post-fertilization diet and growth of bull trout and …...post-fertilization diet, condition, and...

POST-FERTILIZATION DIET,CONDITION, AND GROWTH OF BULL

TROUT AND RAINBOW TROUT INARROW LAKES RESERVOIR

PREPARED BY:

STEVE ARNDT, M.SC.

November 2004

COLUMBIA BASINFISH & WILDLIFECOMPENSATION

PROGRAM

www.cbfishwildlife.org

Post-Fertilization Diet, Condition, and Growth of Bull Trout

and Rainbow Trout in Arrow Lakes Reservoir

Steve Arndt, M.Sc.

Columbia Basin Fish & Wildlife Compensation Program 103-333 Victoria St., Nelson, B.C.

November 2004

Post-fertilization Diet of Rainbow and Bull trout in ALR

Executive Summary

Fish habitat and populations in Arrow Lakes Reservoir (ALR) have undergone significant changes in recent decades as a result of dam construction upstream (Mica, 1973; Revelstoke, 1984) and at the lake outlet (Hugh Keenleyside, 1969). Among other impacts, upstream dams have acted as nutrient traps, reducing the already low level of nutrients in the reservoir. In 1999, a large scale fertilization program was initiated, which aims to replace nutrients lost in upstream reservoirs to enhance the productivity of the reservoir. Post-fertilization monitoring has provided evidence of success in restoring kokanee numbers; however, little information has been available on the effects of fertilization at higher trophic levels. The objective of this study was to determine whether the quantity or species of prey has changed since the beginning of fertilization, and whether the growth rates or condition of bull trout and rainbow trout have changed.

From late winter to early summer 2003, 53 bull trout and 51 rainbow trout stomach samples were collected at Nakusp near the south end of the upper basin of ALR. Stomachs were preserved in 10% formalin for later examination, and species, length, and weight were recorded. Scales and otoliths were obtained for ageing. An additional six rainbow trout and eight bull trout samples were obtained at a fish derby on June 7-8, 2003.

Stomach analysis showed that kokanee were the primary prey species of bull trout and rainbow trout > 50 cm in 2003, as was the case prior to fertilization. Rainbow trout also fed upon winged terrestrial ants, and bull trout on Mysis shrimp. There was evidence of a slight but statistically significant increase in the number of fish prey per stomach in post-fertilization bull trout, and also the percentage of bull trout with Mysis shrimp in the stomach increased significantly from 5% pre-fertilization (Sebastian et al. 2000) to 13% in 2003. The presence of two morphs of rainbow trout was indicated by the presence/absence of kokanee in the diet corresponding to differences in length-at-age and weight-at-length. A slow-growing, primarily non-piscivorous morph reaches a maximum of ~45 cm FL, and a fast-growing piscivorous type can exceed 80 cm.

It was not possible to detect a difference in post-fertilization length-at-age with the available data, but there were substantial increases in the condition of bull trout and piscivorous rainbows. Post-fertilization bull trout were 20-30% heavier at a given length, and piscivorous rainbow trout were 17-24% heavier than pre-fertilization samples. These increases support the data suggesting increased number of prey/stomach and provide evidence that fertilization is benefiting the higher trophic levels in the ALR. These increases in condition are biologically significant and may result in more rapid recruitment to the fishery, earlier age of maturity, and perhaps greater fecundity in the predator species.

It is recommended that additional stomach samples be collected to allow a better characterization of diet over 12 months, and improved methods of age assessment be used (e.g., otolith sections). In conjunction with hydroacoustic estimates of predator numbers, these data could be used to estimate the predation rate on kokanee in the reservoir. Existing creel survey data should be used to monitor trends in predator condition factor, as this appears to be a sensitive and easily-measured indicator of prey availability.

Columbia Basin Fish & Wildlife Compensation Program ii


Acknowledgements

I would like to thank the anglers who donated samples to this study. Thanks also go to Glen and Gail Olson for collecting the stomach and age structure samples at Nakusp, and to Grant Thorp for identifying and quantifying stomach contents. Gary Carder provided otolith ages for rainbow and bull trout and Les Fleck provided scale ages for rainbow trout. Karen Bray kindly provided data from the Nakusp fish derby, and Beth Woodbridge assisted with data entry. The report was improved by comments from Harald Manson and Colin Spence on a draft. The Columbia Basin Fish and Wildlife Compensation Program is a joint initiative of BC Hydro and the Government of British Columbia (Ministry of Water, Land, and Air Protection, BC Fisheries) to conserve and enhance fish and wildlife populations affected by BC Hydro dams.

Columbia Basin Fish & Wildlife Compensation Program iii


Table of Contents Executive Summary.................................................................................................................. ii Acknowledgements.................................................................................................................. iii Table of Contents......................................................................................................................iv List of Tables and Figures ........................................................................................................v

1.0 INTRODUCTION .................................................................................................................1 2.0 METHODS ..............................................................................................................................2 3.0 RESULTS AND DISCUSSION ..............................................................................................4 3.1 Post-Fertilization Diet .....................................................................................................4

3.1.1 Bull Trout ...................................................................................................................4 3.1.2 Rainbow Trout ...........................................................................................................6 3.1.3 Comparison of Bull Trout and Rainbow Trout Diet ..................................................8

3.2 Post-Fertilization Growth and Condition .......................................................................9 3.2.1 Bull Trout ...................................................................................................................9 3.2.2 Rainbow Trout .........................................................................................................11

3.3 Pre and Post-Fertilization Diet Comparisons ..............................................................13 3.4 Pre and Post-Fertilization Growth and Condition ......................................................14

4.0 CONCLUSIONS AND RECOMMENDATIONS ...............................................................16

4.1 Recommendations ...........................................................................................................18

5.0 REFERENCES .......................................................................................................................20 6.0 APPENDICES ........................................................................................................................23

1. Data sheet for recording stomach contents 2. Relationship between bull trout length and condition factor 3. Relationship between rainbow trout length and condition factor 4. Rainbow trout length-weight relationship with exponential curve equations 5. Total weight of kokanee in stomach in relation to bull trout size 6. Chi-squared testing of number of fish prey per stomach 7. Testing pre and post-fertilization length-weight slopes for bull trout

Columbia Basin Fish & Wildlife Compensation Program iv


List of Tables and Figures

Tables

1. Comparison of the importance of kokanee in the diet of bull trout and rainbow trout in the Arrow Lakes Reservoir in 2003 ...........................................................................9

2. Comparison of K for rainbow trout less than, and greater than 50 cm in Arrow Lakes Reservoir in 2003 ............................................................................................................12

3. Comparison of bull trout diet pre- (1989-1994; n=988) and post-fertilization (2003; n=53) in the Arrow Lakes Reservoir ............................................................................14

