Keogh River Research Articles

Salmon egg subsidies and interference competition among stream fishes

Resource availability may modulate interference interactions among competitors. For example, competition among stream fishes for drifting eggs from salmon (Oncorhynchus spp.) spawning events may be influenced by the availability of this energy-rich food source. This study used camera-based techniques to evaluate the effect of varied prey availability (i.e., pink salmon (O. gorbuscha) eggs) on rates of interference competition within natural stream fish communities at 10 sites. Aggressive interactions were quantified across different levels of egg additions, ranging from 6 to 3575 O. gorbuscha eggs, at 10 sites on the Keogh River, British Columbia, Canada. There were fewer aggressive interactions among salmonids (O. kisutch, O. mykiss, and O. clarkii clarkii) when there were more available eggs. Aggressive interaction rates were species-dependent; for example, the number of aggressive acts relative to null expectations based on abundances were highest in juvenile coho (O. kisutch) towards conspecifics. For some interactions, size of fish appeared to be a key factor as well. Thus, higher densities of spawning salmon in streams may provide sufficient prey resources in the form of eggs to temporarily decrease interference competition among stream fishes.

The roles of extrinsic and intrinsic factors in the freshwater life‐history dynamics of a migratory salmonid

AbstractKey life‐cycle transitions, such as metamorphosis or migration, can be altered by a variety of external factors, such as climate variation, strong species interactions, and management intervention, or modulated by density dependence. Given that these life‐history transitions can influence population dynamics, understanding the simultaneous effects of intrinsic and extrinsic controls on life‐history expression is particularly relevant for species of management or conservation importance. Here, we examined how life histories of steelhead (Oncorhynchus mykiss) are affected by weather, pink salmon abundance (Oncorhynchus gorbuscha), experimental nutrient addition, and density‐dependent processes. We tested for impacts on the size of steelhead smolts (juveniles migrating to the sea), as well as their age and abundance across four decades in the Keogh River, British Columbia, Canada. Larger steelhead smolts were associated with warmer years and artificial nutrient addition. In addition, higher pink salmon abundance and artificial nutrient addition correlated with juvenile steelhead migrating at younger ages. While density dependence appeared to be the primary factor regulating the abundance of steelhead smolts, nutrient addition and temperature were positively and negatively associated with smolt production, respectively, prior to 1991, and pink salmon spawning abundance was positively associated with smolt production after 1990. Thus, this study provides evidence that the temporal dynamics of one species of salmon is linked to the juvenile life history of co‐occurring steelhead. A complex interplay of species interactions, nutrient subsidies, density dependence, and climatic variation can control the life‐history expression of species with complex life cycles.

Declining patterns of Pacific Northwest steelhead trout (Oncorhynchus mykiss) adult abundance and smolt survival in the ocean

Examination of population abundance and survival trends over space and time can guide management and conservation actions with information about the spatial and temporal scale of factors affecting them. Here, we analyzed steelhead trout (anadromous Oncorhynchus mykiss) adult abundance time series from 35 coastal British Columbia and Washington populations along with smolt-to-adult return (smolt survival) time series from 48 populations from Washington, Oregon, and the Keogh River in British Columbia. Over 80% of the populations have declined in abundance since 1980. A multivariate autoregressive state-space model revealed smolt survival four groupings: Washington and Oregon coast, lower Columbia River, Strait of Juan de Fuca, and Puget Sound – Keogh River populations. Declines in smolt survival rates were seen for three of the four groupings. Puget Sound and Keogh River populations have experienced low rates since the early 1990s. Correlations between population pairs’ time series and distance apart illustrated that smolt survival rates were more positively correlated for proximate populations, suggesting that important processes, including those related to ocean survival, occur early in the marine life of steelhead.

Postsmolt Growth More Important than Initial Growth at Sea; Cluster Sampling Made Easy

WINNER: Best Paper, Marine and Coastal FisheriesOver the last 20–30 years, the abundance of steelhead Oncorhynchus mykiss in the Keogh River, British Columbia, has declined substantially. Increased...

