This section describes physical, oceanographic, and climatic features in the Georgia Basin, more particularly, Puget Sound and the Strait of Georgia, that may contribute to isolation of populations of Pacific herring considered in this review. The Georgia Basin is an international waterbody that encompasses the marine waters of Puget Sound, the Strait of Georgia, and the Strait of Juan de Fuca (Figure1). The coastal drainage of the Georgia Basin is bounded to the west and south by the Olympic and Vancouver Island mountains and to the north and east by the Cascade and Coast mountains. This section further provides a basis for identifying climatic and biological factors that may contribute to extinction risk for this species.
In addition, the general biology of the species is presented. These discussions are included here in order to provide the reader with the background used by the BRT in approaching the issues of distinct population segments and of risk to any DPSs defined. Specific information regarding DPS delineations and risk evaluation are found in their separate sections in this document and present more specific information regarding the species in and around Puget Sound.
The following summary primarily considers the marine waters of Puget Sound that lie south of the boundary between Canada and the United States. However, because the Pacific herring populations are also found in the Strait of Georgia, a brief description of this system will also be presented. Puget Sound is a fjord-like estuary located in northwest Washington State and covers an area of about 2,330 km2, including 3,700 km of coastline. It is subdivided into five basins or regions: 1) North Puget Sound, 2) Main Basin, 3) Whidbey Basin, 4) South Puget Sound, and 5) Hood Canal (Fig. 1). The latter four basins compose the Puget Sound proper. The average depth of Puget Sound is 62.5 m at mean low tide, the average surface water temperature is 12.8oC in summer and 7.2oC in winter (Staubitz et al. 1997). Estuarine circulation in Puget Sound is driven by tides, gravitational forces and freshwater inflows. For example, the average daily difference between high and low tide varies from 2.4 m at the northern end of Puget Sound to 4.6 m at its southern end. Mixing of oceanic and estuarine waters at the sill in Admiralty Inlet substantially reduces the flushing rate of nutrients and contaminants. Concentrations of nutrients (i.e., nitrates and phosphates) are consistently high throughout most of the Sound, largely due to the flux of oceanic water into the Main basin (Harrison et al. 1994). The freshwater inflow into Puget Sound is about 900 million gallons/day (gpd) (3.4 trillion liters /day). The major sources of freshwater are the Skagit and Snohomish Rivers located in Whidbey Basin (Table 1). However, the annual amount of freshwater entering Puget Sound is only 10% to 20% of the amount entering the Strait of Georgia, primarily through the Fraser River. The Fraser River has a drainage area of 234,000 km2 (Bocking 1997). The rate of flow in the Fraser River ranges from an average of 750 m3/sec in the winter to an average of 11,500 m3/sec during the spring freshet, although, flows of 20,000 m3/sec are not uncommon during the spring floods (Bocking 1997).
Eight major habitats occur in Puget Sound (Levings and Thom 1994). Kelp beds and eelgrass meadows cover the largest area (Figs. 2 and 3), at almost 1,000 km2. Other major habitats include subaerial and intertidal wetlands (176 km2), and mudflats and sandflats (246 km2). The extent of some of these habitats have markedly declined over the last century. Hutchinson (1988) indicated that overall losses since European settlement, by area, of intertidal habitat were 58% for Puget Sound in general and 18% for the Strait of Georgia. Four river deltas (the Duwamish, Lummi, Puyallup, and Samish) have lost greater than 92% of their intertidal marshes (Simenstad et al. 1982, Schmitt et al. 1994). At least 76% of the wetlands around Puget Sound have been eliminated, especially in urbanized estuaries. Substantial declines of mudflats and sandflats have also occurred in the deltas of these estuaries (Levings and Thom 1994). The human population in the Puget Sound region is estimated to be about 3.6 million.
The Puget Sound Basin falls within the Puget Lowland, a portion of a low-lying area extending from the lower Fraser River Valley southward to the Willamette Lowland (Burns 1985). In the distant past, the Puget Lowland was drained by numerous small rivers that flowed northward from the Cascade and Olympic mountains and emptied into an earlier configuration of the Strait of Juan de Fuca. During the Pleistocene, massive Piedmont glaciers, as much as 1,100 m thick, moved southward from the Coast Mountains of British Columbia and carved out the Strait of Juan de Fuca and Puget Sound. The deepest basins were created in northern Puget Sound in and around the San Juan Islands. About 15,000 years ago, the southern tongue of the last glacier receded rapidly leaving the lowland covered with glacial deposits and glacial lakes, and revealing the Puget Sound Basin (Burns 1985). The large glacially-formed troughs of Puget Sound were initially occupied by large proglacial lakes that drained southward (Thorson 1980). Almost two dozen deltas were developed in these lakes as the result of streams flowing from the melting ice margins.
Considerable evidence indicates that climate in the Puget Sound region is cyclical, with maxima (warm, dry periods) and minima (cold, wet periods) occurring at decadal intervals. For example, according to the Pacific Northwest Index (PNI), since 1893 there have been about five minima and four maxima (Ebbesmeyer and Strickland 1995). Three minima occurred between 1893 and 1920, one between the mid-1940s and 1960, and one between the mid-1960s and mid-1970s. Two maxima occurred between the early-1920s and the early-1940s, and two more occurred between the late-1970s and 1997.
Mantua et al. (1997) and Hare and Mantua (2000) evaluated relationships between interdecadal climate variability and fluctuations in the abundance and distribution of marine biota. These authors used statistical methods to identify the Pacific Decadal Oscillation (PDO). The PDO shows predominantly positive epochs between 1925 and 1946 and following 1977, and a negative epoch between 1947 and 1976. For Washington State, positive epochs are characterized by increased flow of relatively warm-humid air and less than normal precipitation, and the negative epochs correspond to a cool-wet climate. Mantua et al. (1997) reported connections between the PDO and indicators of populations of Alaskan sockeye and pink salmon and Washington-Oregon-California coho and chinook salmon, although the coho and chinook populations were highest during the negative epochs. Hare and Mantua (2000) found evidence for major ecological and climate changes for the decade following 1977 (a positive epoch). They also found less powerful evidence of a climate regime shift (a negative epoch) following 1989, demonstrated primarily by ecological changes. Examples of ecological parameters that were correlated with these decadal changes included annual catches of Alaskan coho and sockeye salmon, annual catches of Washington and Oregon coho and chinook salmon, biomass of zooplankton in the California Current, and the Oyster Condition Index (OAI) for oysters in Willapa Bay, Washington (Hare and Mantua 2000). This decadal and interannual scale climate variability is graphically represented in Pinnix’s (1999) principal components analyses of climatic variables affecting Puget Sound as shown in Figure 4.
Few climatological records are available prior to the 1890s. Proxy measures of climatic variation have been used to reconstruct temperature fluctuations in the Pacific Northwest. Graumlich and Brubaker (1986) reported correlations between annual growth records for larch and hemlock trees located near Mt. Rainier and temperature and snow depth. A regression model was used to reconstruct temperatures from 1590 to 1913. Their major findings were that temperatures prior to 1900 were approximately 1oC lower than those of the 1900s, and that only the temperature pattern in the late-1600s resembled that of the 1900s.
Bathymetry and geomorphology—The North Puget Sound region is demarcated to the north by the U.S.-Canadian border, to the west by a line due north of the Sekiu River, to the south by the Olympic Peninsula, and to the east by a line between Point Wilson (near Port Townsend) and Partridge Point on Whidbey Island and the mainland between Anacortes and Blaine, Washington (Fig. 1). The predominant feature of the North Sound is the Strait of Juan de Fuca, which is 160 km long, and 22 km wide at its western end to over 40 km at its eastern end (Thomson 1994).