Figures

1. Timing of the sample collections for the diet and growth study in Arrow Lakes Reservoir in 2003. ............................................................................................................ 2

2. Length distribution of bull trout and rainbow trout used for the diet and growth study in Arrow Lakes Reservoir in 2003. .................................................................... 4

3. Frequency of occurrence for prey items and number of kokanee per stomach for bull trout from Arrow Lakes Reservoir in 2003 ................................................................. 5

4. Number of kokanee per stomach and presence of Mysis relicta in relation to bull trout length in the Arrow Lakes Reservoir in 2003 ...............................................................5

5. Relationship between bull trout length and length of consumed kokanee in the Arrow Lakes Reservoir in 2003 ...................................................................................................6

6. Frequency of occurrence for prey items and number of kokanee per stomach in rainbow trout stomachs from Arrow Lakes Reservoir in 2003 .................................6

7. Number of Kokanee per stomach and presence of ants versus rainbow trout fork length in Arrow Lakes Reservoir in 2003 ......................................................................7

8. Relationship between rainbow trout fork length and length of consumed kokanee in the Arrow Lakes Reservoir in 2003 ................................................................................8

9. Length-frequency of kokanee in the diet of rainbow trout and bull trout from Arrow Lakes Reservoir in 2003....................................................................................................9

10. Length-weight relationship for bull trout sampled in the 2003 Arrow Lakes Reservoir diet study .......................................................................................................10

11. Length at age for bull trout sampled in the 2003 Arrow Lakes Reservoir diet study...........................................................................................................................................11

12. Length-weight relationship for rainbow trout with power equations for fish greater and less than 50 cm ........................................................................................................12

13. Length at age for rainbow trout sampled in the 2003 Arrow Lakes Reservoir diet study .................................................................................................................................13

14. Bull trout length-weight curves compared for pre-fertilization (1998; n=133) and post-fertilization (2003; n=263) in the upper basin of Arrow Lakes Reservoir......15

15. Rainbow trout length-weight relationships compared for pre-fertilization (1997-98; n=263) and post-fertilization (2003; n=218) in the upper basin of Arrow Lakes Reservoir ..........................................................................................................................16

Columbia Basin Fish & Wildlife Compensation Program v


1.0 INTRODUCTION Arrow Lakes Reservoir (ALR) is a large waterbody (~ 46,450 ha at full pool; Pieters et al. 2003) located on the Columbia River between Castlegar and Revelstoke in the West Kootenay Region of British Columbia. The reservoir has undergone significant changes in recent decades in terms of lake level and discharge regime, productivity, and fisheries programs. Construction of Hugh L. Keenleyside Dam at the lake’s outlet in 1969 raised the water level of Upper Arrow and Lower Arrow Lakes to create a single reservoir, and flooded the lower reaches of tributaries as well as a section of the Columbia River in the narrows between the two original lakes. Other dams (Mica, 1973; Revelstoke, 1984) blocked access to historical spawning and rearing habitats upstream, and altered discharge patterns. The upstream reservoirs also acted as nutrient traps, reducing the already low level of nutrients in the ALR (Pieters et al. 2003).

Up to 1999, efforts to mitigate the effects of the dams’ impacts on fish populations focused mainly on spawning channels for kokanee (Oncorhynchus nerka), and hatchery production for rainbow trout (O. mykiss) and bull trout (Salvelinus confluentus). However, declining kokanee numbers in the 1990s and low returns of clipped hatchery fish in the creel led to a recognition that programs simply addressing lost spawning and rearing habitat were not adequate in themselves to maintain the fish community and recreational fisheries in the reservoir. Accordingly, a large-scale fertilization program was initiated in 1999 to restore the productivity of the reservoir by replacing nutrients lost in upstream impoundments (Pieters et al. 2003). Hatchery production was discontinued in 2000, while operation of the kokanee spawning channel is ongoing.

An important goal for the lake fertilization program is restoration of the food web such that piscivorous fish populations at higher trophic levels are restored or enhanced. Initial post-fertilization assessments suggest good success in restoring kokanee numbers in the reservoir (Pieters et al. 2003; D. Sebastian, Ministry of Water, Land, and Air Protection, pers. comm.). However, apart from creel survey results, no data (population estimates or spawner counts) are available as yet to measure bull trout or rainbow trout production in the ALR. Furthermore, aquatic ecosystem structure can be regulated by both “bottom-up” and “top-down” processes (Madenjian et al. 2002), and relationships between the trophic levels are not well investigated in the ALR.

Determining the outcome of predator-prey interactions requires information on both qualitative (what fish are eating) and quantitative (how much the fish are eating) diet (Essington et al. 2001). Size-at-age and condition factor are also important parameters for interpreting relationships between trophic levels in fish communities (e.g., Madenjian et al. 2002). The objective of this study was to provide an initial post-fertilization description of diet, growth, and size-at-age for bull trout and rainbow trout in the ALR. In particular, we wanted to determine whether the quantity or species of prey has changed since the beginning of fertilization, and whether growth rates or condition factor have changed. As a preliminary study, it focused on the late winter to spring period for bull trout, and spring to early summer for rainbow trout because these are the times of year when samples are most easily obtained from the fishery. Current

Columbia Basin Fish & Wildlife Compensation Program 1

Post-fertilization Diet of Rainbow and Bull trout in ALR results were compared with pre-fertilization conditions when comparable data were available. Earlier studies that provide information on pre-fertilization growth rates and diet included McPhail and Murray (1979), Sebastian et al. (2000), and Bray (2002).

This study contributes to a better understanding of the effects of fertilization on ecological processes in the reservoir, and can be applied towards improved management of the multi-species fisheries. It will also complement other life history assessment work such as bull trout spawner and juvenile abundance indexing (which began in 2004), and help anticipate changes in aspects of piscivore population dynamics such as the age and frequency of reproduction.

2.0 METHODS From late winter to early summer in 2003 (Fig. 1), 53 bull trout and 51 rainbow trout stomach samples were collected in conjunction with a creel survey at Nakusp near the southern end of the upper basin of ALR. For rainbow trout, it was specified that 30 of the samples be from fish over 2 kg (5 lb.) reflecting that there are two types of rainbow trout in the reservoir (a smaller “non-piscivorous” stock, and a larger piscivorous stock; Sebastian et al. 2000). For bull trout, a range of sizes including smaller and larger fish in the creel was targeted. An additional six rainbow trout samples, and eight bull trout samples were obtained from a fish derby held in Nakusp on June 7-8, 2003 (Karen Bray, CBFWCP, Revelstoke, unpublished data) bringing the sample sizes to 57 and 61 for rainbow and bull trout respectively.