Implications of spatial contraction for density dependence and conservation in a depressed population of anadromous fish

Changes in density-independent mortality can alter the spatial extent of populations through patch extinction and colonization, and spatial contraction may alter population productivity and compensatory capacity. Here, we analyze a time series of steelhead (Oncorhynchus mykiss) abundance and examine the hypothesis that spatial contraction can decrease compensatory capacity. Over the last 20 years, steelhead in the Keogh River have declined by an order of magnitude because of a period of poor smolt-to-adult survival. Low abundance has been associated with more depressed production of out-migrating smolts than would be expected based on traditional models of compensatory dynamics. Patterns of juvenile density over time show changes in the spatial distribution of the population. We developed a spatially explicit population model to explore spatial structure and juvenile recruitment under varying marine survival. Results suggest that spatial contraction during a period of poor marine survival can strengthen density-dependent population regulation, reducing smolt production at the watershed scale. Our results highlight that spatial contraction can alter the fundamental density-dependent relationships that define population dynamics, recovery trajectories, and sustainable harvest levels of spatially structured populations.

Postsmolt Growth and Thermal Regime Define the Marine Survival of Steelhead from the Keogh River, British Columbia

AbstractThe population of anadromous steelhead Oncorhynchus mykiss in the Keogh River has been studied intensively, in part because of its pattern of declining recruitment, which is largely attributed to poor marine survival. Climate variability has changed the productivity of salmonid species in all regions of the North Pacific, with areas alternately shifting between periods of enhanced and depressed productivity. The mechanisms governing marine survival and adult recruitment are central to contemporary resource management concerns but are also of concern with regard to the long‐term prospects of managing biodiversity. We provide evidence that postsmolt growth contributes to the pattern of marine survival of Keogh River steelhead over the period corresponding to smolt years 1977–1999. Size at ocean entry did not appear to have sufficient contrast to significantly affect survival. However, assessment of scale growth suggested that the fish's initial growth at sea is not as important as the sustained growth conditions during summer and fall of the postsmolt year. The return rate of steelhead was negatively correlated with sea surface temperature in the ocean domains that were assumed to provide postsmolt nursery habitat, suggesting that growth is directly affected by warming conditions or that ocean warming affects the food web upon which steelhead depend. Steelhead appear to respond to changing climate and growth regimes in a manner similar to that of their North Atlantic analog, the Atlantic Salmon Salmo salar. Comparative data show that eastern basin Atlantic Salmon populations are negatively affected by a thermal regime of increasing temperature during the postsmolt year, suggesting a relationship between postsmolt growth and survival.Received August 14, 2013; accepted October 17, 2013

Declivity in steelhead (Oncorhynchus mykiss) recruitment at the Keogh River over the past decade

Survival and return of unharvested winter-run steelhead (Oncorhynchus mykiss) at the Keogh River, British Columbia, declined abruptly and remained persistently low after 1990. Adult returns averaged 1168 fish from 1976 to 1990 but were significantly lower from 1991 to 1998 (mean 223). Forty wild females returned to the 35-km river in 1995-1996, 20 in 1996-1997, and <10 in 1997-1998. The positive linear relationship between smolts and returns was significantly lower after 1990 and no longer correlated with smolt size. Smolt-to-adult survival averaged 15% (1976 to 1989) but recently averaged 3.5% (1990 to 1995). Smolt number steadily declined to <1000 by 1998 from an average annual count of 7000. Smolts per spawner from 1991 to 1994 were, on average, 70% lower than previous estimates based on the same spawner abundance. Recruitment scenarios based on survival histories during freshwater and marine life stages indicated that adult recruits are currently below replacement and unsustainable if conditions continue or worsen. Factors influencing steelhead in the ocean and freshwater are likely similar for other salmonids; harvest impacts must be reduced and appropriate stock rebuilding measures implemented.

Declivity in steelhead (<i>Oncorhynchus mykiss</i>) recruitment at the Keogh River over the past decade

Declivity in steelhead (<i>Oncorhynchus mykiss</i>) recruitment at the Keogh River over the past decade

Parapatric lake and stream sticklebacks on northern Vancouver Island: disjunct distribution or parallel evolution?

