Ecosystem Considerations for 2001 Reviewed by The Plan Teams for the Groundfish Fisheries of the Bering Sea, Aleutian Islands, and Gulf of Alaska Edited by Pat Livingston Resource Ecology and Ecosystem Modeling Program Resource Ecology and Fisheries Management Division Alaska Fisheries Science Center 7600 Sand Point Way NE Seattle, WA 98115 With contributions by Paul Anderson, Chris Blackburn, FOCI, Sarah Gaichas, Jawed Hameedi, Cindy Hartmann, Jon Heifetz, Lee Hulbert, Jim Ingraham, K Koski, NMFS-NMML, Kim Rivera, Joe Terry, Dan Urban, USFWS, Gary Walters, Dave Witherell, Harold Zenger November 2000 ECOSYSTEM CONSIDERATIONS –2001 TABLE OF CONTENTS INTRODUCTION...........................................................................................................................3 ECOSYSTEM STATUS INDICATORS........................................................................................4 Physical Environment.................................................................................................................4 Ocean Surface Currents...........................................................................................................4 Ecosystem Indicators and Trends Used by FOCI...................................................................6 Summer bottom and surface temperatures – Eastern Bering Sea.........................................14 Summer bottom temperatures – Aleutian Archipelago.........................................................17 Habitat.......................................................................................................................................18 Indices of contaminant levels in sediments, groundfish and their prey................................18 Current Research on the Effects of Fishing Gear on Seafloor Habitat in the North Pacific.24 Current Research on the Essential Fish Habitat in the North Pacific....................................30 Benthic Communities and Non-target fish species...................................................................33 Non-target species in the BSAI and GOA: Case studies on Skates, Grenadiers, and Squid....45 Marine Mammals......................................................................................................................68 Steller sea lion.......................................................................................................................68 Northern fur seal....................................................................................................................75 Harbor seal............................................................................................................................78 Cetacea..................................................................................................................................79 Ecological Interactions Between Marine Mammals and Commercial Fisheries..................82 Seabirds.....................................................................................................................................86 Ecological Interactions Affecting Seabirds...........................................................................93 Ecosystem or Community Indicators and Modeling Results..................................................101 Present and Past Ecosystem Observations – Local and Traditional Knowledge................101 ECOSYSTEM-BASED MANAGEMENT INDICES AND INFORMATION.........................102 Ecosystem Goal: Maintain Diversity.....................................................................................102 Time Trends in Bycatch of Prohibited Species...................................................................102 Time trends in groundfish discards.....................................................................................104 Ecosystem Goal: Maintain and Restore Fish Habitats............................................................105 Areas closed to bottom trawling in the EBS/AI and GOA.................................................105 Ecosystem Goal: Sustainability (for consumptive and non-consumptive uses).....................105 Trophic level of the catch....................................................................................................105 Status of groundfish, crab, scallop and salmon stocks........................................................105 Ecosystem Goal: Humans are part of Ecosystems..................................................................106 Fishing overcapacity programs...........................................................................................106 Groundfish and crab fleet composition...............................................................................106 LITERATURE CITED...............................................................................................................108 2 INTRODUCTION Since 1995, the North Pacific Fishery Management Councils (NPFMC) Groundfish Plan Teams have prepared a separate Ecosystem Considerations section to the annual SAFE report. The