kootenay fisheries - field report

1

KOOTENAY FISHERIES - FIELD REPORT SYSTEM: Name: Grave Lake Waterbody ID: 00176ELKR Watershed Code: 349-248100-46000-11500 DATE[s] of Field Work: Oct. 20 and Oct. 21, 2008 PERSONNEL and AFFILIATION: Kevin Heidt and Herb Tepper (MOE) BACKGROUND & OBJECTIVES: Grave Lake is located approximately 15 kilometers northeast of the community of Sparwood. Grave Lake has a surface area of 120.4 hectares, a maximum depth of 28 meters, a mean depth of 17.3 meters and is located at an elevation of 1280 meters (Fish Wizard). In 1952 and again in 1960, fish data and basic physical and water-chemistry attributes of Grave Lake were assessed (summary in Grave Lake file). The 1952 and 1960 surveys indicated that Grave Lake had relatively average productivity with total dissolved solids (TDS) readings of 190 and 245 ppm, respectively, with 19% of the lake basin being littoral area. The 1952 survey indicated that fish sampling was done in Grave Lake; however, there are no details in the file with respect to the number, length and weight of the fish caught (Grave Lake file). In June 1983, the lake was gill netted (set time, number and type of gill nets is unknown) and 11 kokanee (KO), 1 mountain whitefish (MW) and 1 rainbow trout (RB) were caught (Grave Lake file). Kokanee ranged between 230 mm and 245 mm in fork length with a mean length of 237 mm (+/- 95% CI of 3 mm), while the rainbow trout and mountain whitefish had a fork length of 215 mm and 245 mm, respectively. In August 1984, the lake was gill netted with 3 sinking nets (set time unknown) and 75 longnose suckers (LSU), 31 kokanee, 20 mountain whitefish and 4 redside shiners (RSC) were caught (Grave Lake file). Table 1 provides a summary of the fork length data collected from the August, 1984 gill net sample. Table 1. Summary of the species length data collected from the August 1984 gill netting at Grave Lake.

Species Sample Size (n)

Min Length (mm)

Max. Length (mm)

Avg. Length (mm) (+/- 95 CI)

LSU 37 102 480 282 (39) KO 31 180 299 238 (14) MW 20 160 293 214 (16) RSC 4 80 103 95 (16)

In May, 1985, the lake was gill netted (set time, number and type of gill nets is unknown) and 14 kokanee and 9 rainbow trout were measured for fork length (Grave Lake file). It is unknown how many and what other types of fish species (if any) were caught during the May 1985 gill net sampling. Kokanee ranged between 225 mm and 283 mm in fork length with a mean length of 257 mm (+/- 95% CI of 10 mm), while the rainbow trout ranged between 180 mm and 380 mm in fork length with a mean length of 268 mm (+/- 95% CI of 53 mm). In September 1985, a detailed reconnaissance survey was done on Grave Lake, which included setting two sinking gill nets in the lake for a combined set time of 7.8 hours (day time sets) (report in Grave Lake file). A total of 44 longnose suckers, 42 kokanee, 78 mountain whitefish and 5 rainbow trout

2

were caught by the two gill nets. Table 2 provides a summary of the fork length data collected from the September, 1985 gill net sample. Table 2. Summary of the species length data collected from the September 1985 gill netting at Grave Lake.

Species Sample Size (n)

Min Length (mm)

Max. Length (mm)


LSU 2 205 465 KO 31 170 314 268 (13) MW 38 125 398 224 (24) RB 5 252 304 278 (23)

