SECTION 8.  Refuge Pond Studies

Introduction

The Portuguese Creek Watershed Stewards identified thirty-four ponds in the rural residential and lowland agricultural areas of the watershed (Appendix A). This habitat has become the critical link for survival of coho and trout stocks in tributaries to the Tsolum River. Over the last 80 years, land development has resulted in the ditching of many natural watercourses, reducing habitat complexity and eliminating natural pool habitat.  Deep pools are important as rearing habitat for juvenile salmonids, and refuge habitat for migrating adults. Where no natural pools occur, constructed ponds offer the only shelter and cool water available to fish (Norm Sieffert, 1998). 

Nine ponds in the Portuguese Creek and Dove Creek sub-basins were monitored for temperature and dissolved oxygen concentrations during the summer and fall of 1998.

There are two basic types of refuge ponds used by salmon and trout in these sub-basins.  Instream ponds (Appendix B, Fig. B2) maintain a connection to the adjacent stream, while near-stream ponds (Appendix B. Fig. B1) have no water inflow or outflow  during months with low stream flows.  As the water level decreases in nearby streams, fry retreat into near-stream ponds where they live until water levels rise in the fall.  In summer, water levels drop in these ponds due to evaporation, and rainwater is the only source of new water.  Dissolved oxygen levels are controlled by photosynthetic activity in these ponds.

In-stream ponds have year round water flow that helps to maintain higher levels of dissolved oxygen in the pond.  Flow rates may be reduced in dry periods as water levels decline in the streams that flow though them. 

Methodology

In the spring of 1998, the Little River Enhancement Society salvaged coho, chum and cutthroat trout fry, from various locations (Little River Enhancement Society, 1998). Fry salvaged in the Tsolum River watershed were relocated to the Tsolum River mainstem or to refuge ponds near their streams of origin.  These salvaged fry added to the natural population of fish in the refuge ponds.

Water quality was sampled weekly in the nine index ponds from July 29 to September 21.  Dissolved oxygen and water temperature were measured  at three depths: surface, 0.5 m and 1.0 m. and ambient air temperature was  also recorded.  Measured physical dimensions and characterization are documented for five ponds by Raudzins, 1998.

Fish sampling occurred at five ponds in October 1998 using a  ‘Super Dave’ trawl sampler.  This is a netting device made of a light PVC box frame with one side open to capture fish as it is pulled through the pond.   Bait is thrown into the pond to entice fish into the trawl’s path and facilitate capture. 

Site Descriptions 

Results

Results of the pond fish sampling carried out October 21, 1998 are summarized in Appendix D.  Table D2 summarizes physical dimensions for five of the ponds, while  Table D3 tabulates the quantities of juvenile salmonid species sampled at these ponds.  Table D4 summarizes fry length and weight measurements.  Water quality parameters are summarized in Table D1.

Discussion

The main threats to fry survival in refuge ponds is believed to be poor water quality and predation.  This predation may be from other fish in the pond or from terrestrial predators. Survival in refuge ponds may be increased if a greater understanding of pond carrying capacity was developed.  This would require a survey of pond volume as well as regular monitoring of water quality.  Monitoring diurnal patterns of temperature and dissolved oxygen would indicate which ponds have critical oxygen shortages.

This information would be useful to groups conducting fry salvage operations for determining which ponds offer suitable summer rearing habitat and have excess capacity.  Ponds which require increased oxygenation, more shade or more refuge habitat could be enhanced to become better rearing and refuge areas for juvenile and adult salmon.

The condition index [wt (mg)/fork length (mm)3 ] is an indicator of fish health.  Optimum condition is reported with an index of approximately 1.0.  In all cases, coho fry sampled from refuge ponds in October 1998 had condition indices > 1 suggesting that pond carrying capacity had not been exceeded.

Recommendations

2. Fry sampling should be conducted in October when water temperatures are lower.  It is important that samples be taken before water levels rise in the adjacent streams to ensure that fish sampled are summer residents, and not recent migrants from the adjacent stream. 

3. Increasing pond dissolved oxygen levels is recommended for ponds 2, 29, and 30.  Pond aeration may be accomplished with mechanical aerators, oxygen cylinders, and/or with oxygenating plants.  Such plants may include the creeping underwater coontail (Ceratophyllum demersum) (Pettinger, 1996).  For pond 29 and 30, diverting stream flow to the ponds may be another method for increasing pond dissolved oxygen levels.

4. More vegetated rafts are recommended to increase riparian cover.  Earlier spring planting and initial plant maintenance will improve survival rates for plants surrounding the ponds.  It is also advisable to protect this vegetation from deer by using fencing or vexar tubes.

5. Strategic placement of logs, stumps and boulders will increase the value of refuge habitat by providing cover and shade.  Pond habitat complexing is recommended for ponds 18, 19, 20, 29 and 30. 

References

Kuta, Christine. 1999. Tsolum River E-team crew member, Comox, BC. Personal Communication, January 1999.

Little River Enhancement Society. 1998. Smolt/Fry Salvage Report.  Little River Enhancement Society, Courtenay, BC. 19 June, 1998.

Pettinger, April.  1996.  Native Plants in the Coastal Garden – A Guide for Gardeners in British Columbia and the Pacific Northwest. Whitecap Books, Vancouver, BC.

Raudzins, Ilze. 1998.  A Biophysical Assessment of Five Salmon Summer Refuge Ponds in the Portuguese Creek Watershed.  Renewal Resources 290 Course Project, Environmental Assessment Program, North Island College, Courtenay, December 7, 1998.

Sieffert, Norm. 1998.  Resident and Streamkeeper, Courtenay, BC. Personal Communication, September 1998.

Pond Photos
Refuge pond sites
Pond Study Data
 
 

Pond Photos
Refuge pond sites
Pond Study Data
 
 

Pond #	Stream Name	Pond Type	% Cover	Site Descrip- tion	UTM North	UTM East	Add- ress
2		Near- Stream	<50%	Click	5510992	355286	Sunny- dale
13		Near- Stream	>50%	Click	5515219	352563	Gunter Road
18		Near- Stream	>50%	Click	5516104	352027	Poulton Road
19		In- Stream	<50%	Click	5516227	351887	Poulton Road
20		Near- Stream	<50%	Click	5516380	351616	Poulton Road
21		In Stream	<50%	Click	5516545	351332	Merville Road
29		Near- Stream	>50%	Click	5517294	351882	N. Island Hwy.
30		Near- Stream	>50%	Click	5517247	351911	N. Island Hwy.
34	Smit Cr.	Near- Stream	<50%	Click	5508681	353048	Conden- sory Rd.

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