Walleye restoration and conservation in the Lake Champlain Basin 

Marking of Stocked Fish 

Like any other program measures of success are important. After stocking Walleye for a period of years LCWA and VTF&W wanted to know if their efforts were paying off. In the past, fin clipping and other methods tried just did not work well. We lost more fish using these methods that are commonly used on other species.  

It was decided that a new method, marking them with a chemical named Oxytetrcycline which is actually an antibiotic might fit the bill. The fish would be placed in the Oxytetracycline bath for an extended period. This bath would place a mark on the otolith bone of the fish.  In 1999 the program started. Fish were marked and samples were planned to be taken of 3 year old fish in the rivers. All stocked fish were marked. They were marked as fry and fingerlings giving some fish two marks. This allowed us to know if the fish were stocked as fry or fingerlings. It also told us statistically what fish in that 3 year old age class were stocked or natural production fish. 

 A difficult picture to see but if you look were the picture is marked OTC Fry Mark you can see the small round circle that was created by the OTC. As the fish grows so does his otilith bone. This fish was marked again as a fingerling and you can see the second mark created. 

Results from OTC marks have been interesting to say the least. As you will see from the tables below a few things stand out. Most importantly, the stocking program is working. It also shows us that a very large percentage of these fish are stocked fish which does not

show well for natural reproduction in our rivers. It also suggests that fingerling returns are better than fry. 

2006 Walleye OTC Marking Results Summary 

In 2006, there were 13,896,800 eggs collected from the Winooski River walleye spawning run and 1,572,500 eggs were collected from the Clyde River walleye spawning run.  All eggs from both rivers were cultured at the Bald Hill Fish Culture Station (BHFCS). 

The Winooski River eggs produced a total of 8,492,100 walleye fry with 8,297,100 fry being stocked into Lake Champlain at or near the mouth of the river.  The other 195,000 Winooski-strain walleye fry were used for advanced fry production, and resulted in 190,000 advanced fry being available for fingerling production.  110,000 advanced fry were stocked in outdoor rearing ponds at the BHFCS for fingerling production and 80,000 were supplied to the Lake Champlain Walleye Association (LCWA) for fingerling production at their Ferrisburgh (10,000), St. Albans (60,000) and Swanton (10,000) pond locations.  The BHFCS ponds produced 56,080 fingerlings, all of which were stocked into Lake Champlain off the mouth of the Winooski River.  The LCWA’s St. Albans ponds produced 49,300 fingerlings and the Swanton pond produced 4,160 walleye fingerlings.  These walleye fingerlings were also stocked off the mouth of the Winooski River.  The LCWA’s Ferrisburgh pond produced 730 walleye fingerlings which were stocked into lower Otter Creek. 

The Clyde River eggs produced a total of 743,100 walleye fry, 693,100 of which were stocked into Island Pond.  The remaining 50,000 were used for advanced fry production at the BHFCS and resulted in 40,000 advanced fry being stocked into outdoor rearing ponds at the BHFCS for fingerling production.  There were 38,400 fingerlings produced and stocked into Island Pond. 

Both strains of walleye fry received an oxytetracycline (OTC) mark at 3 or 4-days of age.  All walleye fingerlings were doubled marked, once as fry, and again as fingerlings at 43 to 46 days of age.  The only exception is the 730 fingerlings harvested from the LCWA’s Ferrisburg pond.  These were marked as fry prior to stocking into the pond, but they were not marked again as fingerlings prior to stocking into Otter Creek. 

Analysis of Grown-Out Walleye Lots 

Sub-samples of some stocked lots of walleye were kept at the Bald Hill Fish Culture Station and grown out for 7 (fry) to 10-14 (fingerlings) days.  Fish were then frozen and sent to the Rutland North District Office to be assessed for OTC mark efficacy.  OTC marks were found on all subsampled fry and fingerlings (Tables 1 and 2).
 

Table 1.  OTC mark results for grown-out sub-samples of walleye fry. 

Table 2.  OTC mark results for grown-out sub-samples of walleye fingerlings. 

 Island Pond Walleye 

Island Pond was stocked with 38,400 OTC-marked walleye fingerlings in the July of 2006.  Nighttime nearshore electrofishing was conducted during 2 nights in October 2006.  Only one (1) fall fingerling was collected, measuring 155mm in length.  The specimen was sent to the Rutland North District Office for OTC analysis in the winter of 2007.  Results for this fish are not currently available. 