One of the deepest sections of this region is near the western mouth (about 200 m) (Holbrook et al. 1980), whereas the deepest sections of eastern portions are located northwest of the San Juan Islands (340-380 m) (Puget Sound Water Quality Action [PSWQA] 1987).
Subtidal depths range from 20 m to 60 m in most of the northwest part of the region. Deeper areas near the entrance to the Main Basin north of Admiralty Inlet range from 120 m to 180 m in depth (PSWQA 1987). Most of the rocky-reef habitat in Puget Sound is located in this region.
Sediment characteristics—The surface sediment of the Strait of Juan de Fuca is composed primarily of sand, which tends to be coarser and includes some gravel toward the eastern portion of North Sound and gradually becomes finer towards the mouth (Anderson 1968). Many of the bays and sounds in the eastern portion of the North Sound have subtidal surface sediments consisting of mud or mixtures of mud and sand (PSWQA 1987, Washington Department of Ecology [WDOE] 1998). The area just north of Admiralty Inlet is primarily gravel in its deeper portions, and a mixture of sand and gravel in its shallower portions, whereas the shallow areas north of the inlet on the western side of Whidbey Island and east of Protection Island consist of muddy-sand (Roberts 1979). The majority of the subtidal surface sediments among the San Juan Islands consist of mixtures of mud and sand. Within the intertidal zone, 61.2 ± 49.7% of the area also has mixed fine sediment and 22.6 ± 27.5% has sandy sediment (Bailey et al. 1998).
Currents and tidal activity—The Strait of Juan de Fuca is a weakly stratified, positive estuary with strong tidal currents (Thomson 1994). The western end of the Strait is strongly influenced by ocean processes, whereas the eastern end is influenced by intense tidal action occurring through and near the entrances to numerous narrow passages (Fig. 5). Seasonal variability in temperature and salinity is small because the waters are vertically well-mixed (Thomson 1994). On average, freshwater runoff makes up about 7% of the water by volume in the Strait and is derived primarily from the Fraser River. Generally, the circulation in the Strait consists of seaward surface flow of diluted seawater (<30.0‰) in the upper layer and an inshore flow of saline oceanic water (>33.0‰) at depth (Thomson 1994, Collias et al. 1974). Exceptions include an easterly flow of surface waters near the shoreline between Port Angeles and Dungeness Spit, landward flows of surface waters in many of the embayments and passages, and flows of surface water southward toward the Main Basin near Admiralty Inlet (PSWQA 1987).
Water quality—Temperatures generally range between 7o and 11oC, although occasionally surface temperatures reach as high as 14oC (WDOE 1999). In the eastern portion of North Sound, temperature and salinity vary from north to south, with the waters in the Strait of Georgia being slightly warmer than the waters near Admiralty Inlet. Waters near Admiralty Inlet also tended to have a higher salinities than waters to the north (J. Newton2). Dissolved oxygen levels vary seasonally, with lowest levels of about 4 mg/L at depth during the summer months, and highest levels of about 8 mg/L near the surface during the winter.
Macro vegetation—Eelgrass is the primary vegetation in the intertidal areas of the Strait of Juan de Fuca, covering 42.2 ± 27.2% of the intertidal area (Fig. 3), and green algae is the second most common covering 4.4 ± 3.7% of the intertidal area (Bailey et al. 1998). About 45% of the shoreline of this region consists of kelp habitat, compared to only 11% of the shoreline of the other four Puget Sound Basins (Shaffer 1998). Nevertheless, both intertidal areas each have approximately 50% of the total kelp resource. Most species of kelp are associated with shoreline exposed to wave action, whereas eelgrass is found in protected areas, such as Samish and Padilla Bays (Fig. 2). Some of the densest kelp beds in Puget Sound are found in the Strait of Juan de Fuca. Kelp beds at the north end of Protection Island declined drastically between 1989 and 1997, decreasing from about 181 acres to "nothing" (Sewell 1999). The cause of this decline is currently unknown.
Urban, industrial, and agricultural development—The North Puget Sound Basin is bordered primarily by rural areas with a few localized industrial developments (PSWQA 1988). About 71% of the area draining into North Sound is forested, 6% is urbanized, and 15% is used for agriculture. Among the five Puget Sound basins, this basin is used most heavily for agriculture. The main human population in this area centers around Port Angeles (17, 710), Port Townsend (7,000), Anacortes (11,500), and Bellingham (52,174) (Rand McNally 1998). About 10% of the total amount of wastes discharged from point-sources into Puget Sound comes from urban and industrial sources in this basin (PSWQA 1988). About 17% of the nutrients (in the form of inorganic nitrogen) entering Puget Sound originate from rivers carrying runoff from areas of agricultural and forest production (Embrey and Inkpen 1998). The Washington State Department of Natural Resources (WDNR 1998) estimated that 21% of the shoreline in this area has been modified by human activities.
Bathymetry and geomorphology—The 75 km-long Main Basin is delimited to the north by a line between Point Wilson (near Port Townsend) and Partridge Point on Whidbey Island, to the south by Tacoma Narrows, and to the east by a line between Possession Point on Whidbey Island and Meadow Point (near Everett) (Fig. 1). The western portion of the Main Basin includes such water bodies as Sinclair and Dyes inlets, and Colvos and Dalco passages. Large embayments on the east side include Elliott and Commencement bays.
Among of the most important bathymetric features of the Main Basin are the sills at its northern and southern ends. The sill at the north end of Admiralty Inlet is 30 km wide and is 65 m deep at its shallowest point. The sill at Tacoma Narrows is 45 m deep (Burns 1985). South of Admiralty Inlet, depths generally range from 100 m to 140 m in the central part of the basin, and 10 m to 100 m in the waterways west of Bainbridge and Vashon islands. The central basin consists of five sub-basins: 1) one near the southern end of Admiralty Inlet, west of Marrowstone Island, with depths to 190 m, 2) one near the southern tip of Whidbey Island with depths to 250 m, 3) one west of Port Madison, north of Seattle with depths to 400 m, 4) one northeast of West Point in Seattle with depths to 350m, 5) one south of Seattle, near Point Pulley, with depths to about 250 m (Burns 1985). Elliott and Commencement bays, associated with Seattle and Tacoma, respectively, are relatively deep, with depths in excess of 150 m. Freshwater flows into Elliott Bay through the Duwamish-Green River System, and into Commencement Bay through the Puyallup River.
Sediment characteristics—Subtidal surface sediments in Admiralty Inlet tend to consist largely of sand and gravel, whereas sediments just south of the inlet and southwest of Whidbey Island are primarily sand (PSWQA 1987). Sediments in the deeper areas of the central portion of the Main Basin generally consist of mud or sandy mud (PSWQA 1987, Washington Department [WDOE] 1998). Sediments in the shallower and intertidal areas of the Main Basin are mixed mud, sand, and gravel. Bailey et al. (1998) reported that 92% of the intertidal area of the Main Basin consisted of mixed sand and gravel. A similar pattern is also found in the bays and inlets bordering this basin.
