Effects of Hurricane Katrina on the fish assemblage of Bayou Lacombe, LA.

1
Effects of Hurricane Katrina on the fish
assemblage of Bayou Lacombe, LA. Jeffrey M. Van
Vrancken Nekton Research Laboratory University
of New Orleans

• Introduction
• Natural disturbances, such as droughts and
  hurricanes, can alter fish assemblage structure
• August 29th, 2006, Hurricane Katrina made
  landfall on southeastern Louisiana and the
  surrounding Gulf Coast areas
• The western part of the eye-wall, with winds in
  excess of 150 mph, passed directly over Bayou
  Lacombe, Louisiana, which interrupted a previous
  study of the system for historical fish
  assemblage comparisons (Figure 1)
• This presented a unique opportunity for a
  natural experiment by exploring the effects of
  a catastrophic hurricane on stream fish
  assemblage
• The saltwater storm surge tore apart healthy
  marshes and aquatic habitat in the lower portions
  of the bayou (Figure 2)
• In addition, persistent high winds caused trees
  to fall into the bayous headwaters (Figure 3)
• My objectives were to see if the local fish
  assemblages were resilient to the effects of this
  disturbance or if the diversity and the
  populations of fishes were significantly impacted

Table 1 Significant water quality changes of
Bayou Lacombe before and after Hurricane Katrina
Table 2 Significant water quality changes of
Bayou Lacombe before and after debris-removal
from Hurricane Katrina
Stream Position Salinity Dissolved Oxygen
Downstream (pre/post-Katrina) Significant P lt 0.001 NS
Upstream (pre/post-Katrina) NS Significant P lt 0.001
Stream Position Salinity Dissolved Oxygen
Downstream (pre/post-debris removal) Significant P lt 0.001 NS
Upstream (pre/post-debris removal) NS Significant P lt 0.001
Figure 4 n-MDS plot comparison of downstream
fish assemblages before (green triangles) and
after (blue triangles) Hurricane Katrina
ANOSIM R0.382 SIMPER 51
Figure 7 n-MDS plot of downstream fish
assemblages after the debris was removed (purple
squares) from Bayou Lacombe
ANOSIM R0.444 SIMPER 50
Figure 1 Hurricane Katrina landfall. The
western eye-wall of the storm passed directly
over Bayou Lacombe
ANOSIM R0.842 SIMPER 65
Figure 5 n-MDS plot comparison of upstream fish
assemblages before (green triangles) and after
(blue triangles) Hurricane Katrina
ANOSIM R0.402 SIMPER 46
Figure 8 n-MDS plot of upstream fish
assemblages after the debris was removed (purple
squares) from Bayou Lacombe

• Results pre/post-Hurricane Katrina
• There was little to no change in downstream fish
  assemblages sampled before and after the
  hurricane (Figure 4, ANOSIM R0.444)
• The salinity increase from the saltwater storm
  surge seemed to have minimal effects on fish
  assemblage structure downstream (Table 1)
• However, there was drastic change in upstream
  fish assemblage comparisons before and after the
  event due to a significantly lower dissolved
  oxygen (DO) content (Figure 5, ANOSIM R0.842,
  Table 1)
• This was caused by numerous debris dams which
  trapped dead plant material
• The high demand for oxygen in decaying plant
  matter caused the Lepomis spp. dominated
  pre-Katrina fish assemblage to swim downstream or
  die. Lepomis spp. were the most abundant fish
  taken before the storm and were rarely captured
  after the storm
• As a result, pirate perch, Aphredoderus sayanus,
  became the most abundant fish sampled after the
  hurricane because of their ability to tolerate
  such low DO
• The weed shiner, Notropis texanus, found in low
  abundance before the hurricane, disappeared after
  the storm

• Results pre/post-Hurricane Katrina debris
  removal
• There was little to no change in downstream fish
  assemblages sampled before and after the debris
  was removed from Bayou Lacombe (Figure 7, ANOSIM
  R0.382), even though the salinities were
  significantly different (Table 2)
• Upstream, once again, had changes in its fish
  assemblage composition due to the alteration of
  the bayou. The removal of the debris reduced the
  decomposition of dead plant material drastically
  and also allowed the water to flow as it did
  before the storm. One can see from Figure 8 that
  the fish assemblage is actually moving back to
  where it was before Hurricane Katrina
• Over several months of sampling, fewer
  Aphredoderus sayanus were sampled and increasing
  numbers of Lepomis spp. were taken leading one to
  conclude that Bayou Lacombes upstream fish
  assemblage is recovering to its pre-Hurricane
  Katrina fish assemblage
• Finally, I have concluded that Notropis texanus
  has been extirpated out of this system. The few
  that were collected in the samples before
  Hurricane Katrina were the only Cyprinids left in
  the system. This may have implications towards
  solving the mystery of why the most abundant fish
  species, the Cyprinid Cyprinella venusta (sampled
  30 years ago from the same bayou), disappeared
  with out a trace in the early 1990s

Figure 3 A debris dam located upstream in Bayou
Lacombe resulting from high winds of Hurricane
Katrina
Figure 2 Storm surge contours and flood
inundation on the northshore of Lake Pontchartrain

• Materials and Methods
• Downstream samples in the summer of 2005 and
  throughout 2006-2007 were taken using a Coeffelt
  boat electrofishing unit. Three two-hundred
  meter reaches (with length determined by a GPS
  unit) were electrofished using a single-pass
  technique. All structures within the reach
  (fallen trees, marsh balls, fishing docks, etc.)
  were targeted for sampling
• For the headwater portions of Bayou Lacombe, a
  Smith-Root backpack electrofisher was used for
  sampling for a standard time of 45 minutes
• Water quality parameters (temperature, salinity,
  specific conductance, and dissolved oxygen) were
  also taken at the end of each sample using a
  Yellow Springs Instruments model 85 meter
• Fish sampled were identified to species, a
  standard length range of the individual species
  and total weight of the individual species
• Fish assemblage comparisons were made using
  Analysis of Similarity (ANOSIM), Similarity
  Percentages (SIMPER) and non-Metric Dimensional
  Scaling (n-MDS) with PRIMER software

Figure 6 Picture taken in same direction as
Figure 3 but five months after Hurricane Katrina.
FEMA paid to have Bayou Lacombe debris cleared
out and created a twist on year-long fish
assemblage survey