Abstracts of Fisheries Management Reports, Technical Circulars
and Project Reports of the Fisheries Branch

Daiva O. Zaldokas & Debra L. Aird

B.C. Fisheries Branch, 2204 Main Mall, U.B.C.,
Vancouver, B.C. V6T 1Z4

Fisheries Technical Circular No. 91
1992

1) Ludwig, B.W., and R. Clough.  1989.  Performance of trout fed a variety 
of feeds at British Columbia trout hatcheries, 1985-87.  Prov. B.C. Fish. 
Manage. Rep. No. 93:22p.
2) Parkinson, E.A., J.M.B. Hume, and R. Dolighan.  1989.  Size selective 
predation by rainbow trout on two lacustrine Oncorhynchus nerka 
populations.  Prov. B.C. Fish. Manage. Rep. No. 94:14p.
3) Ward, B.R., and J.C. Wightman.  1989.  Monitoring steelhead trout at the 
Keogh River as an index o stock status and smolt-to-adult survival:  
correlations with other data sources.  Prov. B.C. Fish. Manage. Rep. No. 
95:21p.
4) Parkinson, E.A.  1990.  An evaluation of adaptive management and 
minimal sampling as techniques for optimizing rainbow trout stocking 
rates.  Prov. B.C. Fish. Mange. Rep. No. 96:14p.
5) Oliver, G.G.  1990.  An evaluation of special angling regulations for 
cutthroat trout in the lower St. Mary river.  Prov. B.C. Fish. Mange. Rep. 
No. 97:19p.
6) Walters, C., J. DiGisi, J. Post and J. Sawada.  1991.  Kootenay Lake 
fertilization response model.  Prov. B.C. Fish. Mange. Rep. No. 98:36p.



FISHERIES MANAGEMENT REPORTS

Ludwig, B.W., and R. Clough.  1989.  Performance of trout fed a variety 
of feeds at British Columbia trout hatcheries, 1985-87.  Prov. B.C. Fish. 
Manage. Rep. No. 93:22p.

The dietary performance and cost efficiency of production diets currently 
used for culturing trout at Provincial trout hatcheries were compared to 
several other diets available in British Columbia.  Seven studies were 
conducted over three brood years at three different hatcheries.  Six starter 
diets (BioDiet, Silver Cup Softmoist, Oregon Moist Pellet (O.M.P.), Ewos 
and Rangen's Softmoist) were tested.  Of the starter and grower diets 
tested, BioDiet and BioMoist resulted in the best performance in terms of 
survival and production, while for the grower diets, Silver Cup provided 
the lowest cost per kg of fish produced. Several other diets including 
O.M.P., Ewos and Rangen showed promise but require further testing.  
BioDiet was recommended as the starter feed.  Based strictly on 
production costs, the recommended grower feed would be Silver Cup, but 
a final recommendation cannot be made until a comparison of the relative 
survival in lakes for fish fed BioDiet and Silver Cup is completed.

Parkinson, E.A., J.M.B. Hume, and R. Dolighan.  1989.  Size selective 
predation by rainbow trout on two lacustrine Oncorhynchus nerka 
populations.  Prov. B.C. Fish. Manage. Rep. No. 94:14p.

Size distributions of prey from the lake and in the diet of large (>350 mm) 
rainbow trout feeding on O. nerka were compared in two lakes.  In both 
lakes, O. nerka made up over 98% of the fish in both rainbow trout 
stomachs and midwater trawl catches.  In Kootenay Lake, where there 
were no anadromous sockeye, kokanee (the non-anadromous morph) that 
were 100 - 200 mm fork length made up 42% of trawl catches, but in 
Quesnel Lake, which supports both kokanee and a large run of 
anadromous sockeye, trawl catches consisted on 95% age-0+ O. nerka (<80 
mm fork length).  Although the size of prey in Quesnel Lake (104 mm) 
was smaller than in Kootenay Lake (139 mm), most of this difference 
appeared to be due to differences in the size of the trout predators which 
averaged 540 mm in Quesnel Lake and 713 mm in Kootenay Lake.  Few 
fry (<80 mm) were observed in the stomach samples of rainbow trout 
caught in either lake.  In both lakes, the largest prey taken by rainbow 
trout predators were less than about 1/3 of the predator length.

Ward, B.R., and J.C. Wightman.  1989.  Monitoring steelhead trout at the 
Keogh River as an index o stock status and smolt-to-adult survival:  
correlations with other data sources.  Prov. B.C. Fish. Manage. Rep. No. 
95:21p.