Morphological analysis of sticklebacks from Misty Lake and its inlet stream (Keogh River system, northern Vancouver Island) reveals two forms of Gasterosteus. Sticklebacks from the lake are large and slender bodied with a black back and sides, while sticklebacks from the inlet stream are smaller with a stockier body and mottled brown back and sides. Lake fish also have shorter jaws, longer spines, and more gill rakers than the stream fish. These differences in body shape, trophic structures, and colour are inherited, and the two forms breed true in the laboratory. This implies that they are independent gene pools rather than a single gene pool containing some complex polymorphism. The pair from Misty lake and stream is compared with ecologically similar pairs from Graham Island in the Queen Charlotte Archipelago. The lake–stream pairs on the two islands are strikingly similar. Two hypotheses are examined that might explain the origins and remarkable resemblance of these widely disjunct lake–stream pairs. One hypothesis is historically based and argues that the lake–stream pairs on northern Vancouver Island and the Queen Charlotte Islands share a common origin. The other hypothesis argues that the similarities between the lake–stream pairs on the two islands are the result of parallel evolution (i.e., independent evolution of similar phenotypes in response to similar selection regimes). The available data do not allow a distinction to be made between the hypotheses. The historical hypothesis, however, argues for a divergence that predates the Fraser glaciation, whereas the parallel-evolution hypothesis requires postglacial divergence. Since the two hypotheses differ in the amount of time available for divergence, it may be possible to distinguish between the hypotheses at the molecular level.

Returns of Pen-Reared Steelhead from Riverine, Estuarine, and Marine Releases

Hatchery-reared steelhead (anadromous rainbow trout Oncorhynchus mykiss) were released as smolts in 1982 and 1983 at four locations in and near the Keogh River on northern Vancouver Island, British Columbia, to determine the effect of release location on adult return rate, Smolts were released at four sites simultaneously: 10 km upstream from the river mouth (10km site), 0.4 km upstream from the river mouth above a fish-counting fence (0.4-km site), in the tidal area below the fence (0.3 km upstream), and in the ocean about 1.6 km off the mouth of the river. Return rates were estimated by mark and recapture of adults and kelts at the counting fence 1–3 years later. Based on numbers released, the return rates of the 1982 groups were 7% for the 10-km site, 11% for the 0.4-km site, 10% for the tidal site, and 11% for the ocean site, The respective return rates of the 1983 groups were 3, 5, 7, and 5%. We suggest that failure to migrate, as well as predation, accounted for the lower return rates offish released at the 10-km site because few of the nonmigrant fish released at this site were collected at the fence as smolts the next year. Smolts that were acclimatized to salt water at the river mouth and then released at the ocean site returned at a rate similar to that of fish released into the lower reach of the river (0.3- and 0.4km sites). Release of cultured smolts into the lower reaches of small coastal rivers is therefore recommended to maximize adult survival and to minimize competition with wild steelhead.

Increased Juvenile Salmonid Growth by Whole-River Fertilization

Nutrient concentrations, periphyton standing crop and size of steelhead trout (Oncorhynchus mykiss) and coho salmon (O, kisutch) fry increased after the fertilization of a nutrient-deficient stream with inorganic phosphorus (P) and nitrogen (N). Whole-river fertilization of the Keogh River, British Columbia, during 1983–86 to increase summer average nutrient concentrations from < 1 μg P∙L−1 and 25 μg N∙L−1 to 10–15 μg P∙L−1 and 30–100 μg N∙L−1 resulted in five- to 10-fold increases in periphyton standing crops on artificial substrata and 1.4- to 2.0-fold increases in late-September salmonid fry weights. Diatoms and chlorophytes dominated the algal periphyton on artificial substrata at fertilized sites. Cyanophytes were unimportant despite low N:P ratios in some cases. Juvenile salmonids fed primarily on benthic insects. These results suggest that autochthonous primary production can be an important energy source in forested, middle-order streams, and indicate that the manipulation of autochthonous primary production can be a useful management tool to increase salmonid growth in nutrient-poor coastal streams.

Size-Biased Survival in Steelhead Trout (Oncorhynchus mykiss): Back-Calculated Lengths from Adults' Scales Compared to Migrating Smolts at the Keogh River, British Columbia

Lengths of wild, winter-run steelhead smolts, estimated by back-calculation procedures from adults' scales, were compared with observed lengths of migrating smolts sampled near the mouth of the Keogh River, Vancouver Island. Size-biased smolt-to-adult survival rates were estimated for several length categories by utilizing length frequencies from observed smolts, smolt length frequencies which were back calculated from adults' scales, smolt yield, and adult returns. Back-calculated smolt length (BSL) of adults returning from smolts of 1977 to 1982 averaged 193 mm compared to 176 mm for observed smolt length (OSL). Mean BSL was larger than OSL in every year. Adults from odd-numbered smolt years had larger BSL than adults from even-numbered smolt years similar to the pattern in OSL. BSL increased with increased years spent in salt water, based on ageing adults' scales. Males and females had different BSL based on number of years spent in fresh water and salt water, although they exhibited the same mean BSL overall. The smolt-to-adult survival estimates were in close agreement with previous estimates derived from the mean OSL. Predictability of survival in the ocean based on the length of smolts was extended over a broad range of the length distribution of wild steelhead smolts.

