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Pacific Sardines and Herring: Lives of Food Fish

Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about living things.

Sardines and Herring

Sardines and herring are very nutritious and popular fish. They are both valuable foods. It's interesting to study these fish while they are alive and in their natural environment, however. They live in large groups and have some unusual behaviours.

The words "sardine" and "herring" apply to a variety of fish species that belong to the family Clupeidae. Sardines are small, silvery fish that are named after the island of Sardinia in the Mediterranean. This was once an important area for the sardine fishery. Herring are also silver in colour, but they are bigger than sardines. In this article, I focus on the Pacific sardine and the Pacific herring but also refer to some of their relatives.

Sardines and herring are rich in omega-3 fatty acids, which are thought to have important health benefits. The chemicals may improve memory and mood. They may also help to prevent cardiovascular disease and improve arthritis symptoms.

Nutritious Fish

Sardines are eaten by marine animals and birds as well as by humans. They are an excellent source of protein, omega-3 fatty acids, calcium (if the bones are eaten), vitamin D, vitamin B12, and selenium. The fish are sold fresh, frozen, and canned. Canned sardines are healthiest when water-packed and unsalted. Sardines are very low in mercury, an environmental poison that enters water and contaminates the bodies of fish. Herring are also a nutritious, low-mercury food and a good source of omega-3 fatty acids. Confusingly, young herring are sometimes known as sardines.

Sardinops sagax, which is known as a sardine or a pilchard

Sardinops sagax, which is known as a sardine or a pilchard

Distribution of Pacific Sardines

Sardines generally live in temperate and subtropical oceans but may also be found in estuaries. There is a freshwater species in the Philippines. The “true” sardine (Sardinus pilchardus) is also known as the European pilchard. As its name suggests, it's found in ocean waters around Europe.

The Pacific sardine (Sardinops sagax) lives along the coasts of countries bordering the Pacific Ocean. It's found on the west coast of Central and North America from Baja California to Alaska, although its exact location depends on the time of year. The fish migrate to find a suitable water temperature as the year progresses. The sardines off the coast of Peru and Chile are the same species as the Central and North American fish but a different subspecies. Pacific sardines can also be found off the coast of South Africa.

The Indian oil sardine, or Sardinella longiceps

The Indian oil sardine, or Sardinella longiceps

Physical Appearance

Pacific sardines have an attractive, elongated body that is silvery and iridescent. The upper surface is blue or green, depending on the subspecies and the angle at which a fish is viewed, while the sides and belly are silver. The fish has a row of dark spots along its side, only one dorsal fin on the top of its body, and a strongly forked tail. Sardines may reach a length of fourteen inches but are usually about nine inches long when they are adults.

Diet and Feeding

Sardines are filter feeders and eat plankton, which consists of tiny plants and animals moved by water currents. The sardines open their mouths as they swim through a collection of plankton. The plankton and sea water enter a fish's mouth, pass over its gills, and then flow back into the water through the opening under the gill cover. As the water flows through the gills, structures called gill rakers trap the plankton. The gill rakers direct the food into the esophagus, which then transports it to the stomach.

Reproduction

The main breeding area for the Pacific sardines in North America is located off the coast of southern California. The fish reproduce multiple times in a breeding season. Fertilization is external. The eggs and sperm are released into shallow water, where they join.

Pacific sardines are broadcast spawners. The female releases 30,000 to 60,000 eggs at a time. Multiple females in a group release their eggs at the same time. In addition, multiple males release their sperm into the area at the same time as the females release their eggs. The strategy increases the chance that some eggs and sperm will meet.

If they aren't eaten by predators, the fertilized eggs hatch into larvae in about three days. The time depends on the water temperature. A sufficient number of larvae survive to enable the species to survive and thrive (barring environmental problems or overfishing).

Sardines can live as long as fourteen years. The majority of the population is younger than six years of age, however.