Currents and tidal activity—About 30% of the freshwater flow into the Main Basin is derived from the Skagit River. The Main Basin is generally stratified in the summer, due to river discharge and solar heating, and is often well-mixed in the winter due to winter cooling and increased mixing by wind. Circulation in the central and northern sections of the Main Basin consists largely of outflow through Admiralty Inlet in the upper layer and inflow of marine waters at depth (below approximately 50 m) (Fig. 6) (Strickland 1983, Thomson 1994). Oceanic waters from the Strait of Juan de Fuca flow over the northern sill at Admiralty Inlet into the Main Basin at about two-week intervals (Cannon 1983). In the southern section, currents generally flow northward along the west side of Vashon Island and southward on the east side through Colvos Passage. The sill at Tacoma Narrows also causes an upwelling process that reduces the seawater/freshwater stratification in this basin (Figs. 7a and b). With freshwater inflow, comes sediment deposits at an estimated rate of 0.18 to 1.2 grams/cm²/year (Staubitz et al. 1997).
Major circulation patterns in the Main Basin are greatly influenced by decadal climate regimes (Ebbesmeyer et al. 1998). During cool periods with strong oceanic upwellings and heavy precipitation, the strongest oceanic currents entering from the Strait of Juan de Fuca flow near mid-depth when the basin is cooler than 9.7oC. However, the strongest oceanic currents move toward the bottom of the basin, during warmer, dryer periods when waters are warmer than 9.7oC.
Water quality—Water temperature, salinity, and concentration of dissolved oxygen in waters of the Main Basin are routinely measured by the WDOE at six sites (WDOE 1999). Subsurface temperatures are usually between 8oC and 12oC. However, surface temperatures can reach 15oC to 18oC in summer, and temperatures at depth can get as low as 7.5oC in winter. Salinities in the deeper portions of the Main Basin are generally about 30‰ in summer and fall, but decrease to about 29‰ during the rainier months. Surface waters are also usually about 29‰, but occasionally have salinities as low as 25-27‰ during the rainy season (WDOE 1999).
The mid-basin site had consistently higher temperatures and lower salinity values compared to the water quality parameters at the site near the northern entrance to Admiralty Inlet (WDOE 1999). To demonstrate this trend, values from near mid-basin at West Point in Seattle, considered to be representative of this basin, were compared to values from the northern end of Admiralty Inlet. Values measured on the same dates (a summer month and a winter month) and depths at each site for two different years (1993 and 1996) were compared. For the summer month, the mean temperature at mid-basin site was 12.25oC vs. 9.19oC for the entrance site. The mean salinities for this same month were 29.65‰ and 31.43‰, respectively. For the winter month, the mean temperature at mid-basin site was 9.71oC and 8.11oC for the entrance site. The mean salinity values for this same month were 30.24‰ and 30.84‰, respectively.
Dissolved oxygen varies seasonally, with lowest levels of about 5.5 mg/L occurring at depth in summer months, and highest levels of about 7.5 mg/L near the surface. Occasionally summer-time highs reach 13-14 mg/L at the surface.
Macro vegetation—The Main Basin has a relatively small amount of intertidal vegetation, with 28.3 ± 10.4% of the intertidal area containing vegetation (Bailey et al. 1998). The predominant types are green algae (12.0 ± 4.4%) and eelgrass (11.4 ± 6.6%). Most eelgrass is located on the western shores of Whidbey Island and the eastern shores of the Kitsap Peninsula (Fig. 3) (PSWQA 1987). Although Figure 3 suggests a continuous distribution of eelgrass on the eastern shores of the Main Basin, a recent report by the Puget Sound Water Quality Action Team (PSWQAT 2000) indicates that only 8% of the shoreline has a continuous distribution of eelgrass beds and 40% of the shoreline has a patchy distribution.
Urban, industrial and agricultural development—Areas bordering the Main Basin include the major urban and industrial areas of Puget Sound: Seattle, Tacoma, and Bremerton. Human population sizes for these cities are about 522,500, 182,900, and 38,142, respectively (Rand McNally 1998). Approximately 70% of the drainage area in this basin is forested, 23% is urbanized, and 4% is used for agriculture (Staubitz et al. 1997). About 80% of the total amount of waste discharged from point-sources into Puget Sound comes from urban and industrial sources in this region (PSWQA 1988). Moreover, about 16% of the waste entering Puget Sound, overall, enters this basin through its major river systems, in the form of inorganic nitrogen (Embrey and Inkpen 1998). The Washington State DNR (1998) estimates that 52% of the shoreline in this area has been modified by human activities.
Bathymetry and geomorphology—The Whidbey Basin includes the marine waters east of Whidbey Island and is delimited to the south by a line between Possession Point on Whidbey Island and Meadowdale, west of Everett. The northern boundary is Deception Pass at the northern tip of Whidbey Island (Fig. 1). The Skagit River (the largest single source of freshwater in Puget Sound) enters the northeastern corner of the Basin, forming a delta and the shallow waters (<20 m) of Skagit Bay. Saratoga Passage, just south of Skagit Bay, separates Whidbey Island from Camano Island. This passage is 100 to 200 m deep, with the deepest section (200 mi) located near Camano Head (Burns 1985). Port Susan is located east of Camano Island and receives freshwater from the Stillaguamish River at the northern end and from the Snohomish River (the second largest of Puget Sound’s rivers) at southeastern corner. Port Susan also contains a deep area (120 m) near Camano Head. The deepest section of the basin is located near its southern boundary in Possession Sound (220 m).
Sediment characteristics—The most common sediment type in the intertidal zone of the Whidbey Basin is sand, representing 61.4 ± 65.5% of the intertidal area. Mixed fine sediments is the next most common sediment type covering 25.6 ± 18.9% of the intertidal area (Bailey et al. 1998). Similarly, subtidal areas near the mouths of the three major river systems are largely sand. However, the deeper areas of Port Susan, Port Gardner and Saratoga Passage have surface sediments composed of mixtures of mud and sand (PSWQA 1987, WDOE 1998). Deception Pass sediments consist largely of gravel.
Currents and tidal activity—Although only a few water circulation studies have been performed in the Whidbey Basin, some general observations are possible. Current profiles in the northern portion of this basin are typical of a close-ended fjord (Fig. 8). For example, currents during the summer tend to occur in the top 40 m, moving at low velocities in a northerly direction (Cannon 1983). Currents through Saratoga Passage tend to move at moderate rates in a southerly direction. Due to the influences of the Stillaguamish and Snohomish River systems, surface currents in Port Susan and Port Gardner tend to flow toward the Main Basin, although there is some evidence of a recirculating pattern in Port Susan (PSWQA 1987).
Water quality—The waters in this basin are generally stratified, with surface waters being warmer in summer (generally 10-13oC) and cooler in winter (generally 7-10oC) (Collias et al. 1974, WDOE 1999). Salinities in the southern section of the Whidbey Basin in Possession Sound are similar to those of the Main Basin. In Port Susan and Saratoga Passage, salinities of surface waters (27.0-29.5‰) are generally lower than in the Main Basin, due to runoff from the two major rivers; moreover, after heavy rain these salinities range from 10-15‰. However, salinities in deeper areas often parallel those of the Main Basin (WDOE 1999).
Concentrations of dissolved oxygen in the waters of the Whidbey Basin are routinely measured by the WDOE in Saratoga Passage and in Port Gardner (WDOE 1999). Concentrations were highest in surface waters (up to 15 mg/L) and tended to be inversely proportional to salinity. Samples collected during spring run-off had the highest concentrations of dissolved oxygen. The lowest values (3.5 to 4.0 mg/L) were generally found at the greatest depths in fall.
