Fishery managers, modelers, and ecologists who wish to predict variation in salmon population size need to utilize a more complete understanding of the mechanisms that control early salmonid growth and survival at sea. Currently predictions of run size are based primarily on counts of precocious early spawners (“jacks”) or on the size of a previous year’s cohort, but a more sophisticated forecasting approach would also consider the effects of ocean conditions on salmon growth and survival—beginning at the time young fish enter the sea. Such an approach would also increase the forecast period for many populations, allowing for improved strategic planning for recovery and enhancement efforts.
The former NOAA ship David Starr Jordan is now the research vessel Ocean Starr. By any name she is a bright star indeed and one of our most reliable survey vessels.
The broad objective of our Ocean Salmon Survey is to quantify the spatial distribution and physiological condition of salmonid stocks in the central portion of the California Current Ecosystem. Beginning in 2010 we expanded the scope and range of our existing program through partnership with the NWFSC to develop a unified annual collaborative coast-wide survey of salmon and their ocean habitat. We use a surface trawl to collect juvenile and subadult salmonids (including several ESA-listed populations of Chinook and coho salmon and steelhead) and other epipelagic fish and invertebrates that co-occur with them. We also collect spatially matched biological and physical oceanographic data to describe the range of conditions in this complex and variable habitat. Data from this continuing time series of ocean salmon condition and distribution are increasingly valuable as California endures a prolonged drought and major changes in freshwater transport and storage are proposed for some of the state’s principal salmon rivers in the coming years.
A modest haul of juvenile Chinook salmon.
The Ocean Salmon Survey relates to a larger series of projects and research plans being conducted in California rivers. The Fisheries Ecology Division of the SWFSC is currently expanding several ongoing projects to track juvenile salmon passage through the Sacramento and San Joaquin Rivers to the delta and the San Francisco Bay. These studies measure migration speeds and mortality rates from spawning grounds (or hatcheries) to the sea, and pinpoint problem areas where unusually high mortality occurs, often as a consequence of introduced predatory fishes and the effects of man-made structures and water diversions. Young salmon face additional obstacles in dry years when river flows are low and slow, and warmer water temperatures increase the physiological stress of migration. Ultimately, the agency’s goal is to develop comprehensive full lifecycle models that incorporate both fresh and salt water conditions and recognize the synergism between these habitats.
Sampling Design: Our current study area for the Ocean Salmon Survey is a narrow strip of coastal ocean between Heceta Head, Oregon (44°00′) and Pigeon Point, California (37°10′), a distance of 754 km north to south. The sampling grid consists of 16 east-west transect lines spaced about 50 km apart, with five fixed stations located on each line (figure 1) over the continental shelf.
Figure 1. (click image to view full size)
Left: map of study area for Juvenile Salmon Survey, showing transect lines and sampling stations. The ship’s track for the July 2014 cruise is shown in green, starting in Newport, Oregon (top) and ending in San Francisco, California.
Right: sea surface temperature (°C) in one minute intervals along the ship’s track during the July 2014 cruise.
Surface Trawl: To collect salmon and their associated fish and invertebrate community, we use a 264 Nordic Rope Trawl and light pelagic doors. Large floats attached to the headrope keep the top of the net at the surface while it fishes. The net is towed for 30 minutes at about 3.5 knots, and the fish and invertebrates caught in each haul are identified, counted, and released. Juvenile salmon are frozen and taken back to our laboratory in Santa Cruz for further study.
Setting a trawl from the shelter deck of the chartered fishing vessel Frosti.
Trawl net going out in calm water. Floats keep it fishing at the surface.
Sorting a large mixed catch of market squid, jacksmelt, and juvenile salmon.
A scientist deploys the CTD package.
CTD: We use a Conductivity-Temperature-Depth sensor, or CTD, to collect hydrographic data at each one of our trawl stations. Additional sampling instruments in the CTD package included a light sensor, a fluorometer to measure chlorophyll, an oxygen sensor, a transmissometer to measure water turbidity, and several Niskin bottles to collect subsurface water samples.
Rinsing the vertical net after a deep cast into glassy seas.
Vertical net: A 50cm diameter, 200 micron ring net is used to collect zooplankton samples down to depths of 100 meters. The contents of the net are placed in a dilute preservative and later analyzed for species composition and volume.
Bongo net: Zooplankton are also collected with a bongo net, a weighted pair of 71cm anodized aluminum rings connected by a central yoke to which a towing wire is attached. Each ring is fitted with a 300 micron plankton net and slowly towed alongside the boat down to a depth of 30 meters. The bongo and vertical net catch small planktonic animals including copepods, larval crabs and fish, krill, and small gelatinous animals such as comb jellies. The numbers and species of organisms in the plankton community are quite variable and are useful indicators of ocean conditions.
The bongo net collects two plankton samples at once and resembles its namesake drum.
A day’s catch of multicolored plankton.
Hydroacoustic data: Underway hydroacoustic sampling is conducted continuously over the survey using a multi-frequency echosounder. The strength of the backscattering signal from the resulting echograms can be used to measure the abundance and distribution of organisms that generate acoustic signals, such as krill and schooling forage fishes.
