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Below is a figure that illustrates monthly chlorophyll-a climatologies published in a recent paper produced by the retrospective data analysis component of the Gulf of Alaska Project. The authors found that the variability in the chlorophyll-a in each of four distinct and spatially contiguous regions that differed in the timing and magnitude of the spring and fall blooms was associated with different combinations of environmental variables. Click here to download the full paper.
Primary production was anomalously low in 2011, so the retrospective data analysis team examined the chlorophyll-a anomaly with respect to the mean chlorophyll-a time series for 2002 – 2010 for the western and eastern Gulf of Alaska (divided at 145° W longitude). The figure below illustrates that in 2011 the two regions displayed markedly different patterns. The pattern in the western Gulf of Alaska was similar to previous years, though the spring and fall blooms began and ended earlier than usual. The apparent early spring bloom is due primarily to unusually high chlorophyll concentrations in the off-shelf waters. Concentrations on the shelf were slightly lower than usual, compared to the 2002 – 2010 mean.
Chlorophyll-a concentrations in the eastern Gulf of Alaska were low throughout the year; however, the biggest feature was what appears to be the lack of a spring bloom (see the figure below). 2011 appeared as an obvious outlier, both in terms of environmental factors and chlorophyll patterns. In particular, 2011 was characterized by a high Southern Oscillation Index (SOI), low Pacific Decadal Oscillation (PDO), high winter freshwater discharge, low spring freshwater discharge, and low upwelling, as well as higher than normal springtime chlorophyll-a concentrations in the western offshelf region, and lower than normal concentrations in the eastern and western shelf regions.
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The retrospective analysis group also investigated the typical phenology of larval fish in the Gulf of Alaska. The following table illustrates the timing of production and peak abundance of larvae relative to zooplankton production cycles and associated availability of larval prey. This information is will allow the ecological modeling team to initialize their models and will allow comparison of field data collected by this program to long-term patterns.
A manuscript is being developed (Doyle, Coyle and others) that will incorporate this seasonal schematic and investigate the early life history phenologies further with respect to detailed information on seasonality in the Gulf of Alaska zooplankton.
In 2011, field biologists caught very few young of the year fish that they were looking for offshore. The figure below illustrates the number of fish caught in the Gulf of Alaska in 2011. Summer Catches of age-0 arrowtooth flounder, rockfish, Pacific cod, sablefish, and pollock were low in 2011 and preliminary analyses indicate that the body sizes of both larval and juvenile fish were atypically small.
Fish sampling was only conducted in offshore waters during summer in 2012 and spring, summer, and fall in 2013. The highest fish biomass levels were located on the shelf seaward of Cross Sound and Chichagof Island in the eastern study region and over the shelf between Harris Bay and Stevenson Entrance in the western study region (see figures below). Age-0 rockfish and pollock were abundant in both study regions with the largest densities of rockfish encountered to date in slope and offshore habitats off Kodiak Island. Age-0 arrowtooth founder were abundant in the eastern region, but not in the western region.
Below are the results of acoustic surveys for fish and zooplankton collected in nearshore bays in the Gulf of Alaska in 2010 and 2011. Data were collected during spring, summer, and fall in 2013 and preliminary results will be available soon.
The sampling stations for the Gulf of Alaska Project are illustrated on the series of maps below. The project will make regional comparisons between the central and eastern Gulf of Alaska. In the central Gulf of Alaska, the continental shelf is broad, with high demersal fish biomass but low species diversity. In the eastern Gulf of Alaska, the continental shelf is narrow and biomass is lower, but species diversity is higher.
The legend in the maps below identifies the type of sample collected at each station. Each of the field sampling components of the project are abbreviated according to the tropic level they address. Trophic levels refer generally to levels in the food chain. The lower trophic level (LTL) refers to the organisms at the base of the food chain (e.g., plankton, fish eggs, larval fish) and this level is addressed by the component of the project called “Controlling Mechanisms for Nutrients, Plankton and Larval Fishes”. This aspect of the project is also collecting physical and chemical oceanography data. The middle trophic level (MTL) refers to the organisms that feed on LTL organisms but that are themselves prey for larger marine predators. The “Understanding the Structure of Forage Fish Communities” component of the project is addressing the middle trophic level. The upper trophic level (UTL) refers to the organisms at the top of the food chain, such as large fish, seabirds, and marine mammals. The “Surviving the Gauntlet” component of the project is addressing the upper trophic level. The IERP common stations (blue dots) represent sites where fish (UTL) and oceanography (LTL) samples are collected.
Retrospective analyses allow us to put the data collected during this short-term study into context by examining patterns in historical data collected over the past few decades. Examining long-term patterns allows us to ask informed questions about the possible environmental drivers of fish survival and recruitment in the Gulf of Alaska.
Studying patterns in data collected in the same manner over long periods of time (called time-series) allows us to see how much things typically change over time and also allows us to identify points in time when changes are out of the ordinary. For example, natural variability may cause a measurement like water temperature to be a little higher in some years and a little lower in other years, and that variation may not be enough to cause effects on fish survival. We need to know how much change is natural in order to identify years when changes are extreme. If we can identify extreme years, we may be able to find a link to fish survival. Ultimately we are trying to identify a few environmental measurements that can be monitored to predict fish recruitment, which allows scientists to better predict future abundances and managers to set more appropriate quotas for fisheries.