A Shoal or a School

Pacific sardine groups may contain millions of fish. Fish come together for protection from predators. An individual fish is less likely to be eaten when travelling in a group than when travelling as an individual.

A group of fish is known as a shoal or a school. The two words may be used interchangeably. Many fish researchers use the word "shoal" to refer to a social group of fish and "school" for a shoal in which all the fish's movements are coordinated, however. The fish in a school move in a synchronized fashion, with the fish suddenly changing their swimming direction in the same way at the same time. The school acts as thought it's one creature. A shoal may temporarily become a school and then go back to becoming a shoal again.

A Shoal of Sardines in South Africa

The Annual South African Sardine Run

Every year between May and July—with a few exceptions—sardines migrate along the coast of South Africa in a huge group. Eager predators include dolphins, sharks, seals, gannets, cormorants, and humans. They all converge for a fantastic feast as the sardines travel northwards.

The gigantic sardine group is referred to as a shoal and may be several miles long. Dolphins herd the sardines into dense, dark balls of fish, which make it easy for the animals to catch their prey. Sharks also herd the sardines. Sometimes the sardines are driven on to the shore where eager humans grab as many fish as they can. A dive festival is held in conjunction with the sardine run. The run is a very exciting event for both predators and observers.

The scientific name of the fish involved in the South African sardine run varies according to the source. Many sources list its name as Sardinops sagax ocellatus, making it a subspecies of the Pacific sardine. Some sources give its name as Sardinops ocellatus, however, making it a different species from the Pacific sardine.

Pacific herring (Clupea harengus) are very similar in appearance to Atlantic herring but are a little smaller. They also have somewhat different reproductive behaviour.

Pacific Herring

The Pacific Herring (Clupea pallasii) may reach eighteen inches in length. Most adults are around twelve inches long, however. Like Pacific sardines, Pacific herring have a blue-green upper surface, silver sides, and a silver belly. Also like the sardines, herring travel in large groups and are filter feeders. They have a protruding lower jaw and eat mainly zooplankton (tiny animals). They spend the day in deep water and move close to the surface at night to feed. According to some sources, they have no lateral line, an organ along the sides of most fish that that detects vibrations. Other sources say that they have no visible lateral line.

The females lay their eggs in shallow water. The eggs stick to subtidal and intertidal vegetation, where they are fertilized by the male. The male releases his sperm in milt, a milky white liquid that colours the water. The eggs hatch into larvae after about two weeks, the exact time depending on the water temperature. A Pacific herring may live for as long as eight years if it isn't caught by a predator.

Pacific herring eggs are negatively buoyant. By depositing many layers of eggs on fronds of kelp, the spawn of herring has been known to sink entire kelp forests. Upon hatching and the release of tiny, swimming herring larvae, the forests rise again.

— Rainforest Conservation Foundation

The Pacific herring performs a behaviour known as "flashing". As it turns suddenly while it's swimming, its silvery, reflective body produces what looks like a flash of light. The effect is especially noticeable when multiple fish in a school flash at once.

Herring in the Environment

Pacific herring play an important role in their ecosystem and have been very important in the lives of indigenous people. Many marine mammals, fish, and birds feed on the herring and/or their eggs. Even land animals such as bears visit beaches to eat herring eggs from seaweed that washes ashore. When the fish spawn, it's time for a feast for many animals.

As a food, herring are energy-rich and nutritious. They have a short shelf life, however. Humans eat them when they are fresh, frozen, dried, smoked, salted, pickled, or canned. The fish are also used to produce a meal and an oil.

In the past, herring played a dominant role in the life and culture of the First Nations groups along the Pacific Coast of North America. These groups still catch the fish, as do commercial fisheries. The herring population is not as large as it once was, however. The fish are abundant in some areas but are reduced in number in other parts of their range.

Herring are so important in the food chain that a collapse in the fish stocks could be disastrous. Collapses have occurred periodically in recent times, probably due to overfishing by commercial fisheries, although there may be other contributing factors. There are signs that some populations are in trouble, including slow return from a collapse and smaller fish size.

