Research Document - 2001/144
Status in 2000 of Coho Stocks Adjacent to the Strait of Georgia
By Simpson, K., Dobson, D., Semple, R., Lehmann, S., Baillie S., and I. Matthews
Abstract
Escapements in 2000 remained poor relative to 10 year averages in all areas of the Georgia Basin except in the lower Fraser system. In terms of the provisional limit reference point of three females/km, virtually all enumerated stocks in the Basin were probably above the limit. Escapements were the result of poor escapements in 1997 and poor marine survival. Most indicator stocks did not improve on their 1997 escapements. Extremely low marine survival is the driving short-term cause of poor abundances. Survival of populations on south-east Vancouver Island is a particular concern. However, the decline has stabilised, with survivals of virtually all indicator stocks in the Basin improving at least slightly. Largely as a result of Selective Mark Fisheries, exploitation of hatchery stocks about doubled to 24% in 2000. Exploitations of wild coho probably also increased with the increased fishing effort, but the level is uncertain and will vary with ocean distribution.
Smolt runs were probably above average in 2000 on Vancouver Island but remained poor on the Sunshine Coast (Areas 15 and 16). The number of smolts was not exceptional at Salmon River in the lower Fraser Valley but fry densities and sizes in 1999 suggest smolt abundances elsewhere in the area may have shown a greater improvement. Smolt runs may have been comparable to 1997, the previous smolt run in this brood line. In a previous Pacific Scientific Advice Review Committee (PSARC) Working Paper, marine survivals and abundances were forecast to remain about the same as in 2000. Forecasts were based on time series projections but the probability of increased ocean recruitment means the forecast abundance (which we are not revising) is more likely to be an under-estimate than an over-estimate. Assuming continued low exploitation of wild stocks, most monitored populations will probably exceed the provisional limit reference point of three females per kilometre of stream, as they have in 1998 and 1999. Considering the current low productivity of Georgia Basin coho, we recommend that fishing mortality remain similar to existing minimal levels in order to ensure that there is a sufficient proportion of escapements that exceed the provisional limit reference point.
The abundance of smolts this spring will probably be below the 10 year average. We expect smolt numbers to remain especially poor on the Sunshine Coast. Throughout all monitored areas of the Basin, fry densities were below average in 2000. This probably resulted from low escapements in 1999. Fry were small, despite lower densities, suggesting over-winter survival may have suffered. However, this winter has been unusually dry and it is not clear what the effect on survival has been.
Two areas of particular concern with respect to their status are the Sunshine Coast (Area 15 and 16) and Southeast Vancouver Island (Areas 18 and 19).
We recommend in the paper that Regional rules or guidelines for the collection and analysis of escapement data are required, especially if stock assessment frameworks use Limit Reference Points of spawner abundance. The likelihood of obtaining reasonably accurate absolute, as opposed to index, measures of escapement needs to be carefully considered. We also recommended that the lower Fraser area requires another full indicator facility or, failing that, more smolt enumerations coupled with fry and adult estimates.
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