A creel survey was done on Grave Lake, likely by the Sparwood Rod and Gun Club, from May 1st to August 31st, 1987 (summary in the Grave Lake file). The extrapolated results indicated that Grave Lake had 2,550 angler days, and 3,701 kokanee and 1,557 rainbow trout were caught by anglers. Finally, in October 1992, the lake was gill netted (set time, number and type of gill nets is unknown) and 4 mountain whitefish and 10 longnose suckers were measured for fork length (Grave Lake file). It is unknown how many and what other types of fish species (if any) were caught during the October 1992 gill net sampling. Mountain whitefish ranged between 260 mm and 375 mm in fork length with a mean length of 304 mm (+/- 95% CI of 80 mm), while the longnose suckers ranged between 290 mm and 420 mm in fork length with a mean length of 370 mm (+/- 95% CI of 31 mm). Grave Lake has been stocked yearly with rainbow trout since at least 1923. The historic stocking records also indicate that the lake was stocked with kokanee in 1945, 1946, 1947 and 1949 and then with Eastern brook trout in 1989 and 1990. In 2004, Grave Lake was stocked with 10,000 Blackwater 3N yearlings (YE) and then from 2005 to 2008 with 10,000 Gerrard 3N YE (Appendix 1). The most recent stocking of 10,000 YE per year represents a stocking rate of 54% of the theoretical stocking rate (TSR). The TSR is determined from the following formula: number of yearlings = TDS * ((2.47 * Littoral Area(ha)) + (0.247 * Surface Area(ha)); for fall fry determinations: two fall fry are considered equivalent to one yearling (Stringer et. al., 1980). Only the regional regulations currently apply to Grave Lake. The objectives of the 2008 assessment of Grave Lake were the following:

• Obtain current water chemistry data (Conductivity, TDS, and pH); • Sample a minimum of 60 fish utilizing standard gill nets and obtain length, weight, sex, maturity,

and age data from a minimum of 60 fish caught; and, • Utilizing condition factors obtained from length-weight relationships, evaluate the current stocking

rates and management regimes. MATERIALS & METHODS: Conductivity, TDS, pH and water temperature were measured with a YSI 63 combination meter at the water surface of the lake after the setting of the gill nets. The meter was calibrated with reference samples prior to use at each lake to assess precision and maintain accuracy.

3

Resource Inventory Committee (RIC) ninety-two meter standard experimental gill nets, consisting of six 15 X 2.5 meter variable mesh panels (ordered as 25, 76, 51, 89, 38 and 64 mm mesh sizes shoreward to lakeward), were deployed in littoral habitats and typically set perpendicular to the shoreline. As seen in Appendix 3, two sinking and two floating nets were set in Grave Lake. Net 1 (floating), net 2 (sinking), net 3 (sinking) and net 4 (floating) were set at 11:45 am, 11:50 am, 11:55 am and 12:00 pm on October 20, 2008, and retrieved at 10:55 am, 11:00 am, 10:30 am and 10:25 am on October 21, 2008, respectively. Individual fish were collected as a composite sample from all panels and CPUE was reported as fish per hour by species for each gill net. Fork lengths were obtained with a measuring board to the nearest millimeter and weights were measured to the nearest gram with an AND Model SK5001WP (0-5 kg) electronic balance. Each fish (target species only) had its’ body cavity examined for sex and maturity and a representative sample were examined for diet. A representative number of otoliths (and some scales) across the size range of the target species sampled were removed and stored in individual scale envelopes. Each otolith and/or scale was later magnified and the image printed as a hard copy and aged. Ages were assigned to length frequency distributions for the target species sampled. The condition of each fish was determined using both the Fulton’s Condition Factor (FCF) and Relative Weight (Wr) equations and then average values and 95% confidence intervals (CI) for the sample were obtained (Appendix 3). Statistical analysis of fish length, FCF and Wr utilized JMP version 7.0 statistical software, and mean comparisons between age classes, sampling years and other lakes were done using the “Tukey-Kramer” analysis (p=0.05). RESULTS & OBSERVATIONS: Analysis of the water sample taken from Grave Lake on October 30, 2008, resulted in a conductivity of 311 uS, a TDS of 218 ppm, a pH value of 8.62 and a water temperature of 9.10C. Gill net numbers 1, 2, 3 and 4 were each deployed for 23.2, 23.2, 22.6, and 22.4 hours in Grave Lake and, when retrieved, 3, 11, 4 and 11 rainbow trout were in each net, respectively, for a combined total of 29 rainbow trout. This equates to a CPUE of 0.13, 0.47, 0.18 and 0.49 for net numbers 1, 2, 3 and 4, respectively, for a combined CPUE of 0.32 for rainbow trout. In addition, 321 longnose suckers, 113 mountain whitefish, 42 kokanee and 12 redside shiners were caught in the gill nets. The CPUE for all species caught was 1.0, 6.0, 14.8 and 0.9 for net numbers 1, 2, 3 and 4, respectively, for a combined CPUE of 5.7. Appendix 4 and 5 contain individual fish records and representative photos of the fish sampled, respectively. The size distribution of rainbow trout ranged from 227 to 535 mm (mean = 348 mm; +/- 95% CI of 31 mm), with age groups ranging from 1+ to 4+ (Fig. 2 and Table 3). For ninety-three percent (n=27) of the rainbow trout sampled the sex was unknown and 7% (n=2) were mature males. All twenty-nine rainbow trout were examined for stomach content and 24% (n=7) had fish in their stomachs. Two of the rainbows with fish in their stomachs were only 2+ years old, with a forklength of 325 and 335 mm. The size distribution of the other species of fish caught is summarized in Table 3. Table 3. Summary of the species length data collected from the October 2008 gill netting at Grave Lake.