Herring FRTs

Herring release gas from the anal duct in a noisy stream of bubbles. This activity is believed to be a form of communication. Researchers have named the signals "Herring FRTs". FRT stands for "Fast, Repetitive Ticks". Both Atlantic and Pacific Herring make FRTs.

The bubbles are released at night when many herring are in the same area. Tests with captive fish show that the sound is produced whether or not they have recently fed. This suggests that the gas bubbles are not simply a by-product of food digestion. In addition, the frequency of the bubble release doesn't increase when the scent of a shark is placed into the tank holding the herring, so the bubble production doesn't seem to be a response to fear.

The researchers say that herring gulp air from the water surface. The air is transferred from the stomach to the swim bladder of the fish, which provides buoyancy. Some of the gas in the swim bladder is later released via the anal duct, producing the FRTs.

Herring have good hearing. Their sounds are thought to be used for communication between the fish, enabling them to come together in the dark and maintain contact with each other. Herring and sardines can hear higher pitched sounds than most other fish. Most marine predators can't hear the herring sounds. Dolphins and whales can, however.

The Importance of Sardines and Herring

Sardines and herring are interesting fish that play an important role in their environment. If they disappear, many animals will be adversely affected. Human collection of the fish needs to be a sustainable industry, both for our benefit and for the benefit of animals.

There is still much to be learned about the behaviour of sardines and herring and the ways in which they communicate with each other. There are probably many more interesting discoveries to be made about the animals. Though they are an excellent source of nutrients, it's sad that the fish are often thought of as only a food.

References

  • Facts about Pacific sardines from the University of California, San Diego
  • Pacific sardine facts from Oceana
  • More sardine information from the California Ocean Protection Council
  • Facts about omega-3 fatty acids and health from WebMD
  • Nutrients in Pacific sardines from SELFNutritionData
  • List of nutrients in Pacific herring from SELFNutritionData
  • Information about Pacific herring from the Capital Regional District of British Columbia
  • Pacific herring in the coastal food web from Rainforest Conservation Foundation
  • Information about herring FRT sounds from Simon Fraser University

Questions & Answers

Question: During the sardine run, how do the sardines try to survive? Also, how have the sardines evolved?

Answer: Sardines form a tight group in the presence of predators. This is believed to be a protective mechanism that sacrifices some of the group to a predator but protects the others. The group of fish also changes direction rapidly and repeatedly, which confuses the predators. These behaviors may not be beneficial in the South African sardine run, however, because multiple predators surround the fish and they are herded into a tight ball that can’t escape.

The evolution of sardines is an exciting topic. Some of the details are known, but scientists still debate others. A complete article would be required to describe the evolution of the fish and the different theories related to the topic.

© 2011 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on January 26, 2012:

Yes, I agree, BlissfulWriter - it is important to make sure that canned sardines are packed in something healthy. It's a shame to ruin a healthy and nutritious food!

BlissfulWriter on January 26, 2012:

Great BBC video. I love eating canned sardines. Yeah, get the water-packed or olive-oil packed ones instead of the tomato-sauce-packed one.

Linda Crampton (author) from British Columbia, Canada on October 03, 2011:

Thanks a lot, Eiddwen. I appreciate all your comments very much! I love writing hubs about animals, and it's wonderful when people enjoy reading them.

Eiddwen from Wales on October 03, 2011:

Brilliant as always ,I love your hubs on this series and every single one is bookmarked and I am learning so much.

Take care

Eiddwen.

Linda Crampton (author) from British Columbia, Canada on September 11, 2011:

Thanks a lot for the visit and the funny comment, Nell! Herring certainly do have a strange way of communicating with each other.