Jan Feb Mar April May June July Aug Sept Oct Nov Dec

0

10

20

30

40

Num

ber o

f Sto

mac

h Sa

mpl

es

Bull TroutRainbow Trout

Figure 1. Timing of the sample collections for the diet and growth study in Arrow Lakes Reservoir in 2003.

Each sample included two ageing structures (scale, otolith) and the intact stomach with its contents. Date, species, sex, fork length (FL), and weight were recorded for each sample at the time of capture and stomachs were preserved in 10% formalin (as per Bowen 1996) for later analysis. Fulton’s condition factor (K) for each fish was calculated as K = [body weight in g/(fork length in cm)3 X 100] (Anderson and Neumann 1996).


Post-fertilization Diet of Rainbow and Bull trout in ALR Examination of the stomach contents was done in October and November of 2003. Diet was quantified by recording the number, length (where possible) and weight of prey fish by species for each stomach. The estimated percentage of digestion was also recorded for prey fish. In cases where fish prey was partially digested the length of the remaining portion was recorded. Other stomach contents (e.g., aquatic or terrestrial invertebrates) were identified to order or genus if possible and counted to the nearest 10 individuals. All data were recorded on datasheets provided by CBFWCP (Appendix 1). This study assumes that the diets of angled fish collected at the Nakusp access point are representative of the populations in the upper basin, and probably the lower basin as well. For bull trout and rainbow trout, otolith photographs and age interpretations were provided by an experienced contractor (G. Carder, Salmon Arm) according to the methods in Mackey et al. (1997). Reported ages counted the outside of the otolith as the last annulus for fish caught prior to April, and designated this as “+” growth later in the season (i.e., it assumes new growth occurs in April or later). Rainbow trout ages were also assessed by a different contractor (L. Fleck, Nelson) using scale samples for comparison to the otolith ages. Asymptotic “maximum” length (Linf) for bull trout and rainbow trout was estimated visually from length at age graphs because the lack of data on younger ages resulted in negative slopes using the Walford plot method (Everhart and Youngs 1981). Length-weight regressions were calculated using the Chart-Trendline option in Microsoft ExcelTM, and the slopes of the length-weight regressions were compared using the method in Mackay et al. (1997). A pre-fertilization diet description was available from Sebastian et al. (2000); these stomach samples were also obtained from the Nakusp access point and preserved in formalin prior to examination (G. Olson, pers. comm.) Pre- and post-fertilization diets of bull trout were compared using a Chi-squared test (Zar 1974). Other statistical analyses were performed with Systat Version 10.


Post-fertilization Diet of Rainbow and Bull trout in ALR 3.0 RESULTS AND DISCUSSION Sampled bull trout ranged from 42 to 94.5 cm FL with a mean weight of 2,736 g (range 794 – 10,376 g). Rainbow trout ranged from 36 to 73 cm FL, and included 22 fish less than 2 kg and 30 greater than 2 kg1. (Fig. 2)

30 40 50 60 70 80 90 100Length (cm)

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Cou

nt

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0.1

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Proportion per B

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nt0.0

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Figure 2. Length distribution of bull trout and rainbow trout used for the diet and growth study in Arrow Lakes Reservoir in 2003.

3.1 Post-Fertilization Diet

3.1.1 Bull Trout

Kokanee were the most frequently found component of the bull trout diet (61%of all fish or 86% of non-empty stomachs), followed by the freshwater shrimp (Mysis relicta) at 13% overall (19% of non-empty stomachs). One stomach contained three redside shiners (Richardsonius balteatus) and another had one rainbow trout and two kokanee. About one quarter of the stomachs were empty (Fig. 3). The majority of bull trout feeding on kokanee had one kokanee/stomach, although up to five were found in an individual fish and the average was 1.85 kokanee/stomach. Weight of kokanee/stomach ranged from 4-136 grams with an average of 34.5 g. For fish with Mysis relicta in the stomach, amounts ranged from 20 to 50 shrimp/stomach. All sizes of sampled bull trout were feeding on kokanee, and Mysis were found in fish up to 60 cm (Fig. 4). There was no evidence of a significant positive relationship between size of bull trout and size of consumed kokanee in this sample (Fig. 5).


1 one stomach sample was lost from the larger fish


Empty29%

Mysis only8%

Other Fish3%

Mysis & Kokanee5%

33%

46%

52%

215%

134%

Kokanee only55%

Number of Kokanee per Stomach

Figure 3. Frequency of occurrence for prey items and number of kokanee per stomach for bull trout from Arrow Lakes Reservoir in 2003 (n=52).

40 50 60 70 80 90 100Bull Trout Length (cm)

-1

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Num

ber o

f Kok

anee

in G

ut

KokaneeMysis

Figure 4. Number of kokanee per stomach and presence of Mysis relicta in relation to bull trout length in the Arrow Lakes Reservoir in 2003.




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25

Leng

t h o

f Con

sum

ed K

okan

ee (c

m)

Figure 5. Relationship between bull trout length and length of consumed kokanee in the Arrow Lakes Reservoir in 2003 (regression P=0.34).

3.1.2 Rainbow Trout

The most frequent prey for rainbow trout was kokanee, occurring in 55% of all stomachs (74% of non-empty stomachs). Terrestrial insects (mainly the winged stage of carpenter ants, Camponotus spp.) were found in 18% (23% of non-empty stomachs). Ants occurred primarily in April samples although there was one fish on July 6 with ants. Twenty-six percent of rainbow trout stomachs were empty; most of these (12 of 15) were < 50 cm FL. Stomachs containing more than one prey type were not encountered. (Fig. 6)

Empty26%

Terrestrial Insects18%

218%

39%4

2%

127%Kokanee

55%

Figure 6. Frequency of occurrence for prey items and number of kokanee per stomach in rainbow trout stomachs from Arrow Lakes Reservoir in 2003.


Post-fertilization Diet of Rainbow and Bull trout in ALR Most rainbow trout that had consumed kokanee had only one in the gut, but the average was 1.77 kokanee/stomach with a maximum of 4 kokanee/stomach (Fig. 6). Weight of kokanee/stomach ranged from 6 to 84 g with an average of 28.1 g/stomach. Examination of the relationship between size of trout and diet showed that 45 to 50 cm was the approximate length at which kokanee became the primary prey of rainbow trout (Fig. 7). In other words, rainbow trout over 50 cm in the ALR have switched to pelagic piscivory (see section 3.2.2). This is not necessarily the size at which they begin feeding on kokanee; smaller rainbows (< 30 cm) with kokanee in the gut have been observed in Kootenay Lake (Andrusak and Parkinson 1984), Quesnel Lake (Sebastian et al. 2003) and Wilson Lake (J. Burrows, Kootenay Region Fisheries Biologist, pers. comm.). In Quesnel Lake, the volume percentage of kokanee in the diet increased from 10% for rainbows < 30 cm to 64 % for fish > 60 cm. The lack of kokanee prey in smaller rainbow trout in this study could be misleading if few of the smaller piscivores are caught or retained, as might be expected for anglers targeting large fish in pelagic waters using large lures. Most of the smaller rainbow trout harvested in the fishery are likely to be of the non-piscivorous type. These are usually captured using tackle and techniques suitable for kokanee and smaller rainbows. Interestingly, carpenter ants were found in an equal number of fish above and below the 50 cm length, including one fish of 62 cm (Fig. 7).

