Results

Water Temperature Regime

6.3 Results

6.2.2 C. anoterus condition factor index

Determining a condition factor involved defining the relationship between the lengths (mm) and masses (g) ofC. anoterus. Thisrelationship is used for calculating condition factors in fish (Ricker (1968), due to allometric scaling between body mass and body length in fish (Equation 6.4a) (Ricker 1968; Peters 1983; McEwan and Hecht 1984;

Schmidt-Nielsen 1984). Condition factors were calculated by dividing mass by length, according to Equation 6.4b. A subsequent step in using the condition factor as an index of thermal change was to determine whether a trend existed between the condition factor, and downstream distance (km) along the longitudinal axis of the Sabie River. Box-and- whisker plots were used to illustrate the relationship between condition factor variability and downstream distance.

[6.4a]

[6.4b]

where M is body mass (g), L is body length (mm), a is the proportionality coefficient or intercept; b is the exponent or slope; and CF is the condition factor.

The influences of sampling date and sex, on the condition factor were tested for using one- way analyses of variance (no blocking). ANOV As of length, mass and condition versus sampling dates (May 2000, October 2000, May 200 I and May 2002); and length,mass and condition versus sex (male and female), were performed, with the hypothesis (p <0.01) that sampling dates and sex had no effect on body length, mass or condition. Results from these analyses are presented in Section 6.3.2.

May 2001 and October 2001 surveys respectively. Conversely, the abundance peaks for C.

paratus displayed an upstream movement, which appeared to stabilize in October 2001, viz. 149.10, 138.48 and 138.48 kilometres for the same sample dates, respectively.

I- ca no- Cpar

I

120

100

..

80 uc

"

..

^c

"

,Q

.. _..

60

'">

.!!

..

« ₄₀

20

0

0 20 40 60 80 100 120 140 160 180 200

Downstream distance (km)

Figure 6.3a Relativeabundance curves ofC.anoterusandC.paratusfor May 2001 electrofishing survey

I- - canooo - - ·CparOO-cano01- -CparOl I

400

350

300

..

250 uc

"

..

^c

"

,Q

.. _..

200

'">

.!!

..

150

«

100

50

0

0 20 40 60 80 100 120 140 160 180 200

Downstream distance (km)

Figure 6.~bRelative abundance curves ofC.anoterus and C.paratus for October 2000 and October 200 I electrofishmg surveys

The MWAT for C. anoterus was estimated to be 25°C. The annual frequency of exceedance of MWAT was plotted as a function of downstream distance (Figure 6.4); this relationship could be approximated by a fitted logistic equation (Equation 6.5).

I

^{_ MWAT} -MWAT simulated

I

/I ^{/ '}

V

. -4 fJ

200

sc

al

..

¹⁵⁰

~~

:l!

(;

~ 100 c!

I

iij ::l C

~ ₅₀

o

o ^{20 40 60 80 100 120 140 160 180}

Downstream distance(km)

Figure 6.4 Observed and simulated annual frequency of exceedance of a MW AT of 25°C forC.anoterus,as a function of downstream distance

[6.5]

MWAT_D *r MWAT^D+1

=

1+ (r-l)* MWAT_D

K

where MWATD+1is the MWAT atxkilometres downstream from MWATD, ris the rate of increase of MWAT with downstream distance (10\ andK is the upper limit of the 25°C MWAT for C. anoterus in the Sabie River (206²days per annum exceeding this MWAT).

Annual frequency and duration of exceedance of MWAT are shown in Table 6.2.

Frequencies and durations of MWAT exceedances were highly correlated (R²

=

0.95), so that two separate alternative logistic regression equations (Equations 6.6.a-b) were developed to calculate the probabilities of occurrence based on water temperatures metrics, rather than a single combined logistic regression. Both logistic regression models were

1Fitted value

2Derivedfrom Table 6.2 for downstream distance of 177 kilometres

significant (p < 0.05). The annual probability of occurrence (P) of C. anoterus was calculated for the annual frequency (Equation 6.6a)and cumulative annual hourly duration (Equation 6.6b) of exceedance of MWAT (x) in the range 0-206 days (Figure 6.5a) and 0- 3600 hours (Figure 6.5b) respectively. The duration and frequency of exceedance of MWAT at which the probability of not finding C. anoterus versus finding C. anoterns at a site was greater than 0.5 were 2796 hours (or 32% of the annual time) and 198 days respectively.