Results and conclusions
We recorded 52 species of fish and 17 species of invertebrates in our trawl catch since 2010. Some of these animals are common and consistently taken by us every year, while others show up unexpectedly in some years and then seemingly disappear.
Salps are common pelagic invertebrates, appearing suddenly in large numbers in some years.
Pacific saury are brilliant metallic silvery fish we occasionally catch at stations farther from shore.
Unusually warm water in 2014 brought large ocean sunfish into coastal areas within reach of our trawl.
The annual variation in catch rates that we observe on our surveys often correlates with local, and even global, climatic processes that are known to affect ocean conditions in California. For example, the strong La Niña event of 2010-2011 in the tropical Pacific was accompanied by above average winter precipitation in northern California, high springtime river volumes, and perhaps not coincidentally, our highest juvenile Chinook salmon catch in the survey’s history. In July 2014 we encountered weak upwelling and a large pool of unusually warm water off central California. Combined with three consecutive years of extreme drought, these conditions may have been responsible for our lowest recorded juvenile salmon catch. At the same time, the warm coastal water that year ushered in some unusual species we rarely see, such as the bizarre ocean sunfish.
Although our survey was not specifically designed to rigorously measure juvenile salmon abundance at sea for the purpose of stock assessment, our results do show that salmon catch per unit effort (CPUE) varies widely among years and regions (figures 2-3). Our eventual goal is to use the physiological and genetic information gathered from the salmon we catch, in tandem with matching ecosystem and oceanographic information, to make predictions about the conditions that favor or disfavor salmon growth and survival at sea.
Figure 2. Mean annual CPUE (fish/106m3) of Chinook salmon, coho salmon, and steelhead on Juvenile Salmon Surveys during the period 2010-2014. Error bars are ±1 standard error of the mean. Note different scales used on each graph. “Juveniles” ≤250mm fork length, “adults” >250mm fork length.
Figure 3. Percent CPUE by size class of steelhead, coho salmon, and Chinook salmon among four regions (SO, KT, LC, and GF) during the period 2010-2014. Ellipses on the coastal map show the division of the sixteen transects into four regional community groups, with group membership based on similarity in multivariate structure of all species in the trawl catch from 2010-2013.
Juvenile salmon ready for initial processing. Further analysis of each fish is conducted back on shore at our laboratory in Santa Cruz, California.
A few scales for age and growth analysis are taken from a subadult Chinook salmon before it is released back into the sea.
Fiechter, J., Huff, D.D., Martin, B.T., Jackson, D., Edwards, C.A., Rose, K.A., Curchitser, E.N., Hodstrom, K.S., Lindley, S.T., Wells, B.K. 2015. Environmental conditions impacting juvenile Chinook salmon growth off central California: an ecosystem model analysis. Geophysical Research Letters 42:2910-2917.
Hassrick, J.L., Henderson, M.J., Huff, D.D, Sydeman, W.J., Sabal, M.C., Harding, J.A., Ammann, A.J., Crandall, E.D., Bjorkstedt, E., Garza, J.C., Hayes, S.A. 2015. Early ocean distribution of juvenile Chinook salmon in an upwelling ecosystem. Fisheries Oceanography, in press.
Woodson, L.E., Wells, B.K., Weber, P.K., MacFarlane, R.B., Whitman, G.E., Johnson, R.C. 2013. Size, growth, and origin-dependent mortality of juvenile Chinook salmon Oncorhynchus tshawytscha during early ocean residence. Marine Ecology Progress Series 487:163-175.
Wells, B.K., Santora, J.A., Field, J.C., MacFarlane, R.B., Marinovic, B.B., Sydeman, W.J. 2012. Population dynamics of Chinook salmon Oncorhynchus tshawytscha relative to prey availability in the central California coastal region. Marine Ecology Progress Series 457: 125-137.
Harding, J.A., Ammann, A.J., MacFarlane, R.B. 2011. Regional and seasonal patterns of epipelagic fish assemblages from the central California Current. Fishery Bulletin 109:261-281.
MacFarlane, R.B. 2010. Energy dynamics and growth of Chinook salmon (Oncorhynchus tshawytscha) from the Central Valley of California during the estuarine phase and first ocean year. Canadian Journal of Fisheries and Aquatic Sciences 67(10): 1549-1565.
MacFarlane, R.B., Ralston, S., Royer, C., Norton, E.C. 2005. Juvenile Chinook salmon (Oncorhynchus tshawytscha) growth on the central California coast during the 1998 El Nino and 1999 La Nina. Fisheries Oceanography 14(5): 321-332.
MacFarlane, R.B., Norton, E.C. 2002. Physiological ecology of juvenile Chinook salmon (Oncorhynchus tshawytscha) at the southern end of their distribution, the San Francisco Estuary and Gulf of the Farallones, California. Fishery Bulletin 100: 244-257.
Contact: SWFSC Fisheries Ecology Division, Salmon Ocean Ecology Team