiting step and the model reduces to first order growth. The resulting curves indicate that there is a substantial difference in the estimated size at time t during the period of active growth. This novel two-step rate model generates a growth surface that allows for changes in the rate parameters over time as reflected in the new parameter n(t) = k<sub>1</sub>(t) - k<sub>2</sub>(t). The added degree of freedom brings about individual growth trajectories across the growth surface that is not easily mapped using conventional growth modeling techniques. This two (or more) stage growth model yields a growth surface that allows for a wide range of growth trajectories, accommodating staged growth, growth lags, as well as indeterminate growth and can help resolve debates as to which growth curves should be used to model animal growth. This flexibility can improve estimates of growth parameters used in population models influencing model outcomes and ultimately management decisions.=
文摘West Nile virus,a mosquito-vectored flavivirus of the Japanese encephalitis serogroup,was first detected in North America following an epizootic in the New York City area in 1999.In the intervening 11 years since the arrival of the virus in North America,it has crossed the contiguous USA,entered the Canadian provinces bordering the USA,and has been reported in the Caribbean islands,Mexico,Central America and,more recently,South America.West Nile virus has been reported in over 300 species of birds in the USA and has caused the deaths of thousands of birds,local population declines of some avian species,the clinical illness and deaths of thousands of domestic horses,and the clinical disease in over 30000 Americans and the deaths of over 1000.Prior to the emergence of West Nile virus in North America,St.Louis encephalitis virus and Dengue virus were the only other known mosquito-transmitted flaviviruses in North America capable of causing human disease.This review will discuss the North American experience with mosquito-borne flavivirus prior to the arrival of West Nile virus,the entry and spread of West Nile virus in North America,effects on wild bird populations,genetic changes in the virus,and the current state of West Nile virus transmission.
