Common bottlenose dolphins (Tursiops truncatus) in Lake Pontchartrain, Louisiana, 2007 to mid-2014.
Creators: name: Mullin, Keith (Keith D.)
name: Barry, Kevin
name: Sinclair, Carrie
name: Litz, Jenny
name: Maze-Foley, Katherine
name: Fougeres, Erin
name: Ewing, Ruth
name: Gorgone, Antoinette M.
name: Adams, Jeff
name: Tumlin, Mandy
Publisher: name: U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Oceanic and Atmospheric Research, Office of Policy, Planning and Evaluation
Year: 2015
Subjects: subject: Bottlenose dolphin--Stranding--Louisiana--Pontchartrain, Lake
subject: Bottlenose dolphin--Estimates--Louisiana--Pontchartrain, Lake
subject: Bottlenose dolphin--Effect of water quality on--Louisiana--Pontchartrain, Lake
subject: Bottlenose dolphin--Effect of salt on--Louisiana--Pontchartrain, Lake

description: Lake Pontchartrain (LP) is a brackish lagoon (1,630 km2) in southeastern Louisiana connected by two passes on the eastern end to open estuarine waters. Salinity in LP varies seasonally and is generally lowest in late spring and highest in summer and fall (range ≈ 0–15 ppt). Common bottlenose dolphins (Tursiops truncatus; dolphins) are distributed throughout estuarine waters in the northern Gulf of Mexico but records of dolphins in LP were historically rare. In 2007, 30‒40 dolphins were reported in eastern LP just to the west of the Norfolk Southern railroad and U.S. Route 11 bridges ('target area') and reports suggested that dolphins had been there since Hurricane Katrina in August 2005. An initial survey in May 2007 confirmed the location and number of dolphins and revealed that most of them had minor to severe skin lesions that were thought to result from exposure to low salinity water. Periodic photo-identification surveys (n = 35) were conducted from spring 2007 through spring 2010 in the target area, eastern LP (east of the bridges) and the two passes. Dolphins were sighted in the target area during 90% of the surveys through winter 2010 after which none were sighted. Seventy-four dolphins were identified in the target area and averaged 34.2 dolphins/survey (n = 25, S.D. = 6.73, range 22‒45). Dolphins with unmarked dorsal fins, including calves and neonates, averaged 2.0 dolphins/survey (S.D. = 1.76, range = 0‒6). Twenty-three identified dolphins in the target area had more than 700 days from their first to their last sighting and these individuals were sighted during 8 to 11 of the 11 seasons surveyed where dolphins were sighted. Sixty-one dolphin groups were sighted in eastern LP and the passes with 141 individuals identified, but none were sighted more than four times. There were few identified individuals that were sighted in multiple locations (i.e., target area, eastern LP, the two passes). Skin lesions occurred on over 90% of the target area dolphins and on 30‒100% of those from other locations. Lesion severity appeared to be seasonal, and worsened and improved with lower and higher salinities, respectively. Twenty-seven dolphin strandings occurred in the LP area in spring 2010. Salinity and water temperatures in the LP area were unusually low in winter 2010. Only one target area dolphin was sighted in another location post winter 2010. While it was presumed that most of the target area dolphins likely died, only one target area dolphin was among the 12 stranded dolphins from the LP area with a dorsal fin photo of sufficient quality to attempt to match to previously identified dolphins. Twenty-four dolphin strandings also occurred in the LP area in 2013 after only three strandings in 2011and 2012. The origin of the 2013 strandings is unknown, due in part to the lack of LP monitoring after 2010.