Species Total # Caught

Sample Size (n)

Min Length (mm)

Max. Length (mm)


LSU 321 33 107 450 266 (46) KO 42 36 170 258 214 (9)

4

MW 113 34 125 408 231 (23) RSC 12 12 98 112 105 (3) RB 29 29 227 535 348 (31)

Average FCF, by age class, for the sample of Grave Lake rainbows was 1.03 (+/- 95% CI of 0.03), ranging from 1.01 (+/- 95% CI of 0.03) to 1.09 (+/- 95% CI of 0.78) (Table 4). Average Wr, by age class, was 76.9 (+/- 95% CI of 2.3), ranging from 75.2 (+/- 95% CI of 2.6) to 90.0 (+/- 95% CI of 7.9). Table 4. Average Fulton’s Condition Factor (FCF) and Relative Weight (Wr) by age class, for the sample of Grave Lake rainbow trout.

Age Sample Size (n)


Min – Max Length (mm)

Avg. FCF (+/- 95 CI)

Avg. Wr (+/- 95 CI)

1+ 8 242 (10) 227 – 268 1.06 (0.11) 90.0 (7.9) 2+ 6 325 (21) 292 - 343 1.01 (0.03) 75.2 (2.6) 3+ 13 400 (13) 366 – 440 1.02 (0.03) 75.2 (2.4) 4+ 2 510 (318) 485 - 535 1.09 (0.78) 80.4 (56.3)

Total 29 348 (31) 227 - 535 1.03 (0.03) 76.9 (2.3)

Grave Lake 2008 - Length Frequency Distribution of Rainbow Trout

0%

2%

4%

6%

8%

10%

12%

14%

16%

18%

20%

200

210

220

230

240

250

260

270

280

290

300

310

320

330

340

350

360

370

380

390

400

410

420

430

440

450

460

470

480

490

500

510

520

530

540

550

Size Category (mm)

Perc

ent O

ccur

ance

Avg. Length = 348 mmRange = 227 -535 mm

n= 29

1+2+

3+

4+

Figure 2. Length frequency distribution of rainbow trout sampled in Grave Lake on October 21, 2008.

