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OCR for page 12

based on the assessment of physiological signifi- selected using the balanced design, Treatment 1 was
cance, which considered the significance of multi- added to the analysis to refine the results. A com-
ple injuries and inspection of data for the occurrence plete statistical analysis is shown in Appendix E.
of injury combinations. For example, the occurrence
of two injuries categorized as Moderate was assessed
CHAPTER 3 RESULTS
to have physiological costs similar to that of one injury
categorized as Mortal. Sound Exposures
An RWI was calculated for each treatment fish
A primary objective of this project was to test
and each control fish. The formulas used were:
the hypothesis that the magnitude of barotrauma
m effects increased with increasing exposure to pile
RWI ( Control ) = ( Wi × Ci ) Equation 1.1 driving sounds as measured in terms of cumulative
i
sound exposure level (SELcum). Each experimental
m animal was exposed to one of the pile driving treat-
RWI ( Treatment ) = ( Wi × Ti ) Equation 1.2 ments shown in Table 2. The maximum exposure
i had an average SELss of 187 dB re 1 Pa2s and a
SELcum of 219 dB re 1 Pa2s. This level of SELss had
Where an average peak SPL of 213 dB re 1 Pa, which was
RWI = response weighted index, the maximum amount of energy that could be safely
i = injury type index, generated by the HICI-FT. Therefore, for Treatment
m = 22, number of injury types (Table 1), 1's "pair," a SELcum of 219 dB re 1 Pa2s could not
Ti = the proportion of the sample of fish exposed be generated with 960 strikes since this would have
to a treatment that experienced injury type i, required a peak SPL above 215 dB re 1 Pa. The
Wi = the Trauma Category weight (5, 3, or 1) for remaining treatments were conducted in pairs since
injury type i, the same SELcum could be reached with both 1,920
Ci = the proportion of the sample of control fish for and 960 strikes by having a higher SELss (and thus
a treatment that experienced injury type i. higher peak SPL) for 960 strikes than for 1,920. In
each treatment pair, the goal was to present the same
SELcum value but vary the number of pile strikes,
Statistical Analysis which altered the SELss value.
The response variable RWI was transformed, Holding the SELcum steady was done to imple-
as shown in Equation 1.3, before analysis in order ment treatments that could be used to explore the
to stabilize variance and linearize the response equal energy hypothesis while providing insight into
curve. the relative importance of SELss and SELcum in deter-
mining effects of sound on fish.
yi = ln ( RWI i + 1) Equation 1.3 Each treatment pair was aimed at a specific SEL
value. However, many variables affect the ability to
present the precise signal level, and thus the range of
In addition, cumulative energy was expressed as:
SELcum treatments was continuous, rather than dis-
SEL cum = SEL ss + 10 log10 ( number of strikes )
crete points. Each treatment blends with the next
SELcum, such that each treatment is ± 1.5 dB of its
Equation 1.4 specified value, i.e., 216 ± 1.5. Because the data are
continuous, an RWI was calculated for each individ-
Analyses of covariance (ANCOVA) were per- ual fish. However, in Table 2, the average RWI is
formed regressing yi against SELcum and assessing reported for each treatment.
whether number of strikes (960 or 1,920) had an
additional effect on fish response beyond that de-
Barotrauma
scribed by SELcum. Initial analyses were conducted
on Treatments 2 through 11 to balance the design. Inspection of the log-transformed RWI values
Treatments 2 through 11 were paired while Treat- show that fish with 960 strikes had a statistically
ment 1 lacked a counterpart. Once a model was significant higher RWI value than fish exposed to
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Table 2 Study exposure treatments and exposure details.
Treatment Avg. Number of Avg. Avg. Peak Duration, Exposed Control Avg.
No. SELcum Strikes SELss SPL min Fish, n Fish, n RWI
1 219 1920 187 213 48 44 33 15.318
2 216 1920 183 210 48 36 16 5.971
3 216 960 186 213 24 28 10 6.071
4 213 1920 180 207 48 26 5 2.346
5 213 960 183 210 24 31 7 4.323
6 207 960 177 203 24 24 8 1.042
7 207 1920 174 201 48 43 17 0.581
8 210 960 181 208 24 31 10 4.032
9 210 1920 177 204 48 30 11 3.433
10 203 960 174 201 24 32 11 0.656
11 204 1920 171 199 48 31 12 0.419
1,920 strikes at the same value of SELcum. This can cepts for fish exposed to either 960 or 1,920 strikes
be seen when comparing the ln (RWI+1) regression (Table 3).
lines for each 960- and 1,920-strike treatment. In Adding treatment 1 (i.e., SELss = 187, SELcum
other words, for common values of SELcum, higher = 219, number of strikes = 1,920) to the analysis did
values of SELss resulted in significantly higher val- not change the linearity of the data on the natural
ues of RWI for 960 strikes (Figure 4). log scale or the regression relationships (Table 4,
The ANCOVA demonstrated that ln (RWI+1) Figure 4). The final model was based on the use of all
was linearly related to SELcum, and fish exposed to Treatments 1-11.
a common value of SELcum using 960 or 1,920 The RWI values were calculated and plotted for
strikes had statistically different RWI values. Using each fish as shown in Figure 5.
a balanced design for Treatments 2 through 11 (i.e., Distributions of 1,920 and 960 strikes in Figure 5
these had pairs of common values; Treatment 1 did show an increase of RWI values correlated with an
not), common slopes were found for the regression increase of exposure severity (SELcum). The increase
of ln (RWI+1) versus SELcum, but different inter- in RWI was the result of both the number of injuries
All Treatments: Model Ln(RWI+1) ~ SELcum + #strikes
4
960 Strikes 960 Strikes
3 1920 Strikes 1920 Strikes
2
Ln(RWI+1)
1
0
1
2
200 205 210 215 220 225
SELcum
Figure 4 Scatterplots of SELcum vs. ln (RWI+1) for all treatments. Solid
line shows predicted ln (RWI+1) values for 960 strikes and dashed line
for 1,920 strikes. Red squares denote the 960 strikes and blue diamonds
denote the 1,920 strikes.
