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Survival of Salamanders in a Severe Flood Event in Louisiana
Catherine E. Newman*
Abstract - In August 2016, a park of roughly 200 ha of bottomland hardwood forest in East Baton
Rouge Parish, LA, was inundated by up to 5.28 m of water for 5 days in one of southeast Louisiana’s
most severe floods in recorded history. Here, I document post-flood observations of a terrestrial salamander
species at the park, Ambystoma opacum (Marbled Salamander). To my knowledge, this is the
first documentation of survival of terrestrial salamanders after a freshwater flood event. As such floods
are predicted to increase in frequency in the future, it is encouraging that salamanders may be able to
tolerate such changes to some extent.
Louisiana has 22 native salamander species (Mitchell and Gibbons 2010). Seven
(32%) of those species are protected by the Louisiana Department of Wildlife and Fisheries
(LDWF) as Critically Imperiled (LDWF 2017). In addition, LDWF (2017) notes that
many of these species are declining in Louisiana due to habitat modification or destruction,
as well as pollution of water from agricultural runoff. Bottomland hardwood forests are
characterized by alternating wet and dry seasons with regular flooding. In the Mississippi
River Alluvial Plain region of southeastern Louisiana, bottomland hardwood forest is the
predominant ecosystem type (Holcomb et al. 2015) and is the primary habitat for many of
the state’s salamander species (Mitchell and Gibbons 2010). The persistence of salamander
populations in this region is therefore dependent upon bottomland habitat availability and
its climate and flooding regime.
Seasonal flooding from river overflow is a defining feature of bottomlands (Kellison and
Young 1997). However, in August 2016, the region experienced one of the most severe flood
events in its recorded history. On 12 August 2016, the National Weather Service recorded
28.55 cm of rain at the Baton Rouge Metropolitan Airport station in Louisiana, compared
to a normal average daily rainfall for August of 0.48 cm (NOAA 2016). This was 4 times
greater than the previous record rainfall for 12 August and the second-largest 1-day rain on
record (NOAA 2016). Due to this extreme rain event, area rivers rapidly rose and caused
catastrophic flooding in East Baton Rouge and adjacent parishes. At the Denham Springs
gauge, the Amite River crested at 14.08 m on 14 August 2016, breaking the previous record
of 12.65 m (USGS 2016a); the Comite River at the Joor Road gauge crested at 10.43 m on
the same date, breaking the previous record of 9.45 m (USGS 2016b). At the confluence of
the Amite and Comite rivers in East Baton Rouge Parish is Frenchtown Road Conservation
Area, a park of roughly 200 ha of bottomland hardwood forest habitat, maintained by the
Recreation and Park Commission (BREC) of East Baton Rouge Parish (Fig. 1). The average
elevation of Frenchtown is 7–8 m, and most of the park was flooded, with the exception of
the highest elevations (Amanda Takacs, BREC, Baton Rouge, LA, pers. comm.).
Members of the North American Field Herping Association (NAFHA) had previously
observed 3 species of terrestrial salamanders at Frenchtown: Ambystoma opacum (Gravenhorst)
(Marbled Salamander), Ambystoma talpoideum (Holbrook) (Mole Salamander),
and Plethodon mississippi Highton (Mississippi Slimy Salamander) (NAFHA 2012). The
ability of local salamanders to survive such an extreme flood event was unknown. High
discharge and debris during flood events have been associated with mortality of stream-
*Louisiana State University, 119 Foster Hall, Baton Rouge, LA 70803; newma014@gmail.com.
Manuscript Editor: Kristen Cecala
Notes of the Southeastern Naturalist, Issue 16/3, 2017
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dwelling amphibians (Cover et al. 2010), and similar dangers would presumably exist for
terrestrial salamanders caught in overflowing rivers. In addition, hurricane storm surge has
been shown to decrease abundance and community diversity of anuran species in coastal
Louisiana ecosystems (Schriever et al. 2009), though those declines may have been caused
at least in part by increases in salinity (but see Gunzbur ger et al. 2010).