Table 6.2 Frequency and duration of exceedance of MW AT for C.anoterus, based on seven-day moving average of maximum daily water temperatures from 31 May 2001 to 30 June 2002.

MWATexceedances

Downstream

Duration

distancelRiver^Frequency_(hours)

30.09 0 0

57.29 0 f49

67.88 0 _~9

77.34 0 49

86.69 138 1116

97.60 138 1116

98.62 199 2269

106.58 199 2269

125.17 183 2717

138.48 183 2717

141.40 183 2717

149.14 183 2717

165.66 206 3535

177.05 206 3535

Sand River 205 2419

Marite River 107 982

e23.0-0.0117(x )

p

=

¹+^e23.0-0.0117(x)

[6.6a]

10.02-0.0036(.1)

e

p

=

1+eI0.02-0.0036(x)

[6.6b]

1.1

0.9

0.8

8~ 0.7

"_~ 0.6

'Q

~0.5 :;;

.lle0.4

...

0.3 0.2

~ \ -

\ \

\ ~

~

0.1

o

1 21 41 61 81 101 121 141 161 181 201

Frequency of MWAT exceedance

Figure 6.5a Probabilityof occurrence of C.anoterus~ith annual cumulative frequency of exceedance of MWAT

~

<,

'\. -, , . ,,

-, <,

...

o

1 201 401 601 801 1001 1201 1401 1601 1801 2001 2201 2401 2601 2801 3001 3201 3401 3601 Durationof MWAT exceedance

0.1 0.2

8~ 0.7

"

II ^0.6

'Q

~0.5 :;;

.lle0.4

...

1.1

0.8 0.9

0.3

Figure 6.5b Probability of occurrenceof C.anoteruswith cumulativeannual hourly durationof exceedance ofMWAT

6.3.1 Chiloglanis ratio of relative abundances index

While both Chiloglanid species tended to occur together more often than expected (13 observed versus 12.75 expected), there was no significant association between C. anoterus and C. paratus, and the null hypothesis of no association between these species was accepted (Table 6.3, X²=0.13; I df,p < 0.05).

Table 6.3 2x2 Species association table forC.anoterus andC.paratus, based on combined presence/absence data for all sites surveyed between May 2000 and May 2002

C. paratus

Totals Present Absent

Present 13 4 17

C. anoterus

Absent 2 1 3

Totals 15 5 20

According to the Spearman's Rank correlations (Tables 6.4-5), most sites showed a non- significant (p < 0.05) negative association between C. anoterus and C. paratus. The exceptions to this generalization were:October 2001 (non-significant positiveassociation), October 2000 (significant negative association), and the combined May data sets (significant negative association). A weak negative association appeared to exist between C. anoterus and C. paratus, which changed on an intra- and inter-annual basis. The strength of this association may be a function of different population dynamics for the two species, as they respond to different abiotic drivers in different ways, but may also be a function of electrofishing efficiency at the different sites (cf.Section 4.4.1).

Simple linear regressions of ratio versus downstream distance using both methods for calculating ratios ofC.anoterusto C.paratus (Equations 6.3a-b) were significant for each of the sampling periods. However, while the correlations tended to be weaker using Equation 6.3a (Figure 6.6a - correlations (R²⁾ for October 2000 = 0.77; October 2001: = 0.72; and May 2001: = 0.81) than those based on Equation 6.3b (Figure 6.6b- correlations (R²) for October 2000 = 0.91; October 2001 = 0.67; and May 2001 = 0.90), ratios were calculated using Equation 6.3a for the following reasons:

• The slope of the regression lines using Equation 6.3a were more similar (greater constancy) (Figure 6.6b) than the regression slopes derived using the alternative ratio calculations;

• Correlations were more consistent between years using equation 6.3a than those produced using Equation 6.3b;

• Ratios based on Equation 6.3a are intuitively easier to work with than those values using Equation 6.3b.