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Retrospective analyses are being conducted on a variety of types of data. Sea surface temperature and chlorophyll concentrations have been measured via satellite over decades, and we are putting together multiple streams of data to create a continuous time series and identify important patterns in space and time. Other analyses include salinity, climate indicators, plankton and fish distribution, and others.
Ecosystem modeling is being used to determine which environmental conditions have the greatest effect on the survival of the five groundfish species that are the focus of this study (walleye pollock, Pacific cod, Pacific ocean perch, sablefish and arrowtooth flounder). A series of models is used to examine the effects of oceanography, current patterns, nutrient availability, food availability, predator interactions, and various combinations of these factors on how these fish survive under different conditions. This information will help managers to predict fish survival and therefore predict more accurately the number of fish that should be available to support the ecosystem and commercial fisheries in the future. Historic data is used to develop the models and field data provides information about current conditions and is used to test the predictive power of the models.
Regional Oceanographic Modeling Systems (ROMS) is used to model the oceanography that transports larval fish from areas offshore where they were spawned to nearshore nursery areas. Factors like water temperature, salinity, wind, and current patterns determine if fish are transported to appropriate nursery areas and how they grow and survive.
Nutrient Phytoplankton Zooplankton (NPZ) models examine the effects of varying levels of nutrients, phytoplankton, and zooplankton in the water column, which provides information on the productivity of the system, and the availability of prey, under different environmental conditions.
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Individual Based Models (IBM) developed for each of the five focal groundfish species provide information about the basic life history and behavior of these fish as they grow from eggs to larvae and juveniles and are transported from spawning to nursery areas. Information about the typical depth at which the fish spend time during a given life stage, and the time that elapses between stages, is included the models. The IBM, NPZ, and ROMS models are nested so that the oceanography determines the location of a given fish at a particular time, the NPZ model determines the productivity at that location, and the IBM determines if the habitat is suitable for the fish during that stage of its life cycle. The combination of these environmental conditions determines fish survival.
A genetics model is used to compare the connectivity between spawning and nursery areas predicted by the IBM models with genetic variation observed in samples collected during prior field studies.
A multi-species model is used to examine the interactions of the five focal fish species with one another and predators and will also address the potential impacts of fishing.
This aspect of the project focuses on the physical and biological oceanography that influences the survival of the five focal groundfish species (Pacific cod, pollock, Pacific ocean perch, sablefish, and arrowtooth flounder) during their first year of life. Oceanographers are testing the hypothesis that cross-shelf and along-shelf transport of nutrients and plankton differs in the central and southeast Gulf of Alaska and that the mechanisms controlling primary production differ as a result. They are also testing the hypothesis that the food webs leading to larval and juvenile fish differ between these regions.
Cross-shelf transport is the process by which nutrient-rich water from the deep ocean basin is carried by currents or upwelling into the shallower waters over the continental shelf. Nutrients collect in deeper waters when organisms die and sink to the sea floor. When they are brought up into shallower waters, nutrients act as the fertilizer that planktonic algae need to grow. When these planktonic plants are exposed to sunlight in the presence of nutrients, they can grow very quickly in what is known as a plankton bloom and form the base of the marine food web. This project will contribute to our understanding of the processes controlling when and where these blooms occur and how that influences the food web in the Gulf of Alaska.
Along-shelf transport is the movement of water along the coast over the continental shelf. In the Gulf of Alaska, coastal water typically flows counter-clockwise, northward along the coast of Southeast Alaska, westward along the central Gulf of Alaska coast, and southwest as it moves past Kodiak Island toward the Aleutian Island chain. This project is describing this movement of water and how it changes both seasonally and inter-annually to better understand how currents may affect the transport of zooplankton and larval fish from their offshore spawning areas to nearshore nursery areas. It is also providing information about the transport of iron, zooplankton, and fish off of the continental shelf into the deeper waters of the basin.
Field data collection is conducted in spring and fall throughout the study region (to see maps of the sampling sites, please visit the Study Region page under the About the Project menu). A variety of data are collected aboard the oceanographic vessels. An instrument is lowered at each sampling station to collect infomation about salinity, temperature, and depth to create a profile of the water column. Water samples are also collected at depth.
Iron sampling is conducted aboard the oceanographic vessels as well. Iron is necessary for primary production to occur, and iron is typically input into coastal Gulf of Alaska waters via terrestrial freshwater runoff. Understanding the processes that concentrate iron in the ocean, such as eddies (circular currents), will further our understanding of primary production and allow us to better predict when and where plankton blooms are likely to occur.
Satellite-tracked drifters are deployed from the oceanographic vessels to illustrate the actual movement of water around the Gulf of Alaska. Researchers watch the movment of these drifters over time to learn about the passive transport of larval fish and how their trajectories may change based on climatic conditions.