Nell Rose from England on September 11, 2011:

Hi, well I have heard of people talking out of their backsides before but never fish! lol really interesting, great info, I do eat quite a lot of fish, but never knew all this, thanks nell

Linda Crampton (author) from British Columbia, Canada on September 10, 2011:

Hi, moneycop. Goldfish and koi will eat mosquito larvae and they can live in garden ponds. I hope that your mosquito problem is solved soon! Thanks for the visit and the comment.

moneycop from JABALPUR on September 10, 2011:

alicia C ..it was very help ful to me. last week i had a search about the fish which eat mosquito larva , we have a very good storage facility in roof to collect the rain water but , mosquitoes larva have troubled us.

at shop i gone through many fishes and to my knowledge not after reading you hub, i can buy one for my aquarium also

thanks for sharing

Linda Crampton (author) from British Columbia, Canada on September 09, 2011:

Hi, Prasetio! Thanks a lot for the comment and for the votes. Like you, I enjoy fish. I think that they are very interesting animals to observe and study, and some fish are a wonderful food source.

prasetio30 from malang-indonesia on September 09, 2011:

This was so beautiful hub. I love fish and I really enjoy this information. Unfortunately, I can't find Herring in my country. But Thanks for writing and share with us. Well done, Alicia. Vote up and useful.

Prasetio

Linda Crampton (author) from British Columbia, Canada on September 09, 2011:

Thank you very much for the comment and the vote, Tina. I appreciate your visit.

Christina Lornemark from Sweden on September 09, 2011:

Very interesting hub about sardines and herring. Even though herring is very common where I live I have learned so much new and fascinating info about them! Great videos too!

Voted up,

Tina

Linda Crampton (author) from British Columbia, Canada on September 09, 2011:

Hi, Ingenira. I eat canned sardines too instead of fresh ones. I like to eat sardines because they can be part of a healthy meal or can be eaten as a healthy snack. Thanks for the visit and the vote.

Ingenira on September 09, 2011:

We can't easily buy fresh sardines here, but we get them in cans, and we love to have it on toast too !

Very informative hub, voted up !

Linda Crampton (author) from British Columbia, Canada on September 07, 2011:

I agree with you, writer20, sardines on toast are tasty. I feel kind of bad eating sardines and herring because I'd like them to live, but they do contain healthy fats and other nutrients that are important for our health. Thanks for the comment.

writer20 on September 07, 2011:

I was surprised this morning see your hub.I used to eat Sardines in England but since coming to the U.S. I told forgot about until I saw the in Costco. I use to have them on toast, so I tried them again this way and yes they are still very tasty.

Linda Crampton (author) from British Columbia, Canada on September 07, 2011:

Hi, b. Malin. I'll have to try picked herring - it sounds very tasty. Sardines and onions sound good too! Thanks for commenting.

Linda Crampton (author) from British Columbia, Canada on September 07, 2011:

Thank you, drbj. I appreciate the comment. Herring FRT's are interesting to investigate!

Linda Crampton (author) from British Columbia, Canada on September 07, 2011:

Thanks for the vote, Movie Master. I eat sardines too, and herring occasionally. Like you, I want to include omega-3's in my diet. Yes, herring communication by bubbles is certainly interesting!

Linda Crampton (author) from British Columbia, Canada on September 07, 2011:

Hi, A.A. Zavala. Thanks a lot for the visit and the comment.

b. Malin on September 07, 2011:

I'm probably one of those nuts who now and then likes to eat Sardines in the oil with some sweet onions...and they are Healthy! I also enjoy Herring (pickled) as well. As usual a Fun and Informative, as well as Interesting read Alicia.

drbj and sherry from south Florida on September 07, 2011:

What a wealth of sardine and herring information here, Alicia. Thank you. So herring FRT? To communicate? Wow, who knew?

Movie Master from United Kingdom on September 07, 2011:

Hi Alicia, well these little unassuming fish are a lot more interesting than I realised.

I eat them both, as they are rich in omega 3.

I thought the herring bubbles release was really intriguing.

Great hub, thanks for sharing and voting up.

Augustine A Zavala from Texas on September 07, 2011:

Fascinating hub. I've always wondered about these fish, their varieties, their consumption. Now I know!