Seasonal Use of a Nonnatal Marine Basin by Juvenile Hatchery Chinook Salmon

Abstract

Information on the movement patterns of fishes is essential for managers that are making critical resource decisions. We examined the frequency of a keystone species, Chinook Salmon Oncorhynchus tshawytscha that migrated from different marine basins to the Nisqually River estuary, which lies within the southernmost marine basin (hereafter, “South basin”) in Puget Sound (Washington, USA). Hatchery-reared juvenile fish were sampled by using beach seine, lampara seine, and fyke nets to determine seasonal trends in frequency, habitat use, and the influence of different capture methods. The captured fish originated from three marine basins, nine Puget Sound rivers, and fourteen hatcheries. The data revealed a consistent pattern showing that most of the tagged fish (72%) were from the nearby Nisqually River (in the South basin), but fish from more northerly marine basins (hereafter, “Outbasin”) were also common. Although the majority of the tagged fish (99%) that were captured during April and May were originally released into rivers adjacent to the South basin, 90% of the fish that were captured in August and September had originated from rivers adjacent to Outbasin locations (up to 130 km distant). A comparison of sampling methods showed that the beach seine produced 27% Outbasin fish compared with 53% that were obtained with the lampara seine. The analysis of habitat use suggested that during June and July, more Outbasin fish (>40%) were captured in delta flats and nearshore habitats than in estuarine emergent marsh habitat (26%). Release location (river basin), but not distance, appeared to be an important factor that influenced the percentage of Outbasin fish that were captured in the South basin. However, it appeared that the fish that were released at light weights and early dates were more likely to be captured. Information on the movement of juvenile salmon to a nonnatal marine basin may help to increase our understanding of features of life history and survival, and it has application elsewhere, as many marine species are artificially propagated, released in large numbers, and have the potential to use nonnatal habitats.