intent of the Ecosystems Considerations section is to provide the Council with information about the effects of fishing from an ecosystem perspective, and the effects of environmental change on fish stocks. The effects of fishing on ecosystems have not been incorporated into most stock assessments, in part due to data limitations. Most single species models cannot directly incorporate the breadth and complexity of much of this information. ABC recommendations may or may not reflect discussion regarding ecosystem considerations. This information is useful for effective fishery management and maintaining sustainability of marine ecosystems. The Ecosystems Considerations chapter attempts to bridge this gap by identifying specific ecosystem concerns that should be considered by fishery managers, particularly during the annual process of setting catch limits on groundfish. Each new Ecosystem Considerations report provides updates and new information to supplement the original report. The original 1995 report presented a compendium of general information on the Bering Sea, Aleutian Island, and Gulf of Alaska ecosystems as well as a general discussion of ecosystem-based management. The 1996 Ecosystem Considerations report provided additional information on biological features of the North Pacific, and highlighted the effects of bycatch and discards on the ecosystem. The 1997 Ecosystems Considerations report provided a review of ecosystem –based management literature and ongoing ecosystem research, and provided supplemental information on seabirds and marine mammals. The 1998 edition provided information on the precautionary approach, essential fish habitat, an overview of the effects of fishing gear on habitat, El Nino, collection of local knowledge, and other ecosystem information. The 1999 report again gave updates on new trends in ecosystem-based management, essential fish habitat, research on effect of fishing gear on seafloor habitat, marine protected areas, seabirds and marine mammals, oceanographic changes in 1997/98, and local knowledge. If you wish to obtain a copy of a previous Ecosystem Considerations Chapter, please contact the Council office (907) 271-2809. In 1999, a proposal came forward to enhance the Ecosystem Considerations Chapter by including more information on ecosystem indicators of ecosystem status and trends and more ecosystem-based management performance measures. This enhancement, which will take several years to fully realize, will accomplish several goals: 1) Track ecosystem-based management efforts and their efficacy 2) Track changes in the ecosystem that are not easily incorporated into single-species assessments 3) Bring results from ecosystem research efforts to the attention of stock assessment scientists and fishery managers, and 4) Provide a stronger link between ecosystem research and fishery management The 2000 Ecosystem Considerations document included some new contributions in this regard and will be built upon in future years. It is particularly important that we spend more time in the development of ecosystem-based management indices, which are poorly represented in this year’s document. Ecosystem- based management indices should be developed that track performance in meeting the stated ecosystem- based management goals of the NPFMC, which are: 1. Maintain biodiversity consistent with natural evolutionary and ecological processes, including dynamic change and variability. 2. Maintain and restore habitats essential for fish and their prey. 3. Maintain system sustainability and sustainable yields for human consumption and non- extractive uses. 4. Maintain the concept that humans are components of the ecosystem. 3 ECOSYSTEM STATUS INDICATORS The main purpose of this section on Ecosystem Status Indicators is to provide new information and updates on the status and trends of ecosystem components. This section has two purposes. The first is to bring the results of ecosystem research efforts to the attention of stock assessment scientists and fishery managers, which will provide stronger links between ecosystem research and fishery management. The second purpose, and perhaps the main one, is to spur new understanding of the connections between ecosystem components by bringing together many diverse research efforts into one document. As we learn more about the role that climate, humans, or both may have on the system, we will be able to derive ecosystem indicators that reflects that new understanding. Physical Environment Ocean Surface Currents Contributed by W. James Ingraham, Jr. Recently, ocean surface current modeling has been used increasingly to understand the year-by-year movements of larval fish in the eastern Bering Sea and Gulf of Alaska, in order to predict such things as survival and spatial overlap with predators (Wespestad et al., 1999). Everything you always wanted to know about surface currents in the North Pacific ocean and Bering Sea is contained in the test computer model “Ocean Surface CURent Simulator” (OSCURS). With this numerical