Population estimates of adult steelhead trout, obtained at the Keogh River 
on northern Vancouver Island, were compared to catch statistics and 
underwater fish counts collected elsewhere in British Columbia.  Also, 
survival rates from smolt-to-adult for Keogh steelhead were compared to 
rates obtained at another research station, Snow Creek, Washington.  
Similar trends were found in all comparisons.  Angler catch of wild fish in 
the Keogh River and neighbouring streams was closely correlated with the 
run size estimates of the Keogh River adult steelhead (n=13).  Annual 
catch of wild fish on Vancouver Island followed a similar trend as the 
winter run of the Keogh but the statistical correlation was weak unless 
years were sequentially paired (n=6).  Representative winter-run streams 
to the south displayed catch statistics that weakly correlated with Keogh 
run sizes unless also sequentially paired.  Of the larger rivers, there was 
close correlation between Nimpkish River catch, on northern Vancouver 
Island, but not Cowichan River catch on southern Vancouver Island, and 
Keogh run size.  Underwater counts of steelhead in two summer-run 
streams had similar trends but failed to correlate with Keogh stock size, 
even with years paired.  Survivals at the smaller Snow Creek in northwest 
Washington were similar to survivals obtained at the Keogh in 4 of 6 
years, and differences in the other two years were possibly due to smolt 
size, handling effects and anomalous oceanographic conditions.  
Implications for future stock monitoring are discussed including the 
effects of introductions of hatchery fish and regulation changes on the 
validity of use of results from the Steelhead Harvest Analysis for 
interpretation of steelhead abundance.

Parkinson, E.A.  1990.  An evaluation of adaptive management and 
minimal sampling as techniques for optimizing rainbow trout stocking 
rates.  Prov. B.C. Fish. Mange. Rep. No. 96:14p.

Following a change in stocking rate of +40% Kentucky Lake and -40% on 
Alleyne Lake, length of age-3 rainbow trout declined by over 40 mm in 
Kentucky Lake and increased by over 50 mm in Alleyne Lake.  Length at 
age 2 remained the same in Kentucky Lake but increased by 25 mm in 
Alleyne Lake.  Higher stocking rates were associated with higher ages at 
harvest but variation in stocking rate had little effect on either the length 
of creeled fish or CPUE.  An intense fishery, which rapidly removes 
recruitable sized fish was suggested to be the factor that decouples CPUE 
and fish size from stocking rate.  High variation in CPUE and length at 
capture among years suggests that more years of data collection and 
larger management perturbations will be needed if the effects of changes 
in management policy are to be detected.

Oliver, G.G.  1990.  An evaluation of special angling regulations for 
cutthroat trout in the lower St. Mary river.  Prov. B.C. Fish. Mange. Rep. 
No. 97:19p.

Annual studies of wild westslope cutthroat trout (Oncorhynchus clarki 
lewisi) were conducted at the lower St. Mary River in the East Kootenay 
for a ten year period from 1980 to 1990.  The effects of progressive fishery 
regulation changes on the population were examined by underwater 
surveys and standardized angling techniques. Age and growth 
characteristics of the cutthroat population were also documented.  After 
pollution abatement in the late 1970's, the lower river supported a largely 
unexploited fluvial trout population (adult spawning and juvenile rearing 
in tributaries; adult rearing in the mainstem river) with a mean length of 
342 mm and a range from 260 to 440 mm.  Estimated trout abundance was 
118 per km of stream  channel.  Angling regulations in 1980/81 included 
catch and possession limits of 4 fish and a 'flyfishing' only restriction for 
approximately 18.5 km.  In 1982, the total estimated population was 6400 
cutthroat trout >20 cm.  From 1984 to 1990, population trends were 
monitored using a 3.3 km "index section" of the river.  In the presence of 
an expanding fishery, numbers of catchable wild fish declined from a peak 
of 96 per km in 1986 to 47 per km in 1990.  Despite further restrictive 
regulations including a 2 fish catch limit, a bait ban, a winter trout closure 
and a 30 cm minimum size limit, the estimated population in 1989 was 
2921 fish and mean size had dropped to 271 mm in contrast to 342 mm 7-8 
years earlier.  An experimental shift in 1988 to a catch and release 
regulations on a 13 km section of river resulted in an increase in the 
proportion of larger fish after a single year although further sampling and 
counts are needed to confirm this improvement.  Only 34% of the 
population exceeded 300 mm in the section with a kill fishery, but in 
contrast 51% of the population were >300 mm within the trout release 
section, although with the small size (n=4,2) a difference could not be 
statistically confirmed.  A comparison of counts in a 4 km catch and 
release "index site" after two years however, indicated a significant 
difference as the percentage of trout >300 mm increased from 18% (prior) 
to 33% after regulation.  Future intensive management options to improve 
the age structure, and thereby fishery quality, in the kill zone include 
catch-and-release or an increased minimum size limit of 35 cm.  The latter 
would permit a small harvest of trophy fish and diversify the fishery.

Walters, C., J. DiGisi, J. Post and J. Sawada.  1991.  Kootenay Lake 
fertilization response model.  Prov. B.C. Fish. Mange. Rep. No. 98:36p.