30 40 50 60 70 80Rainbow Trout Length (cm)

-1

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anee

in G

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KokaneeAnts

Figure 7. Number of Kokanee per stomach and presence of ants versus rainbow trout fork length in Arrow Lakes Reservoir in 2003. Dotted line indicates approximate point at which kokanee became the primary item in the diet.


Post-fertilization Diet of Rainbow and Bull trout in ALR There appears to be a strong positive relationship between the size of kokanee consumed and the size of rainbow trout with larger trout targeting larger kokanee (Fig. 8). This result was significant even though the measures included some partly digested kokanee.


0

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30Le

ngth

of C

onsu

med

Kok

anee

(cm

)

Figure 8. Relationship between rainbow trout fork length and length of consumed kokanee in the Arrow Lakes Reservoir in 2003. (Regression: y = 0.44x –13.67; r2= 0.45, P<0.01 )

3.1.3 Comparison of Bull Trout and Rainbow Trout Diet Diets of bull trout and rainbow trout in this study were nearly identical with respect to the presence of kokanee as prey (Table 1). Both species depend primarily on kokanee once they reach larger sizes (45 - 50 cm for rainbow trout and perhaps smaller for bull trout). In rainbow trout over 50 cm, the occurrence of kokanee was 90%. The length of kokanee found in stomachs was also similar for the two species (Fig. 9), except that there was evidence that larger rainbow trout selectively target the larger age-classes of kokanee to 25 cm. For bull trout, the predator versus prey length regression was not statistically significant, but there was still a high proportion of kokanee that were age 1 or older (> 9 cm). These results are similar to a study in Quesnel Lake (Sebastian et al. 2003), where age 1 and 2 kokanee were far more important than age 0 kokanee due to the large increase in size of older kokanee (2.1 g, 25.8 g, and 95.7 g for ages 0, 1, and 2 respectively). In that study, the total mass of kokanee/stomach was strongly related to changes in abundance of older year classes of kokanee, whereas high abundance of age 0 kokanee appeared inadequate to support growth of large rainbows.


Post-fertilization Diet of Rainbow and Bull trout in ALR Table 1. Comparison of the importance of kokanee in the diet of bull trout and rainbow trout in the Arrow Lakes Reservoir in 2003. % Occurrence Number of

Kokanee/StomachaWeight of

Kokanee/Stomachb

all samples non-empty stomachs

Mean Range Mean (g)

Range (g)

Bull Trout 61 86 1.20 0 - 5 32.7 1-136 Rainbow Trout 56 74 1.08 0 - 4 28.1 6-84 a for all fish b for fish with kokanee in stomach

0

4

8

12

16

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Length (cm)

% F

requ

ency

Rainbow TroutBull Trout

Figure 9. Length-frequency of kokanee in the diet of rainbow trout and bull trout from Arrow Lakes Reservoir in 2003.

To a lesser extent, both bull trout and rainbow trout utilized invertebrate prey. Bull trout consumed Mysis shrimp, probably obtained in deep water or as the shrimp migrate upwards under low light conditions, whereas rainbow trout fed upon terrestrial-source carpenter ants that are obtained at the surface when the ants fall into the lake during their mating flights. Thus rainbow trout appear to combine surface and pelagic feeding while bull trout combine deep (probably in some cases benthic) and pelagic feeding. The relative importance of these invertebrate foods could be under-estimated if they pass out of the gut more quickly than kokanee, as might be the case with Mysis. Carpenter ants have a more chitinous exoskeleton and might persist longer in the gut, although I am not aware of information on the rates of digestion for these prey types.


Post-fertilization Diet of Rainbow and Bull trout in ALR 3.2 Post Fertilization Growth and Condition

3.2.1 Bull Trout Bull trout K values averaged 1.18 (range 0.85 – 1.56), and the slope of the power length-weight function was > 3.0 (Fig. 10), indicating that fish become more rotund as they increase in length (Anderson and Neumann 1996; also see Appendix 2). Length at age data (Fig. 11) suggest an Linf for bull trout of about 80 cm although one fish of over 90 cm was recorded (age not available). Bull trout recruited to the fishery as early as age 3 at a length of ≈ 50 cm.

y = 0.0048x3.2186

R2 = 0.9619

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ght (

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Figure 10. Length-weight relationship for bull trout sampled in the 2003 Arrow Lakes Reservoir diet study (n= 52).



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0 2 4 6 8 10 1Otolith Age

Fork

Len

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(cm

)

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Figure 11. Length at age for bull trout sampled in the 2003 Arrow Lakes Reservoir diet study. 3.2.2 Rainbow Trout

For rainbow trout, there was a distinct upward shift in the length-weight relationship at the 50 cm mark (Fig. 12) that was not evident for bull trout (Fig. 10). The gap in length measurements between 45 and 50 cm (Fig. 12) is an artifact of the sampling instructions, but the upward shift in weight-at-length is not, and in fact occurs in data from other years (Section 3.4). The slope of the power equation was less than 3 for fish under 50 cm, indicating fish were becoming less rotund with increasing length, while for fish over 50 cm the slope was greater than 3 indicating increasing condition with increasing length (Anderson and Neumann 1996). This shift in the length-weight curve corresponds with the length at which kokanee became prevalent in the diet (Fig. 7). Fish that were feeding on kokanee were in better condition than those which were not. To illustrate the difference, the estimated weight for an intermediate-sized fish of 50 cm (using the regressions in Figure 12) is 1176 g for a non-piscivorous type and 1645 g for a piscivorous type, i.e, a 50 cm piscivorous rainbow would be about 40% heavier than a 50 cm non-piscivorous rainbow. The K values also were substantially higher for rainbow trout over 50 cm (Table 2), although this may be partially a reflection of the overall tendency for K to increase with length (Appendix 3).



y = 0.0528x2.5591

R2 = 0.6525

y = 0.003x3.3779

R2 = 0.9581

0

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7000

20 30 40 50 60 70 80Length (cm)

Wei

ght (

g)>50 cm<50 cm

Figure 12. Length-weight relationship for rainbow trout with power equations for fish greater and less than 50 cm. Note the upward shift in weight per length at 50 cm.

