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Mercury and selenium concentrations in stranded bottlenose dolphins from the Indian River Lagoon system, Florida

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  • Cape Canaveral Scientific
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Mercury and selenium concentrations in stranded bottlenose dolphins from the Indian River Lagoon system, Florida

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Mercury is a toxic metallic element that is known to bioaccumulate in many marine organisms. Mercury concentrations are routinely evaluated in Indian River Lagoon (IRL) fish, however, there are no published reports of these concentrations for IRL bottlenose dolphins, Tursiops truncatus (Montagu, 1821). Muscle (n = 30) and liver (n = 19) samples from stranded IRL dolphins were collected and analyzed for total mercury and selenium. Total mercury concentrations in liver samples ranged from 0.42 to 240 ppm wet weight (ww) (mean = 73.01 ppm) and concentrations in muscle samples ranged from 0.26 to 47 ppm ww (mean = 5.68 ppm). Mercury concentrations were not significantly different between males and females for both tissue types. Selenium concentrations ranged from 1.20 to 90.70 ppm ww (mean = 29.81 ppm) in liver tissue and 0.75 to 16.10 ppm ww (mean = 1.92 ppm) in muscle tissue. Selenium concentrations were positively correlated with mercury in both tissue types. Age and total length were good predictors for mercury concentrations in both tissue types. Future studies are needed to determine what effect mercury may have on the overall health of IRL dolphins.
The Indian River Lagoon, Florida (study site) consists of three interconnected bodies of water: the Indian River, the Banana River, and Mosquito Lagoon. Bottlenose Dolphin Tissue Collection.—Tissue samples were collected from 30 stranded bottlenose dolphins and one fetus that were recovered from the Indian River La- goon (Fig. 1) from May 2001 to July 2003. Total length (TL) was measured as straight-line length from the tip of the rostrum to the fluke notch (Norris, 1961). Sex was determined by external examination and examination of gonads. When possible, teeth were extracted from each animal for age estimation. Teeth were decalcified, sectioned using a freezing microtome, and stained with hematoxylin using standard methods (Myrick et al., 1983). Ages were deter- mined by counting growth layer groups (annual layers) in teeth (Hohn et al., 1989). Calves were considered to be < 1.5 yrs, juvenile females (1.5–7 yrs), juvenile males (1.5–10 yrs), adult females ≥ 8 yrs, and adult males ≥ 11 yrs of age. In four cases, age was not available, and age classes were estimated based on TL of the animal (Wells et al., 1987). We report the accumulation of total mercury by age and TL separately because the two are loosely cor- related in male and female IRL dolphins (Stolen and Barlow, 2003). Moreover, total mercury may accumulate similarly in animals of similar size but different ages, and vice versa (Honda et al., 1983; Andre et al., 1991a,b). Lastly, often only one of these parameters is reported in the literature (Andre et al., 1991b; Leonzio et al., 1992; Kuehl and Haebler, 1995; Chen et al., 2002; Law et al., 2003). Location, date of stranding, and additional necropsy findings were also recorded for each specimen.
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... These lesions show excessive production of pigment, which can cause hepatic failure (Resendes et al., 2002). These lesions were observed in other cetaceans during a morbillivirus outbreak (Fern andez et al., 2008;Resendes et al., 2002) and in the liver of bottlenose dolphins (Tursiops truncatus) with high Hg concentrations (Rawson et al., 1993;Durden et al., 2007;Stravos et al., 2011). The liver impairment is caused by a sudden MeHg increase in the bloodstream and transport to other organs, such as liver, as a result of probable remobilization of MeHg stored in the muscle (Dietz et al., 2013;Shoham-Frider et al., 2016). ...
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... In Guiana dolphins, all individuals' concentrations were below that baseline (highest concentration: 44.4 mg kg À1 ww). However, it is important to highlight that chronic bioaccumulation in the liver can lead to hepatic diseases and abnormalities (Rawson et al., 1993;Durden et al., 2007;Karshaw and Hall, 2019). ...
... These lesions show excessive production of pigment, which can cause hepatic failure (Resendes et al., 2002). These lesions were observed in other cetaceans during a morbillivirus outbreak (Fern andez et al., 2008;Resendes et al., 2002) and in the liver of bottlenose dolphins (Tursiops truncatus) with high Hg concentrations (Rawson et al., 1993;Durden et al., 2007;Stravos et al., 2011). The liver impairment is caused by a sudden MeHg increase in the bloodstream and transport to other organs, such as liver, as a result of probable remobilization of MeHg stored in the muscle (Dietz et al., 2013;Shoham-Frider et al., 2016). ...
