We reviewed 24 sockeye salmon (Oncorhynchus nerka) nursery lake experiments that involved whole-lake fertilization with appropriate treatment and control years. We found that: 21 of 21 studies showed that fertilization was associated with increased chlorophyll a concentrations, 16 of 16 showed increased zooplankton biomasses, 16 of 16 demonstrated increased average smolt weights, and 11 of 13 showed increased smolt biomasses. Studies involving assessments of egg-to-smolt survival were rare, but all (4 of 4) showed increased survival rates. Studies involving increased smolt-to-adult survival (i.e., marine survival) were even rarer, but all (3 of 3) showed that lake fertilization and increased smolt size were associated with increased marine survival. Several fertilization studies reported problems, and some offered solutions. For instance, when whole-lake fertilization stimulated the growth of blue-green algae, fertilizer with higher nitrogen to phosphorus ratios was used to control the problem. Conversely, when high nitrogen to phosphorus ratios were associated with blooms of ungrazable diatoms, notably Rhizosolenia eriensis, reduced nitrate concentrations were recommended. To date, solutions designed to constrain the growth of both blue-green algae and Rhizosolenia blooms remain elusive. Some studies showed that when both mysids (large invertebrate planktivores) and juvenile sockeye inhabit the same lake, sockeye suffer from a competitive disadvantage and mysids consume 80–90% of the available zooplanktonic food production. Similarly, a small number of studies demonstrated that competition from sticklebacks (Gasterosteus aculeatus) adversely affected sockeye growth rates, and although the problem remains unresolved, ongoing work in lakes containing kokanee (O. nerka), suggests that stocked cutthroat trout (Salmo clarki) may be capable of controlling stickleback densities through predation. Despite all of these difficulties, in almost all cases, when lakes were fertilized with various mixtures of inorganic nitrogen and phosphorus, pelagic food web bottom-up control was strong enough and predictable enough to ensure that sockeye smolt biomass increased. We conclude that sockeye nursery lake fertilization is a technique that can contribute usefully to both the enhancement and conservation of sockeye salmon populations. Key words: sockeye salmon, lake fertilization, bottom-up, aquatic food web.

We summarized existing knowledge on behavioural and physiological responses of Okanagan sockeye salmon (O. nerka) adults to annual and seasonal variations in aquatic thermal regimes during migration. This enabled us to identify an underlying set of 'decision rules' as a biophysical model of how temperature mediates en-route delays as a specific element of annual migrations by sockeye salmon. Several sets of results indicate that adult sockeye migrations stop as seasonal water temperatures increase and exceed 21 o C and then restart when temperatures decrease and fall below 21 o C. Model predictions of annual variations in the duration of migratory delay exhibited close agreement with independent estimates of observed delays available from a subset of years (predicted delay = 1.23 observed delay + 2.08, r 2 = 0.92, p < 0.001, n = 10). We applied the model in a retrospective analysis of the likely impacts of climate variation and change events on adult sockeye migrations in freshwater over the 70 plus year interval between 1924 and 1998. Results indicate that migration delays for a significant portion of the sockeye population averaged 29 days per year (range 0-55). Average annual migration delays roughly equal the 33 day estimate of time required, given continuous migration, to traverse the 986 km distance from the Columbia River mouth to terminal spawning grounds near Osoyoos Lake, BC. Alternating intervals of above-average and below-average migration delays corresponded closely with 'warm-phase' and then 'cold-phase' periods of the Pacific Interdecadal Oscillation. Circumstantial evidence suggests alternating periods of sub-average and above-average productivity for salmon on the southern end of their range are linked to climate variation and change events in both freshwater and marine environments. Climate impact and adaptation responses that register first at the level of salmon, propagate rapidly through both salmon resource users and fisheries managers. Consequently, future climate warming episodes will complicate the manageability and threaten the sustainability of many salmon populations in the southern end of their range (Georgia Basin and the Pacific Northwest). This requires strategies that minimize the impact of uncertain climate variability and change scenarios on the resilience of the salmon resource, and maximize our adaptive capacity for both short-and long-term fisheries planning and management decisions. RÉSUMÉNous avons résumé les connaissances actuelles au sujet des réactions comportementales et physiologiques du saumon sockeye adulte (O. nerka) dans l'Okanagan face aux variations annuelles et saisonnières dans les régimes thermiques aquatiques pendant la migration. Cela nous a permis de cerner et de déterminer un ensemble de règles de décision comme modèle biophysique de la façon dont la température modifie légèrement les délais de parcours en tant qu'élément spécifique des migrations annuelles du saumon sockeye. Plusieurs séries de résultats indiquent que les migrations du saumon soc...