Consequently, Equations 6.7a-c derived from the ratios calculated using Equation 6.3a were used to calculate expected ratios for the TPC (Table 6.7). However, in spite of the significance of these regressions, data did show a marked degree of scatter, which reinforces the results of the Spearman's Rank correlations of a weak negative association between these two species.

October 2000: Ratio= -0.821(downstream distance)

+

153.12

October 2001: Ratio

=

-0.724(downstream distance)

+

151.06

May 2001: Ratio= -0.813(downstreamdistance)

+

142.28

[6.7a]

[6.7b]

[6.7c]

Site numbers''

Correlation Date I Species

Ca3 Ca4 CaS Ca6 CaS Ca9 Ca 10 Ca12 Ca 13

C. anoterus112 146 92 36 40 9 35 11 0

-0.648·

October 2000

Ciparatus 1 8 3 64 25 46 105 13 16

C.anoterus73 1 86 326 378 98 13 .43 188 5 0

October 2001 ^0.187

C.paratus 1 0 3 4 7 79 123 III 16 4

C. anoterus82 114 59 11 45

_~~¥_lIJi~.I-o.821· May 2001

Ciparatus 0 7 10 97 60

iC omb lned

Ic.

anoterus93 74 89 326 227 26 112

1-0.351

October I~aratus ^{11 14 13 14 18 172 154 185 1108 115 110}

Significantnegativeassociation (p <0.05)

#Refer to Figure 6.2

154

Site numbers'[

Date Species Correlation

3 5 21$ _{7 9 20} 11§ 19§ 14§ 26§

C.anoterus7 31 11 4 . ' "0 29 14 0 11

May 2000 -0.566

Ciparatus 0 0 0 11 ' 13 ₀ 1 5 61

C. anoterus36 32 47 40 0 0 15 34 0

•

^,'"

. ..

May 2001 .. ,." -0.371

C.paratus 0 0 0 6 0 22 0 8 29 ^{.'.... :( '"j}

jI" ,' " j~: ,t

C.anoterus20 34 61 25 1 0 31 10 0 0

May2002 -0.452

C.paratus 0 0 0 11 3 2 0 6 32 0

C. anoterus21 32 40 23 1 0 25 19 0 6

-0.759·

Combined May

C.paratus 0 0 0 9 2 12 0 5 22 31

Significant negativeassociation (p < 0.05)

#Refer to Figure 4.1 s Marite River

§SandRiver

155

• Oct20oo • Oct2001 " May2001 Linear(May2001) Linear (Oct2001) - - • Linear (Oct2oo0)

140.00.,--- - - -- - - - -- - -- - -- -- -- - -- -- - -- - - - - -- - -1

180 200

•

160

•

140 III

y =-0.82lx + 153.120 R'=0.775

120

•

100 80

=-0.724x+151.061 R' =0.719

60 40

y = ·0.813x + 149.279 R'=0.808

20

120.00+---~~~___rL---1

100.00

80.00

.:=-:;

~ 60.00

40.00

20.00

0.00 0

Downstreamdistance(km)

Figure 6.6a Ratio of relativeabundances ofC.anoterustoC.paratus,determined using Equation 6.3a, as a function of downstream distance on the Sabie River. Trend lines and their significances are shown.

• O.t-oO • O.t-ol .. May-ol- -Linea r (May-Ol)- - Linear (O.t-OO)-Linear (O.t-ol)I

4.,--- - - -- - - -- - -- - - -- - - --,

t

•

.. '"

..

•

~ y = -0.035x + 4.335

________ R'=0.900

2-t---~---'''''''''~ ~---__- - - - - - - -- - - - -- - - -- -- -__I

3+--- - - ,...:"""":--- - - - . .- - - - -- - - - - - - - -- - - - - - - - - --1

.s

-:;

~

0

20 40 60 80

-1

-2

-3

Downstream distance (km)

Figure 6.6b Ratio of relative abundances ofC. anoterus to C.paratus, determined using Equation 6.3b, as a function of downstream distance onthe Sabie River. Trend lines and their significances are shown.

