Limits...
Were multiple stressors a 'perfect storm' for northern Gulf of Mexico bottlenose dolphins (Tursiops truncatus) in 2011?

Carmichael RH, Graham WM, Aven A, Worthy G, Howden S - PLoS ONE (2012)

Bottom Line: During the 4-month period starting January 2011, 186 bottlenose dolphins, including 46% perinatal calves (nearly double the percentage for the same time period from 2003-2010) washed ashore from Louisiana to western Florida.Comparison of the frequency distribution of strandings to flow rates and water temperature at a monitoring buoy outside Mobile Bay, Alabama (the 4(th) largest freshwater drainage in the U.S.) and along the nGOM coast showed that dolphin strandings peaked in Julian weeks 5, 8, and 12 (February and March), following water temperature minima by 2-3 weeks.Targeted analyses of tissues from stranded dolphins will be essential to define a cause of death, and our findings highlight the importance of considering environmental data along with biological samples to interpret stranding patterns during and after an unusual mortality event.

View Article: PubMed Central - PubMed

Affiliation: University Programs, Dauphin Island Sea Lab, Dauphin Island, Alabama, United States of America. rcarmichael@disl.org

ABSTRACT
An unusual number of near term and neonatal bottlenose dolphin (Tursiops truncatus) mortalities occurred in the northern Gulf of Mexico (nGOM) in 2011, during the first calving season after two well documented environmental perturbations; sustained cold weather in 2010 and the Deepwater Horizon oil spill (DWHOS). Preceding the stranding event, large volumes of cold freshwater entered the nGOM due to unusually large snowmelt on the adjacent watershed, providing a third potential stressor. We consider the possibility that this extreme cold and freshwater event contributed to the pattern of perinatal dolphin strandings along the nGOM coast. During the 4-month period starting January 2011, 186 bottlenose dolphins, including 46% perinatal calves (nearly double the percentage for the same time period from 2003-2010) washed ashore from Louisiana to western Florida. Comparison of the frequency distribution of strandings to flow rates and water temperature at a monitoring buoy outside Mobile Bay, Alabama (the 4(th) largest freshwater drainage in the U.S.) and along the nGOM coast showed that dolphin strandings peaked in Julian weeks 5, 8, and 12 (February and March), following water temperature minima by 2-3 weeks. If dolphin condition was already poor due to depleted food resources, bacterial infection, or other factors, it is plausible that the spring freshet contributed to the timing and location of the unique stranding event in early 2011. These data provide strong observational evidence to assess links between the timing of the DWHOS, other local environmental stressors, and mortality of a top local predator. Targeted analyses of tissues from stranded dolphins will be essential to define a cause of death, and our findings highlight the importance of considering environmental data along with biological samples to interpret stranding patterns during and after an unusual mortality event.

Show MeSH

Related in: MedlinePlus

Dolphin strandings in 2011.A) Total weekly bottlenose dolphin strandings for each state compared to surface water temperature (30 min intervals), flow (15 min intervals), and salinity (30 min intervals) measured at Mobile Bay, AL. B) Weekly perinatal dolphin strandings, separated by state (following the same legend as panel A). C) Total weekly bottlenose dolphin strandings, separated by carcass condition on the day of response in 2011. Carcass condition is reported using NMFS standard 5-point code in which 1 is live stranded, 2 is freshly dead, and 5 is most highly decomposed. NR  =  Not reported.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3399803&req=5

pone-0041155-g003: Dolphin strandings in 2011.A) Total weekly bottlenose dolphin strandings for each state compared to surface water temperature (30 min intervals), flow (15 min intervals), and salinity (30 min intervals) measured at Mobile Bay, AL. B) Weekly perinatal dolphin strandings, separated by state (following the same legend as panel A). C) Total weekly bottlenose dolphin strandings, separated by carcass condition on the day of response in 2011. Carcass condition is reported using NMFS standard 5-point code in which 1 is live stranded, 2 is freshly dead, and 5 is most highly decomposed. NR  =  Not reported.

Mentions: Days prior to the start of the perinatal dolphin stranding event in January 2011, there was a third potential environmental stressor, the rapid entry of large volumes of cold freshwater to near shore coastal waters associated with the melt water from an unusually large winter snowfall in the upper reaches of the Mobile Bay watershed (Fig. 2, III and Fig. 3A). Mobile Bay has the 6th largest watershed and represents the 4th largest freshwater drainage in the U.S. [7]. Although nearshore areas in the nGOM outside Mobile Bay are regularly influenced by this substantial freshwater drainage [8], the watershed had experienced moderate to severe drought conditions for several years [9]. Following a particularly cold winter and the DWHOS in 2010, this subsequent entry of cold freshwater at the nGOM coastline imposed additional stress on the already affected local coastal ecosystem.