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Table 3 Sequential analysis of covariance (ANCOVA) results
for Treatments 211. Response: ln (RWI+1). Best model
contains the covariate SELcum followed by number of strikes.
Treatments 211
Source df SS MS F-value P-value
SELcum 1 103.22 103.22 281.240 <0.0001
Residuals 309 113.41 0.37
Source df SS MS F-value P-value
SELcum 1 103.22 103.22 289.679 <0.0001
Strikes 1 3.95 3.95 11.077 0.0010
Interaction 1 0.07 0.07 0.196 0.6583
Residuals 307 109.39 0.36
Best Model
Source df SS MS F-value P-value
SELcum 1 103.22 103.22 290.437 <0.0001
Strikes 1 3.95 3.95 11.106 0.0010
Residuals 308 109.46 0.36
each exposed fish experienced as well as the biologi- defined by the SELss and number of strike variables
cal significance of those injuries. The increase in the (Figure 8), Figures 8A and 8B, are presented sepa-
number of injuries per test fish with increase in sever- rately to show the construction of 8C.
ity of exposure is shown in Figure 6. Figure 8A is the background layer of the plot and
Additional insight can be obtained by examining represents the sample space for the study. The x- and
Figure 7. As SELss increases, RWI increases as well. y-axes are SELss and number of strikes, respectively,
However, the indication is that as SELss increases, while the z-axis is SELcum. The blue dashed contours
the severity of barotrauma response is differentially represent SELcum values, which were generated by
amplified as the number of strikes increases. There calculating the relationship between the number of
is a higher level of RWI values for the 960 strike strikes and the SELss (see Equation 1.4). For exam-
treatments, which can be seen when comparing the ple, a SELcum of 208 dB is produced when there are
ln (RWI+1) regressions lines for each 1,920 and 960 strikes at a SELss of 178 dB, or when there are
960-strike treatment (Figure 4). 1,920 strikes at a SELss of 175 dB.
Figure 8C summarizes study findings. However, Figure 8B shows the RWI contour lines in black.
because of the complexity of the response of fish to Axes are the same as for Figure 8A with treatment
exposure over the SELcum treatments as they are RWI in the z-axis for this layer. Note that the top
Table 4 Analysis of covariance (ANCOVA) from the best
model from Table 6 applied to all Treatments 111.
Response: ln (RWI+1).
All Treatments
Source df SS MS F-value P-value
SELcum 1 201.30 201.30 542.039 <0.0001
Strikes 1 2.24 2.24 6.033 0.0145
Residuals 352 130.72 0.37
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45
40
40 RWI 1920
35 RWI 1920
RWI 960
35
RWI 960
30
30
25
25
RWI
RWI
20
20
15
15
10 10
5 5
0 0
203 206 209 212 215 218 221 170 173 176 179 182 185 188
SELcum SELss
Figure 5 RWI values for each fish by SELcum for Figure 7 Individual RWI values by SELss.
1,920 and 960 pile strikes.
30
25
20
Number of Fish
15
10
5
0
0
2
Nu 4
mb 6
er T1
of T2 T3
inj 8 T8 T4 T5
uri 10 T9
es T7 T6 EL cum)
12 T11 T10 t (o rd e red by S
en
Treatm
Figure 6 Frequency of barotrauma injury occurrence per fish. The
number of test fish (z-axis) with number of unweighted-barotrauma
injuries (y-axis) by each treatment (x-axis). For example, in the most
severe exposure (Treatment 1 = T1), 1 fish had 13 injuries, and 10 fish
had 8 injuries. Similarly, for the least severe exposure (T11), 6 fish had
1 injury, and 24 fish had 0 injuries.
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Dotted Lines = SELcum = SELss + 10Log10(Num.Strikes)
2200
1800
Number of Strikes
1400
1000
20 20 20 20 20 21 21 21 21
0 2 4 6 8 0 2 4 6
600
170 172 174 176 178 180 182 184 186 188
A SELss
Black Lines = RWI = exp(-30.050 + 0.149*SELcum - 0.000171*Num.Strikes)-1
2200
1 2 3 4 5 6 7 8 9 10
1800
Number of Strikes
1400
1000
600
170 172 174 176 178 180 182 184 186 188
B SELss
Dotted Lines = SELcum = SELss + 10Log10(Num.Strikes)
Black Lines = RWI = exp(-30.050 + 0.149*SELcum - 0.000171*Num.Strikes)-1
2200
1 2 3 4 5 6 7 8 9 10
1800
Number of Strikes
1400
1000
20 20 20 20 20 21 21 21 21
0 2 4 6 8 0 2 4 6
600
170 172 174 176 178 180 182 184 186 188
C SELss
Figure 8 Panel A is the background layer plotting the SELcum contours
(dashed lines) by SELcum, by SELss, and number of strikes within the treatment
range. Panel B is a contour plot of ln (RWI+1) (the solid lines labeled 1-10),
which illustrates values increase as SELss increase. The upper horizontal line
indicates the 1,920 strike-line, and the bottom horizontal line indicates the
960 strike-line. Panel C is the composite of B on top of A, and shows where
the RWI contours fall over the SELcum and SELss in relation to number of
strikes. See text for further discussion.