We evaluated the relative success of sockeye salmon hatchery fry stocking in two British Columbia-Alaska transboundary lakes (1,622-ha Tatsamenie Lake and 492-ha Tahltan Lake). Fry stocking began in the late 1980s and is still under way. During the study period, survival patterns in the two lakes were different. At Tatsamenie Lake, wild egg-to-fry survival was higher than hatchery egg-to-fry survival (11.3% versus 4.3%) and wild egg-to-smolt survival was higher than hatchery egg-to-smolt survival (5.8% versus 2.5%). We found no relationship between fry survival and stocking date, spawner abundance, or food availability in Tatsamenie Lake, but we did find a significant positive relationship between early-spring fry length and egg-to-fry survival. Also, we found that in net-pen experiments, larger fry survived better. From this, we concluded that hatchery fry stocked into Tatsamenie Lake may suffer from size-mediated mortality and that net-pen supplemental feeding could be used to overcome this problem. However, because eggs used for hatchery production come from the lake, fry stocking can only be justified when hatchery fry survival exceeds wild fry survival. At Tatsamenie Lake, this goal has not yet been attained. At Tahltan Lake, wild egg-to-fry survival was lower than hatchery egg-to-fry survival (1.5% versus 6.3%) and wild egg-to-smolt survival was lower than hatchery egg-to-smolt survival (3.6% versus 12.8%). Hatchery fry release date and food availability both failed to explain these differences in fry and smolt survival at Tahltan Lake. However, there was a strong negative relationship between total female escapement and wild egg-to-smolt survival. This supported the results of an earlier investigation, which suggested that Tahltan Lake was spawning-site limited. We concluded that at Tahltan Lake, hatchery fry stocking increased smolt numbers, is biologically justified, and should be continued.

In recent decades, the abundance of sockeye salmon Oncorhynchus nerka in the Nimpkish River watershed (Vancouver Island) has declined by more than 80%. To improve sockeye salmon abundance, one of three Nimpkish nursery lakes (Woss Lake, 13.6 km 2 ) was fertilized; a second (Vernon Lake, 8.4 km 2 ) was maintained as an unmanipulated reference. For 3 years (2000)(2001)(2002), we assessed changes in phytoplankton, zooplankton, and juvenile sockeye salmon and then used food web analysis to model the fate of fertilizer phosphorus (FP) as it moved up the food web to juvenile sockeye salmon. As the experiment progressed, we found two distinctly different results. During the first 2 years (2000 and 2001), fertilization was associated with higher concentrations of P, chlorophyll, and phytoplankton. However, because most of the algae were inedible diatoms (principally Rhizosolenia eriensis), only 8% of the algal standing stock was available to zooplankton and less than 0.1% of the FP was incorporated into sockeye salmon biomass via limnetic pathways. The result was that juvenile sockeye salmon growth rates in the treated and control lakes were not significantly different. During the third year (2002), a bloom of the diatom Leptocylindrus increased Woss Lake edible algal biomass by a factor of 7; zooplankton production tripled, and juvenile sockeye salmon production increased by 19%. Consequently, Woss Lake juvenile sockeye salmon grew twice as fast as they did in untreated Vernon Lake, and juvenile sockeye salmon fall weights were 50% higher than those recorded before the lake was fertilized. We conclude that for north Pacific coastal lakes, bottom-up effects resulting from changes in phytoplankton species composition can profoundly alter rates of juvenile sockeye salmon production. Regulation of algal species composition through manipulations of fertilizer composition and application timing might be used to reduce blooms of nuisance algae and increase age-0 sockeye salmon yield.

The life history and production characteristics of Neomysis mercedis from two British Columbia lakes were examined for their potential influence on zooplankton and limnetic fish communities. During the day, mysids in shallow Muriel Lake (1 45 m) were on or near the bottom; in Kennedy Lake (> 100 m), mysids remained deeper than 50 m. In both lakes, mysids spent summer nights at 0-15 m depths despite > 20 "C temperatures. Mysid density was not strongly correlated with lake depth. Mysids generally displayed spring to early summer minima and late summer to fall maxima in numbers and biomass. Single peaks in gravid females and juvenile mysid abundance, and the absence of pronounced seasonal size changes of gravid females suggest that N. mercedis produced a single generation each year. Fecundities of study lake mysids are the lowest on record, and although size-dependent, exhibited unusually high variability.Annual productivity of mysids averaged 485 mg m W 2 y -' (range 205-690). Calculations indicate mysids consume several times more zooplankton per annum than limnetic fish do. N. mercedis is likely an important competitor of juvenile sockeye salmon (Oncorhynchus nerka) since: (i) sockeye exhibit food limited growth and survival patterns in coastal lakes, (ii) mysids and sockeye consume similar zooplankton prey and (iii) mysids do not contribute greatly to sockeye diet (i.e. < 26% of summer and fall diets by numbers or weight).