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Background and Historical Review

Recruitment Processes Program Ichthyoplankton Sampling Studies
(for a complete discussion see Matarese et al., 2003)

The Recruitment Processes Program has been collecting and analyzing ichthyoplankton for over 40 years (Fig. 1). Beginning in 1965, AFSC, then known as the Bureau of Commercial Fisheries (BCF) Seattle Biological Laboratory, started an ichthyoplankton program off the Northeast Pacific coast to determine the northernmost extent of Merluccius productus (Pacific Hake) spawning. Only data on Pacific hake were kept and analyzed. The Marine Resources Monitoring, Assessment, and Prediction Program (MARMAP) began in 1971, sampling in the eastern Bering Sea, off Kodiak Island, Alaska, and off Vancouver Island, British Columbia. Samples were collected using MARMAP standard protocol (Jossi and Marak, 1983) and all taxa were sorted, counted, and identified by larval taxonomists at the Seattle laboratory, at that time known as the Northwest Fisheries Center (NWFC). The Outer Continental Shelf Environmental Assessment Program (OCSEAP) supported five cruises conducted 1977–1979 in the shelf waters east of Kodiak Island in the Gulf of Alaska. These studies were developed to assess the spatial and temporal distribution of plankton that might be affected by oil exploration and development. In 1980, the Plankton Sorting and Identification Laboratory in Szczecin, Poland, began processing ichthyoplankton samples collected by our center, which had been renamed the Northwest and Alaska Fisheries Center (NWAFC) in 1974. For most of the early 1980s, sampling was conducted along the Washington, Oregon, and northern California coasts in cooperation with the Soviet Union (USSR/USA cruises, 1980-87). As the first large-scale ichthyoplankton surveys to be done in this region, this work sought to document patterns in occurrence, distribution, and abundance of ichthyoplankton in coastal waters of the Northeast Pacific. The Fisheries Oceanography Coordinated Investigations (FOCI) Program began in 1985 and was initially focused on physical and biological factors affecting survival of ELH stages of walleye pollock (Gadus chalcogrammus) in the Gulf of Alaska. Bering Sea FOCI was established in 1991 (after the NWAFC was split into two centers, the Northwest Fisheries Science Center (NWFSC) and the AFSC) under the auspices of NOAA's Coastal Ocean Program (COP) to address similar research in the eastern Bering Sea shelf region. Bering Sea FOCI ended in 1996, but was immediately followed in 1997 by the Southeast Bering Sea Carrying Capacity Program (SEBSCC), also sponsored by COP. This program sought to document the role of juvenile Walleye Pollock in the eastern Bering Sea ecosystem, to examine the factors affecting their survival, and to develop and test annual indices of pre-recruitment abundance (Dagg and Royer, 2002). The Northeast Pacific Global Ocean Ecosystems Dynamics Program (GLOBEC) was added to the Recruitment Processes Program in 1998. The GLOBEC research, in addition to compiling a comprehensive atlas that presents data on spatial and temporal trends in the dominant fish eggs and larvae (Matarese et al., 2003), included studies comparing multi-species ichthyoplankton assemblages from the Gulf of Alaska, Bering Sea, and U.S. west coast (Doyle et al., 2002a; Doyle et al., 2009) and larval flatfish transport studies, concentrating on the influence of El Niño in the Gulf of Alaska (Bailey and Picquelle, 2002). These investigations provided insight into the spawning strategies of the fish populations in these regions and how they relate to oceanographic conditions. Steller sea lion research was undertaken in 2002 to provide a retrospective analysis of ichthyoplankton data from the Gulf of Alaska and Bering Sea. This analysis contributed to understanding ecosystem dynamics in relation to Steller sea lion decline.