Were multiple stressors a 'perfect storm' for northern Gulf of Mexico bottlenose dolphins (Tursiops truncatus) in 2011?

Carmichael RH, Graham WM, Aven A, Worthy G, Howden S - PLoS ONE (2012)

Dolphin strandings in 2011.A) Total weekly bottlenose dolphin strandings for each state compared to surface water temperature (30 min intervals), flow (15 min intervals), and salinity (30 min intervals) measured at Mobile Bay, AL. B) Weekly perinatal dolphin strandings, separated by state (following the same legend as panel A). C) Total weekly bottlenose dolphin strandings, separated by carcass condition on the day of response in 2011. Carcass condition is reported using NMFS standard 5-point code in which 1 is live stranded, 2 is freshly dead, and 5 is most highly decomposed. NR  =  Not reported.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3399803&req=5

pone-0041155-g003: Dolphin strandings in 2011.A) Total weekly bottlenose dolphin strandings for each state compared to surface water temperature (30 min intervals), flow (15 min intervals), and salinity (30 min intervals) measured at Mobile Bay, AL. B) Weekly perinatal dolphin strandings, separated by state (following the same legend as panel A). C) Total weekly bottlenose dolphin strandings, separated by carcass condition on the day of response in 2011. Carcass condition is reported using NMFS standard 5-point code in which 1 is live stranded, 2 is freshly dead, and 5 is most highly decomposed. NR  =  Not reported.
Mentions: Days prior to the start of the perinatal dolphin stranding event in January 2011, there was a third potential environmental stressor, the rapid entry of large volumes of cold freshwater to near shore coastal waters associated with the melt water from an unusually large winter snowfall in the upper reaches of the Mobile Bay watershed (Fig. 2, III and Fig. 3A). Mobile Bay has the 6th largest watershed and represents the 4th largest freshwater drainage in the U.S. [7]. Although nearshore areas in the nGOM outside Mobile Bay are regularly influenced by this substantial freshwater drainage [8], the watershed had experienced moderate to severe drought conditions for several years [9]. Following a particularly cold winter and the DWHOS in 2010, this subsequent entry of cold freshwater at the nGOM coastline imposed additional stress on the already affected local coastal ecosystem.

Bottom Line: During the 4-month period starting January 2011, 186 bottlenose dolphins, including 46% perinatal calves (nearly double the percentage for the same time period from 2003-2010) washed ashore from Louisiana to western Florida.Comparison of the frequency distribution of strandings to flow rates and water temperature at a monitoring buoy outside Mobile Bay, Alabama (the 4(th) largest freshwater drainage in the U.S.) and along the nGOM coast showed that dolphin strandings peaked in Julian weeks 5, 8, and 12 (February and March), following water temperature minima by 2-3 weeks.Targeted analyses of tissues from stranded dolphins will be essential to define a cause of death, and our findings highlight the importance of considering environmental data along with biological samples to interpret stranding patterns during and after an unusual mortality event.

View Article: PubMed Central - PubMed

Affiliation: University Programs, Dauphin Island Sea Lab, Dauphin Island, Alabama, United States of America. rcarmichael@disl.org

ABSTRACT
An unusual number of near term and neonatal bottlenose dolphin (Tursiops truncatus) mortalities occurred in the northern Gulf of Mexico (nGOM) in 2011, during the first calving season after two well documented environmental perturbations; sustained cold weather in 2010 and the Deepwater Horizon oil spill (DWHOS). Preceding the stranding event, large volumes of cold freshwater entered the nGOM due to unusually large snowmelt on the adjacent watershed, providing a third potential stressor. We consider the possibility that this extreme cold and freshwater event contributed to the pattern of perinatal dolphin strandings along the nGOM coast. During the 4-month period starting January 2011, 186 bottlenose dolphins, including 46% perinatal calves (nearly double the percentage for the same time period from 2003-2010) washed ashore from Louisiana to western Florida. Comparison of the frequency distribution of strandings to flow rates and water temperature at a monitoring buoy outside Mobile Bay, Alabama (the 4(th) largest freshwater drainage in the U.S.) and along the nGOM coast showed that dolphin strandings peaked in Julian weeks 5, 8, and 12 (February and March), following water temperature minima by 2-3 weeks. If dolphin condition was already poor due to depleted food resources, bacterial infection, or other factors, it is plausible that the spring freshet contributed to the timing and location of the unique stranding event in early 2011. These data provide strong observational evidence to assess links between the timing of the DWHOS, other local environmental stressors, and mortality of a top local predator. Targeted analyses of tissues from stranded dolphins will be essential to define a cause of death, and our findings highlight the importance of considering environmental data along with biological samples to interpret stranding patterns during and after an unusual mortality event.

Show MeSH
Related in: MedlinePlus