Table 2. Comparison of K for rainbow trout less than, and greater than 50 cm in Arrow Lakes Reservoir in 2003.

Size Class Mean (95% confidence interval)

Range N

< 50 cm 1.04 (0.97-1.11) 0.70-1.34 17 > 50 cm 1.41 (1.37-1.46) 1.20-1.71 35

Length at age for rainbow trout showed a very large degree of variability (using scale or otolith derived ages) indicating the probability of two different groups with differing life histories (G. Carder, L. Fleck, pers. comm.). Consequently, separate plots were made for fish greater and less than 50 cm based on the diet and K differences noted earlier. Growth rates of piscivorous and non-piscivorous rainbows are markedly different. Non-piscivorous fish are slow-growing and appear to reach Linf at about 45 cm; the decreasing condition with length indicates the likelihood of food-energetic limitations. Piscivorous rainbows have much faster growth rates than non-piscivores and have a much larger Linf, perhaps around 80 cm; the increasing K for larger piscivores indicates that kokanee abundance and size distributions were adequate to support the energetic demands of the number and size of predators in 2003.



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0 1 2 3 4 5 6 7 8Otolith Annulli

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Trout < 50 cmTrout > 50 cm

Figure 13. Length at age for rainbow trout sampled in the 2003 Arrow Lakes Reservoir diet study. Fish were grouped by size category because of differences in diet and condition occurring above and below 50 cm.

3.3 Pre- and Post-Fertilization Diet Comparison Sebastian et al. (2000) summarized pre-fertilization diet for a large sample (n=988) of bull trout collected from 1989-1994 at the same location as the current study (Olson’s Marina, Nakusp). Comparison of these data to the present study suggests a minor increase in the number of fish per stomach since fertilization began. Average number of fish per bull trout stomach was 1.11 fish/stomach in the pre-fertilization sample and 1.13 fish/stomach in this study (including empty stomachs). Although this difference appears negligible, there was an increase in the percentage of fish with 4 or 5 fish (Table 3). The post-fertilization frequency distribution was statistically different from the pre-fertilization sample (X2 = 11.7, P <0.05); subdivision of the categories for further analyis (as recommended by Zar 1974) showed that the difference was not significant for up to 3 fish in the gut, but the number of bull trout with 4 or 5 fish in the gut was significantly higher in the post-fertilization period (P <0.025, Appendix 6). In addition to the increase in number of fish prey, the percentage of bull trout with Mysis in the gut was significantly higher in 2003 than in the earlier period (13% and 5% of all stomachs, respectively; P <0.001). Although the length range of consumed kokanee was similar in the pre- and post-fertilization periods (most from 5-20 cm), the distribution appears much more skewed towards smaller fish in the post-fertilization sample (data not shown). This may be reflecting higher densities of younger kokanee in 2003, or differences in the sampling methods (partly digested fish were measured in 2003 and it is not known if this was the case for the pre-fertilization sample). Species composition of fish prey has remained essentially the same for bull trout since fertilization, other than the presence of redside shiner, Richardsonius balteatus, which was recorded as a prey item (in one stomach) for


Post-fertilization Diet of Rainbow and Bull trout in ALR the first time in 2003 (Table 3). Unfortunately, there are no comparable diet data from the pre-fertilization period for rainbow trout in the ALR. Table 3. Comparison of bull trout diet pre- (1989-1994; n=988) and post-fertilization (2003; n=53) in the Arrow Lakes Reservoir. Pre-fertilization data are from Sebastian et al. (2000). % by number % by number Number of fish/stomach

Pre-Fertilization

Post-fertilization

Fish Prey Species Pre-Fertilization

Post-fertilization

0

37

38

Kokanee

98.4

97.1

1 27 34 Rainbow trout 0.6 2.9 2 28 15 Sculpin spp. 0.9 0 3 5 5 Mountain whitefish 0.3 0 4 2 7 Redside shiner 0 2.9* 5 1 2

* found in one 49 cm bull trout 3.4 Pre- and Post-Fertilization Growth and Condition Length-at-age of post-fertilization bull trout in this study was similar to that of a pre-fertilization sample in Sebastion et al. (2000), except that their 1989-94 sample did not include any fish less than age 5. In the 2003 sample there were three age-3 and two age-4 fish. This may be an indication of more rapid recruitment into catchable size (approximately 50-55 cm) since fertilization. Since growth tends to slow down in older fish, an increase in length-at-age is expected to be more difficult to detect in older fish.

To compare condition of bull and rainbow trout before and after fertilization, I added additional length-weight data from the 2003 creel survey in the upper basin (Nakusp and Shelter Bay access points) to the post-fertilization diet sample, and used creel data collected at the same access points in 1997 and 1998 to represent the last years of unfertilized conditions.

Length-weight data show a strong improvement in post-fertilization condition of bull trout, as has been reported by anglers (G. Olson, creel technician, pers. comm.). Bull trout over 60 cm were 20% to 30% heavier at a given length in 2003 (Fig. 14), and differences between the slopes of the lines were significant (P ≅ 0.025, Appendix 7). The pre-fertilization slope is less than 3, indicating that fish were becoming less rotund as length increased (i.e. condition was decreasing), whereas for the 2003 fish a slope greater than 3 indicates fish becoming more rotund as length increases (Anderson and Neumann 1996). The difference in condition is also reflected in the mean K values for the 1998 and 2003 samples (0.98 and 1.18 respectively) which were also significantly different (t-test, P <0.001).



y = 0.0064x3.1493

R2 = 0.9147

y = 0.0128x2.9325

R2 = 0.9323

0

2000

4000

6000

8000

10000

12000

0 10 20 30 40 50 60 70 80 90 100

Bull trout Length (cm)

Wei

ght (

g)

20031998

Figure 14 . Bull trout length-weight curves compared for pre-fertilization (1998; n=133) and post-fertilization (2003; n=263) in the upper basin of Arrow Lakes Reservoir.

