| Juvenile/Adult Assessment | Juvenile Assessment
Stock Assessment Techniques
order to determine Vancouver Island steelhead stock status, regional fisheries
staff use a combination of assessment techniques. These vary from in-season methods
such as direct observations of adults (by snorkeling or fence/trap counts), to
post-season review of sport fishing catch and effort statistics from angler responses
to a mail-out questionnaire. Juvenile abundance in measured with electrofishing
surveys and downstream traps. The following summarizes the strengths and weaknesses
of each technique, and describes their history of use for determining abundance
trends in Vancouver Island steelhead populations:
- have been used for the enumeration of both summer and winter steelhead.
Summer steelhead surveys generally take place between August to October, when
streams are at base flows and very clear, and after most escapement has taken
place. Winter surveys generally occur between February and April during periods
of low flow and turbidity.
reaches varying in length from 6-10 km are swum by experienced crews of 2-3 biologists
and technicians, with each crew swimming about half of the survey section. In
general, the index reaches were found from earlier basin-wide surveys (1970s)
to contain a majority of adult steelhead. Summer run surveys provide a very good
indication of steelhead populations while winter run surveys provide a relative
or stock minimum abundance.
rivers like the upper Gold, Heber and Tsitika rivers, there are more than 20 consecutive
years of summer steelhead snorkel counts, using the same methods and many of the
same crew members. There are from 10-15 years of steelhead escapement counts for
another six streams, and 5-10 years of escapement observations for about another
long-term trend in combined snorkel counts from the Gold, Heber and Tsitika rivers
follows a similar pattern to that of Vancouver Island steelhead catch. Further,
snorkel counts from the Gold River correlated well with high angler catches reported
for that stream (r = .84, p<.001), even though sport caught fish are predominantly
winter steelhead. Regional staff have observed a similar correlation between snorkel
counts of winter steelhead and angler catches in the Englishman River on the Island's
east coast. Strong correlations between mean wild steelhead catch per angler day
for west coast Vancouver Island streams and snorkel counts of summer steelhead
in the Gold (r = 0.87) and Heber (r = 0.89) rivers since have also been reported.
testimony to the strength of the technique is DFO's use of provincial counts of
summer coho in the upper Gold River, done coincidentally with enumeration of summer
steelhead. DFO uses the annual Gold River count in combination with counts from
Carnation Creek and the Stamp River, as key indicators of the "health" of west
coast Vancouver Island coho stocks (K. Simpson, Coho Response Team, DFO, pers.
to use of snorkel surveys include the fact that they are labour intensive and
subject to weather and streamflow conditions. On streams with marginal water clarity
(less then 3 m), they are not recommended. Where rivers are lake-headed, or contain
many tributaries, steelhead can disperse before swims are completed. Hence they
are more useful as relative rather than absolute predictors of abundance.
Harvest Questionnaire - sent randomly to about 60% of steelhead anglers who
purchased a licence to angle for steelhead during the previous fiscal year (April
1 - March 31). Anglers are asked to report what river they fished and how many
wild and hatchery steelhead they caught, including the number released or retained.
steelhead now comprise an important part of angler catch on Vancouver Island,
and only hatchery steelhead can be legally harvested. By regulation, these must
be recorded directly on an angler's licence, whereas released fish and the number
of days spent fishing are not. This means that an angler's ability to recall individual
fishing trips and catch success will affect the reliability of data collected
by the Steelhead Harvest. Furthermore, active and successful anglers are known
to respond at a higher rate than inactive or unsuccessful anglers, consequently
population estimates derived from such procedures are generally biased upwards
(known as positive response bias).
spite of these sampling limitations, the questionnaire provides a province-wide
database of steelhead angler catch and effort, by stream, that allows for an improved
understanding of steelhead abundance trends using estimates of catch per angler.
The reliability of the questionnaire's trend data can be reinforced by other stock
assessment techniques described in this section.
Returns and Hydroacoustic Technology - for two rivers on Vancouver Island,
hatchery summer steelhead return to the hatchery site and are captured in brailer
facilities. These include DFO's Robertson Creek Hatchery on the Stamp River on
the west coast, and the Puntledge River Hatchery on the east coast. For these
two systems, brailer returns provide a convenient measure of annual escapements
for at least the hatchery summer fish. |
to the brailer do not account for hatchery steelhead remaining in the rivers,
or those taken in various fisheries downstream or at sea. At the Robertson Creek
Hatchery, steelhead return to their rearing site volitionally (i.e., swim unassisted
into the brailer), whereas Puntledge steelhead are directed into the hatchery
by an impassable fence spanning the river.
and electronic counters have been used mainly by DFO and the Pacific Salmon Commission
for enumerating salmon escapements to the Fraser River and on larger Vancouver
Island streams like the Stamp on the west coast. They work best in confined river
channels or in fish passage structures (like fishways) where flows are laminar
with little or no turbulence. They must be regularly calibrated for target fish
size and checked for performance. Based on results from a trial at the Keogh River
fence in 1998, electronic counters may have greater potential for enumerating
winter steelhead in several Island streams where fish migrate past fences or through
fishways at natural obstructions or dams (e.g., Stamp, Quinsam, Salmon, Big Qualicum
and Cowichan rivers). An important limitation to more widespread use of this technology
is its relatively high cost.