Patterns of Timing and Size of Wild Coho Salmon (Oncorhynchus kisutch) Smolts Migrating from the Keogh River Watershed on Northern Vancouver Island

Coho salmon (Oncorhynchus kisutch) smolts leaving the Keogh River and its tributaries demonstrated consistent patterns in their timing and size. An initial early peak in the mean size of migrating smolts occurred several weeks before the peak in their timing, and in several years when smolt migration was monitored until July, a late peak in size occurred near the end of the smolt migration. Changes in the mean size of smolts were not related to their origin within the watershed, and varying age compositions were only partially responsible for the two peaks in mean size. Fish overwintering in tributary lakes grew faster than fish overwintering in tributary streams. A greater proportion of lake-origin smolts migrated to sea after only 1 yr in freshwater than stream-origin smolts. It appears that fish that wait until their second spring to smoltify are among the first to emigrate that spring. These relatively large 2 + smolts, combined with fast growing 1 + smolts that leave early during their first spring, cause the first peak in size. The small numbers of large smolts leaving the Keogh River at the ends of several of the smolt runs apparently left then because of minor flow increases in the river. As has been found with releases of coho smolts from nearby hatcheries, fish that left the Keogh River early in the smolt run generally had a more northerly marine catch distribution than later migrating smolts. A greater proportion of fish migrating to sea late in the smolt run were caught in the fishery than fish migrating early. Additional work examining the marine survival of early and late migrating wild smolts is recommended to enable detailed comparisons to be made between the optimal timing and size of wild and hatchery smolts.

Overwintering habitats of coho salmon (Oncorhynchus kisutch) and other juvenile salmonids in the Keogh River system, British Columbia

Catches of overwintering juvenile coho salmon (Oncorhynchus kisutch) in the Keogh River system, Vancouver Island, were higher in two small (8 and 25 ha), shallow (mean depth 2 – 3 m) lakes and their outlet and inlet streams than in the main river, where steelhead trout (Salmo gairdneri) were predominant. Dolly Varden char (Salvelinus malma), cutthroat trout (Salmo clarki), and threespine stickleback (Gasterosteus aculeatus) were also present in the lakes. The distribution of coho salmon in the lakes was restricted largely to areas close to the bank, with few fish being captured in offshore areas or in mid-water. Apparent differences in the abundance of coho salmon between the two lakes may have been related to differences in fish community composition, with sticklebacks being particularly numerous in Misty Lake, where catches of coho salmon were lower than in Long Lake. The population density and biomass of coho salmon overwintering in Long Lake were estimated to be 176 fish/ha and 1.14 kg ha−1, respectively. The mean length of coho salmon in the lakes was greater than that of coho salmon in the tributary streams and main river, and the mean length of the salmon in the lakes generally increased with distance away from shore.

Experimental Enrichment of a Coastal Stream in British Columbia: Effects of Organic and Inorganic Additions on Autotrophic Periphyton Production

Periphyton accumulation rates and alkaline phosphatase activity were examined in reaches of the Keogh River, British Columbia, following additions of grain and inorganic fertilizer as separate treatments during spring–summer 1981. Two different levels of N and P addition were used: one to attain ambient N and P concentrations of 200 and 15 μg∙L−1, respectively, and the other to attain 400 and 20 μg∙L−1, respectively. Grain (rolled barley) was added monthly at 280 g∙m−2. N and P additions increased chlorophyll a accrual rates by more than an order of magnitude. Diatoms dominated the periphyton community until midsummer. In July and most of August, the relative importance of chlorophytes increased and biomass levels declined markedly in spite of continued nutrient additions. Grain additions resulted in no detectable change in periphyton accrual, but alkaline phosphatase activity increased by 35% over control levels. These results suggest that additions of labile organic matter to nutrient-deficient coastal streams can increase autotrophic P deficiency. Based on responses of juvenile salmonids, additions of inorganic nutrients to increase autotrophic production can maximize trophic enhancement in nutrient-deficient streams.