Macro vegetation—Vegetation covers 23.6 ± 8.8% of the intertidal area of the Whidbey Basin (Bailey et al. 1998). The three predominant types of cover include green algae (6.8 ± 6.2%), eelgrass (6.5 ± 5.8%), and salt marsh (9.0 ± 9.4%). Eelgrass beds are most abundant in Skagit Bay and in the northern portion of Port Susan (Fig. 3) (PSWQA 1987).
Urban, industrial, agricultural, and development—Most of the Whidbey Basin is surrounded by rural areas with low, human population densities. About 85% of the drainage area of this Basin is forested, 3% is urbanized, and 4% is in agricultural production. The primary urban and industrial center is Everett, with a population of 70,000 (Rand McNally 1998). Most waste includes discharges from municipal and agricultural activities and from a paper mill. About 60% of the nutrients (as inorganic nitrogen) entering Puget Sound, enter through the Whidbey Basin by way of its three major river systems (Embrey and Inkpen 1998). The WDNR (1998) estimated that 36% of the shoreline in this area has been modified by human activities.
Bathymetry and geomorphology—The Southern Basin includes all waterways south of Tacoma Narrows (Fig. 1). This basin is characterized by numerous islands and shallow (generally <20 m) inlets with extensive shoreline areas. The mean depth of this basin is 37 m, and the deepest area (190 m) is located east of McNeil Island, just south of the sill (45 m) at Tacoma Narrows (Burns 1985). The largest river entering the basin is the Nisqually River which enters just south of Anderson Island.
Sediment characteristics—A wide assortment of sediments are found in the intertidal areas of this basin (Bailey et al. 1998). The most common sediment and the percent of the intertidal area they cover are as follows: mud, 38.3 ± 29.3%; sand, 21.7 ± 23.9%; mixed fine, 22.9 ± 16.1%; and gravel, 11.1 ± 4.9%. Subtidal areas have a similar diversity of surface sediments, with shallower areas consisting of mixtures of mud and sand, and deeper areas consisting of mud (PSWQA 1987). Sediments in Tacoma Narrows and Dana Passage consists primarily of gravel and sand.
Currents and tidal activity—Currents in the Southern Basin are strongly influenced by tides, due largely to the shallowness of this area. Currents tend to be strongest in narrow channels (Burns 1985). In general, surface waters flow north and deeper waters flow south. Among the five most western inlets, Case, Budd, Eld, Totten, and Hammersley, the circulation patterns of Budd and Eld inlets are largely independent of those in Totten and Hammersley inlets due largely to the shallowness of Squaxin Passage (Ebbesmeyer et al. 1998). These current patterns are characterized by flows of high-salinity waters from Budd and Eld inlets into the south end of Case Inlet, and from Totten and Hammersley inlets into the north end of Case Inlet. Flows of freshwater into the north and sound ends of Case Inlet originate from surface water runoff and the Nisqually River, respectively.
Water quality—The major channels of the Southern Basin are moderately stratified compared to most other Puget Sound basins, because no major river systems flow into this basin. Salinities generally range from 27-29‰, and, although surface temperatures reach 14-15oC in summer, the temperatures of subsurface waters generally range from 10-13oC in summer and 8-10oC in winter (WDOE 1999). Dissolved oxygen levels generally range from 6.5 to 9.5 mg/L. Whereas salinities in the inlets tend to be similar to those of the major channels, temperatures and dissolved oxygen levels in the inlets are frequently much higher in summer. Two of the principal inlets, Carr and Case inlets, have surface salinities ranging from 28-30‰ in the inlet mouths and main bodies, but lower salinities ranging from 27-28‰ at the heads of the inlets (Collias et al. 1974). Summertime surface waters in Budd, Carr and Case Inlets commonly have temperatures that range from 15-19oC and dissolved oxygen values of 10-15 mg/L. Temperature of subsurface water tends to be elevated in the summer (14-15oC); however, temperatures are similar to those of the main channels in other seasons of the year (WDOE 1999).
Macro vegetation—Among the five basins of Puget Sound, the Southern Basin has the least amount of vegetation in its intertidal area (12.7 ± 15.5% coverage), with salt marsh (9.7 ± 14.7% coverage) and green algae (2.1 ± 1.9% coverage) being the most common types (Bailey et al. 1998).
Urban, industrial, and agricultural development—About 85% of the area draining into this basin is forested, 4% is urbanized, and 7% is in agricultural production. The major urban areas around the South Sound Basin are found in the western portions of Pierce County. These communities include west Tacoma, University Place, Steilacoom, and Fircrest, with a combined population of about 100,000 (Puget Sound Regional Council [PSRC] 1998). Other urban centers in the South Sound Basin include Olympia with a population of 33,729 and Shelton with a population of 7,200 (Rand McNally 1998). Important point sources of wastes include sewage treatment facilities in these cities and a paper mill in Steilacoom. Furthermore, about 5% of the nutrients (as inorganic nitrogen) entering Puget Sound, enter into this basin through non-point sources (Embrey and Inkpen 1998). The WDNR (1998) estimated that 34% of the shoreline in this area has been modified by human activities.
Bathymetry and geomorphology—Hood Canal branches off the northwest part of the Main Basin near Admiralty Inlet and is the smallest of the Puget Sound basins, being 90 km long and 1-2 km wide (Fig. 1). Like many of the other basins, it is partially isolated by a sill (50 m deep) near its entrance that limits the transport of deep marine waters in and out of Hood Canal (Burns 1985). The major components of this basin consist of its Entrance, Dabob Bay, the central region, and The Great Bend at the southern end. Dabob Bay and the central region are the deepest sub-basins (200 and 180 m, respectively), whereas other areas are relatively shallow, <40 m for The Great Bend and 50-100 m at the entrance (Collias et al. 1974).
Sediment characteristics—Sediment in the intertidal zone consists mostly of mud (53.4 ± 89.3% of the intertidal area), with similar amounts of mixed fine sediment and sand (18.0 ± 18.5% and 16.7 ± 13.7%, respectively) (Bailey et al. 1998). Surface sediments in the subtidal areas also consist primarily of mud, with the exception of the entrance, which consists of mixed sand and mud, and The Great Bend and Lynch Cove, which have patchy distributions of sand, gravelly sand, and mud (PSWQA 1987, WDOE 1998).
Currents and tidal activity—Aside from tidal currents, currents in Hood Canal are slow, perhaps because the basin is a closed-ended fjord without large-volume rivers. The strongest currents tend to occur near the entrance and generally involve a northerly flow of surface waters.
Water quality—Water temperature, salinity, and concentration of dissolved oxygen in Hood Canal are routinely measured by the WDOE at two sites, which are near The Great Bend and the Entrance (WDOE 1999). Salinities generally range from 29-31‰ and tend to be similar at both sites. In contrast, temperature and dissolved oxygen values are often markedly different between the two sites. Values measured on the same dates (a summer month and a winter month) and at the same depths at each site for 1993 and 1996 demonstrate these differences. Mean temperature in the summer month at The Great Bend site was 9.9oC, but 12.1oC at the Entrance site. Mean dissolved oxygen values for this same month were 3.24 mg/L and 6.67 mg/L at The Great Bend and Entrance sites, respectively. For the winter month, the mean temperature at The Great Bend site was 10.6oC, but 9.1oC for the Entrance site. Mean dissolved oxygen values for this same month were 4.22 mg/L and 6.78 mg/L at the Great Bend and Entrance sites, respectively.