5

INTERPRETATION/CONCLUSIONS/RECOMMENDATIONS: The water chemistry results for 2008 were comparable to 1960, with a TDS of 218 and 245 ppm, respectively. The pH of Grave Lake has also remained relatively similar over time since 1985, when the pH recorded was 8.2 compared to the 2008 value of 8.6. The low CPUE of 0.3 rainbow trout caught per hour, when the results of all gill nets are combined, would indicate that the survival of rainbow trout is very poor in Grave Lake. The average FCF and Wr values of 1.03 and 76.9, respectively, indicate that the condition of the fish sampled from Grave Lake is “Average” to “Poor”. Table 5 compares average FCF, Wr and/or length from rainbow trout sampled in Grave Lake from 1983 to 2008. The average length of fish has not significantly (p=0.05) changed from 1983 to 2008; however, given the small sample sizes of rainbow trout in 1983 and 1985, this result may be questionable. Condition of the fish have significantly (p=0.05) changed between the 2008 (Avg. FCF of 1.03; +/-95% CI of 0.03) and 1985 (Avg. FCF of 1.17; +/-95% CI of 0.25) samples; however, this result may again be questionable due to the small sample size (n=5) obtained in September of 1985. Table 5. Average Fulton’s Condition Factor (FCF) and Relative Weight (Wr) and/or Length comparison from rainbow trout sampled from Grave Lake from 1983 and 2008.

Year Sample Size (n)


Min – Max Length (mm)


Avg. Wr (+/- 95 CI)

1983 1 215 N/A N/A 1985 (May)

9 268 (53) 180 - 380 N/A N/A

1985 (Sept)

5 278 (23) 252 - 304 1.17 (0.25) 87.2 (19.0)

2008 29 348 (31) 227 - 535 1.03 (0.03) 76.9 (2.3) N/A – indicates calculation was not possible as weight data was not obtained from the fish sampled.

Table 6 compares lake characteristics (TDS, surface area and % littoral area), stocking rate (number of yearling equivalents stocked per hectare and % TSR), and number of angler days per hectare (where data is available), with the condition (average FCF and Wr) of fish sampled from gill net assessments (2005 to 2008) done in Grave, Mitten, Suzanne, and Whitetail Lakes. These East Kootenay lakes range in size from 57 to 166 hectares and have all been stocked with Gerrard 3N yearlings. All four lakes contain at least one other species of fish in addition to the stocked rainbow trout. The main difference between Grave Lake and the other three lakes is that it has less shoal area and its average depth is significantly greater. When comparing the average FCF and Wr of these four lakes, only the condition of the Gerrard 3N fish from Mitten Lake is significantly (p=0.05) different than the other three lakes. These results would indicate that the condition of the Gerrard 3N rainbow trout sampled in Grave Lake is similar to Gerrards stocked in most of the other lakes in the East Kootenays and may indicate the “average” or “typical” condition of Gerrard rainbow trout that are stocked in a mixed species environment.

6

Table 6. Comparing lake characteristics, stocking rates and angler days with the condition of the Gerrard 3N strain of rainbow trout sampled in the fall of 2005 to 2008 at Grave, Mitten, Suzanne, and Whitetail Lakes. Lake TDS

(ppm) Surface

Area (ha)

% Littoral

Area # Stocked /Ha (YE)

% TSR (YE)

Angler Days /ha

Fish Sample Size (n)


Avg. Wr (+/- 95 CI)

Grave 218 120 19 83 54 N/A 29 1.03 (0.03) 76.9 (2.3) Mitten 247 65 52 124 33 15 35 1.19 (0.03) 87.9 (2.2) Suzanne 234 57 49 Varied Varied 24 17 1.05 (0.04) 77.4 (2.9) Whitetail 190 166 77 60 15 58 49 1.04 (0.03) 77.3 (2.1) The apparent poor survival of the rainbow trout in Grave Lake, indicated by the low CPUE of rainbow trout in all gill net sampling periods since 1983, likely is a result of the competition for food resources with the presence of other fish species, especially in the first year after stocking. However, given the high density of course and game fish in Grave Lake, if the stocked rainbow can survive to 2+ years old or older, they will start to utilize the abundant food source in the lake and their ability to survive should increase. Thus, a higher density of rainbow trout should ultimately be available to be caught by anglers. The following measures will be attempted over the next five years at Grave Lake in an effort to try to increase the number of rainbow trout surviving to a catchable size for anglers: The lake will be stocked at 35,000 Gerrard 3N YE per year, compared to the present 10,000 YE per

year. The Gerrard 3N YE will be stocked at a large size, preferably over 20 grams, as research has shown

that survival of yearlings stocked in lakes with course fish significantly increases if they are stocked at 20 grams or greater (Godin and Tsumura, 1999).