model just pick your own input: 1) a start-point on the graphic chart; 2) any start-day from January, 1980 to July, 1999; and 3) a duration, the number of days to drift. In about 20 seconds up pops a chart showing the vectors of daily movement strung together in a trajectory giving you the net drift from the start-point. These experiments can now be run by the general public on the World Wide Web by connecting to the REFM Division’s home page, http://www.refm.noaa.gov, and clicking on “OSCURS” then linking to either the information article “Getting to Know OSCURS” which describes the model and its uses or clicking “Live Access Server”. Alternatively, connect directly to http://shark.pmel.noaa.gov/kobin- las/GenericLAS. Development of OSCURS was motivated by the need in fisheries research for indices that describe variability in ocean surface currents. Historical pattern recognition in the time-series data provides some limited forecasting value. These synthetic data, derived through empirical modeling and calibration, provide insights, which far exceeds their accuracy limitations. OSCURS daily surface current vector fields are computed using empirical functions on a 90 km ocean-wide grid based on daily sea level pressures (1946-1997); long-term-mean geostrophic currents (0/2000 db) were added. The model was tuned to reproduce trajectories of satellite-tracked drifters with shallow drogues from the eastern North Pacific. Output is in 2 forms; 1) a graphic image chart with trajectory in red or 2) ascii data file of daily latitude- longitudes of water movement. Trajectories replicate satellite drifter movements quite well on time- scales of a few months. You can produce trajectories up to one year long, but their absolute accuracy diminishes with time. By repeating the runs from the same point year-by-year gives the time history of surface current variability from that location, serving one of the main purposes of OSCURS for comparison with fisheries data. See the information article for a summary of such experiments I have already run. 4 Your e-mail feedback is welcome at [email protected]. A century (1901-2000) of winter climate variability as it effects surface ocean currents in the Gulf of Alaska is shown by the Papa Trajectory Index (PTI) which is calculated using OSCURS (Figure 1). Papa Trajectory End-point Latitudes 1902-2000 L-T-M PTI 5-Yr Running ) N 60 ( 58 E 56 D 54 U 52 T 50 I T 48 A 46 L 0 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 5 6 7 8 9 0 9 9 9 9 9 9 9 9 9 9 0 1 1 1 1 1 1 1 1 1 1 2 Figure 1. Annual and 5-year running mean values of the PAPA Trajectory Index (PTI) time-series from winter 1902-2000. Large dots are annual values of latitude of the end points of 90-day trajectories started at Station PAPA (50º N, 145º W) each December 1, 1901-1999. The straight line at about 55º N is the mean latitude of the series. The oscillating thick line connecting the squares is the 5-year running means. Sea surface drift trajectories with start-points from Ocean Weather Station PAPA (50° N, 145° W) were simulated using the OSCURS model for each winter (Dec. 1- Feb 28), 1901-2000. To reveal decadal fluctuations in the oceanic current structure, the trajectories were smoothed in time with a 5-year running boxcar filter. Values above the mean indicate winters with anomalous northward surface water circulation in the eastern Gulf of Alaska; values below the mean indicate winters with anomalous southward surface water circulation. The 5-year running mean shows four complete oscillations but the time intervals were not constant; 28 years (1902-1930), 17 years (1930-1947), 17 years (1947-1964), and 33 years and continuing (1964-1997). The drift from Ocean Weather Station Papa has fluctuated between north and south modes about every 23 years over the last century and the shift from north to south modes appears to be overdue or at least the longest oscillation this century. The time-series has been updated with winter 2000 calculations. 5 Ecosystem Indicators and Trends Used by FOCI Contributed by FOCI NORTH PACIFIC REGION Recent indicators suggest that the climate of the North Pacific region is changing. Scientists think this may have started as early as 1989 when the Arctic Oscillation (AO) changed phase. However, the most significant change is the cooling of coastal waters of the Pacific Northwest and Alaska since 1997-1998 when the Pacific Decadal Oscillation (PDO, see below) probably switched phase. With coastal cooling have come shifts in marine abundance, e.g., West Coast salmon that were suffering declines in abundance early in the 1990s appear to be recovering, while Alaska salmon abundance is waning. The following sections discuss some of FOCI's climate and pollock abundance indicators in light of climate change. Interannual variability of atmospheric forcing The winter magnitude and position of the Aleutian Low explain much of the interannual variability of atmospheric forcing and physical oceanographic response of the North Pacific Ocean and Bering Sea. The Aleutian Low