Macro vegetation—Vegetation covers 27.8 ± 22.3% of the intertidal areas of the Hood Canal Basin. Salt marsh (18.0 ± 8.8%) and eelgrass (5.4 ± 6.3%) are the two most abundant plants (Bailey et al. 1998). Eelgrass is found in most of Hood Canal, especially in the Great Bend and Dabob Bay (Fig. 3).
Urban, industrial, and agricultural development—The Hood Canal Basin is one of the least developed areas in Puget Sound and lacks large centers of urban and industrial development. About 90% of the drainage area in this basin is forested (the highest percentage of forested areas of the five Puget Sound basins), 2% is urbanized, and 1% is in agricultural production
(Staubitz et al. 1997). However, the shoreline is well developed with summer homes and year-around residences (PSWQA 1988). A small amount of waste is generated by forestry practices and agriculture. Nutrients (as inorganic nitrogen) from non-point sources in this basin represent only 3% of the total flowing into Puget Sound annually (Embrey and Inkpen 1998). The WDNR (1998) estimated that 33% of the shoreline in this area has been modified by human activities.
Algal productivity in the open waters of the central basin of Puget Sound is dominated by intense blooms of microalgae beginning in late April or May and recurring through the summer. Annual primary productivity in the central basin of the Sound is about 465 g C/m2. This high productivity is due to intensive upward transport of nitrate by the estuarine mechanism and tidal mixing. Chlorophyll concentrations rarely exceed 15 u g/L. Frequently, there is more chlorophyll below the photic zone than within it. Winter et al. (1975) concluded that phytoplankton growth was limited by a combination of factors, including vertical advection and turbulence, light, sinking and occasional rapid horizontal advection of the phytoplankton from the area by sustained winds. Summer winds from the northwest would be expected to transport phytoplankton to the south end of the Sound which could exacerbate the anthropogenic effects that are already evident in some of these inlets and bays (Harrison et al. 1994).
The abundance and distribution of zooplankton in Puget Sound is not well understood. A few field surveys have been conducted in selected inlets and waterways, but reports on Sound-wide surveys are lacking. In general, the most numerically abundant zooplankton throughout the Puget Sound region are the calanoid copepods, especially Pseudocalanus spp. (Giles and Cordell 1998, Dumbauld 1985, Chester et al. 1980, Ohman 1990). Giles and Cordell (1998) reported that crustaceans (primarily calanoid copepods) were most abundant in Budd Inlet in South Puget Sound, although larvae of larvaceans, cnidarians, and polychaetes in varying numbers were also abundant during the year. A similar study conducted by Dumbauld (1985) at two locations in the Main Basin (a site near downtown Seattle and a cluster of sites in the East Passage near Seattle covering a variety of depths from 12 to 220 m), found that calanoid copepods and cyclopoid copepods, and two species of larvaceans were numerically dominant. Dominant copepods at deeper sites were Pseudocalanus spp. and Corycaeus anglicus. The larvacean, Oikopleura dioica, was also relatively common at the shallow sites. Similarly, the most abundant zooplankton in the Strait of Juan de Fuca were reported by Chester et al. (1980) to be calanoid copepods, including Pseudocalanus spp. and Acartia longiremis, and the cyclopoid copepod, Oithona similis.
It is likely that zooplankton assemblages vary both seasonally and annually. Evidence of depth-specific differences was reported by Ohman (1990). In studies conducted in Dabob Bay near Hood Canal, Ohman (1990) compared the abundance of certain zooplankton species at a shallow and deep site. Ohman found one species of copepod (Pseudocalanus newmani) that was common at both sites, whereas species (e.g., Euchaeta elongata and Euphausia pacifica) that prey upon P. newmani were abundant at the deep site, but virtually absent from the shallow site. An example of seasonal variability was reported by Bollens et al. (1992). In Dabob Bay, E. pacifica larvae were abundant in the spring and absent in the winter, and juveniles and adults were most abundant in the summer and early fall, with their numbers declining in the winter (Bollens et al. 1992).
A few Sound-wide surveys of abundance and distribution of benthic invertebrates have been performed (Lie 1974, Llansó et al. 1998). A common finding among these surveys is that certain species prefer specific sediment types. For example, in areas with predominantly sandy sediments, among the most common species are Axinopsida serricata (a bivalve) and Prionospio jubata (a polychaete). In muddy, clayey areas of mean to average depth, Amphiodia urtica-periercta (a echinoderm) and Eudorella pacifica (a cumacean) are among the most common species. In areas with mixed mud and sand, Axinopsida serricata and Aphelochaeta sp.(a polychaete) are commonly found. And lastly, in deep muddy, clayey areas, the predominant species tend to be Macoma carlottensis (a bivalve) and Pectinaria californiensis (a polychaete). In general, areas with sandy sediments tend to have the most species (Llansó et al. 1998), but the lowest biomass (Lie 1974). Areas with mixed sediments tend to have the highest biomass (Lie 1974).
As with zooplankton, assemblages of benthic invertebrates vary both seasonally and annually. Lie (1968) reported seasonal variations in the abundance of species, with the maxima taking place during July-August, and the minima occurring in January to February. However, there were no significant variations in the number of species during different seasons. Annual variation was examined by Nichols (1988) at three Puget Sound sites in the Main Basin: two deep sites (200-250 m) and one shallow site (35 m). For one of the deep sites, he reported that M. carlottensis generally dominated the benthic community from 1963 through the mid-1970s. Subsequently, these species were largely replaced by A. serricata, E. pacifica, P. californensis, Ampharete acutifrons (a polychaete), and Euphiomedes producta (an ostracod). A similar dominance by P. californensis and A. acutifrons was reported for the other deep site over approximately the same time period.
Several macroinvertebrate species are widely distributed in Puget Sound. Among the crustacean species, Dungeness crab (Cancer magister) and several species of shrimp (e.g., sidestripe [Pandalopsis dispar] and pink [Pandalus borealis]) are the most commonly harvested species (Bourne and Chew 1994). The non-indigenous Pacific oyster (Crassostrea gigas) accounts for approximately 90% of the landings of bivalves. Other abundant bivalves are the Pacific littleneck clam (Protothaca staminea), Pacific geoduck (Panopea abrupta), Pacific gaper (Tresus nuttalii), and the non-indigenous Japanese littleneck clam (Tapes philippinarum) and softshell clam (Mya arenaria) (Kozloff 1987, Turgeon et al. 1988).
The most common Pacific salmon species utilizing Puget Sound during some portion of their life cycle include chinook (Oncorhynchus tshawytscha), coho (O. kisutch), chum (O. keta), pink (O. gorbuscha), and sockeye salmon (O. nerka). Anadromous steelhead (O. mykiss) and cutthroat trout (O. clarki clarki) also utilize Puget Sound habitats.
