Accepted Reports

Researchers cautiously optimistic about increase in young herring

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A new study hints that the herring population in Prince William Sound could be on the rise.

In the early 1990s, the numbers of herring declined drastically, destroying a healthy fishery. The reason for that crash has never been confirmed, though the Exxon Valdez oil spill is considered a contributing factor.

Since then, the herring population has never recovered to the point that fisheries could permanently reopen. Then in 2015, the population crashed again, possibly due to a disease outbreak.

Researchers at the Prince William Sound Science Center have been studying herring for several decades to find out why the population is struggling to recover. The author of the report, Dr. Scott Pegau, coordinates the center’s herring research and monitoring programs. Part of his work includes surveying the coastline of Prince William Sound from a small plane to count the size, numbers, and age of schools of juvenile herring.

The Council sponsored the last four years of these surveys. Forage fish species, such as herring, are often found in shallow coastal waters, so they are particularly susceptible to the effects of an oil spill. The data on where schools of herring and other “forage fish” tend to congregate could be used to help protect those areas in case of a spill.

Second year of increased numbers of herring

This image is an aerial photos of one school of herring and three schools of sand lance. The herring is round and compact while the sand lance are irregular.
Shape and behavior tell the story
The different species have different characteristics, for instance, herring form circular or oval-shaped schools, while sand lance schools are irregular.
The age of the fish can be identified from the air too. Schools of young herring sparkle as light reflects from the fish as they roll. Older herring have larger, more distinct flashes.

The populations of forage fish can fluctuate, so it’s important to be able to compare the numbers and sizes of schools to past years. Similar surveys have been conducted as far back as the 1990s.

The number of schools of 1-year-old herring is used to estimate future population growth. Surveys conducted in 2022 found an increase in these young herring for the second year in a row. The researchers are hopeful that this means an increase in the number of herring that will return to spawn in the next two years.

“If this is true, we can expect that the herring population will have robust growth in the near future,” Dr. Pegau notes in the report.

Dr. Pegau also advises caution. He notes that these surveys were conducted during a period of unusually warm and sunny weather, and that this could have inflated the count. Future surveys will confirm whether this increase will be permanent.
Read more about the Prince William Sound Science Center’s herring research on their website: Prince William Sound Science Center’s Herring Research and Monitoring Program

Electric current can find damage in underground liners

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A new Council report shows how electricity can be used to “see” damage in the asphalt liners that are intended to contain oil in case of a spill at the Valdez Marine Terminal.

The terminal’s vast crude oil storage tanks are surrounded by a secondary containment system. This system consists of huge containment cells (two tanks per cell) that would act like a bathtub, holding the oil until it can be cleaned up.

To keep oil from leaking into the surrounding environment, these cells are lined with a special type of asphalt. About 5 feet of gravel fill sits on top of this liner.

These asphalt liners can become brittle with age and are susceptible to physical and chemical damage. Over the years, the gravel fill has been removed in a few places to visually inspect the liner. About 20% of the time, holes or cracks were found.

Removing all the fill to visually inspect and repair the liner would be an expensive and time-consuming project, and the excavation equipment could cause further damage to the liner. Alyeska is looking for ways to evaluate the liner without having to excavate.

To help identify the best liner testing methods, the Council has been working with Dr. Craig H. Benson, who has been teaching and practicing environmental and civil engineering for over 40 years, and has extensive experience in containment systems. A new report by Dr. Benson has several recommendations to help the Council provide advice to Alyeska regarding the secondary containment systems at the terminal in Valdez.

This image shows how electric current can flow through holes in a liner, allowing a technician with a sensor to locate damage in the liner.Dr. Benson evaluated several liner inspection techniques and determined that electrical leak location would likely be the best. This type of survey is done by applying electric currents to the ground outside the liner and measuring electric currents on the surface of the fill inside the liner. A solid liner would block the currents. Holes or cracks would allow the current to flow through. Currents that flow through the liner can be detected from the surface, allowing technicians to create a map of damaged areas.

Dr. Benson also analyzed how much of the liner would need to be tested to have confidence that the liner will reliably hold spilled oil. He determined that testing at least 20% of the liner would be enough to estimate how many holes may exist in the liner, with acceptable accuracy. However, 100% of the liner would need to be tested to find all the actual damage.

The importance of an undamaged liner

The Alaska Department of Environmental Conservation, or ADEC, gives Alyeska a 60% “prevention credit” because this secondary containment system is in place. This means that instead of having to provide response equipment to clean up a spill equal to the contents of the largest tank at the terminal (over 23 million gallons), Alyeska only has to provide response equipment and personnel to clean up a little over 8.5 million gallons.*

This is a substantial reduction in the amount of response personnel and equipment.

In May 2022, ADEC notified Alyeska that they needed to identify preliminary methods to evaluate the integrity of the liners by October 2023. Alyeska must identify final methods to evaluate these liners by March 2025.

Dr. Benson’s report is available online: Methodologies for Evaluating Defects in the Catalytically Blown Asphalt Liner in the Secondary Containment System at the Valdez Marine Terminal

*8.5 million gallons, or 204,180 barrels, is the volume of the largest tank, less a 5% prevention credit for drug/alcohol testing, 2% prevention credit for on-line leak detection, and 60% prevention credit for the secondary containment system.

Plankton change with the seasons in Prince William Sound

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In this photo, a Council staff member holds a sample, which is green due to the tiny plants, or phytoplankton, in the sample.
Staff member Joe Lally holds a sample collected during the spring phytoplankton bloom.

A new Council study will help improve monitoring for invasive species, such as tunicates, that live on the sea floor or hard surfaces.

Researchers collected samples of zooplankton and used an identification technique called DNA metabarcoding. This technique allows researchers to identify multiple species from the same sample.

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Cleaning up a big oil spill

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A large spill would require equipment brought in from other regions. The Council recently sponsored a study on the availability of equipment on short notice.

The oil industry in Prince William Sound has one of the best-equipped spill prevention and response systems in the world. However, if a big spill were to occur, more equipment would still be needed.

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