is a statistical feature formed by averaging North Pacific sea level pressure for long periods. Because this is a region of frequent storms, the averaged pressure pattern describes a closed-cell, low-pressure area over the North Pacific, much like an individual storm on a weather map. The amplitude and location of the Aleutian Low have a strong bearing on weather and ocean conditions in the region and are correlated with other climate indices such as ENSO (El Niño Southern Oscillation), AO, and PDO. A strong Aleutian Low (low pressure) is accompanied by strong winds that drive warm water from the central Pacific into the coastal regions of Alaska and the Pacific Northwest. Conversely, when the Aleutian Low is weak (higher pressure), winds are weak and coastal sea surface temperatures cool. A measure of the strength of the Aleutian Low is the North Pacific Index (NPI, Fig. 1). It is the sea level pressure over the North Pacific averaged for January through February. The index contains strong decadal variability. For example, there is a shift from high to low values of the index in 1925, a return to high values in 1946, and a shift back to low in 1977. If the data are smoothed, secondary shifts appear (one and a half secondary shifts for each major shift) such as in 1958 and 1989. In the past two years, NPI values have been higher, indicating a weaker Aleutian Low. Consequently, wind-driven advection of warm water from the central North Pacific into the coastal regions of Alaska and the U.S. Pacific Northwest has diminished, and local processes play a larger role in determining ocean temperature near the coast. Figure 2 shows the averaged monthly anomaly of sea surface temperature for the North Pacific during May 2000. Note the relative cooling of the coastal waters. This signature is indicative of a recent change in the PDO (see next section). The cooling began in 1998 associated with the La Niña, but has persisted in the NE Pacific, which is taken as an indicator of a change in the PDO. Ocean temperatures throughout the North Pacific continued to cool during June relative to long-term climatology. Figure 1. The North Pacific Index (NPI) from 1900 through 2000 is the sea-level pressure averaged for January through February. 6 Figure 2. The pattern of sea surface temperature anomalies for May 2000 shows a return to cool coastal waters with warmer central Pacific waters. Pacific Decadal Oscillation The Pacific Decadal Oscillation (PDO) Index (Fig. 3) is defined as the leading principal component of North Pacific monthly sea surface temperature variability. The PDO is a long-lived, El Niño-like pattern of North Pacific Ocean climate variability. Two main characteristics distinguish PDO from ENSO. First, 20th century PDO "events" persisted for 20-to-30 years, while typical ENSO events persisted for 6 to 18 months. Second, the climatic fingerprints of the PDO are most visible in the North Pacific/North American sector, while secondary signatures exist in the tropics - the opposite is true for ENSO. Several independent studies find evidence for just two full PDO cycles in the past century: "cool" PDO regimes prevailed from 1890-1924 and again from 1947-1976, while "warm" PDO regimes dominated from 1925- 1946 and from 1977 through (at least) the mid-1990s. Some researchers have identified a cold phase 7 Figure 3. Monthly and smoothed (black line) values of the Pacific Decadal Oscillation (PDO) index, 1900-2000. starting in 1989, others point to 1997. Beginning in early 2000, it became apparent that a shift had occurred from changes in ocean temperature (Fig. 2) and distribution of salmon and other marine species. A weaker Aleutian Low (Fig. 1) certainly is associated with this change. Major changes in northeast Pacific marine ecosystems have been correlated with phase changes in the PDO. Warm eras bring enhanced coastal ocean biological productivity in Alaska and inhibited productivity off the west coast of the contiguous United States, while cold PDO eras produce the opposite north-south pattern of marine ecosystem productivity. Causes for the PDO are not currently known. Even in the absence of a theoretical understanding, PDO climate information improves season-to-season and year-to-year climate forecasts for North America because of its strong tendency for multi-season and multi-year persistence. From a societal perspective, recognition of PDO is important because it shows that "normal" climate conditions can vary over time periods comparable to a human's lifetime. WESTERN GULF OF ALASKA Seasonal rainfall at Kodiak Patches of larval walleye pollock have been located within mesoscale eddies. For early larvae, presence within an eddy may be conducive to survival. Eddies in Shelikof Strait are caused by baroclinic instabilities in the Alaska Coastal Current (ACC). The baroclinity of this current fluctuates with the amount of fresh water discharged along the coast. A time series of Kodiak rainfall (inches) is a proxy for baroclinity and thus an index for survival success of species such as