Marine Vegetation and Forage Fish

Part Two

Editor’s Note: This is the second of a multi-part series on the health of northern Puget Sound and Georgia Strait. It was first published under the title, “State of the North Sound and Straits,” by RE Sources and North Sound Baykeeper in October of 2002.

The marine environment is rich with vegetation that provides the basis of the marine food web. Not only does it provide food for many marine organisms, but marine vegetation provides refuge and rearing habitat, as well as habitat for many commercially and recreationally significant species. While there are over 200 varieties of macro-algae (seaweed) and sea grasses in area waters, we’ll focus on two cornerstone species: eelgrass and kelp.

Puget Sound is home to approximately 26,000 acres, or almost 41 square miles, of eelgrass. Eelgrass is a true flowering vascular plant that supports a wide diversity of aquatic organisms. This important grass grows in the intertidal and shallow subtidal zone in depths of up to 22 feet deep.

Eelgrass meadows provide a home for many small organisms at the base of the food chain and are optimal spawning habitat for Pacific herring. These meadows provide protective cover for migrating salmon and other marine life, as well as critical winter feeding habitat for birds and ducks.

Brant, for example, depend on eelgrass beds for feeding grounds during migration and travel from extensive beds in Alaska to Padilla Bay every winter (Boulthuis, 2002). Eelgrass is also extremely important in absorbing the impact of waves and currents, thus preventing coastal erosion and stabilizing shorelines.

In Whatcom County, 55 percent of our shorelines have nearshore eelgrass. Fifty-one percent of Skagit County’s shores also host eelgrass (Puget Sound Water Quality Action Team [PSQWAT], 2002).

The most extensive eelgrass meadows in the area are found in Padilla Bay. The extent of eelgrass in the bay was mapped in 1989. At that time, Padilla Bay held 7,900 acres of eelgrass, making it the second largest continuous meadow of eelgrass of the Pacific coast (Boulthuis, 2002).

Current acreage is assumed to be the same, since no major marine development projects have been allowed in the area for the over the last 20 years (Pentilla, 2002).

Eelgrass beds throughout the rest of the state have not fared as well. Washington State has lost an estimated 33 percent of its eelgrass beds (Washington Department of Fish and Wildlife [WDFW]). Bellingham Bay has lost 50 percent of its eelgrass as a result of dredging and filling (Department of Natural Resources, 2000).

Large kelp beds are often referred to as “forests.” Similar to their terrestrial counterparts, kelp forests have tall plants that form a canopy, with understory plants that grow beneath. The canopy layer of a floating kelp bed is formed by two species–giant kelp and bull kelp.

These plants have float-like structures to hold the upper portion of the plant at the surface and a small “holdfast” that anchors the plant to the sea bottom. Other kelp species dominate the understory level, providing a dense layer of vegetation used as shelter for small invertebrates and larval fishes, including various species of forage fish and rockfish.

In Skagit County, 38 percent of the shoreline is home to floating and non-floating kelp. Twenty-five percent of Whatcom County’s shorelines host various kelp species. Extensive kelp beds are also found in the San Juan Islands. (PSQWAT, 2000)

Kelp populations in the Northwest vary from year to year. While the overall numbers seem stable, some local losses have occurred. For example, historically a large kelp bed flourished north of Protection Island National Wildlife Refuge.

In 1989, there were 181 acres of kelp in this area, but by 1997 the kelp had completely disappeared. The reason for this relatively sudden shift in habitat type is unknown. (PSQWAT, 2000)

Human influences such as sewage and fertilizer runoff are major threats to marine vegetation. Fertilizers promote the growth of algae in the water. This algae reduces the amount of sunlight that can reach kelp and eelgrass. Excess nutrients can also cause algae to grow on eelgrass leaves, again reducing the amount of sunlight that reaches the plant.

Herbicides and pesticides used for the control of unwanted plants and invertebrates can kill or damage marine vegetation, while boat propellers can also destroy kelp beds and eelgrass meadows. Rising ocean temperatures, oil spills and chemical contamination also negatively impact marine vegetation.