6.3.2 C. anoterus condition factor index

As the initial step in calculating a condition factor index (cf. Section 6.2.2), the relationship between mass and length for C. ana/ernswas shown to be significant(n

=

360;R²= 0.85)(Figure6.7),and could be predictedby Equation 6.8.

M

=

0.1121eo.o582L

whereM is mass (g),andLis length (mm).

[6.8]

Furthermore, length and mass showed a sign ificant negati ve trend with downstream distance, with massdecreasing at a faster rate (six times) than length (Figure 6.8).

10

9

8

7

6

§

.. ....

5 ::E

4

•

3

2

0

• • ^••

20 30 40

y=0.1121eo.0^582• R =^0.8538

• •

50 length (mm)

•

60 70 80

Figure 6.7 Relationshipbetweenmass (g)and length (mm) forC.anoterus

... Mean L • MeanW - Linear(MeanL) -Unear(MeanW)I

4.50 4.00 3.50

A 3.00

I

-

2.50El

""

- - ^2.00:I:

..

•

_1.50

1.00 0.50

0.00

120.0 140.0 160.0

:A

100.0 80.0

y=-o.0966x+58.449 R' =0.6807

... 1

A

60.0 40.0

20.0

0.00-1----_---_ - - - - - - - +

0.0

60.00+---.---:-:-:::-~~ro;~----­

A

20.00t -- - -- -- - -- - - -- - - - - - -- - - - - - - -

E40.00+---=---=~~~-- .___- - - -- - ·- - - -1

§.

.c-;;,

~ 30.00+--- - - - - - - - - - - - --.•.---.~!'Iooooo,_..::::_---

70.00..---~

10.001- - - - - - - - - - - - - - - -

Downstreamdistance(km)

Figure 6.8Change in meanlengthand masswith downstreamdistance

Based on the analyses of variance to test for the effects of sampling date and sex on the lengths,masses and conditions ofC. anoterus adults,itwas shown that lengths did not vary between sampling dates,but that mass and conditiondid vary significantly (p

< 0.01) between sampling dates (Table 6.6a). Conversely, males tended to be significantly longer than females (p < 0.01), although there were no significant differences in mass or condition between male and female C. anoterus adults (Table 6.6b). The implication of these results in calculating a condition index is that data for lengths and masses of males and females for C. anoterus need not be separated in calculating a condition index. Due to the inter-annual variation in condition, conditions calculated based on data from all four electrofishing surveys were combined, althou gh it is recognized that a·more reliable relationship between condition and downstream distance should be based on data collectedat the same time each year,for a number of years.

Significant difference between sample dates (p<0.01)

Table 6.6a Summary of analysis of variance output to test for differences between length,mass and

d

r

^d

condition base on samo mz ate

Sample Sample size Mean± s.d. Mean ± s.d. Mean ± s.d.

date (n) length (mm) mass (g) condition

May 2000 61 48.12 ± 11.30 1.98 ± 1.42 1.57± 1.10

October 159 52.05 ± 9.12 2.83 ± 1.31 2.24 ± 1.02

2000

May 2001 430 50.42 ± 8.27 2.31±1.18 1.84 ± 0.92

May 2002 117 50.33 ± 10.65 2.70 ± 1.54 2.14± 1.20

F-value 0.033 <0.001 <0.001"

.

^.

Table 6.6b Summary of analysis of variance output to test for differences between length, mass and condition based on sex

Significant difference between sexes(p<0.01)

Sample size Mean ± s.d. Mean ± s.d. Mean± s.d.

Sex

(n) length (mm) mass (g) condition

Female 355 50.51 ± 8.75 2.46 ± 1.23 1.95 ± 0.98

Male 304 52.43 ± 8.56 2.68 ± 1.35 2.12± 1.04

F-value 0.005· 0.034 0.035

•

A Box-and-whisker plot (Figure 6.9) of condition factor (as a combined data set from all four electrofishing surveys; n = 629) versus downstream distance along the longitudinal axis of the Sabie River, showed that while the range in condition was greatest at the upstream sites, median condition followed a downward trend, where condition was highest at the top of the catchment, and decreased with downstream distance. Based on the trend in lengths and masses with downstream distance (Figure 6.8), this is more likely to be a function of a change in mass than a change in length.