Palsson et al. (1997) identified about 221 species of fish in Puget Sound. The marine species are generally categorized as bottomfish, forage fish, non-game fishes, and other groundfish species. In addition to Pacific hake, Pacific cod, and walleye pollock, other important commercial marine fish species in Puget Sound are Pacific herring, spiny dogfish (Squalus acanthias), lingcod (Ophiodon elongatus), various rockfish species (Sebastes spp.), and English sole (Pleuronectes vetulus). English sole are thought to be relatively healthy in the central portions of Puget Sound; however, significant declines have been recorded in localized embayments, such as Bellingham Bay and Discovery Bay. Other species of bottomfish species found throughout Puget Sound include skates (Raja rhina and R. binoculata), spotted ratfish (Hydrolagus cooliei), sablefish (Anoplopoma fimbria), greenlings (Hexagrammos decagrammus and H. stelleri), sculpins (e.g., cabezon [Scorpaenichthys marmoratus], Pacific staghorn sculpin [Leptocottus armatus], and roughback sculpin [Chitonotus pugetensis]), surfperches (e.g., pile perch [Rhacochilus vacca] and striped seaperch [Embiotoca lateralis]), wolf-eel (Anarrhichthys ocellatus), Pacific sanddab (Citharichthys sordidus), butter sole (Pleuronectes isolepis), rock sole (Pleuronectes bilineatus), Dover sole (Microstomus pacificus), starry flounder (Platichthys stellatus), sand sole (Psettichthys melanostictus), and over one dozen rockfish species (e.g., brown rockfish [Sebastes auriculatus], copper rockfish [S. caurinus], greenstriped rockfish [S. elongatus] yellowtail rockfish [S. flavidus], quillback rockfish [S. maliger], black rockfish, [S. melanops] and yelloweye rockfish [S. ruberrimus]) (DeLacy et al. 1972, Robins et al. 1991). Additional fish species that are less known, but widely distributed in Puget Sound, include surf smelt (Hypomesus pretiosus), plainfin midshipman (Porichthys notatus), eelpouts (e.g., blackbelly eelpout [Lycodopsis pacifica]), pricklebacks (e.g., snake prickleback, [Lumpenus sagitta]), gunnels (e.g., penpoint gunnel [Apodichthys flavidus]), Pacific sand lance (Ammodytes hexapterus), bay goby (Lepidogobius lepidus), and poachers (e.g., sturgeon poacher [Podothecus acipenserinus]) (DeLacy et al. 1972, Robins et al. 1991).
About 66,000 marine birds breed in or near Puget Sound (Mahaffy et al. 1994). About 70% of them breed on Protection Island, located just outside of the northern entrance to the Sound. The most abundant species are rhinoceros auklet (Cerorhinca monocerata), glaucous_winged gull (Larus glaucescens), pigeon guillemot (Cepphus columba), cormorants (Phalacrocorax spp.), marbled murrelet (Brachyramphus marmoratus), and the Canada goose (Branta canadensis). Examples of less abundant species include common murre (Uria aalge) and tufted puffins (Fratercula cirrhata). A number of additional bird species use Puget Sound during the winter months. Dabbling ducks, including American wigeon (Anas americana), mallard ducks (A. platyrhynchos) and northern pintail (A. acuta), are the most common, followed by geese and swans, such as trumpeter swans (Cygnus columbianus), tundra swans (C. columbianus), and Canada geese (Branta canadensis) (Mahaffy et al. 1994).
Populations of rhinoceros auklet and pigeon guillemot appear to be stable, whereas populations of glaucous_winged gull have increased slightly in recent years, especially in urban areas (Mahaffy et al. 1994). Accurate estimates of current populations of marbled murrelet and the Canada goose are not available, but the population of marbled murrelet has been greatly reduced and this species has been listed as threatened. Thirty years ago, year_around resident Canada geese were rare, but current anecdotal evidence from observations in waterfront parks suggests that their population is growing rapidly. The common murre and tufted puffin populations have declined drastically during the last two decades.
Nine primary marine mammal species occur in Puget Sound including (listed in order of abundance): harbor seal (Phoca vitulina), California sea lion (Zalophus californianus), Steller sea lion (Eumetopias jubatus), Northern elephant seal (Mirounga angustirostris), harbor porpoise (Phocoena phocoena), Dall's porpoise (Phocoenoides dalli), killer whale (Orcinus orca), gray whale (Eschrichtius robustus), and minke whale (Balaenoptera acutorostrata). Harbor seals are year_round residents, and their abundance has been increasing in Puget Sound by 5% to 15% annually at most sites (Calambokidis and Baird 1994).
California sea lions, primarily males, reside in Puget Sound between late summer and late spring, and spend the remainder of the year at their breeding grounds in southern California and Baja California. Sea lion populations are growing at approximately 5% annually. Populations of the remaining species are quite low in Puget Sound. Steller sea lions and elephant seals are transitory residents, whereas the Steller sea lion is currently listed as threatened in the U.S., the elephant seal is abundant in the eastern North Pacific but has few haul_out areas in Puget Sound. Although harbor porpoises are also abundant in the eastern North Pacific and were common in Puget Sound 50 or more years ago, they are now rarely seen in the Sound (Calambokidis and Baird 1994). Low numbers of Dall's porpoise are observed in Puget Sound throughout the year, but little is known about their population size—they are also abundant in the North Pacific.
A pod of resident fish_feeding killer whales, numbering about 100, resides just north of the entrance to Puget Sound, and the size of this group had reached about 100 by the mid-1990s and was increasing at about 2% per year. However, by 1999, the size of this population had decreased to about 83 whales, a decline of more than 15% (M. Dahlheim3). The causes of this decline are unknown, but could include exposure to chemical contaminants, reduced availability of prey items and increased human activities.
Minke whales are also primarily observed in this same northern area, but their population size is unknown. Gray whales migrate past the Georgia Basin en route to or from their feeding or breeding grounds; a few of them enter Puget Sound during the spring through fall to feed.
The Strait of Georgia covers an area of approximately 6,800 km2 (Thomson 1994) (Fig. 9) and is approximately 220 km long and varies from 18.5 to 55 km in width (Tully and Dodimead 1957, Waldichuck 1957). Both southern and northern approaches to the Strait of Georgia are through a maze of islands and channels from the San Juan and Gulf islands to the south and a series of islands to the north that extend for 240 km to Queen Charlotte Strait (Tully and Dodimead 1957). Both northern channels (Johnstone Strait and Cordero Channel) are from 1.5 to 3 km wide and are effectively two-way tidal falls, in which currents of 12-15 knots occur at peak flood (Tully and Dodimead 1957). However, both lateral and vertical constriction of water flow at the narrowest points in these northern channels are even more severe. Constrictions occur at Arran Rapids, Yuculta Rapids, Okisollo Channel, and to a lesser degree at Seymour Narrows (0.74 km wide, minimum depth of 90 m) in Discovery Passage (Waldichuck 1957). Overall, these narrow northern channels have only about 7% of the cross-sectional area as do the combined southern entrances into the Strait of Georgia (Waldichuck 1957).
The Strait of Georgia (Fig. 9) has a mild maritime climate and is dryer than other parts of the coast due to the rain shadow of the Olympic and Vancouver Island mountains. At sea level, air temperatures range from 0o to 5oC in January and 12o to 22oC in July, and winds are typically channeled by the local topography and blow along longitudinal axes of the straits and sounds. Winds are predominantly from the southeast in winter and the northwest in summer. It has a mean depth of 156 m (420 m maximum) and is bounded by narrow passages (Johnstone Strait and Cordero Channel to the north and Haro and Rosario straits to the south) and shallow submerged sills (minimum depth of 68 m to the north and 90 m to the south).
Freshwater inflows are dominated by the Fraser River, which accounts for roughly 80% of the freshwater entering the Strait of Georgia. Fraser River run-off and that of other large rivers on the mainland side of the Strait are driven by snow and glacier melt and their peak discharge period is generally in June and July. Rivers that drain into the Strait of Georgia off Vancouver Island (such as the Chemainus, Cowichan, Campbell, and Puntledge rivers) peak during periods of intense precipitation, generally in November (Waldichuck 1957).