This report describes a computer simulation model developed to make 
predications about the response of Kootenay Lake plankton and fishes to 
restoration of higher nutrient loading.  The model was developed using 
the Adaptive Environmental Assessment (AEA) workshop process, where 
a team of scientist with programming experience works with an 
interdisciplinary participant group of scientists and managers to translate 
the ideas, data, and policy concerns of that group into a working model 
for quantitative prediction.  While group ultimate aim of the AEA process 
is to produce useful models for management, the initial aim in the 
workshop development is to clarify research priorities by directing 
attention to processes that are key to the model predictions but are 
difficult to quantify, to discrepancies between historical data and model 
predictions, and to alternative hypotheses that would give the same 
predictions.

The model appears to give credible quantitative predictions of basic 
nutrient dynamics and budgets (phosphorus inputs, outputs, horizontal 
and vertical transport, epilimnetic concentration patterns, responses of 
concentration to fertilization).  However, there are major uncertainties in 
the model relationships that translate nutrient concentrations into 
predictions of phytoplankton and grazing zooplankton production, the 
utilization of zooplankton production by Mysis relicta and kokanee 
salmon (Oncorhynchus nerka), and the effect of changing kokanee and 
Gerrard rainbow trout (Oncorhynchus mykiss).

With the best available parameter estimated, the model "reconstructs" 
recent population declines in kokanee abundance as a combined effect of 
reduced food availability (on growth, fecundity, and time spent in sizes 
vulnerable to trout prediction) and depensatory predation by trout.  While 
the calculations attribute the reduced food availability partly to reductions 
in nutrient loading to the lake, the main impact is due to competition with 
Mysis for grazing zooplankters, particularly Daphnia.  The model does 
not predict favourable responses of kokanee to lake fertilization; instead it 
predicts that fertilization will mainly enhance Mysis abundance and hence 
possibly even hasten the kokanee decline.  Further, calculated prediction 
rates by Gerrard trout are presently high enough to cause further kokanee 
declines, and search efficiencies by the trout are high enough to cause 
even higher mortality rates, so the kokanee may soon be unable to recover 
even if their growth rates are substantially enhanced by fertilization.

Thus it appears that the key uncertainties now are about how the 
zooplankton community (grazer species and size composition, Mysis) will 
respond to fertilization.  At least four processes were identified that may 
counter the pessimistic baseline prediction that fertilization will enhance 
Mysis to the detriment of kokanee: (1) cannibalism preventing further 
Mysis increase; (2) increased export of Mysis over the West Arm sill under 
fertilization conditions, (3) increases in predation on Mysis by kokanee 
and other fishes; and (4) reduced relative importance of Mysis predation 
on early spring development of grazing zooplankton populations, under 
more fertile conditions.  One or more of these processes apparently does 
operate in Kennedy Lake, where K. Hyatt and K. Cooper have measured 
positive responses of both Neomysis and fish to fertilization.

All indications from the model are that the kokanee are now caught in a 
squeeze between competition and predation that will result in collapse of 
the kokanee population (and hence the prized Gerrard stock) if no action 
is taken soon to control either one or both sides of the squeeze.  Control of 
predation could not easily be accomplished by reduction in the Gerrard 
stock, due to its high recruitment rate per spawner, even if such 
reductions were politically feasible.  Control of other predators is likely 
impractical for the same reasons.  Hence it appears that the best 
management options are those related to kokanee productivity and 
competition with Mysis.

We conclude that it is  still worthwhile to conduct a major fertilization 
experiment in the lake.  It will be particularly critical during this 
experiment to closely monitor responses of Mysis (abundance, size, 
distribution, export to West Arm), grazing zooplankton (seasonal 
abundance, size distribution), growth of kokanee, and characteristics (size, 
number) of kokanee appearing in the stomachs of major predators - 
Gerrard trout, dolly varden (Salvelinus malma).

The situation with kokanee is now desperate enough, and the risk of its 
recovery being jeopardized by Mysis is high enough, that extreme options 
should now be considered to reduce Mysis abundance.  These options 
include introduction of Mysis predators (such as deep water sculpin), use 
of bubblers or hydrodynamic oscillations to push Mysis toward the 
surface near the West Arm sill, and use of high fertilizer loads near the sill 
to reduce water clarity and induce Mysis to spend more time near the 
water surface (where they are vulnerable to export over the sill). 

Parkinson, E.A. 1990.  Impaired school formation at low density: A 
mechanism for depensatory mortality in sockeye salmon.  B.C. Fish. Br., 
Fish. Mgmt. Rep. No. 99:17p.

A simple encounter model was used to simulate the process of school 
formation at dawn for different densities of juvenile sockeye salmon.  The 
results suggest that the process of school formation may be severely 
inhibited by a low encounter rate among juvenile sockeye at the lowest 
densities commonly observed in natural populations.  Encounter rates of 
predators with schools are insensitive to density because, under a given 
set of conditions, asymptotic school density is similar over a wide range of 
initial densities of prey individuals.  Enhanced school formation may 
reduce predation risk at high sockeye density and provide a mechanism 
for the multiple equilibrium hypothesis of sockeye dominance cycles.