Length-at-age of rainbow trout < 50 cm in this study was comparable to pre-fertilization measurements of rainbow trout from Hill Creek and Halfway River (Sebastian et al. 2000). Unfortunately, there were not enough larger fish in their samples to allow a length-at-age comparison for piscivorous rainbows. Length-weight data, however, show evidence of an improvement in post-fertilization condition, especially for the larger rainbow trout (Fig. 15). Piscivorous rainbows were 17% to 24% heavier for a given length, and mean K was 1.22 and 1.40 for the 1997-98 and 2003 samples respectively (t-test, P=0.001). The mean K of rainbow trout < 50 cm was 1.13 and 1.10 respectively for the 1997-98 and 2003 samples (t-test, P=-.39; some outliers in the pre-fertilization sample may be errors). Examination of the pre-fertilization rainbow trout weight-at-length (Fig. 15) shows a similar upward shift at about 50 cm to that noted earlier for the 2003 sample. This lends credence to the notion that rainbow trout above 50 cm have shifted to a kokanee diet, and these piscivorous fish have a higher condition factor and growth rate than the non-piscivorous stock.



y = 0.0037x3.2829

R2 = 0.8331

y = 0.1021x2.3741

R2 = 0.8381

y = 0.0144x2.9242

R2 = 0.8957

y = 0.0028x3.3939

R2 = 0.9195

0

2000

4000

6000

8000

10000

12000

0 10 20 30 40 50 60 70 80 90

Length (cm)

Wei

ght (

g)Pre-Fertilization

Post-Fertilization

Fig 15. Rainbow trout length-weight relationships compared for pre-fertilization (1997-98; n=263) and post-fertilization (2003; n=218) in the upper basin of Arrow Lakes Reservoir. Lines are drawn separately for fish greater and less than 50 cm to separate piscivorous fish from smaller stocks.

4.0 CONCLUSIONS AND RECOMMENDATIONS Reservoir fertilization is a costly compensation initiative and its benefits should be investigated at all trophic levels. This study has demonstrated that both bull trout and larger rainbow trout are highly dependent on kokanee in the ALR as was the case prior to fertilization. Post-fertilization bull trout had a slightly higher number of kokanee and a higher frequency of Mysis in the gut than pre-fertilization fish (pre-fertilization data were not available for rainbow trout). In addition, there have been substantial increases in the weight-at-length of both bull trout and rainbow trout that corroborate the findings of increased food consumption for bull trout, and imply a similar benefit for piscivorous rainbow trout. The substantial increases in condition are biologically significant and may result in more rapid recruitment to the fishery, earlier and more frequent spawning, and perhaps greater fecundity. Shuter et al. (1998) surveyed life history attributes of 54 lake trout (Salvelinus namaycush) populations and found that lakes with higher productivity had higher growth rates early in life, younger ages at maturity, and larger size at maturity. Lake trout are a closely related char, and have a similar life history to adfluvial bull trout except that they do not normally use streams for spawning and early rearing. In summary, the results of this study are consistent with a hypothesis that higher densities of kokanee since fertilization are providing


Post-fertilization Diet of Rainbow and Bull trout in ALR benefits to higher trophic levels of the aquatic ecosystem; changes to the population dynamics of bull trout and larger rainbow trout in the reservoir should be expected. Conversely, the marked increase in the condition of predator species implies that predator populations were prey-limited prior to fertilization. Other studies that have found a relationship between prey densities and salmonid condition are Luecke et al. (1999) and Johnson and Martinez (2000). The finding of increased Mysis in the stomachs of bull trout is noteworthy. Johnson et al. (2002) found that all sizes of lake trout consumed Mysis in Granby Lake, Colorado, and that juvenile lake trout fed heavily on Mysis. In Flathead Lake, Montana, Mysis establishment appears to have improved survival of young lake trout, leading to a strong population expansion (Stafford et al. 2002). If bull trout are filling a similar niche in the ALR, fertilization-related increases in Mysis production may increase juvenile growth rates and recruitment of bull trout. An increase in bull trout abundance has been observed after Mysis introduction in Swan Lake, Montana, although the trend is confounded by changes in angling regulations (Stafford et al. 2002). Another species which is known to feed heavily on Mysis in the ALR is burbot (Lota lota) (CBFWCP, field observations). This predation may help keep Mysis densities lower than they would be otherwise, thus reducing their adverse competition effects on kokanee and smaller rainbows. As expected from other studies, Mysis contributed very little to rainbow trout diets in ALR. However, it is possible that the shallower narrows area between the upper and lower basins might be an exception since it is somewhat similar to the West Arm of Kootenay Lake, where both rainbow and kokanee are known to feed on Mysis. The narrows area is within boating range of Nakusp, but it is not known whether any of the samples were caught there. Although both rainbow and bull trout feed extensively on kokanee, they likely occupy different depths during the summer and early autumn when there is thermal stratification. Bull trout typically occupy the lower portion of the thermocline where temperatures are < 13 oC, whereas rainbows are more tolerant of temperatures up to 20 oC (Ford et al. 1995). The physiological differences between these two predators result in a wider range of habitat conditions under which kokanee are vulnerable to predation. With the available age interpretations, it was not possible to show whether there has been an increase in the length-at-age of bull trout or rainbow trout. Age interpretations did not agree well between scales and otoliths, although both methods indicated that there are two morphs of rainbow trout in the lake, a slow-growing (primarily non-piscivorous) group and a rapid-growing piscivorous stock. Disagreement between scales and otoliths may be due to missed early annulli in un-split otoliths and non-annual checks on scales. There is a need to develop and validate more reliable age assessments (see below).


Post-fertilization Diet of Rainbow and Bull trout in ALR A key question as the reservoir and its fish populations adjust to the change in productivity will be the interactions between piscivore abundance and their kokanee prey, and angler harvest. There are a number of examples of predators depressing prey populations (e.g., Rand and Stewart 1998; Johnson and Martinez 2000, and references therein), although they tend to be in systems where either the predators or prey are stocked from hatcheries. Currently, CBFWCP and WLAP are determining the feasibility of obtaining hydroacoustic estimates of predators for the ALR using existing kokanee surveys. If this method proves successful, it may be possible to estimate the predation rate on kokanee, which would be valuable for choosing best adaptive management policies. Studies on the Great Lakes have used estimates of prey production and predation rates to evaluate the sustainability of food webs and recommend changes in fisheries management strategies (e.g., Stewart and Ibarra 1991, Jones et al. 1993, Rand and Stewart 1998). 4.1 Recommendations 1. This study has provided a first approximation of the post-fertilization diet of bull

trout and rainbow trout; however, the sample size is relatively small and does not cover the whole year. If diet data are to be used at some point to estimate the predation rate, additional stomach samples should be obtained that will provide a diet description over 12 months for both species. Future sampling should be modified to obtain better data on the size distribution of kokanee prey. Length of partially digested kokanee could be approximated to the nearest cm by fitting undigested portions to template outlines of whole kokanee. Once these data are available, they should be compared to length-frequency estimates from hydroacoustic data to determine use versus availability. Volume and/or weight measurements should be obtained for all prey types.

