Movement patterns and feeding behavior of juvenile salmon (Oncorhynchus spp.) along armored and unarmored estuarine shorelines

Abstract

Estuarine nearshore environments are impor- tant habitats for many organisms, including juveniles of several Pacific salmon species (Oncorhynchus spp.). These habitats provide shallow water and high prey productivity, but are increasingly modified by anthropo- genic activity including shoreline armoring, which dis- rupts connectivitybetween aquatic and terrestrial realms and artificially steepens the shore. Such effects may have adverse consequences for juvenile salmon, partic- ularly Chinook (O. tshawytscha) and chum (O. nerka), which are known to rely on shallow, productive near- shore habitats for foraging and refuge from predators during their outmigration from natal streams to the sea. We developed snorkel methods to quantify feeding rates, movement rates, and path complexity of juvenile salmon along armored and unarmored shorelines in Puget Sound, WA, USA. We found that juvenile salmon had relatively high feeding rates along all shoreline types, but that path straightness and movement rates showed some variation between armored and unar- mored sites. Feeding fish swam in more complex paths and were observed in larger schools than non-feeding fish, and path straightness and movement rate were negatively correlated with proportion of time feeding. Feeding behavior, school size, and movement rates also showed variation byspecies. Shorelinetype(armoredor unarmored)influencedjuvenilesalmondistribution,and unarmored shorelines appear to accommodate a greater diversity ofmovementpatterns thanarmoredshorelines. Our results show that juvenile salmon feed at high rates along armored and unarmored estuarine shorelines, thus decreased prey availability or altered prey resources are likely the most detrimental foraging effects of armoring in estuarine nearshore ecosystems.