Mean, median and modal condition factor values, calculated using combined data from all sampling occasions, were each regressed against downstream distance to determine which statistic provided the best prediction (or correlation) of the condition factor index (Figure 6.10). The mean condition factor was found to provide the best correlation with downstream distance, and was consequently chosen as the statistic by which to calculate average C. anoterus condition factors on the Sabie River.

7

6

;.,

0 5

...

~~

=

⁴

.... _... ....

0

"0

=

3 U0

2 1

0

30 57 68 77 87 98 107125 138149 166

Downstream distance(km)

Figure 6.9 Box-and-whisker plot of condition (mass to length ratio) ofC.anoterus adults versus site.

Whiskers show maximum and minimum values, while the box shows the middle 50% of the data,with the median shown as a linewithin the box.

... Mean Median 0 Mode -Linear (Mean)- Linear (Median) - - Linear (Mode)

I

3.50-,---~

--1

o

^{- -}

y=-0.0113x+2.81 R²=0.6569 0

J>..

fl"1

. . . .

2.50~---~~~---","---_j

2.00~---__.__-~"""""'~~::__-~----_+---_j 3.00~----_<~---

1.00~---1-'---n---'---""...~-__1 y=-O.0037x + 1.7056

R²=0.0682

o o

0.50+-- - - - - - - - - - - - - -- - - - _ j

180 140 160

100 120 80

40 60 20

0.00+----~---~--~---~---~---~---~---~---j

o

Downstream distance (km)

Figure 6.10 Linear regressions of condition versus downstream distance using mean, median and modal values ofC.anoteruscondition.

In calculating the linear relationship between the mean condition factors of C.

anoterus and downstream distance along the Sabie River, the May 2001 data were

used as these gave the most comprehensive distribution of sites along the longitudinal axis of the Sabie River. The October 2001 survey data were excluded from the relationship to standardize the data by time of year; additional motivating factors in choosing the May 2001 survey period were that mean conditions were available for two and three sites for the May 2000 and May 2002 survey sites respectively. Based on these data, the condition factor (CF) showed a decrease with downstream distance (Figure 6.11) (R² = 0.71). Mean condition factors ofC.anoterus remained within a ten percent envelope of the regression line between condition and downstream distance (Equation 6.9), with the exception of the site 86 kilometres downstream from the top of the Sabie River.

I ^A Mean" _. --+10%envelope _. _. --·10%env -Linear (Mean)I

3.5.---~

3+--- - - - . - - - -- - - - - - - - - - - - - - - - - - - ---1 -"

' "

2.5t - - - " " " " " " ':c--- . : . . . : . . , . . . - - - = - ; : c - - - -- - - - - - - - 1

'"

-" --.

_-'.

y=^{-0.0112x+2.8277}

R²=0.7092

..

_o

~ 2-I---:..=...-~

.!!c

~_o ^1.5+------J2-~ ;:c__--=_...=_---=..:.~~----1

o

180.0 160.0

140.0 120.0

100.0 60.0 80.0

40.0 20.0

o+----~--~---~--~--~--~---~--_--~

0.0

Downstream distance(km)

Figure 6.11 Condition index forC.anoteruswith downstream distance along the longitudinal axis of the Sabie River.

May2001: CF= -0.0112(downstream distance) +2.8277 [6.9]

The relationship between relative abundance and mean condition for the May 2001 data was approximated by a third order polynomial (Figure 6.12), although this relationshipwas not significant, which suggests that condition and abundance are not correlated.

•

^y.1EoOSx' • 0.0019x'+0.108x+0.1528 R'·0.3514

~ ^• _• --- ^•

^~

_-l

^II

I_I ---j

I I

3.5

3

2.5

~o 13 2 :!e

,g

'651.5 tJ

0.5

o

o 20 40 60

Relative abundance

80 100 120

Figure 6.12 Relationship between mean condition factor ofC.ana/erns adults, and relative abundances based on the May2001electrofishing survey in the Sabie River.

6.4 Discussion and conclusions