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An unusual mortality event (UME) attributed to morbillivirus infection was identified in two Guiana dolphin populations from the Southeastern Brazilian coast. The aim of this study was to characterize total mercury (THg), methylmercury (MeHg) and selenium (Se) bioaccumulation and body burden in Guiana dolphins from Sepetiba Bay (RJ) collected before (n = 61) and during the UME (n = 20). Significantly lower Se concentrations were found in the livers of individuals collected during the UME (Mann-Whitney test; p = 0.03), probably due to impairment of the detoxification process in the liver. There were differences in THg and Se concentrations in the organs and tissues of individuals (Kruskal-Wallis test,p < 0.05), but not MeHg (Kruskal-Wallis test, p =0.07). For THg, the liver showed the higher concentrations and differed among organs and tissues analyzed such as blubber (Tukey’s test for unequal N; p = 0.003). For Se concentrations, the skin and kidney presented the higher concentrations and varied among other tissues/organs, like muscle (Tukey’s test for unequal N; p = 0.02). Differences in body burdens were observed among specimens collected previously and during the UME probably due to the remobilization and transport of the muscle-stored MeHg to other tissues/organs. This abrupt input of MeHg into the bloodstream may cause serious health damage. Indeed, evidences of methylmercury intoxication was observed in Guiana dolphins in Sepetiba Bay. In conclusion, bioaccumulation patterns, the detoxification process and body burden were affected by morbillivirus.
... Several previous studies have focused on the accumulation of more well-known EDCs in marine mammal tissues including BPA, PCBs, organochlorines, and triclosan Fair et al., 2009;Jepson et al., 2015;Xue and Kannan, 2016;Damseaux et al., 2017). Additionally, previous studies measuring toxicants and essential and non-essential elements in free-ranging odontocete species have been conducted globally, in a variety of tissues including blood, skin, blubber, kidney, liver, muscle, and brain (Kemper et al., 1994;Bryan et al., 2007;Durden et al., 2007;Stavros et al., 2011;Schaefer et al., 2011Schaefer et al., , 2015Beck et al., 2013;Monteiro et al., 2016a,b). To date, however, this is the first published report examining concentrations of atrazine, DEP, NPE, and triclosan in blubber tissues of stranded cetaceans. ...
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... We examined immune function in two populations of noncaptive turtles, comparing resident turtles from an area of poor water quality with those in a more pristine environment. Florida's Indian River Lagoon (IRL) is a heavily polluted estuary with high levels of heavy metals and persistent organic pollutants (Wang et al. 1992;Durden et al. 2007;Fair et al. 2010) and eutrophication (Lapointe et al. 2015;Barile 2018). As with other animals in the IRL, resident juvenile green turtles exhibit high rates of disease, with approximately 50% of green turtles showing tumors (Hirama and Ehrhart, 2007;Lawrance et al. 2018). ...
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Common bottlenose dolphins (Tursiops truncatus truncatus) inhabiting the Indian River Lagoon (IRL) estuarine system along the east coast of Florida are impacted by anthropogenic activities and have had multiple unexplained mortality events. Given this, managers need precise estimates of demographic and abundance parameters. Mark-recapture photo-identification boat-based surveys following a Robust Design were used to estimate abundance, adult survival, and temporary emigration for the IRL estuarine system stock of bottlenose dolphins. Models allowed for temporary emigration and included a parameter (time since first capture) to assess evidence for transient individuals. Surveys (n = 135) were conducted along predetermined contour and transect lines throughout the entire IRL (2016-2017). The best fitting model allowed survival to differ for residents and transients and to vary by primary period, detection to vary by secondary session, and did not include temporary emigration. Dolphin abundance was estimated from 981 (95% CI: 882-1,090) in winter to 1,078 (95% CI: 968-1,201) in summer with a mean of 1,032 (95% CI: 969-1,098). Model averaged seasonal survival rate for marked residents was 0.85-1.00. Capture probability was 0.20 to 0.42 during secondary sessions and the transient rate was estimated as 0.06 to 0.07. This study is the first Robust Design mark-recapture survey to estimate abundance for IRL dolphins and provides population estimates to improve future survey design, as well as an example of data simulation to validate and optimize sampling design. Transients likely included individuals with home ranges extending north of the IRL requiring further assessment of stock delineation. Results were similar to prior abundance estimates from line-transect aerial surveys suggesting population stability over the last decade. These results will enable managers to evaluate the impact of fisheries-related takes and provide baseline demographic parameters for the IRL dolphin population which contends with anthropogenic impacts and repeated mortality events.