Circulation in the Strait of Georgia occurs in a general counter-clockwise direction (Waldichuck 1957). Tides, winds, and freshwater run-off are the primary forces for mixing, water exchange, and circulation. Tidal flow enters the Strait of Georgia predominantly from the south creating vigorous mixing in the narrow, shallow straits and passes of the Strait of Georgia. The upper, brackish water layer in the Strait of Georgia is influenced by large freshwater run-off and salinity in this layer varies from 5 to 25‰. Deep, high-salinity (33.5 to 34‰), oceanic water enters the Strait of Georgia from the Strait of Juan de Fuca. The surface outflowing and deep inflowing water layers mix in the vicinity of the sills, creating the deep bottom layer in the Strait of Georgia, where salinity is maintained at about 31‰ (Waldichuck 1957). The basic circulation pattern in the summer is the southerly outflow of relatively warm, low-salinity surface, with the northerly inflow of high salinity oceanic water from the Strait of Juan de Fuca at the lowest depths. In the winter, cool, low-salinity near surface water mixes with the intermediate depth high salinity waters; however, oceanic inflow is generally confined to the intermediate depths. Crean et al. (1988) reported that "the freshwater discharge finds primary egress through the southern boundary openings into the Strait of Juan de Fuca" and that subsurface waters (5 to 20 m below the region of the Fraser River discharge) also have "a predominantly southerly flow" (Fig. 10). Since surface water run-off peaks near the time of peak salinity of inflowing source water, the salinity of the deepwater in the Strait of Georgia undergoes only a small seasonal change in salinity (Waldichuck 1957).
Pacific herring, Clupea pallasi (Valenciennes, 1847), in the Eastern Pacific, range from northern Baja California to St. Michael Island and Cape Bathurst in the Beaufort Sea (Hart 1973, Lassuy 1989). It is also found in Arctic waters from Coronation Gulf, Canada, to the Chuckchi Sea and the Russian arctic. In the Western Pacific, it is found from Toyama Bay, Japan, west to Korea, and the Yellow Sea (Haegele and Schweigert 1985, Wang 1986). In the Eastern Pacific, the effective commercial use is between San Francisco, California, and Central Alaska.
The general distribution and major spawning sites of Pacific herring along the Pacific Coast are shown in Figure 11 (Lassuy 1989). In the state of Washington, there are 19 well-defined spawning locations including three coastal locations (Willapa Bay, Grays Harbor and Columbia River Estuary) and 18 locations within Puget Sound (Fig. 12) (Bargman 1998, Lemberg et al. 1997, Pederson and Di Donato 1982). The location and timing of spawning at each location are very consistent and predictable from year-to-year (Hay and Outram 1981, O’Toole et al. 2000).
Although Pacific herring are not considered to be a migratory species, they exhibit onshore-offshore movements associated with spawning and feeding (Morrow 1980). Adults move onshore during winter and early spring, residing in "holding" areas before moving to adjacent spawning grounds (Emmett et. al 1991, Hay and McCarter 1997b). Their populations consist of many discrete stocks (Grosse and Hay 1989); however, offshore distributions of adults for many Pacific coast stocks are unknown (Barnhart 1988). Not all stocks of Pacific herring make extensive offshore migrations, however, many small resident populations remain in coastal inlets and bays (Stevenson 1962). For instance, following metamorphosis, Puget Sound stocks of herring spend their first year in Puget Sound. Some stocks of Puget Sound herring spend their entire lives within Puget Sound while other stocks summer in the coastal areas of Washington and southern British Columbia (Trumble 1983a).
Tagging studies in British Columbia have shown that herring exhibit homing to the geographical regions near where they were spawned, however, their straying rates are relatively high, about 20 percent on average (Hourston 1982). See further discussion in the "Tagging and distribution" section, specifically under the British Columbia tagging section. Pacific herring larvae may be transported by currents but their behavior and local currents often retain them in specific areas (Emmett et al. 1991). Some juveniles stay in nearshore shallow-water areas until fall when they disperse to deeper offshore waters. However, others may reside year-round in some estuaries (San Francisco Bay) (Wang 1986). Adult Pacific herring are found between 100-150 m, with vertical distribution influenced by temperature (Grosse and Hay 1989). It has also been observed that larvae, juveniles, and adult herring move toward the surface to feed at dawn and dusk.
Pacific herring are gonochoristic, oviparous, and iteroparous with external fertilization (Emmett et al. 1991). Fecundity increases with female size, producing on average 19,000 eggs annually at 19 cm standard length and 29,500 at 22 cm (Hart 1973). On a large geographic scale, there appears to be a decline in fecundity for a given length when moving from south (Puget Sound) to north (Prince William Sound) and northwest (Peter the Great Bay) (Garrison and Miller 1982). Unfertilized Pacific herring eggs are about 1.0 mm in diameter (Outram 1955) and the fertilized egg is 1.2-1.5 mm in diameter (Hart 1973, Hourston and Haegele 1980). Salinity effects on egg development are relatively unimportant (Hart 1973).
Within the range of the species, there is a latitudinal cline in spawning time (Figs. 13a-d). Spawning begins in November in the southern part of the range to August in the far north (Emmett et al. 1991, Lassuy 1989). Spawning peaks in December and January in California (Spratt 1981) and February and March in Puget Sound (Trumble 1983b). Peak spawning in Puget Sound starts the last week of February or the first week of March, except for the Cherry Point spawners (Fig. 13b) (O’Toole et al. 2000). Spawning at Cherry Point begins in early April and ends in early June with peak spawning activity around May 10th.
Pacific herring usually spawn at night in the shallow subtidal zone (Bargman 1998, Emmett et al. 1991). They spawn in water temperatures between 3.0 to 12.3oC. Most egg deposition occurs from 0-10 feet in tidal elevation. Pacific herring spawn by depositing eggs on vegetation or other shallow water substrate such as seagrass (Zostera), brown and red algae (Macrocystis, Fucus, and Gracilaria) (Haegele and Schweigert 1985). The eggs hatch in 11-12 days at 10.7oC, 14-14 days at 8.5oC, and 28-40 days at 4.4oC (Outram 1955).
Spawning grounds of Pacific herring are typically in sheltered inlets, sounds, bays, and estuaries rather than along open coastlines (Haegele and Schweigert 1985). The Pacific herring is particularly susceptible to influences of shoreline development because spawning grounds are limited to these rather specific intertidal and shallow subtidal locations. Substrates that herring spawn on may vary from eelgrass and kelp to gravel depending on location, however, eelgrass is the most often utilized spawning substrate. When shoreline development, and particularly shoreline armoring occurs, the dynamics of current and wave action are altered and may result in the loss of eelgrass or change in the physical substrate of the intertidal area (Thom and Hallum 1990).
Pacific herring larvae range from 5 to 26 mm total length (TL) (Emmett et al. 1991). Following hatching, the larvae drift in the ocean currents. Acuity of the larval eye is low until they are 10-12 mm long at which time they are able to detect prey at short distances (Blaxter and Jones 1967). Survival in these early stages therefore depends on stable current patterns that promote larval retention in areas favorable to feeding and growth (Stevenson 1962). They begin to metamorphose at 26 mm TL and complete this process by 35 mm TL (Hourston and Haegele 1980, Hay 1985). Metamorphosis is complete in about two to three months.