Grave Lake should be re-assessed in five to six years to determine if the above measures have been successful. Finally, if possible, SLIM boat counts or creel surveys should be done on a three year cycle (i.e. 3 years of counts/surveys and then 3 years without counts/surveys) at Grave Lake, so that angler effort can be monitored to determine if changes in effort occur as a result of the proposed management actions. References Godin, T.I. and K. Tsumura. 1999. Size at release comparisons of Blackwater strain rainbow trout in

monoculture and coursefish lakes (1995-1998). Ministry of Environment, Fisheries Management Report. No. 111.

Stringer, G.E., A. F. Tautz, T. G. Halsey and C. Houston. 1980. Further development and testing of a

lake stocking formula for rainbow trout in British Columbia. Ministry of Environment, Fisheries Management Report. No. 75.

Will this information be reported elsewhere? At the next Provincial Small Lake Committee meeting in Spring 2009. Prepared by: Herb Tepper Date: May 4, 2009

7

Appendix 1. Stocking Record for Grave Lake (2004 - 2008).

Date Stocked Species Stocked Stock Number

Stocked Average Size (g)

Life Cycle Stage Brood Year

2004-04-27 Rainbow Trout BLACKWATER 3N 10,000 8.9 YEARLING 2003

2005-04-27 Rainbow Trout GERRARD 3N 10,000 10.5 YEARLING 2004




8

Appendix 2. Location of the gill nets set in Grave Lake on October 20, 2008.

9

Appendix 3. Fulton Condition Factor and Relative Weight Equations.

Fulton Condition Factor (FCF)

FCF = 100,000 * ((Fish Weight (g)/(Fish Fork Length (mm))3)

Relative Weight (Wr)

Wr = (Fish Weight (g)/Ws) * 100 Where: Ws = 10 (log Ws) Log Ws = 3.024 * (Log Total Fish Length (mm)) – 5.023 Total Length = -0.027 + 1.072 * Fish Fork Length (mm) Note: Ws = Standard Weight of a Rainbow Trout

10

Appendix 4. Fish data collected from the gill nets retrieved from Grave Lake on October 21, 2008.

Species Scale # Age Length (mm)

Weight (g) Sex Maturity

Comments (condition of fish, any marks/clips, etc.)

RB 1 4+ 485 1176 M M Otolith; Empty RB 2 3+ 404 715 U IM Scale & Otolith; Empty RB 3 3+ 387 616 U IM Scale & Otolith; Fish & Beetles RB 4 3+ 423 714 U IM Otolith; Empty RB 5 3+ 418 727 U IM Otolith; Empty RB 6 3+ 390 581 U IM Otolith; Chronomid RB 7 2+ 343 401 U IM Scale & Otolith; Chronomid RB 8 2+ 292 262 U IM Scale & Otolith; Unknown RB 9 1+ 246 167 U IM Scale & Otolith; Unknown & Chronomid RB 10 1+ 243 138 U IM Otolith; Beetles & Daphnia RB 11 1+ 227 129 U IM Otolith; Unknown & Daphnia RB 12 3+ 414 766 U IM Otolith; Fish (3) RB 13 3+ 380 563 U IM Otolith; Chronomid & Daphnia RB 14 1+ 268 171 U IM Otolith; Chronomid & Unknown RB 15 1+ 235 136 U IM Otolith; Caddis & Leech RB 16 4+ 535 1767 M M Scale & Otolith; Empty RB 17 3+ 413 670 U IM Otolith; Unknown & Daphnia RB 18 3+ 366 477 U IM Otolith; Daphnia RB 19 3+ 440 925 U IM Otolith; Fish RB 20 3+ 373 492 U IM Otolith; Caddis RB 21 3+ 387 589 U IM Otolith; Fish & Caddis RB 22 2+ 343 400 U IM Otolith; Caddis & Unknown RB 23 1+ 239 144 U IM Otolith; Caddis & Daphnia RB 24 1+ 235 171 U IM Otolith; Snails, Eggs & Caddis RB 25 1+ 245 153 U IM Otolith; Chronomid & Daphnia RB 26 2+ 314 318 U IM Otolith; Empty RB 27 3+ 400 679 U IM Otolith; Fish RB 28 2+ 325 332 U IM Otolith; Fish RB 29 2+ 335 388 U IM Otolith; Fish KO 235 164 M ST KO 225 115 F ST KO 246 152 U IM KO 215 100 U IM KO 175 60 U IM KO 216 112 U IM KO 210 93 F IM KO 220 108 F IM KO 219 105 U IM KO 208 96 U IM KO 175 57 F IM KO 176 54 F IM KO 248 183 F ST KO 258 175 F SP KO 235 149 F SP KO 230 136 M ST