- places highly skilled anglers (regular fisheries staff and contractors) on rivers
they know well under a range of "fishable" conditions. Season-long catch per angler
day (CpAD) on each stream is generally a good indicator of trends in steelhead
run strength. Keogh run size was significantly correlated to the combined sport
catch from the neighboring Quatse and Cluxewe rivers (r = 0.66, p<.05), after
removal of an outlier for the 1985-86 datum. While regional data from broodstock
programs (exclusively) have yet to be statistically analyzed with other measures
of steelhead stock abundance (like fence and snorkel counts), similarly strong
correlations are expected.
of the limitations of this method include its relatively high cost (i.e., contracting
skilled anglers), susceptibility to weather and flow conditions, and repeat capture
rates on released fish which can significantly increase CpAD.
Guide Reports - written reports from licenced freshwater angling guides describing
results from guided fishing trips (i.e., number of angler days and catch by stream
or lake), must be submitted annually (by May 31) to WLAPs regional headquarters
in Nanaimo. This information, combined with in-season contacts between guides
and regional fisheries staff, is useful in assessing relative steelhead run strengths
in various rivers.
limitations to written guide reports include the fact they are generally received
well after the winter steelhead season has ended, and secondly, they tend to vary
in quality depending on an individual guide's business skills.
Surveys and Conservation Officer Checks - creel surveys were conducted on
several Vancouver Island rivers in the late 1970s and early 1980s. There were
extremely useful for determining in-season angler effort and catch for direct
comparison to similar estimates from the Steelhead Harvest Questionnaire. Since
the late 1980s, regional fisheries ability to undertaken comprehensive creel surveys
has been appreciably affected by budget/staff cuts and changing workload priorities.
Habitat Conservation Trust Fund supported the hiring of up to four contract employees
to undertake intensive winter steelhead stock monitoring throughout Vancouver
Island between 1998 and 2002. These technicians conducted roving creel surveys,
snorkel counts and angling to determine run strengths in various Vancouver Island
streams. This information proved invaluable in better defining winter steelhead
stock sizes, angler effort and catch rates, as well as changes in the distribution
of steelhead fishing on the Island following ongoing regulation amendments.
officer checks serve two important purposes, namely enforcement of existing sport
fishing regulations, and data acquisition on angler effort and catch. Uniformed
staff are also perceived as "ambassadors" of the ministry's steelhead conservation
message, and so serve an important angler education role as well.
alluded to previously, the primary constraint on both creel surveys and more conservation
officer involvement revolves around operational budgets and workplan priorities.
Click region on map or watershed name to view information about the Adult Stock
Assessment activities we are working on there
/ ADULT ASSESSMENT|
and Trap Counts
- fish counting fences equipped with traps capable of holding adult steelhead
are currently located on the Keogh, Quinsam and Big Qualicum rivers on the Island's
east coast. These can provide very reliable estimates of adult returns when fished
over the full run timing period.|
with any instream structure, however, there are operational problems at certain
streamflows. For example, steelhead can bypass the traps at Keogh and Quinsam
when fence panels are lifted to prevent damage during floods. Similarly, at very
low flows the fences can impede steelhead migration, leaving fish more susceptible
to natural predators (like otters and harbour seals on the Big Qualicum). ||
same fences and traps are used for sampling downstream migrating steelhead smolts
in the spring, along with comparable facilities on the Little Qualicum River (DFO's
fence at the outlet of a chum spawning channel), and on the upper Puntledge River
where BC Hydro has installed Eicher fish screens in its diversion penstocks.
from operational problems due to streamflow conditions, fences and traps are expensive
to annually operate and maintain. Consequently, the likelihood of a significant
expansion in the number of such facilities within the steelhead recovery plan
area is remote.
Population Census - uses standardized electrofishing and habitat partitioning
(net enclosures) to estimate standing stocks (densities or fish per unit area)
of juvenile steelhead in representative stream habitats. The main focus is on
fry since they are the easiest to sample based on their small size and habitat
preference (i.e., shallow riffles/glides). |
abundance can be an indicator of brood strength and the number of eggs deposited.
Sampled fry abundance and size can be compared to predicted stream carrying capacity
based on regression models developed by Conservation Section staff (Ministry of
Water, Land and Air Protection, Victoria).|
technique has experienced wide use on Vancouver Island streams over the last 20
years. It has been used for determining steelhead life histories (from scale analysis),
rearing habitat capacity, and as a measure of previous spawner abundance. Most
recently it has been used to assess the efficacy of stream fertilization (Salmon
River), conservation escapement requirements (Stamp/Somass/Sproat/Ash rivers),
and on the Keogh River to corroborate steelhead escapement estimates through the
counting fence.|| |
terms of limitations, fry counts do not reflect pre-spawning mortalities related
to fisheries or natural predation and disease. Density-independent factors like
floods and droughts can drastically reduce egg to fry survival, masking original
spawner abundance. The work is labour intensive and requires a well-trained (and
certified) crew for field sampling and data analysis.
Click region on map or watershed name to view information about the Juvenile Stock
Assessment activities we are working on there
Assessment in a Watersheds of Interest:
Ash River Watershed | Harris Creek Watershed
| Sooke River Watershed
ASSESSMENT REPORTS |
1 (Vancouver Island, Central Coast) | Region
2 (Lower Mainland)
BC Conservation Foundation 2003-2006
Princess Royal Avenue Nanaimo BC V9S 3Z7