Polymerase chain reaction (PCR) and microscopic examination of stained kidney sections were used to diagnose infections with the myxozoan parasite Parvicapsula minibicornis in maturing Fraser River salmon. In 2 series of collections, the parasite was detected in 109 of 406 migrating sockeye salmon Oncorhynchus nerka belonging to Early Stuart, Early Summer and Summer run-timing groups, mainly upper Fraser River stocks. However, the parasite was detected neither in fish at sea nor once they had migrated several 100 km upstream. Prevalence then increased to 95% or greater at the spawning grounds. Histological examination of kidney was less sensitive than PCR in detecting the parasite in salmon collected from the earliest sites in both collections found positive by PCR. Severity of infection was greatest at the spawning grounds. Development of infection in sockeye, measured by prevalence, severity or by the rate of false-negative histological diagnoses, appeared to be a useful estimate of in-river residence time. Prevalence and severity of infections in sequential samples of Harrison River and Weaver Creek sockeye stocks collected from the Harrison River indicated that more time had elapsed since parasite transmission than would be predicted based on migration distance alone. Pink salmon Oncorhynchus gorbuscha, coho salmon O. kisutch and chinook salmon O. tshawytscha were found to be infected with the parasite. Development of P. minibicornis in pink salmon was most similar to that in sockeye. Pink and coho salmon may be at risk to the pathological consequences of P. minibicornis infection.

Late-spawning Fraser River sockeye salmon, Oncorhynchus nerka, stocks have suffered signi®cant prespawn mortality associated with an unusually early freshwater migration pattern and the myxosporean parasite Parvicapsula minibicornis. Surveys of migrating adult salmon from several spawning populations were conducted in 1999 and 2000 to determine the extent of infection with P. minibicornis, when and where the parasite ®rst becomes detectable during migration, and whether early migrating stocks might be used as sentinels to assess risk of infection in late-spawning stocks. Posterior kidney, preserved in 95% ethanol, was examined for P. minibicornis in stained histological sections and using a polymerase chain reaction (PCR) test. The prevalence of this parasite in all Fraser River sockeye salmon stocks examined was high (range 47±100% infected). In contrast, P. minibicornis was not detected in the ®sh tested from the two sockeye salmon stocks outside the Fraser River drainage in either 1999 or 2000. The parasite was also not detected histologically or by PCR in the kidney tissue of the ®sh from the Fraser River that were sampled in salt water or early during their freshwater migration up the river. These ®ndings and the progression in the prevalence and intensity of infection as the ®sh from three stocks (early Stuart, Weaver Creek and Cultus Lake) were monitored over time, suggest salmon acquired the parasite either in the lower Strait of Georgia or in the lower Fraser River before the con¯uence of the Harrison River. In both 1999 and 2000 the parasite was present in all Fraser River sockeye salmon stocks sampled, which suggests that early Stuart salmon may be valuable as a sentinel stock for the presence of the parasite in later-spawning stocks.

We determined the postmortem specific gravity and examined the relationship between water temperature and the time to surface for carcasses of adult sockeye salmon Oncorhynchus nerka. These results, in conjunction with other biophysical factors, were used to explain the difficulties associated with the detection of the carcasses of sockeye salmon that die during upstream migration in the Fraser River. Large negative differences have occurred between the sockeye salmon estimates at the river entry and spawning escapement (.0.5 million in 8 of the past 15 years), but relatively few carcasses are observed. Without confirmation of mortality, managers are left with the dilemma of how to partition these differences among lower river escapement, spawning ground escapement, catch, en route mortality, and unreported catch. We investigated the reasons for the paucity of carcass observations by experimentally testing the influence of water temperature on carcass buoyancy and by examining hydrological factors that may affect carcass visibility. Because the Fraser River is turbid (Secchi depth, ,40 cm), only carcasses on the surface can be observed. Initially, all fish had specific gravity estimates of greater than 1 (mean 6 SD, 1.057 6 0.010) and were negatively buoyant when placed in tanks at different water temperatures. The time for a sockeye salmon carcass to surface was inversely related to water temperature and ranged from 1-3 d at 208C to 12-18 d at 68C. Annual counts of dead fish floating on the surface were positively correlated with river water temperature. Fisheries managers should not always expect to see large numbers of dead salmon in years of high estimated en route losses, given the factors that influence the visibility of salmon carcasses in a large river system. We recommend alternative methods for achieving more accurate and precise estimates of en route mortalities.

In order to provide better estimates of the thermal-induced stress encountered by salmon migrating to their spawning grounds, a model is used to hindcast temperatures throughout the mainstem Fraser and

This paper is dedicated to the late Prof. Dave Barnes who sadly passed away before the publication of this work, to which he had significantly contributed over the years through his work on the ExoMars PanCamA major scientific goal of the European Space Agency?s ExoMars 2018 rover is to identify evidence of life within the martian rock record. Key to this objective is the remote detection of geological substrates that are indicative of past habitable environments, which will rely on visual (stereo wide-angle, and high resolution images) and multispectral (440?1000 nm) data produced by the Panoramic Camera (PanCam) instrument. We deployed a PanCam emulator at four hydrothermal sites in the N?mafjall volcanic region of Iceland, a Mars-analogue hydrothermal alteration terrain. At these sites, sustained acidic?neutral aqueous interaction with basaltic substrates (crystalline and sedimentary) has produced phyllosilicate, ferric oxide, and sulfate-rich alteration soils, and secondary mineral deposits including gypsum veins and zeolite amygdales. PanCam emulator datasets from these sites were complemented with (i) NERC Airborne Research and Survey Facility aerial hyperspectral images of the study area; (ii) in situ reflectance spectroscopy (400?1000 nm) of PanCam spectral targets; (iii) laboratory X-ray Diffraction, and (iv) laboratory VNIR (350?2500 nm) spectroscopy of target samples to identify their bulk mineralogy and spectral properties. The mineral assemblages and palaeoenvironments characterised here are analogous to neutral?acidic alteration terrains on Mars, such as at Mawrth Vallis and Gusev Crater. Combined multispectral and High Resolution Camera datasets were found to be effective at capturing features of astrobiological importance, such as secondary gypsum and zeolite mineral veins, and phyllosilicate-rich substrates. Our field observations with the PanCam emulator also uncovered stray light problems which are most significant in the NIR wavelengths and investigations are being undertaken to ensure that the flight model PanCam cameras are not similarly affectedpublishersversionPeer reviewe