11

KO 235 160 M SP KO 230 121 M ST KO 230 87 F ST KO 215 108 U IM KO 235 118 F IM KO 180 59 U IM KO 175 56 U IM KO 174 56 F IM KO 170 53 U IM KO 242 132 M ST KO 224 144 M SP KO 230 159 M SP KO 230 139 M SP KO 235 136 F SP KO 221 110 M ST KO 186 63 U IM KO 225 145 M ST KO 217 112 F M KO 178 60 U IM KO 178 59 F IM MW 183 65 MW 192 61 MW 176 58 MW 180 59 MW 143 33 MW 408 615 MW 372 477 MW 340 358 MW 350 415 MW 290 270 MW 265 198 MW 280 249 MW 260 203 MW 240 142 MW 175 61 MW 207 69 MW 225 111 MW 235 137 MW 204 98 MW 250 165 MW 236 131 MW 187 67 MW 230 126 MW 185 71 MW 205 97 MW 177 53 MW 163 44 MW 200 68 MW 173 48 MW 310 327 MW 290 301

12

MW 220 96 MW 180 59 MW 125 18 RSC 110 13 RSC 112 17 RSC 112 16 RSC 100 13 RSC 104 13 RSC 98 10 RSC 104 12 RSC 102 12 RSC 102 13 RSC 108 16 RSC 102 13 RSC 104 14 LSU 420 913 LSU 410 760 LSU 404 777 LSU 450 1104 LSU 438 1161 LSU 440 1060 LSU 413 886 LSU 380 657 LSU 410 849 LSU 396 704 LSU 355 480 LSU 326 357 LSU 350 492 LSU 333 389 LSU 330 364 LSU 360 459 LSU 320 355 LSU 260 186 LSU 182 64 LSU 180 77 LSU 194 78 LSU 160 39 LSU 114 18 LSU 120 20 LSU 124 20 LSU 122 24 LSU 123 21 LSU 112 18 LSU 107 16 LSU 109 15 LSU 114 18 LSU 119 20 LSU 110 16

13

Appendix 5. Photos from the 2008 Assessment of Grave Lake. Photo 1. Photo of Grave Lake (view from south to north) on October 20, 2008. Photo 2. Representative sample of rainbow trout from Grave Lake on October 21, 2008.

14

Photo 3. The largest Gerrard (535 mm and 1767 grams) sampled from Grave Lake on October 21, 2008. Photo 4. Representative sample of longnose suckers from Grave Lake on October 21, 2008.

15

Photo 5. Representative sample of mountain whitefish from Grave Lake on October 21, 2008. Photo 6. Representative sample of kokanee from Grave Lake on October 21, 2008.

16

Photo 7. Representative sample of redside shiners from Grave Lake on October 21, 2008.

kootenay fisheries - field report

Documents