On 22 October 2016, I conducted the first of 2 preliminary, partial surveys of Frenchtown
to determine whether or not any salamanders had survived the flood. Due to time
limitations, I did not do a full survey of the entire park. The delay of 2 months between
the flood and the first survey was due to temporary closure of the park from flood damage,
as well as life-history timing of the local salamanders. In particular, the high air temperatures
of late summer and early fall in southeastern Louisiana greatly reduces the chance of
finding salamanders on the surface. On 22 October 2016, I found 2 adult female Marbled
Salamanders guarding eggs under the same log (30°28'44.4", -90° 59'2.4"; elevation 8.8 m;
Fig. 1). During the flood, this site was under up to 5.28 m of water for ~5 days (Fig. 2).
While it is possible these salamanders traveled from a nearby site that was less extensively
flooded, all areas within a reasonable dispersal distance had some level of flooding; even
0.5 m of water is enough to fully submerge the salamanders. In a second survey on 6 November
2016, I found an additional 2 Marbled Salamanders at the same site. Based on color
pattern, these were clearly different individuals from those found in the first survey. I did
not find any Mole Salamanders or Mississippi Slimy Salamanders; however, because other
species of ambystomatid and plethodontid salamanders were found, the failure to find Mole
Salamanders and Mississippi Slimy Salamanders is probably due to lower abundance of
Figure 1. Sampling locality and extent of flooding at Frenchtown. White outline demarcates boundary
of Frenchtown Road Conservation Area. Star indicates locality for A. opacum (Marbled Salamander)
observations. Black lines represent roads. Inset: location of rivers and Frenchtown relative to the
greater Baton Rouge area.
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those species in general, rather than an effect of the flood on those species to the exclusion
of the others. Furthermore, although the system was not closed to migration, dispersal distances
reported for these species in the literature are very small (e.g., average of 0.4 km for
Marbled Salamanders; Gamble et al. 2007), and the park is bounded by 2 rivers and development.
Therefore, I believe immigration into Frenchtown during the 2 months preceding
the surveys is highly unlikely.
These surveys do not provide any insight into the mechanisms of survival. However,
onset of flooding at Frenchtown was sudden and worsened rapidly; in the first 24 h, the
waters of the Amite River at Frenchtown rose by 4.75 m (Fig. 2). Given the limited vagility
of salamanders and extent of flooding at Frenchtown, it is unlikely they would have
been able to escape to higher ground. Studies have shown that lungless salamanders
(family Plethodontidae) can tolerate full submersion in water without access to buccopharyngeal
aerial respiration for at least 2 weeks with no apparent negative effects (Gatz and
Piiper 1979, Gatz et al. 1974, Whipple 1906a). However, lunged terrestrial salamanders
such as the Marbled Salamander appear to be less able to survive long periods underwater,
Figure 2. Amite River height at Denham Springs gauge (USGS 2016a) and approximate height of
water above ground level at site where salamanders were found on 22 October 2016. Gray dashed line
denotes ground level.
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though it is not clear if survival varies among species. Whipple (1906b) showed that
mortality in Marbled Salamanders occurs “in a short time” if restrained in water without
access to air. Wojnowski (2000) also noted that Marbled Salamanders must escape
to higher ground or drown during floods. While lunged salamanders can use hydrostatic
mechanisms to float near the surface, providing access to air (Ultsch et al. 2004, Whipple
1906b), any such floating salamanders would have been transported away from Frenchtown
by the current.
It is therefore most likely that the salamanders at Frenchtown survived the flood in
underground burrows. There is some evidence that terrestrial salamanders may use existing
burrows, often those made by small mammals (Douglas and Monroe 1981, Welsh and
Droege 2001), to prevent desiccation during very warm and/or dry periods. Ambystoma in
particular are rarely seen during July and August in southeastern Louisiana and typically do
not emerge before the fall breeding season. The flood event occurred prior to the breeding
season for both Ambystoma species (AmphibiaWeb 2016), so most adults may have been
sheltering in burrows. Presumably, the salamanders could have survived underground if
they were able to plug burrow entrances, as observed for rodents (Vorhies and Taylor 1922)
and beetles (Lin and Okuyama 2014). Nevertheless, regardless of mechanism, it is important
to document this survival of a lunged salamander species after an extreme flood event,
particularly because data predict that such events will increase in frequency due to climate
change (van der Wiel et al. 2017). Salamander populations inhabiting bottomland hardwood
forest habitat may be able to tolerate changes in flood cycle periodicity or severity, at least
to some extent.
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