Juvenile salmon prey sampled at sea using a pelagic rope trawl and a frame trawl

Abstract

Quantifying the availability of Pacific salmon prey can provide valuable insights into the behavior and survival of commercially important stocks, but discrepancies among sampling gears can make comparisons difficult. We compared two distinct nets, a Methot frame trawl (MIK) equipped with a fine-mesh liner and a pelagic Nordic rope trawl (NRT) equipped with a standard or fine liner, to the stomach contents of juvenile Chinook and coho salmon collected in coastal waters of the northern and central California Current System. Both fine-mesh nets sampled juvenile salmon prey, but while the MIK caught primarily small crustaceans (e.g. larval crabs, shrimp and amphipods) and flatfish larvae, the NRT performed best with other fish larvae, market squid, and krill. Except for squid, this complimentary assortment of fish and invertebrate prey dominated the juvenile Chinook and coho salmon diet in both years. Surprisingly, there was no difference between the abundance or composition of the nekton assemblage sampled with the NRT equipped with a standard or fine liner. While both nets caught similar prey as salmon had consumed, the NRT equipped with a fine liner had the added benefit of capturing juvenile salmon and their dominant prey organisms simultaneously, allowing for synchronous event-scale comparison of consumed and locally available prey.