Effects of Seawalls and Piers on Fish Assemblages and Juvenile Salmon Feeding Behavior

Abstract

Shoreline modifications, such as seawall armoring and piers, are ubiquitous along developed waterfronts worldwide, and recent research suggests that their ecological effects are primarily negative. We utilized snorkel surveys to quantify the effects of seawalls and piers on fish in nearshore habitats of an urbanized estuary in Puget Sound, Washington. We observed 17 species of fish and 4 species of crab during April–August 2012 at sites modified by seawalls and piers and at reference beach sites with minimal anthropogenic structures. Species assemblages at modified sites were significantly different from those at reference beaches. At modified sites, fish distribution and assemblage structure varied with proximity to the shade cast by piers; overall fish abundances were reduced under piers, and the greatest abundances were observed at high tides in areas directly adjacent to piers. Juvenile Pacific salmon Oncorhynchus spp. were the dominant fish species, and piers reduced their presence and feeding, indicating that areas under piers provide less‐valuable habitat to salmon species. Piers may interrupt movements of juvenile salmon when they use shallow waters along shorelines to migrate from freshwater to marine habitats, as juvenile salmon tend to avoid shade under piers, especially at high tides. Our results show that shoreline modifications can alter species assemblage structure, thus potentially creating novel combinations and abundances of species, and can reduce habitat function for species that utilize these and similar habitats elsewhere. Received December 27, 2013; accepted March 27, 2014

Fine-scale habitat use and behavior of a nearshore fish community: nursery functions, predation avoidance, and spatiotemporal habitat partitioning

“…It is also concerning that the connectivity of shallow habitats and their associated benefits (e.g. access to appropriate habitats, frequent conspecific encounters) are threatened by habitat elimination and behavioral barriers such as shading from large piers (Able et al 2013, Munsch et al 2014, Ono & Simenstad 2014. However, some of the functions of degraded ecosystems can be repaired and the benefits of habitat improvements need not be limited to fish.…”

“…Pilings that support piers are also common along shore and add structure to the water column; however, we excluded observations of fish under piers in this analysis because pier shading can influence fish behavior (e.g. Able et al 2013, Munsch et al 2014.…”

“…The salmon were almost entirely age-0 transients migrating through the estuary to marine habitats. Puget Sound is also inhabited by demersal predatory fish such as lingcod Ophiodon elongatus and larger sculpins (family Cottidae) that utilize relatively deep nearshore waters (Toft et al 2007, 2013, Munsch et al 2014. In addition, larger life stages of salmonids (e.g.…”

“…We assembled a long-term dataset of underwater fish surveys to quantify fine-scale habitat use and behavior of the nearshore fish community (original studies: Toft et al 2005, 2007, 2009, 2013, Southard et al 2006, Munsch et al 2014. Snorkel surveys occurred between 2003 and 2013 at 20 sites, and scuba surveys occurred in 2012 at 6 sites ( Fig.…”

Effects of shoreline armouring and overwater structures on coastal and estuarine fish: opportunities for habitat improvement

“…; Munsch et al . ). In the Hudson River estuary, predators aggregated in shaded areas at the edge of piers, potentially to ambush smaller fish (Able, Grothues & Kemp ).…”