... Similar results have been reported for blubber, kidney, liver, muscle, and skin in bottlenose dolphins and striped dolphins (Stenella coeruloabla) (Andre et al., 1991;Monteiro et al., 2016;McCormack et al., 2020b). However, we found no relationship between liver THg concentration and body length, which does not support the finding of previous studies that reported a positive relationship between liver THg concentration and body length in bottlenose dolphins (Durden et al., 2007;Monteiro et al., 2016). The reason for the lack of relationship between body length and THg concentration in the liver in our study is not apparent. ...
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Odontocetes are apex predators that, despite accumulating mercury (Hg) to high concentrations in their tissues, show few signs of Hg toxicity. One method of Hg detoxification in odontocetes includes the sequestering of Hg in toxically inert mercury selenide (HgSe) compounds. To explore the tissue-specific accumulation of Hg and Se and the potential protective role of Se against Hg toxicity, we measured the concentrations of total mercury (THg) and selenium (Se) in multiple tissues from 11 species of odontocetes that stranded along the northern Gulf of Mexico coast [Florida (FL) and Louisiana (LA)]. Tissues were collected primarily from bottlenose dolphins (Tursiops truncatus; n = 93); however, individuals from species in the following 8 genera: Feresa (n = 1), Globicephala (n = 1), Grampus (n = 2), Kogia (n = 5), Mesoplodon (n = 1), Peponocephala (n = 4), Stenella (n = 9), and Steno (n = 1) were also sampled. In all species, the mean THg concentration was greatest in the liver and lowest in the blubber, lung, or skin. In contrast, in most species, the mean Se concentration was greatest in the liver, lung, or skin, and lowest in the blubber. For all species, Se:Hg molar ratios decreased with increasing THg concentration in the blubber, kidney, liver, lung, and skin following an exponential decay relationship. In bottlenose dolphins, THg concentrations in the kidney, liver, and lung were significantly greater in FL dolphins compared to LA dolphins. On average, in bottlenose dolphins, Se:Hg molar ratios were approximately 1:1 in the liver and >1:1 in blubber, kidney, lung, and skin, suggesting that Se likely protects against Hg toxicity. However, more research is necessary to understand the variation in Hg accumulation within and among species, and to assess how Hg, in combination with other environmental stressors, influences odontocete population health.
... Due to their abundance and year-round use of the IRL and adjacent waters, the common bottlenose dolphin (Tursiops truncatus) is the target species for investigating HAB toxin exposure in marine mammals in the present study (Durden et al., 2017;Mazzoil et al., 2005;Odell and Asper, 1990). Due to their role as apex predators, their long life span, large body mass, and ability to accumulate environmental contaminants, they are an important indicator species for assessing potential impacts of HAB toxins in marine wildlife from this ecologically important region of Florida (Bossart, 2006;Durden et al., 2007;Wells et al., 2004). Since IRL dolphins are resident animals that do not migrate or travel large distances between seasons, they are exposed to any HAB toxins that occur in their habitat and are able to move up the food web, resulting in potential dietary exposure (Durden et al., 2011;Landsberg et al., 2005;Mazzoil et al., 2008). ...
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Harmful algal bloom (HAB) toxins have severe negative impacts on marine mammals, particularly for Florida bottlenose dolphins (Tursiops truncatus) which frequently experience mass mortality events. Dolphins on the Florida Atlantic coast inhabit a region endemic to two HAB species, Karenia brevis and Pyrodinium bahamense, which produce the neurotoxins brevetoxin (PbTx) and saxitoxin (STX), respectively. Although toxic HABs and associated dolphin mortality events have been reported from this region, there is a lack of available data necessary for comparing toxin exposure levels between bloom ('exposed') conditions and non-bloom ('baseline') conditions. Here we present a 10-year dataset of PbTx and STX concentrations detected in dolphins stranding in this region, and compare the toxin loads from HAB-exposed dolphins to those detected in dolphins recovered in the absence of a HAB. We analyzed liver tissue samples from dead-stranded dolphins (n = 119) recovered and necropsied between 2002-2011, using an enzyme-linked immunosorbent assay (ELISA) modified for use with mammalian tissues. For dolphins recovered during baseline conditions, toxin-positive samples ranged in concentration from 0.27 to 1.2 ng/g for PbTx and from 0.41 to 1.9 ng/g for STX. For K. brevis-exposed dolphins, concentrations of up to 12.1 ng PbTx/g were detected, and for P. bahamense-exposed dolphins, concentrations of up to 9.9 ng STX/g were detected. Baseline PbTx values were similar to those reported in other regions where K. brevis blooms are more frequent and severe, but HAB-exposed PbTx values were considerably lower relative to these other regions. Since no baseline STX dolphin data exist for any region, our data serve as a first step towards establishing reference STX values for potential dolphin mortality events associated with STX-producing blooms in the future. This study demonstrates that although HABs in eastern Florida are only infrequently associated with dolphin mortalities, the presence of toxins in these animals may pose significant health risks in this region.