2. Better age interpretations are needed to accurately determine growth rates, and size

at age. This may require otolith sectioning, and possibly acetate impressions (J. Casselman, Ontario Ministry of Natural Resources, pers. comm.). Size-at-age can theoretically be used to estimate consumption rates (Essington et al. 2001). Stewart and Ibarra (1991) found a biomass conversion efficiency of 16.6% and Pazzia et al. (2002) 15.8% (range 11-24%) for piscivorous lake trout.

3. Estimate the predation rate on kokanee. Once an annual diet profile (#1) and

accurate size-at-age (#2) are available, it should be possible to combine this with a hydroacoustic estimate of predator numbers and other data collected as part of limnological monitoring to estimate the predation rate on kokanee (e.g., Johnson and Martinez 2000). Currently it is assumed that the post-fertilization kokanee supply is well above predator demands in the ALR, and that the system could sustain additional predators through enhancement of rainbow trout, for example (Andrusak et al. 2004). The high condition factors of fish in this study support this view, but the assumption may not hold if predator recruitment increases appreciably in future years.



A modelling tool that can be calibrated to many coldwater species is available (Fish Bioenergetics 3.0 software for Windows, University of Wisconsin) and has been applied to estimate predator consumption rates in the Great Lakes. Given the similarities of feeding ecology and physiology of lake trout to bull trout, the energetics description developed for lake trout (Stewart et al. 1983) could serve as a starting point for calibrating the above package.

4. Continue the creel survey on the ALR including measurements of fish length and

weight. This allows changes in fish condition and size-at-age to be monitored as the ecosystem adjusts to changes in predator population dynamics, and also tracks human harvest rates on predators and their prey. A change in weight-at-length is an easily measured index that would likely be one of the first population parameters to indicate a decline in prey availability.

5. Consider adding a sampling method to catch smaller bull trout and rainbow trout in

the pelagic zone. Without sampling, we cannot determine the importance of kokanee, Mysis or other species to the diet, growth and survival at younger ages.

6. Complete a literature search for information on the digestion rates of fish, Mysis, and

terrestrial invertebrates in salmonids so that stomach content data can be better interpreted with respect to the contributions of these prey types.



5.0 REFERENCES Anderson, Richard O. and Robert M. Neumann. 1996. Length, weight, and associated

structural indices. Pages 447-482 in B.R. Murphy and D.W. Willis, editors. Fisheries Techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland.

Andrusak, H. and E.A. Parkinson 1984. Food habits of Gerrard stock rainbow trout in

Kootenay Lake, British Columbia. B.C. Ministry of Environment, Fish and Wildlife Branch, Fisheries Technical Circular No. 60, 1984.

Andrusak, H., C.R. Spence, S. Arndt, J.S. Baxter and J.A. Burrows. 2004. Arrow Lakes

Reservoir Rainbow Trout Restoration and Management Operational Plan (2004-2014). Redfish Consulting Ltd. 37 p.

Bowen, Stephen H. 1996. Quantitative Description of the Diet. Pages 513-532 in B.R.

Murphy and D.W. Willis, editors. Fisheries Techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland.

Bray, Karen. 2002. Fish Derby Summary Shelter Bay, Nakusp, and Mica 1997—2001.

Columbia Basin fish and wildlife Compensation Program, Technical Report File 138-27. 25 pp. + Appendices.

Essington, Timothy E. James F. Kitchell, and Carl J. Walters. 2001. The von Bertalanffy

growth function, bioenergetics, and the consumption rates of fish. Can. J. Fish Aquat. Sci. 58: 2129-2138.

Everhart, W. Harry and William D. Youngs. 1981. Principles of Fishery Science, 2nd

Edition. Cornell University Press. 349 pp. Ford, B.S., and 7 authors. 1995. Literature reviews of the Life History, Habitat

Requirements and Mitigation/Compensation Strategies for Thirteen Sport Fish Species in the Peace, Liard and Columbia River Drainages of British Columbia. Canadian Manuscript Report of Fisheries and Aquatic Sciences 2321. 342 p.

Johnson, B.M. and P.J. Martinez. 2000. Trophic economics of lake trout management in

reservoirs of differing productivity. North Amer. J. Fish. Manage. 20: 127-143. Johnson, B.M., P.J. Martinez, and J.D. Stockwell. 2002. Tracking trophic interactions in

coldwater reservoirs using naturally occurring stable isotopes. Trans. Amer. Fish. Soc. 131: 1-13

Jones, M.L., Koonce, J.F., and R. O’Gorman. 1993. Sustainability of hatchery-dependent

salmonine fisheries in Lake Ontario: the conflict between predator demand and prey supply. Trans. Am. Fish. Soc. 122: 1002-1018.


Post-fertilization Diet of Rainbow and Bull trout in ALR Luecke, C., M.W. Wengert, and R.W. Schneidervin. 1999. Comparing results of a

spatially explicit growth model with changes in the length-weight relationship of lake trout (Salvelinus namaycush) in Flaming Gorge Reservoir. Can. J. Fish. Aquat. Sci 56: 162-169.

Mackay, W.C., G.R. Ash, and H.J. Norris (eds) 1997. Fish ageing methods for Alberta

(2nd edition). R.L. & L. Environmental Services Ltd. in association with Alberta Fish & Wildl. Div. And University of Alberta, Edmonton. 113 p.

Madenjian, Charles. P. and fourteen other authors. 2002. Dynamics of the Lake

Michigan food web, 1970-2000. Can. J. Fish Aquat. Sci. 59: 736-753. Martinez, P.J. and W.J. Wiltzius. 1995. Some factors affecting a hatchery-sustained

kokanee population in a fluctuating Colorado reservoir. North Amer. J. Fish. Manage. 15: 220-228.

McPhail, J.D. and C.B Murray. 1979. The Early Life History and Ecology of Dolly

Varden (Salvelinus malmo) in the Upper Arrow Lakes. Report to BC Hydro and Ministry of Environment, Fisheries Branch, Department of Zoology and Institute of Animal Resource Ecology, UBC. 113 pp.

Pieters, Roger and 13 other authors. 2003. Arrow Reservoir Fertilization Experiment

Year 3 (2001/2002) Report. Fisheries Report No. RD 103. Rand, P.S. and D.J. Stewart. 1998. Prey fish exploitation, salmonine production, and

pelagic food web efficiency in Lake Ontario. Can J. Fish. Aquat. Sci. 55: 318-327. Sebastian, D., H. Andrusak, G. Scholten and L. Brescia. 2000. Arrow Reservoir Fish

Summary. Stock Management Report – 2000. Province of British Columbia, Ministry of Fisheries. 106 pp.

Sebastian, D. , R. Dolighan, H. Andrusak, J. Hume, P. Woodruff, and G. Scholten. 2003.

