Diet and Prey Consumption of Juvenile Coho Salmon (Oncorhynchus Kisutch) in Three Northern California Streams

Gonzales, Eric

Abstract: "Diet and prey consumption of juvenile coho salmon (Oncorhynchus kisutch) were studied in three northern California streams. Diet and abundance (to estimate density and survival) of juvenile coho salmon was assessed in July and October 2002 and March 2003. A bioenergetic model developed for juvenile coho salmon was used to estimate prey consumption and prey conversion efficiency. Density estimates varied among creeks and seasons and ranged from 1.45 coho salmon · m-2 in July 2002 to 0.070 coho salmon · m-2 in March 2003. Peak standing stock biomass varied among streams and seasons. Peak biomass estimates raged from 23,339 g · ha-1 in July to 8,578 g · ha-1 in October 2002. No increase in standing stock biomass was observed in the stream with the highest density of coho salmon. Standing stock biomass increased in the low to moderate coho salmon density streams during July through October 2002. Minimum survival estimates varied among streams and seasons and ranged from 9-75%. July to October specific growth rates were highest in streams with the lowest densities. October 2002 to March 2003 minimum survival estimates were highest in streams in which mean weight of juvenile coho salmon was highest in October 2002. Diet of juvenile coho salmon varied among sampling periods and among streams. Terrestrial insects contributed significantly to the diet of juvenile coho salmon in all three streams, making up 25 to 50% of the biomass consumed for all three sampling periods. Amphipods were a significant portion of the biomass consumed in only one of the streams. Seasonal estimates of prey conversion efficiency ranged from 23% during April to July 2002 to 8% during July to October 2002. Prey consumption by each of the juvenile coho salmon populations was highest in the July 2002 and lowest in March 2003. Prey consumption for the population of juvenile coho salmon in the high-density stream was as high or higher than in streams having lower density, even when standing stock biomass was lower. Results from this study suggest that differences between summer and fall rearing potential arising from variation and availability of prey for juvenile coho salmon bearing streams are likely secondary in importance to the amount of available winter habitat in regulating smolt production."

Diet and Prey Consumption of Juvenile Coho Salmon (Oncorhynchus Kisutch) in Three Northern California Streams

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