Ongoing Investigations

Over the years, the Recruitment Processes program has broadened its focus from single species studies to a more holistic ecosystem approach. FOCI, one of our original projects, became so broad that this acronym was being used as the "umbrella" for many different projects. To reflect this broadening of our investigations, in 2005 the group agreed to put all existing and future projects under the Eco-FOCI acronym (Ecosystem & Fishery-Oceanography Coordinated Investigations). This evolution occurred as NOAA Fisheries was also broadening its focus and adopting an ecosystem approach to management. One of our projects that is a perfect fit for Eco-FOCI is the North Pacific Climate Regimes and Ecosystem Productivity project (NPCREP), which seeks to observe and understand how climate determines the structure and function of marine ecosystems (Bering Sea and Gulf of Alaska). Begun in 2002, this project, in collaboration with NOAA's Pacific Marine Environmental Laboratory, applies our new knowledge of climate-ecosystem linkages to the management of living marine resources, as does our original FOCI program. Our original FOCI studies on Walleye Pollock and their ecosystem continue in the Gulf of Alaska and the eastern Bering Sea. For the Gulf of Alaska, FOCI conducts process studies and annual larval surveys and incorporates these data into recruitment estimates for Walleye Pollock (Megrey et al., 1996; Bailey, 2002). Correlation modeling methods have been developed to analyze hydroacoustic survey results of spawning aggregations, ichthyoplankton surveys of larvae, estimates of spawning biomass and recruitment from annual stock assessment, measurements of ocean temperature, winds, rainfall, sea-level pressure gradient, and other biological and physical factors (Megrey et al., 1995). Studies in the Bering Sea continue to document the role of Walleye Pollock in the eastern Bering Sea ecosystem, including their interaction with seabirds and marine mammals. GLOBEC-supported investigations have identified dominant taxa and multispecies assemblages in the ichthyoplankton, described their horizontal distribution patterns, and related these patterns to the oceanographic variables (Doyle et al., 2002a). Temporal variation in the composition, distribution, and abundance of these assemblages is being further investigated. In addition, we are examining temporal variability in the occurrence, abundance, and distribution of many ichthyoplankton species that are numerically dominant (e.g., Hippoglossoides elassodon, Flathead Sole, Porter, 2005; Lepidopsetta polyxystra, Northern Rock Sole, Lanksbury et al., 2007; Atheresthes stomias, Arrowtooth Flounder, Blood et al., 2007) and ecologically important (e.g., Mallotus villosus, Capelin, Doyle et al., 2002b). Seasonal ichthyoplankton assemblages are being identified and described (e.g., summer ichthyoplankton in the Bering Sea, Duffy-Anderson, 2006; fall ichthyoplankton in the Gulf of Alaska, Lanksbury et al., 2005). Other studies are also investigating advective processes associated with onshore transport of ichthyoplankton, developing cross-shelf exchange tracers composed of offshore ichthyoplankton assemblages, and identifying key species that may be indicators of changes in oceanographic conditions or cross-shelf flow.

Our newest programs center on the ecosystems of the Gulf of Alaska and the Arctic. The Gulf of Alaska Integrated Ecosystem Research Project (GOAIERP) was started in 2010 to better understand the mechanisms in which climate and ocean conditions influence the survival of juvenile marine fishes. This project will compare zooplankton, ichthyoplankton, and juvenile fish species occurrence and abundance in the western Gulf of Alaska with that of the eastern Gulf of Alaska, which is an area that had been sporadically sampled only 3 times during the last 25 years. A project also initiated in the Arctic in 2010, the Chukchi Acoustic, Oceanographic, and Zooplankton Study (CHAOZ), is a multi-disciplinary examination of the eastern Chukchi Sea ecosystem to determine the abundance and distribution of whales in areas of potential resource extraction. Ocean circulation and zooplankton, specifically euphausiids, are being examined to describe prey availability and delivery in relation to whale observations and acoustic calls. To better understand the early life histories and distribution of arctic fishes, ichthyoplankton samples have also been collected opportunistically as project time allows.

Geographic and Temporal Coverage (Fig. 2)

Most data for the initial BCF Pacific hake and MARMAP studies in the mid-1960s and early 1970s were not entered into a permanent database. Our database became more consistent in 1977 with OCSEAP, the first broad-scale program offering NWAFC scientists the opportunity to study seasonal occurrences of eggs and larvae in the Northeast Pacific Ocean. During the 1970s, sampling intensity was highest in the Gulf of Alaska east of Kodiak Island (Map 1). The OCSEAP Program offered broad monthly coverage (February–November), but, overall, only 13 cruises were conducted between 1972 and 1979 (no cruises from 1973 to 1976). The graphs adjacent to each map show that the sampling effort over the months of the year varied by decade and by region. In the 1970s, comparatively few cruises were conducted, but most (81%) were conducted in the Gulf of Alaska with the remainder in the Bering Sea.