Summary of Quesnel Lake Kokanee and Rainbow Trout Biology with Reference to Sockeye Salmon. Stock Mgmt Rep. No. 17. 109 pp.

Shuter, B.J. , M.L. Jones, R.M. Korver, and N.P. Lester. 1998. A general, life history based

model for regional management of fish stocks: the inland lake trout (Salvelinus namaycush) fisheries of Ontario. Can J. Fish. Aquat. Sci. 55: 2161-2177.

Stafford, C.P., J.A. Stanford, and F.R. Hauer. 2002. Changes in lake trout growth

associated with Mysis relicta establishment: a retrospective analysis using otoliths. Trans. Amer. Fish. Soc. 131: 994-1003.


Post-fertilization Diet of Rainbow and Bull trout in ALR Stewart, D.J. and M. Ibarra. 1991. Predation and production by salmonine fishes in Lake

Michigan, 1978-88. Can. J. Fish. Aquat. Sci. 48: 909-922. Stewart, D.J., Weininger, D., Rottiers, D.V., and Edsall, T.A. 1983. An energetics model

for lake trout, Salvelinus namaycush: application to the Lake Michigan population. Can. J. Fish. Aquat. Sci. 40: 681-698.

Zar, J.H. 1974. Biostatistical Analysis. Prentice-Hall, Inc. 620 p.



6.0 Appendices



Appendix 1. Stomach Contents Data Sheet - 2003

Stomach Contents Stomach Sample

#

Date Collected Fish

Species Total No. in Gut

Fork Lengths (cm)

Invertebrate Type

Quantity (volume/number)

Other Prey Comments


Post-fertilization Diet of Rainbow and Bull trout in ALR Appendix 2. Relationship between bull trout length and condition factor (adjusted

r2=0.09).


0.8

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

Con

ditio

n Fa

ctor

Appendix 3. Relationship between rainbow trout length and condition factor (adjusted

r2=0.61).


0.5

1.0

1.5

2.0

Con

ditio

n Fa

cto r


Post-fertilization Diet of Rainbow and Bull trout in ALR Appendix 4. Rainbow trout length-weight relationship with exponential curve equations.

y = 107.6e0.0554x

R2 = 0.963

y = 53.268e0.0629x

R2 = 0.66630

1000

2000

3000

4000

5000

6000

7000

20 30 40 50 60 70 80Length (cm)

Wei

ght (

g)>50 cm<50 cm

Appendix 5. Total weight of kokanee in stomach in relation to bull trout size.


0

50

100

150

Koka

nee

Stom

ach

Con

ten t

s (g

)



Appendix 6. Chi-squared Testing of Number of fish prey per stomach. Methods from Zar (1974) p.47-48

Test 1. All categories Fish/gut Pre-fert % Post-fert no. Expected Post-fert Obs-Exp squared (obs-exp)^2/exp

0 37 23 22.57 0.1849 0.00821 27 21 16.47 20.5209 1.24602 28 9 17.08 65.2864 3.82243 5 3 3.05 0.0025 0.00084 2 4 1.22 7.7284 6.33485 1 1 0.61 0.1521 0.2493

100 61 61 11.6615

Expected frequency Ho: assumes no change from pre-fertilization

Chi-squared = 11.6615 d.f.= 6-1 = 5 5 0.025<P<0.050 Ho rejected; Post-fert frequencies are not the same.

Test 2. Ho: There is no difference from 0 to 3 fish/gut

Chi-squared= 5.0774 d.f.=4-1=3 3

0.10<P<0.25 Ho accepted, differences not statistically significant

Test 3. Ho: There is no difference in number of fish with 4 or 5 fish in gut

Fish/gut Pre-fert % Post-fert no. Expected Post-fert Obs-Exp squared

(obs-exp)^2/exp

3 or less 97 56 59.17 10.0489 0.16984 or 5 3 5 1.83 10.0489 5.4912

61 61 5.6610

Chi-squared= 5.6610 d.f.=2-1=1 1

0.010<P<0.025 Ho rejected, there are more fish with 4 or 5 in gut than there were pre-fertilization

Test 4. Ho: There is no difference from 0 to 2 fish/gut

Chi-squared= 5.0765 d.f.=3-1=2 2

0.05<P<0.10 Ho accepted, no difference in number with 0-2 fish/gut

Test 5. Ho: There is no difference in number of fish with 3 to 5 fish in gut

Fish/gut Pre-fert % Post-fert no. Expected Post-fert Obs-Exp squared

(obs-exp)^2/exp

2 or less 92 53 56.12 9.7344 0.17353 to 5 8 8 4.88 9.7344 1.9948

61 61 2.1682

Chi-squared= 2.1682 d.f.=2-1=1 1

0.10<P<0.25 Ho accepted; no difference 3-5 fish


Post-fertilization Diet of Rainbow and Bull trout in ALR Appendix 7. Testing Pre and Post-Fertilization length-weight slopes for bull trout.

1998 SUMMARY OUTPUT (from Bull Length-Wt 98-03.xls)

Regression Statistics Multiple R 0.965553 R Square 0.932292 Adjusted R Square 0.931779 Standard Error 0.060172 Observations 134

∑ x2 = 0.765254

∑ y2 = 7.05862

∑ xy = 2.244082 n = 134

ANOVA

df SS MS F Significance F Regression 1 6.580695 6.580695 1817.549 4.76E-79 Residual 132 0.477925 0.003621 Total 133 7.05862

Coefficie

nts Standard

Error t Stat P-value Lower

95% Upper 95%

Intercept -1.89242 0.120488 -15.7063 5.29E-32 -2.13075 -1.65408 X Variable 1 2.932467 0.068784 42.63273 4.76E-79 2.796405 3.068529

2003 SUMMARY OUTPUT (from Bull Length-Wt 98-03.xls)

Regression Statistics Multiple R 0.956387525 R Square 0.914677098 Adjusted R Square 0.91435019 Standard Error 0.072556201 Observations 263

∑ x2 = 1.485151

∑ y2 = 16.10364

∑ xy = 4.677148

n = 263

ANOVA Df SS MS F Significance F

Regression 1 14.72962738 14.72963 2797.968 1.6462E-141 Residual 261 1.374008985 0.005264 Total 262 16.10363636

Coefficients Standard Error t Stat P-value Lower 95% Upper 95%

Intercept -2.1934284 0.103583719 -21.1754 1.33E-58 -2.397394315 -1.98946X Variable 1 3.149275198 0.059537318 52.89582 1.6E-141 3.032040718 3.26651

COMPARISON OF SLOPES (from Appendix A, Mackay et al. 1990):


post-fertilization diet and growth of bull trout and …...post-fertilization diet, condition, and...

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