Bongo nets are used to catch fish eggs, zooplankton and larval fish to describe the base of the food web and how it differs with geographic region. Information about when and where fish eggs and larval fish of each of the five focal groundfish species are found is being used to initialize ecological models that will simulate the transport of larval fish from their offshore spawning areas to nearshore nursery areas.
Biophysical moorings are deployed throughout the Gulf of Alaska in February and are recovered in October. These moorings collect detailed information about water properties, currents, and phytoplankton and zooplankton concentrations in localized areas. These data represent time-series that provide important insights into how these factors vary seasonally and inter-annually. Little was known about the dynamics of water flow in Southeast Alaska prior to this study and this project is advancing our knowledge of the oceanography in the region considerably.
GOAIERP scientists study what environmental conditions and habitats are important in sablefish survival
In 2008, a team of scientists at the Auke Bay Laboratories initiated several dedicated research projects aimed at understanding ecological and management issues concerning Alaska sablefish (Anoplopoma fimbria). One of these projects is led by Dr. Kalei Shotwell and deals specifically with exploring the driving mechanisms surrounding the highly variable and uncertain survival of young sablefish. The project began with two main goals: 1) determine if an index of young sablefish could be created from historical data and 2) investigate whether measures of the environment can be used in a model to predict the survival of these young fish. Toward the first goal, Dr. Shotwell collected the available data from short-term surveys and found that it was not consistent enough in space and time to be used within the current sablefish assessment model. However, the information can be used for helping understand the best habitat for young sablefish to settle upon after their long journey to the nearshore. Dr. Shotwell along with Dr. Jodi Pirtle of the Benthic Habitat Project will be using this information to develop habitat suitability models and maps to characterize the nearshore benthic habitat for sablefish and the other focal species. These maps will be used by several components of the GOA Project, specifically the modeling component to inform their individual based model trajectories.
The search for environmental predictors for the second goal of Dr. Shotwell’s sablefish project has led to investigating ways to include environmental information in stock assessment. The first breakthrough was the discovery of a relationship between the North Pacific Polar Front and sablefish survival (Shotwell et al. 2014). Colder than average wintertime measures of this large-scale ocean feature in the central North Pacific were found to create good survival conditions for young sablefish. This relationship led Dr. Shotwell and her co-authors (Dr. Dana Hanselman and Dr. Igor Belkin) to put forward a conceptual model of sablefish early-life survival which was termed the ODDS model for Ocean Domain Dynamic Synergy. It is basically a description of the pressures that might influence the survival of young sablefish as they journey from where they are born in the deep ocean slope, through their ride on the waves of the ocean gauntlet, and finally as they settle to their habitat homes in the nearshore. Answering the “What are the Odds?” question for sablefish has led Dr. Shotwell to work with several researchers (GOA Project included) to consider the influence of other environmental measures such as mesoscale eddies, upwelling, freshwater output, nearshore production, pink salmon competitors, and seabird predators. The results of these projects are forthcoming and when completed Dr. Shotwell plans to work with the lead authors of these projects to collect the relevant indicators that will serve as time series that support the ODDS model of early-life survival. These indicators will be compiled in an annual graphical report card to be included in the individual stock assessment reports. The sablefish ODDS report card may be used to assist scientists and managers in understanding what may influence sablefish survival and also visually see the changes of these environmental indicators over time.
Literature Cited:
Shotwell, S.K., D.H. Hanselman, and I.M. Belkin. 2014. Toward biophysical synergy: Investigating advection along the Polar Front to identify factors influencing Alaska sablefish recruitment. Deep-Sea Reaserch II. Special Issue, Fronts, Fish and Top Predators. http://dx.doi.org/10.1016/j.dsr2.2012.08.024.
NPRB staff begins developing draft research priorities for the Core Program in late July and August. Submit before July 2nd to be considered for the current year’s RFP development.
Research programs addressing pressing fishery management issues and Alaska marine ecosystem information needs.
Integrated Ecosystem Research
These are large-scale interdisciplinary ecosystem-based programs, requiring multiple agency coordination, collaboration, and investigation.
Outreach Program
Science communication, engagement, outreach, and education initiatives for NPRB programs.
Core Program
A competitive, peer-reviewed annual request for proposal (RFP) process dedicated to Alaska marine research.
Graduate
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Awards
Supporting next generation scientists, researchers, and resource managers to further studies in marine science and to our mission.
Long-Term Monitoring
These are new or existing time-series projects that enhance the ability to understand the current state of marine ecosystems.
Examining how physical changes in the ocean influenced the flow of energy through the marine food web in the Bering Strait, Chukchi Sea, and western Beaufort Sea.
Studying the survival and recruitment of five focal groundfish species (Pacific cod, Pacific ocean perch, walleye pollock, arrowtooth flounder, sablefish) during their first year of life.
Understanding the impacts of climate change and dynamic sea ice cover on the eastern Bering Sea ecosystem in partnership with the National Science Foundation.
Northern
Bering Sea
JUST LAUNCHED! Focusing on the northern Bering Sea and will include consideration of upstream and downstream ecosystems in the southeastern Bering Sea, western Bering Sea, and Chukchi Sea.
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