Stuart H. Munsch

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

AbstractShoreline 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 feedin...

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

Summary Nearshore ecosystems are increasingly recognized as critical habitats for fish of cultural, ecological and economic significance. These ecosystems are often densely inhabited by juvenile fish, highly productive and refuges from predation, leading ecologists to characterize them as nurseries. However, nearshore ecosystems are being transformed globally to support demands of growing coastal populations. Many shorelines are modified by armouring (e.g. seawalls, riprap) that minimizes erosion, and overwater structures (e.g. piers, docks) that facilitate waterfront use. These modifications affect the ecology of nearshore systems by restructuring, eliminating and shading shallow waters. Here, we review literature examining effects of armouring and overwater structures on coastal and estuarine fishes, and discuss how research and management can coordinate to minimize negative effects. Along armoured shorelines, fish assemblages differed from unarmoured sites, fish consumed less epibenthic and terrestrial prey, beach spawning was less successful and fish were larger. Under large overwater structures, visually oriented fish were less abundant and they fed less. Shade from overwater structures also interrupted localized movements of migratory fish. Thus, shoreline modifications impaired habitats by limiting feeding, reproduction, ontogenetic habitat shifts from shallow to deeper waters and connectivity. Research suggests that restoring shallow waters and substrate complexity, and minimizing shading underneath overwater structures, can rehabilitate habitats compromised by shoreline modifications. Synthesis and applications. Shoreline armouring and overwater structures often compromise fish habitats. These threats to nearshore fish habitats will become more severe as growing coastal populations and rising sea levels increase demands for shoreline infrastructure. Our ability to assess and rehabilitate nearshore fish habitats along modified shorelines will be enhanced by: focusing research attention on metrics that directly indicate fish habitat quality; implementing and evaluating shoreline features that repair compromised habitat functions within human-use constraints; collating natural history knowledge of nearshore ecosystems; and embracing the socio-ecological nature of habitat improvements by educating the public about conservation efforts and fostering appreciation of local nearshore ecosystems. Actions to reduce impacts of shoreline modifications on fish are particularly feasible when they align with societal goals, such as improving flood protection and providing spaces that facilitate recreation, education, and connections between people and nature.

Effects of piers on assemblage composition, abundance, and taxa richness of small epibenthic invertebrates

We examined the effects of two types of piers on composition, abundance, and diversity of small epibenthic invertebrates and on several taxa known to be important prey for juveniles of three species of Pacific salmon. Using an epibenthic pump, invertebrates were sampled under and away from piers. Piers located within a dense urban aggregation of overwater structures and ferry piers occurring singly in less urbanized landscapes negatively impacted small invertebrates. Except for polychaetes at ferry piers and the harpacticoid copepods Tisbe species at urban piers, taxa richness and densities of invertebrate groupings and several juvenile salmon prey taxa were significantly decreased underneath both pier types and also near the edge of ferry piers. Assemblage structure was also greatly influenced by piers, with under-pier assemblages dominated by Tisbe species and several other taxa, and assemblages outside piers characterized by many taxa. Many of the negatively impacted taxa are associates of algae and seagrasses that were reduced under the piers. For juvenile salmon and other fish, reducing shade under piers by adding light to the environment may improve habitat access and quality in areas where piers decrease fish feeding opportunities.

A Quantitative Chronology of Diurnal Feeding in Juvenile Pacific Salmon

AbstractDaily cycles in feeding intensity are common among fish and suggestive of ecological trade-offs and constraints. However, feeding chronologies are typically estimated from diets rather than in situ observations. As a consequence, our understanding of daily feeding patterns is often imprecise, which limits our ability to infer connections between these patterns and their drivers. Here we quantify in unprecedented temporal resolution the real-time diurnal feeding behavior of a fish assemblage. Snorkelers observed juvenile Pacific salmon Oncorhynchus spp. in estuarine waters between dawn and early evening. Fish fed throughout the day, with intake declining after dawn, and individuals allocated about 20% of their time to feeding at sunrise, declining to about 5% in the early evening. Many factors potentially influenced this behavior, including predation avoidance, physiological constraints, prey availability, and mandates for growth and migration. Prey mass in the stomachs of these fish increased shor...