Fellow Anglers, Just received the final report from DFO on the Harrison River sturgeon mortalities. Here is what they had to say: Sturgeon Mortalities along the Harrison River, British Columbia - Stephen Raverty (AHC) and Lee Nikl (Fisheries and Oceans Canada) During late May and early June, 1999, several anglers who frequent the Harrison River reported mortalities of wild, subadult white sturgeons (Acipenser transmontanus). A single dead sturgeon was also found in Harrison Lake. The Harrison River is a clear water river which flows from Harrison Lake, British Columbia, and joins with the Fraser River. The Harrison River has a gross drainage area of approximately 7870 km2 and daily average June flow of 936 m3/s. The system is an important producer of chinook (Oncorhynchus tshawytscha), sockeye (0. nerka), and other salmon species. It also supports an important recreational fishery for white sturgeon.

An investigation into these sturgeon mortalities was under-taken jointly by the federal Department of Fisheries and Oceans, and the provincial Ministry of Environment and Ministry of Agriculture and Food. On an initial survey of the river, June 10, 1999, 6 dead sturgeons were identified by field officers. A compilation of subsequent reports from several anglers and fishing guides placed estimated mortalities between 10 to 12 fish. However; the Harrison River has several very deep pools; in addition, at the time of the incident, there were a number of flooded islands where additional mortalities may have escaped detection. Two of the initial 6 fish were collected and presented to the Animal Health Center for evaluation. Samples of the remaining dead sturgeons were not submitted, either because they were too deep within the water column for retrieval, or because of advanced post-mortem decomposition. On examination, the two sturgeons were subadults, in good flesh, and in suitable condition for post mortem. In the smaller of the two fish (length 160 cm, body weight 21.4 kg), there was abundant blood tinged abdominal fluid (serosanguinous ascites), as well as an enlarged spleen and ulcerative colitis. The larger fish (length 231.1 cm, body weight 72.5 kg), aside from a small number of encapsulated, peritoneal (ab-dominal cavity) nematodes, exhibited no significant gross lesions. Histopathology disclosed subacute inflammation of the spleen. Lesions consistent with bacterial gill disease were also noted. Aerobic bacterial culture yielded moder-ate to heavy growth of Aeromonas hydrophila from multiple tissues in both fish. The polymerase chain reaction procedure (PCR) was negative for infectious hematopoietic virus (IHNV). Trace mineral analyses were within normal limits. Selected tissues have been forwarded to the Institute of Ocean Sciences, Sidney, B.C., for analysis of dioxins, furans, and selected PCB congeners.

The Harrison River watershed has few stressors and is sparsely populated; there is little industry with the exception of tourism at the village of Harrison Hot Springs, and some logging activity in the higher reaches of the watershed. There is a secondary-treated sewage outfall located near the outflow of Harrison Lake; this facility and its records were inspected. No evidence was obtained of process upsets or plant mal-functions at the time of the mortalities or for the month antecedent to the epizootic (an epizootic is an infectious disease, frequently widely diffused and rapidly spread-ing, which is only occasionally present in an animal community). Water Quality testing carried out on the Harrison River and Harrison Lake indicated slightly super-saturated oxygen levels, and a pH approaching neutral; water temperatures in the Harrison River range4 from 1 30C to 1 60C at various locations. These findings are considered unremarkable, and the slight oxygen supersaturation is attributed to photosynthetic activity of aquatic macrophytes along the bottom of the river. At the turn of the century, the sturgeon fishery was a burgeoning industry with up to 100,000 kg. of fish harvested per year. However, through over fishing and other factors, the stock quickly collapsed. Currently, only a catch and release sport fishery is practised, with retention of caught fish prohibited. At present, there is still a profound lack of understanding of wild sturgeon diseases. Whenever mortalities occur, efforts are made to identify potential pathogens and possible contributory, environmental factors. In this case, although the proximate cause of death of the smaller sturgeon could be attributed to septicemia, there were still no identifiable environmental or host factors which may have predisposed this animal to infection. The diseases in these stocks likely reflect complex and dynamic processes which are still only superficially understood. Future work to further define sturgeon pathogens and the development of diagnostic protocols for investigations, will contribute signifi-cantly to resolving the epizootiology of these outbreaks.