Chittenden Reservoir Walleye 

                         No fall young-of-the-year walleye were collected during the standardized sampling at 6 sites in Chittenden reservoir during the fall of 2006. Chittenden Reservoir was not stocked with walleye in 2006.

 2006 Lake Champlain Walleye Spawning Run Sampling Results 

In the spring of 2006, 33 walleye between 356mm and 463mm were randomly collected between April 12 and April 26 from the Winooski River spawning run.  Sampling in this size range targeted age-3 fish in order to assess the contribution of hatchery-reared walleye from 2003 stocking efforts.  Both sagittal otoliths were removed from each walleye and mounted on glass slides with SuperGlue for OTC analysis. 

An informal creel survey was also conducted on opening day of walleye season at the Fish & Wildlife Access Area on the Missisquoi River.  Anglers who had completed their fishing trip and were leaving the river were asked if they would be amenable to providing heads from creeled walleye between 18 and 20 inches in length (457mm to 508mm).  As a result, 13 heads from walleye ranging from 464mm to 558mm were collected.  Sagittal otoliths were removed and mounted as above for OTC analysis.  Final results are not currently available from this group of fish. 

Age 

Walleye collected from the Winooski River were aged using dorsal spines.  Of the 33 walleye collected for OTC analysis, 32 were estimated as age-3 and one was estimated as age-2 (Table 3).  Targeted sampling for 3-year old spawning walleye was more successful than in the past.  No age-4 or age-5 walleye were collected and only one age-2 walleye was collected. 

OTC Marks 

Fry and fingerling OTC marks recovered on the otoliths of walleye sampled from the 2006 Winooski River spawning run indicate that nearly one-quarter of the fish sampled were hatchery-reared fish (Table 3).  Of the 33 adult walleye collected for OTC analysis, 8 (24%) were of hatchery origin.  One walleye was a fingerling-stocked 2-year old and seven walleye were 3-year olds; 5 were fry-stocked and 2 were fingerling-stocked fish. 

Table 3.  Total hatchery contribution by year-class for the Winooski River sampling, 2006. 

Figure 1a.  Percent contribution of hatchery-reared walleye sampled from the Winooski River spawning run, 2002 & 2006. 

Figure 1b.  Percent contribution of hatchery-reared walleye to specific age classes sampled from the Missisquoi, 2002-2005. 

For the first time since walleye stocking assessment using OTC marks began, a higher proportion of fry-stocked walleye were recovered from the spawning run than fingerling-stocked walleye (Table 4 and Figures 2a & 2b).  Ratios of fry- versus fingerling-stocked walleye collected in 2002 and 2006 from the Winooski River spawning run were 0% and 62.5% respectively.  Contrarily, fry-stocked walleye returns from 2002 through 2005 on the Missisquoi River were substantially lower than fingerling-stocked returns.  In 2002, 100% of the hatchery-origin walleye sampled for OTC marks had been stocked as fingerlings.  In 2003, fry-stocked walleye returns increased to 33% while fingerling-stocked fish comprised 67% of the marked fish.  In 2004, 88% of marked walleye collected were fingerling stocked, while only 12% of marked walleye were fry-stocked.  In 2005, the percentages were 87% and 13% respectively.  Reasons for such a difference in fry-stocked versus fingerling-stocked returns in 2006 in the Winooski River compared to 5 years worth of data from the Missisquoi River is unknown at this time. 

Table 4.  Summary of Hatchery Contribution by River, Year and Life Stage Stocked, 2002-2006. 

Figure 2a.  Contribution to the Winooski River spawning run of fry-stocked vs. fingerling-stocked walleye, 2002 & 2006.

Figure 2b.  Contribution to the Missisquoi River spawning run of fry-stocked vs. fingerling-stocked walleye, 2002-2005. 

2007 Walleye Sampling for OTC Assessment 

Annual adult walleye sampling for OTC mark recovery and assessment is conducted in the spring during the spawning run.  For 2007, three year old adults contributing to the Winooski River spawning run were targeted for OTC analysis, as this river was stocked with marked fish in 2004.  Twenty-nine adult walleye were collected.  Otoliths have not yet been analyzed for OTC marks and dorsal spines have not yet been aged.  These results will be presented in the next segment.

Prepared by :    Date :   August 29, 2007
Shawn P. Good, Principal Investigator
Fisheries Biologist