By the mid-1980s, there was a dramatic increase in the number of surveys due to the addition of U.S. west coast cruises (USSR/USA, 1980–1987) and the initiation of the FOCI Program (Map 2). Sampling was greatest in the Gulf of Alaska in Shelikof Strait and southwest of Kodiak Island. The number of cruises increased from 13 during the 1970s to 44 during the 1980s. January was included in the monthly coverage, but 88% of cruises occurred from March to May, which is the peak period of Walleye Pollock spawning in Shelikof Strait. Only three cruises were conducted in the Bering Sea, but coverage was expanded with ten cruises conducted along the U.S. west coast. Sampling distribution along the west coast was highest along the continental shelf region from Washington to northern California, while sampling was limited nearshore and in the deeper offshore waters.

Coverage in the 1990s was expanded to include more sampling in the Bering Sea with the onset of the Bering Sea FOCI and SEBSCC Programs (Map 3). More cruises were conducted than in the 1980s (58 versus 44) and a much higher percentage of Bering Sea cruises were conducted than ever before (46%). Summer coverage (27%) was also more extensive. Sampling gear other than bongo and neuston nets and Tucker trawls was used (e.g., MOCNESS nets to assess fine-scale vertical distribution) and cruises using Methot nets were designed to collect early juveniles; however, these special purpose gears were not included in the abundance and distribution data presented here.

For the years 2000–2009, most cruises were conducted in the Bering Sea (64%). Sampling was extended to the most northern areas of the Bering Sea (Map 4), while also adding some areas in the Gulf of Alaska beyond the shelf break off Southeast Alaska and British Columbia.

Ichthyoplankton collections in the Arctic have been rare up until the 21st century. In 2004, the first cruise of the Russian-American Long-Term Census of the Arctic (RUSALCA), a cooperative long term census of the Arctic between Russian and United States scientists, took place in the northern Bering and Chukchi seas; a second cruise was conducted in 2009. In 2008, ichthyoplankton samples were collected in the Beaufort Sea as part of an initial assessment of the distribution and abundance of fishes and invertebrates in this Arctic area. In 2011, the GOAIERP study conducted sampling in the eastern, north central, and western Gulf of Alaska. The second CHAOZ cruise sampled the benthic layer for ichthyoplankton and zooplankton.

Overview of the Physical Oceanographic Environment

The abundance patterns of ichthyoplankton are summarized for four major ecosystems: the eastern Bering Sea (EBS), western Gulf of Alaska (GOA), the U.S. west coast, and the U.S. Arctic (Beaufort and Chukchi seas). An overall description of the physical and oceanographic characteristics of these three ecosystems is summarized below (Doyle et al., 2002a; Matarese et al., 2003).

The eastern Bering Sea is characterized by an exceptionally broad (>500 km) shelf region with a narrow continental slope adjoining an extensive Aleutian Basin (Map 5). The EBS shelf is one of the most productive regions in the world and sustains a high biomass of higher trophic level organisms (Loughlin et al., 1999). Circulation in the basin is generally cyclonic and is fed by inflow from the Alaskan Stream through the Aleutian Islands (Schumacher and Stabeno, 1998) (Map 6). Flow is greatest in the Bering Slope Current, which transports nutrients onto the outer shelf. Flow over the shelf itself is generally weak and large eddies are a common feature. Ice covers a substantial portion of the EBS each winter and spring, although there is considerable interannual variation in the duration and extent of ice coverage. There are three recognized biophysical domains on the shelf, separated by frontal boundaries at roughly the 50 m, 100 m, and 200 m isobaths, which differ hydrographically depending on the degree of stratification and mixing. Productivity appears to be highest at the shelf-break front and phytoplankton blooms there can begin in May and last throughout the summer (Springer et al., 1996). Zooplankton production is estimated to be highest along the shelf edge and outer shelf where the mesozooplankton consists primarily of large oceanic copepod species.