Juveniles are 35 to 150 mm TL, depending upon region (Emmett et al. 1991). During their first summer, juveniles gather in large schools and remain primarily in inshore waters. Juveniles may gather after their first summer and move offshore until maturation (Stocker and Kronlund 1998) or they may remain inshore until their first spawn (Hay 1985). First-year juvenile fish that move offshore live mainly in waters with depth of 150-200 m. Two- and three-year-old herring are found at depths between 100-150 m (Hourston and Haegele 1980). Age at first maturity is generally 2-5 years but increases with increasing latitude (Hay 1985) and decreases with increasing exploitation (Ware 1985). For example, in Alaska waters, age at first maturity is 3-4 years and 2-6 years in the Bering Sea (Garrison and Miller 1982). In California, herring spawn at age-2 and all are mature by age-3 (Spratt 1981). Pacific herring mature at lengths from 13-26 cm TL, again depending upon region, with fish getting larger as latitude increases (Emmett et al. 1991, Garrison and Miller 1982).
Larvae, juveniles, and adults are selective pelagic plankton feeders, although filter feeding has been observed (Emmett et al. 1991). More specifically, larval Pacific herring start feeding on copepods, invertebrate eggs, and diatoms at a length of 9.5-11.0 mm (Hart 1973, Lasker 1985). Juvenile Pacific herring in sublittoral habitats eat calanoid copepods, decapod crab larvae, and chaetognaths (Fresh et. al 1981). Juveniles in pelagic habitats eat calanoid copepods, harpacticoid copepods, and euphausiids. After Pacific herring mature, copepods remain an important food source but are partly superseded by euphausiids (Hart 1973). As spawning season approaches, herring migrate toward shore and feeding ceases. A characteristic cycle of fattening in the summer and fasting in the winter appears to also coincide with spawning. Adult herring eat planktonic crustaceans (copepods, euphausiids, and amphipods) and small fishes, such as eulachon, herring, starry flounder, ronquil, sand lance, hake, marbled sculpin, and rockfish (Hart 1973).
Herring are an important food source within the trophic web. Eggs and larvae of Pacific herring are eaten by walleye pollock, herring, juvenile salmon, invertebrates, and most notably, birds (Bayer 1980, Hart 1973, Hourston and Haegele 1980). Bayer (1980) directly observed feeding of gulls at low tide and diving ducks obtained eggs by diving, by piracy, or by picking up eggs by swimming at high tide in Yaquina Bay, Oregon. Adult herring are most susceptible to predation while holding inshore before and during the spawning season (Lassuy 1989). Among the predators that prey on herring at these times are salmon, seals, sea lions, killer whales, dogfish, and birds (Hourston and Haegele 1980). In the inshore waters of the northern coast of Washington, it was observed that adult herring were preyed upon by the northern fur seal (Callorhinus ursinus) (Perez and Bigg 1986). When herring are feeding offshore they are preyed upon by hake, sablefish, dogfish, Pacific cod, and salmon (Lassuy 1989).
Coastwide there appears to be an increase in size, with an increase in latitude. Adult herring lengths range from 13-26 cm TL, depending upon region, with fish obtaining a larger length as latitude increases (Garrison and Miller 1982). For example, Pacific herring in San Francisco Bay, California, had an average length-at-age of 200 mm for a 5-year-old fish (Spratt 1981); whereas, herring in the Togiak District, Alaska, had an average length-at-age of 254 mm for a 5-year-old fish (Fried et al. 1983). Herring live up to 19 years and grow to a maximum length of 38 cm TL (Hart 1973).
According to Bargmann (1998), after maturity at ages of two to four years for Puget Sound, they migrate back to their natal spawning grounds. In Puget Sound, herring may reach sexual maturity at age-2 and lengths of 14-16 cm (Katz 1942), but some may not reach sexual maturity until age-4, as in the Strait of Georgia populations (Trumble 1979). Lemberg et al. (1997) presented information about the length-at-age distributions of Pacific herring populations in Puget Sound. Table 2 shows that the average length-at-age for herring collected at Cherry Point are among the largest in the state. For example, the average length-at-age for a 5-year-old herring from Port Gamble was 199 mm but the Cherry Point population had an average length-at-age of 224 mm. The large size seen at Cherry Point suggests that the population may migrate to rich summer feeding grounds on the continental shelf (Lemberg et a. 1997). In Puget Sound, herring formerly lived to ages in excess of 10 years, however, fish older than 6 are now rare.
Ekman (1953), Hedgpeth (1957), and Briggs (1974) summarized the distribution patterns of coastal marine fishes and invertebrates and defined major worldwide marine zoogeographic zones or provinces. Along the coastline of the boreal Eastern Pacific, which extends roughly from Point Conception, California to the Eastern Bering Sea, numerous schemes have been proposed for grouping the faunas into zones or provinces. A number of authors (Ekman 1953, Hedgpeth 1957, Briggs 1974, Allen and Smith 1988) have recognized a zoogeographic zone within the lower boreal Eastern Pacific that has been termed the Oregonian Province. Another zone in the upper boreal Eastern Pacific has been termed the Aleutian Province (Briggs 1974). However, exact boundaries of zoogeographic provinces in the Eastern boreal Pacific are in dispute (Allen and Smith 1988). Briggs (1974) and Allen and Smith (1988) reviewed previous literature from a variety of taxa and from fishes, respectively, and found the coastal region from Puget Sound to Sitka, Alaska to be a "gray zone" or transition zone that could be classified as part of either of two provinces: Aleutian or Oregonian (Fig. 14). The southern boundary of the Oregonian Province is generally recognized as Point Conception, California and the northern boundary of the Aleutian Province is similarly recognized as Nunivak in the Bering Sea or the Aleutian Islands (Allen and Smith 1988).
Briggs (1974) placed the boundary between the Oregonian and Aleutian Provinces at Dixon Entrance, based on the well-studied distribution of mollusks, but indicated that distributions of fishes, echinoderms, and marine algae gave evidence for placement of this boundary in the vicinity of Sitka, Alaska. Briggs (1974) placed strong emphasis on the distribution of littoral mollusks (due to the more thorough treatment this group has received) in placing a major faunal break at Dixon Entrance. The authoritative work by Valentine (1966) on distribution of marine mollusks of the northeastern Pacific shelf showed that the Oregonian molluscan assemblage extended to Dixon Entrance with the Aleutian fauna extending northward from that area. Valentine (1966) erected the term Columbian Sub-Province to define the zone from Puget Sound to Dixon Entrance.
Several lines of evidence suggest that an important zoogeographic break for marine fishes occurs in the vicinity of Southeast Alaska. Peden and Wilson (1976) investigated the distributions of inshore fishes in British Columbia, and found Dixon Entrance to be of minor importance as a barrier to fish distribution. A more likely boundary between these fish faunas was variously suggested to occur near Sitka, Alaska, off northern Vancouver Island, or off Cape Flattery, Washington (Peden and Wilson 1976, Allen and Smith 1988). Briggs (1974) reported that of the more than 50 or more rockfish species belonging to the genus Sebastes occurring in northern California, more than two-thirds do not extend north of British Columbia or Southeast Alaska. Briggs (1974) further stated that "about 50 percent of the entire shore fish fauna of western Canada does not extend north of the Alaskan Panhandle." In addition, many marine fish species common to the Bering Sea, extend southward into the Gulf of Alaska but apparently occur no further south (Briggs 1974). Allen and Smith (1988) stated that "the relative abundance of some geographically-displacing [marine fish] species suggest that the boundary between these provinces [Aleutian and Oregonian] occurs off northern Vancouver Island."
2 J. Newton, Washington Department of Ecology, 300 Desmond
Drive, Lacey WA 98503. Pers. Commun., September 10, 1999.
3 M. Dahlheim, NOAA Fisheries, 7600 Sand Point Way, N.E.,
Seattle, WA 98115. Pers. commun., November, 2000.