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Mercury (Hg) deposited into aquatic sediments can be converted into the more toxic methylmercury (MeHg) by microbial activity. Atlantic stingrays (Hypanus sabinus) are an estuarine and nearshore species found in coastal regions of the western North Atlantic, occurring in multiple habitat types, and feeding mainly on benthic invertebrates. Mercury dynamics and speciation in stingrays have not been well examined. This study quantified total Hg and Hg species (Hg (II) and MeHg) in Atlantic stingrays sampled from Florida’s Indian River Lagoon (IRL) from 2012 to 2013. Tissues (muscle and liver) collected from 29 stingrays were lyophilized and homogenized before being analyzed using a direct mercury analyzer. Concentrations of total Hg in muscle were positively related to stingray disk width, but concentrations in liver were not. Mean (±SD) total Hg in muscle (0.56 ± 0.30 mg/kg dw) was significantly higher than mean total Hg in liver (0.23 ± 0.19 mg/kg dw). Within liver tissue, percent MeHg (of total Hg) ranged from 31 to 99%. The ratio between total Hg in liver and total Hg in muscle was <1 for nearly all individuals, suggesting a lack of active hepatic demethylation and sequestration mechanisms. Concentrations of Hg in IRL Atlantic stingrays fall below concentrations known to result in direct toxicity to fishes; however, effects thresholds are not well understood for elasmobranchs. Comparisons of Hg concentrations in IRL Atlantic stingrays sampled previously (37 individuals in 1994) indicate that total Hg concentrations in muscle of Atlantic stingrays have decreased over the past two decades, suggesting a reduction in the bioavailable Hg in the IRL ecosystem.
... This population faces numerous threats that warrant an improved understanding of these types of behavior. IRL dolphins may be directly (e.g., boat strikes and fishing gear entanglement) and indirectly (e.g., introduction of marine contaminants) impacted by human activities (Noke & Odell, 2002;Durden, 2005;Durden et al., 2007;Stolen et al., 2007Stolen et al., , 2013Bechdel et al., 2009;Fair et al., 2010). Interactions with fishing gear (e.g., entanglement and/or gear ingestion) are the cause of mortality in 4.9% of stranded IRL dolphins (Stolen et al., 2013). ...
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Accurate estimates of abundance are critical to species management and conservation. Common bottlenose dolphins (Tursiops truncatus truncatus) inhabiting the Indian River Lagoon (IRL) estuarine system along the east coast of Florida are impacted by anthropogenic activities and have had multiple unexplained mortality events, necessitating precise estimates of demographic and abundance parameters to implement management strategies. Mark-recapture methodology following a Robust Design survey was used to estimate abundance, adult survival, and temporary emigration for the IRL estuarine system stock of bottlenose dolphins. Models included a parameter (time since first capture) to assess evidence for transient individuals. Boat-based photo-identification surveys ( n = 135) were conducted along predetermined contour and transect lines throughout the entire IRL (2016-2017). The best fitting model included the “transient” parameter to survival, allowed survival to vary by primary period, detection to vary by secondary session, and did not allow temporary emigration. Dolphin abundance ranged from 981 (95% CI: 882-1,090) in winter to 1,078 (95% CI: 968-1,201) in summer with a mean of 1,032 (95% CI: 969 -1,098). Model averaged seasonal survival rate for marked residents ranged from 0.85-1.00. Capture probability ranged from 0.20 to 0.42 during secondary sessions and transient rate from 0.06 to 0.07. This study represents the first Robust design mark-recapture survey effort to estimate abundance for IRL dolphins and provides parameter estimates to optimize sampling design of future studies. Transients included individuals with home ranges extending north of the IRL requiring further assessment of stock delineation. Results were remarkably similar to prior abundance estimates resulting from line-transect aerial surveys and were consistent with a stable population. Data will enable managers to evaluate the impact of fisheries-related takes as well as enable future comparisons of demographic parameters for a dolphin population that continues to sustain large scale mortality events and anthropogenic impacts.
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