walleye pollock that benefit from spending their earliest stages in eddies. Greater than average late winter (January, February, March) precipitation produces a greater snow pack for spring and summer freshwater discharge into the ACC. Similarly, greater than average spring and early summer rainfall also favor increased baroclinity after spawning. Conversely, decreased rainfall is likely detrimental to pollock survival. A pollock survival index based on precipitation is shown in Figure 4. Although there is large interannual variability, a trend 3.0 Precipitation-based pollock survival index 2.5 2.0 1.5 Annual value 3-year running mean 1.0 4 7 0 3 6 9 2 5 8 1 4 7 0 6 6 7 7 7 7 8 8 8 9 9 9 0 9 9 9 9 9 9 9 9 9 9 9 9 0 1 1 1 1 1 1 1 1 1 1 1 1 2 Year Figure 4. Index of pollock survival potential based on measured precipitation at Kodiak from 1962 through 2000. The solid line shows ann8ual values of the index; the dashed line is the 3-year running mean. toward increased survival potential is apparent from 1962 (the start of the time series) until the mid- 1980s. Over the last 15 years, the survival potential has been more level. Are the lower values of the last two years commensurate with a phase change of the PDO? Wind mixing south of Shelikof Strait Another survival index relates to first-feeding pollock larvae, a key survival stage when baby fish have exhausted their yolk sacs and need to capture food. Possibly because increased turbulence interferes with larvae’s ability to feed, strong wind mixing events during the first-feeding period are detrimental to survival of pollock larvae. A time series of wind mixing energy (W m-2) at [57°N, 156°W] near the southern end of Shelikof Strait is the basis for a survival index (Fig. 5) wherein stronger than average mixing before spawning and weaker than average mixing after spawning favor survival of pollock. As with precipitation at Kodiak, there is wide interannual variability with a less noticeable and shorter trend to increasing survival potential from 1962 to the late 1970s. Recent survival potential has been high. Monthly averaged wind mixing in Shelikof Strait has been below the 30-year (1962-1991) mean for the last three January through June periods (1998-2000). This may be further evidence that the North Pacific climate regime has shifted in the past few years. 3.0 Wind-mixing-based pollock survival index 2.5 2.0 1.5 Annual value 3-year running mean 1.0 4 7 0 3 6 9 2 5 8 1 4 7 0 6 6 7 7 7 7 8 8 8 9 9 9 0 9 9 9 9 9 9 9 9 9 9 9 9 0 1 1 1 1 1 1 1 1 1 1 1 1 2 Year Figure 5. Index of pollock survival potential based on estimated wind mixing energy at a location south of Shelikof Strait from 1962 through 2000. The solid line shows annual values of the index; the dashed line is the 3-year running mean. 9 EASTERN BERING SEA Sea ice extent and timing The extent and timing of seasonal sea ice over the Bering Sea shelf plays an important role, if not the determining role, in the timing of the spring bloom and modifies the temperature and salinity of the water column. Sea ice is formed in polynyas and advected southward across the shelf. The leading edge continues to melt as it encounters above freezing waters. The ice pack acts as a conveyor belt with more saline waters occurring as a result of brine rejection in the polynyas and freshening occurring at the leading edge as the ice melts. Over the southern shelf, the timing of the spring bloom is directly related to the presence of ice. If ice is present in mid-March or later, a phytoplankton bloom will be triggered that consumes the available nutrients. If ice is not present during this time, the bloom occurs later, typically during May, after the water column has stratified. The presence of ice will cool the water column to -1.7°C. Usually spring heating results in a warm upper mixed layer that caps the water column. This insulates the bottom water, and the cold water (<2°C) will persist through the summer as the “cold pool.” Fish, particularly pollock, appear to avoid the very cold temperatures of the cold pool. In addition the cold temperatures delay the maturing of fish eggs and hence affect their survival. Figure 6 shows the presence of ice over the southeastern shelf between 57° and 58° N during the last 28 years. The figure is divided into three panels, each representative of a climate regime: 1972-1976 ice conditions occurred during a cold PDO phase, 1977-1989 during a warm PDO and AO phase, and the years hence which seem to be in an intermediate regime reflecting a warm PDO and a cold AO. The possible change in the PDO that may have occurred about 1997 is reflected in the extreme ice conditions observed in 2000. During the first regime ice was common over this part of the shelf. In the warm period thereafter, ice was less prevalent. Since then, ice has been more persistent but not as extensive as it was prior to 1977. Recently, 2000 had the most extensive seasonal sea ice pack since 1976. There appears to be a slight reduction in ice cover during El Niño years, but the relationship is weak. 10