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Research Document - 1999/133

Status of Coho Salmon Stocks Adjacent to the Strait of Georgia, including the lower Fraser River.

By K. Simpson, R. Semple, S. Baillie, B. Adkins and S. Lehmann

Abstract

Lower Fraser and Vancouver Island indicators continue to show different patterns of ocean survival, escapements and possibly smolt production. There is insufficient information to define the situation on the Sunshine Coast/Howe Sound. Escapements in 1997 were improved but still well below recent averages and this was reflected in below average fry densities in 1998. Probably due to dry summer conditions, the fry were not correspondingly large and smolt numbers may be low again this spring. Smolt runs on Vancouver Island were probably below average to well below average in 1998. Coupled with a forecast of continued poor ocean survival (Working Paper S99-2) the abundance of adult coho from the east coast of Vancouver Island is expected to be very poor in 1999.

Although there is some evidence for reduced recruitment to the ocean, it is clear that continuing poor ocean survivals are driving the low abundances. 1997 and 1998 were the third and fourth consecutive years of 'outside' distribution by Georgia Basin coho. The survival of coho in the northern Basin stabilised in 1995-96 while survivals of middle and southern Basin stocks continued to decline. Survivals, although poor, are now better at the north end than to the south. This was apparent in the 1998 escapements. Spawner numbers were probably adequate in SE Vancouver Island and on the Lower Mainland but they have responded sluggishly to the near cessation of exploitation. In the Lower Mainland, both smolts and adults have been relatively stable over the last four years, based on two wild coho monitoring projects. This stabilisation of smolts and adults in one of the indicator stocks, Salmon River (Langley), is at a level much below that seen in the 1980's. Recent declines in survival of Salmon coho up to 1998 appeared as lower exploitations/catches rather than reduced escapements, which we cannot explain. The 1998 escapement to both streams actually declined despite the virtual cessation of fishing, another signal that abundances of some Lower Mainland stocks are very low.

Survivals of hatchery coho, normally not as good as wild survivals, were again poorer in 1997 and 1998, putting them at critically low levels in 1998 of only 0.3 to 1.0 percent. These survival estimates do not include ventral clipped releases which survived on average 38% more poorly.

There are conflicting signals coming from the Lower Mainland data and another wild indicator stock project would be helpful. A wild indicator further north on the mainland remains a pressing need. The fry survey as conducted in the Basin now appears to be useful in estimating parental escapements, at least at low escapement levels. Its economy allows us to survey more streams than other techniques. Fry data will aid us in defining the sample needed to accurately monitor stocks in the Lower Mainland and throughout the Basin.

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