Research Document 1997/24
Stock status of Atlantic salmon (Salmo salar L.) on the eastern shore of Nova Scotia, Salmon Fishing Area 20, in 1996
By S.F. O'Neil, C.J. Harvie, D.A. Longard
Abstract
Atlantic salmon returns to rivers located on the Eastern Shore of Nova Scotia are described in the context of recent abundance of salmon in those rivers. Anglers were permitted to keep grilse (salmon <63 cm in length) only on East River, Sheet Harbour, where natural production of salmon does not occur due to hydroelectric dams. The other rivers were limited to hook-and-release angling for the second consecutive year in 1996. Angling and First Nation catches were among the lowest recorded during the past two decades for the rivers of the area in 1996. Good water levels throughout the angling season and lower than usual angling effort paradoxically resulted in higher than usual catch rates on many rivers, and in particular, on the Musquodoboit River and St. Mary's River.
Rivers on the Eastern Shore of Nova Scotia can generally be divided into two categories, acid-stressed and non-acid-stressed. Salmon returns to the acid-stressed rivers have been declining. A spawning requirement has not been defined for these rivers. Returns of wild fish to Liscomb River in 1996 were the lowest since 1981 when returns were still building after the opening of the fishway in 1979. Inference about returns to the other acid-stressed rivers on the Eastern Shore is made from the Liscomb River where potential egg deposition from spawners was only 15% of the spawning requirement for a non-acidic Liscomb River.
Research data indicates that juvenile salmon numbers on 3 non-acid-stressed rivers in the area were similar in 1996 to numbers observed during the 1980s. Juvenile numbers on the acid-impacted West River, Sheet Harbour, reflect the low spawner numbers. Several of the sites fished had no salmon or the absence of one of the 3 year classes typically found in salmon-producing streams of this area. The acidic water on West River, Sheet Harbour, has been treated at two sites with the distribution of limestone gravel and age 0+ and 1+ parr were found at those sites in numbers greater than elsewhere.
Recent low return rates of hatchery smolts released in Liscomb River imply that factors in the ocean are having a negative impact on returns of Atlantic salmon to this portion of the coast of Nova Scotia. These data are similar to those observed at the counting facility located on the LaHave River at Morgan Falls where return rates for hatchery fish have declined parallel to those of the Liscomb River.
The estimated post-fishery adult salmon population size on the Musquodoboit River in 1996 was 520 fish, or 0.96 million eggs, 51% of the requirement for conservation. The estimated number of spawners in the St. Mary's River achieved approximately 30% of the conservation requirement with only a 1% probability that conservation levels were exceeded. In-season forecast models for the St. Mary's River were found to be of limited application due to the nature of the model and uncertainty in the parameters. The number of large salmon forecast to return to the St. Mary's River in 1997, based on a relationship with wild grilse returns to the LaHave River, was not expected to exceed conservation levels.
Management considerations are described for the acidic and non-acidic rivers for the Eastern Shore. Recommendations for additional research are also given.
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