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Juvenile Surf Smelt and Sand Lance in Central Puget Sound, Washington—Links in a Complex Food Web
U.S. Geological Survey (USGS) scientists have been conducting surveys for juvenile surf smelt (Hypomesus pretiosus) and sand lance (Ammodytes hexapterus) in Washington's Puget Sound—a large estuarine system adjacent to a robust metropolitan area. Surf smelt and sand lance are two species of forage fish in this region that provide a key link in the marine food web between zooplankton (tiny aquatic animals) near the bottom of the food web and larger fish, seabirds, and marine mammals near the top of the food web. In Puget Sound, these forage fish are consumed by such economically and socially valuable predators as salmon, killer whales, and many marine birds. The surveys, conducted by scientists from the USGS Western Fisheries Research Center, Columbia River Research Laboratory, are part of the Coastal Habitats in Puget Sound (CHIPS) program.
Surf smelt and sand lance spawn on the upper intertidal areas of beaches in Puget Sound. As their eggs develop and they transform into juvenile fish, they reside near the beach for an unknown period of time. The movements and distribution of these juvenile fish after the spawning period are poorly understood. We investigated the use of nearshore habitats by juvenile stages of surf smelt and sand lance because nearshore areas are commonly used as nursery and rearing grounds for other species.
Our primary goal was to investigate the possible use of eelgrass (Zostera marina) habitats by the juvenile life stages of these forage fish by comparing their abundance in eelgrass areas with their abundance in areas without eelgrass. Eelgrass is a valued ecosystem component that provides cover and forage opportunities for a wide variety of species within Puget Sound. We hypothesized that juvenile forage fish may preferentially select eelgrass areas over bare habitats. A secondary question that we investigated was the influence of open shorelines versus embayments on the presence of juvenile forage fish. Small embayments—which are in decline in Puget Sound owing to the building of roads and other shoreline development, such as housing and marinas—are valuable habitats for juvenile salmon. We hypothesized that embayments might also be an important habitat for forage fish, which are known to school with juvenile salmon. Combining these questions, we selected study sites in central Puget Sound that are either in embayments or on open shorelines, with or without eelgrass. At each study site, our objectives were to (1) assess the relative abundance of forage fish, (2) describe the extent and characteristics of eelgrass beds (if present), and (3) collect and identify prey items found in the nearshore and in dissected juvenile forage fish to evaluate food-web linkages.
Surveys for juvenile surf smelt and sand lance were conducted during May and June 2012 near Bainbridge Island, Washington, in central Puget Sound (see map). We captured, counted, and released more than 2,500 juvenile surf smelt and 59,000 juvenile sand lance. Our preliminary observations indicate that sand lance are most abundant in areas without eelgrass and that surf smelt have similar abundance in eelgrass and non-eelgrass areas. Both species appear to prefer embayments to open shorelines. Sand lance were caught infrequently but in very high abundance. Surf smelt, on the other hand, appeared to be more broadly distributed and were commonly captured in low numbers at all study sites.
We investigated the food habits of these forage fish by sampling their potential prey items, such as zooplankton and macroinvertebrates (animals that lack backbones and are big enough to be seen with the naked eye). These items were collected with plankton nets and from samples of sediment and vegetation. Some samples of captured juvenile surf smelt and sand lance were retained for diet and stable isotope analysis, which will allow us to map the fishes' position in the food web. The samples that the team collected during this survey are currently being analyzed, and the results will be integrated with other components of the CHIPS program, allowing us to better understand the role of forage fish in the marine food web of Puget Sound.
This study is part of a larger effort within the Effects of Urbanization project task under the CHIPS program. CHIPS is an interdisciplinary collaboration designed to coordinate, integrate, and link USGS studies with the goals and objectives of Federal, State, Tribal, and local governments, along with nongovernmental organizations (NGOs), universities, and private industry. The efforts described here will be integrated with current and future habitat assessments.
If you would like additional information about this work, please contact Theresa Liedtke (email@example.com). To view a selection of photographic highlights from this survey, visit the USGS Facebook page. A USGS Fact Sheet about forage fish studies in Puget Sound is posted at http://pubs.usgs.gov/fs/2012/3023/.
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