Perhaps the most destructive impact to marine vegetation is the industrial, commercial and residential development that continues to exert pressure on shoreline areas.

Dredging sediment for navigation can destroy marine vegetation, while shoreline construction and nearby logging increases erosion and clouds the water and limits photosynthetic activity. Structures built over the water, such as industrial and residential piers, can prevent marine vegetation from getting the sunlight they require for growth.

Outlook Good: Although losses have occurred, eelgrass meadows and kelp beds in north Puget Sound and the Straits seem to be doing well. There is a growing awareness of the importance of these habitat types, and more emphasis is being placed on maintaining and restoring these key vegetative types.

Forage fish, such as Pacific herring, surf smelt and Pacific sand lance, serve as prey for a wide variety of larger fish, marine mammals and seabirds, while providing a valuable indicator of the health and productivity of our marine environment.

Forage fish are popular as recreational fishing bait and are also important to commercial and subsistence fisheries. The habitats that forage fish use, such as eelgrass beds and rocky and sandy beaches, are designated as a critical resource by the state of Washington.

Pacific herring are a vital part of Puget Sound’s food web, as they comprise some 71 percent of the diet of lingcod, and 62 percent of the diet of chinook salmon. Many other species in the Puget Sound food web feed heavily on herring, including coho salmon, Pacific halibut, and a number of seabirds and marine mammals.

At least 20 stocks spawn in the Puget Sound area, depositing their eggs on intertidal and shallow subtidal eelgrass from late January through early June. (WDFW, 1997)

While fluctuations in herring spawning stock sizes are normal, major stocks in the region are declining. Stocks that spawn at Cherry Point, north of Bellingham, Port Susan and Discovery Bay, on the Strait of Juan de Fuca, are at historically low levels, and have been listed by WDFW as critical or depressed. (WDFW, 1997)

Surf smelt, another important forage fish, spawn year around on beaches on and around Whidbey Island, Camano Island, Fidalgo Bay, Birch Point, Cherry Point and the islands (WDFW, 1997). Until recently, relatively little was known about these fish. The spawning behavior of the fish has only been understood by scientists for the last 20 to 30 years, and very little is known about the rest of the fish’s lifecycle.

Surf smelt spawning habitat requires coarse sand and pea gravel beaches as well as a specific tidal elevation. In a unique event, surf smelt come up to the waters edge at highest tide. Several males will align themselves with one female, vibrating in unison, causing her to release her tiny eggs to the surface of the beach. The waves then gently cover the eggs with sediments.

Over 200 miles of smelt spawning beaches are known to exist along Puget Sound. Many other beaches are assumed to have been used by these fish, but the extent of the loss of surf smelt spawning beaches is unknown. All known surf smelt spawning sites have been given “no net loss” protection by the state. (WDFW, 1997)

Pacific sand lance can also be found within Puget Sound, the Strait of Juan de Fuca and the coastal estuaries of Washington. Similar to the other forage fish, sand lance are a significant component in the diet of many economically important species of fish in Washington.

The Washington Department of Fish and Wildlife estimates 35 to 60 percent of juvenile salmon diets are composed of sand lance (WDFW, 1997). In 1998, recognition of the important role of sand lance as forage and the lack of information on their abundance resulted in the Washington Fish and Wildlife Commission ending all commercial fishing for the species.

Habitat alteration is a major threat to all of the forage fish found in this region. Because they spawn in intertidal and subtidal habitats, these species are especially vulnerable to shoreline development. Commercial and recreational harvesting has also contributed to the decline in herring populations in north Puget Sound, while changes in water temperature, salinity and dissolved oxygen can also negatively impact forage fish food supplies and increase the abundance of predators.

Serious Trouble: The sharp declines in Pacific herring stocks in north Puget Sound point to a species in trouble. Continual nearshore development has destroyed critical forage fish spawning habitats while past over-harvesting has led the WDFW Commission to end all commercial fishing of sand lance. §

Next Month—Bottomfish and Salmon