Copepod Community Structure
We are developing an ocean indicator for forecasting salmon returns based the presence/absence of specific copepod community types. Community types are sampled during oceanographic surveys along the Newport Hydrographic line, as well as during the mesoscale juvenile salmonid surveys carried out in June and September.
We hope to determine whether copepod community structure is a better (or simply a complimentary) descriptor of ocean conditions or juvenile salmonid habitat suitability, compared to bulk measures of ocean conditions based on copepod biomass. The indicator of "copepod community structure" is based on multi-dimensional scaling (MDS), an ordination technique (Figure 18a).
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| Figure 18a. |
Top panel: Ordination of average copepod community structure by year during summer months. Years when summer community structure was dominated by cold–ocean species are on the right of axis 1 (1969–1973 and 1999–2002), while years with warm–ocean species are on the left (1983, 1996-1998, and 2003–2006).
Bottom panel: Regression of coho survival on scores over axis 1 of the chart above. The stronger the "cold–water" characteristics of the summer copepod community, the greater coho survival.
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A warm–water community would be expected in continental shelf waters during years of positive PDO. Such a community occurs because a greater proportion of water in the coastal zone has come either from the warm waters offshore of Newport (as during warm but non–El Niño years) or from the south (as during the El Niño years of 1983 and 1998).
The result of MDS analysis was (not surprisingly) that a warm–water community was seen during the warm summers (1983, 1996-1998, 2003-2006), and a cold–water community during the summers of 1969-1973 and 1999-2002. A cold–water community was also seen in spring 2007, a positive indicator for salmon entering the sea at this time.
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