Numerous troughs and shallow banks characterize the topography of the western Gulf of Alaska. The Aleutian shelf area, as defined by the 200 m isobath, is narrower than the EBS shelf (65-175 km) and drops abruptly to depths of 5000-6000 m in the Aleutian Trench, which parallels the shelf edge (Map 5). The Alaskan Stream, which flows southwesterly and roughly parallel to the shelf break at 50-100 cm/sec, dominates offshore, near-surface circulation (Map 6). Nearshore, the Alaska Coastal Current (ACC) is the dominant feature (Reed and Schumacher, 1986). The upper layer flows in a southwesterly direction. With surface speeds of 25-100 cm/sec, the ACC in the vicinity of Shelikof Strait is one of the most vigorous and dynamic coastal currents in the world (Stabeno et al., 1995). Temperatures follow a clear seasonal pattern, with the coldest values occurring in March and the warmest values in August (Reed and Schumacher, 1986). Freshwater discharge into coastal waters peaks in the fall and strongly affects the circulation (Royer, 1998). This region has been referred to as the Coastal Downwelling Domain and is characterized by mainly onshore flow at the surface (Ware and McFarlane, 1989). A seasonal peak in phytoplankton production occurs first in the ACC, and then in the adjacent shelf area, during the first week in May (Napp et al., 1996). Production of copepod nauplii and other zooplankton usually accelerates significantly at this time, but, because of low temperatures and low concentrations of gravid adults, does not reach a maximum until mid-summer (Cooney, 1987).

In contrast to the EBS and the western GOA, the continental shelf is narrow off the U.S. west coast (Map 7). Off Washington and northern Oregon, the shelf width is less than 70 km, whereas off southern Oregon and northern California it narrows to less than 30 km, reaching a minimum of about 10 km off Cape Mendocino. A series of submarine canyons transect the shelf and slope off Washington and California.

These canyons are absent off Oregon where rocky submarine banks are found along the shelf. The U.S. west coast is part of an extensive Coastal Upwelling Domain extending from Baja California to southern British Columbia (Ware and McFarlane, 1989). The oceanography of this region is characterized by the California Current system, a typical eastern boundary current regime (Hickey, 1989; 1998) (Map 6). The main California Current proceeds southwards along the U.S. west coast and is slow, meandering, broad, and indistinct. Prevailing winds cause downwelling close to the coast in winter and upwelling of cold, nutrient-laden, oceanic water close to the coast in summer. The intensity of Ekman transport and associated upwelling is variable along the coast and tends to increase from north to south with a local maximum at Cape Mendocino off northern California (Parrish et al., 1981). Annual sea-surface temperature minimums and salinity maximums generally occur in summer after sustained upwelling-favorable winds. Phytoplankton blooms occur during relaxed upwelling conditions between peak upwelling periods during spring and fall (Small and Menzies, 1981). A zone of high zooplankton standing stock is generally observed 10-30 km offshore in summer and the community is dominated by copepods (Landry and Lorenzen, 1989).

Despite the extreme cold experienced in the Arctic, the ecosystems sustain diverse and robust marine communities (Grebmeier and Maslowski 2014). Sea ice is a dominant environmental parameter that influences the biochemistry, regional climate, and circulation patterns of the Arctic (Wang et al. 2014).Sea ice has also made the region inaccessbile to research, especially outside of the summer months. The U.S. Pacific Arctic encompasses two seas with different shelf characteristics and oceanography (Map 8). The Chukchi Sea is unique among Arctic seas due to its shallow, predominantly less than 50 m deep, and wide shelf (800 km) (Randall et al., 2019; Logerwell et al., 2015). The shelf of the western Beaufort Sea is narrower than the Chukchi Sea (80 km) and relatively flat until the 80 m isobath where depth increases rapidly (Logerwell et al., 2015). The oceanogaphy of the Chukchi Sea is influenced by water flowing through the Bering Strait from the northern Bering Sea whereas the Beaufort Sea oceanography is influenced by the three sources: (1) eastward flow of water from the Chukchi Sea, (2) the southern limb of the Beaufort Gyre, (3) and river discharge from the Mackenzie River.

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last updated: June 2021