Forage fish
Forage fish, also called prey fish or
Forage fish compensate for their small size by forming schools. Some swim in synchronised grids with their mouths open so they can efficiently filter plankton.[1] These schools can become immense shoals which move along coastlines and migrate across open oceans. The shoals are concentrated energy resources for the great marine predators. The predators are keenly focused on the shoals, acutely aware of their numbers and whereabouts, and make migrations themselves that can span thousands of miles to connect, or stay connected, with them.[2]
The ocean's
The
In the oceans
Typical ocean forage fish are small, silvery schooling
The term “forage fish” is a term used in fisheries, and is applied also to forage species that are not true fish but play a significant role as prey for predators. Thus invertebrates such as squid and shrimp are also referred to as "forage fish". Even the tiny shrimp-like creatures called krill, small enough to be eaten by other forage fish, yet large enough to eat the same zooplankton as forage fish, are often classified as "forage fish".[5]
Anchovies | Caribbean reef squid | Menhaden |
Sardines | Shrimp | Northern krill |
Forage fish utilise the biomass of
Though forage fish are abundant, there are relatively few species. There are more species of primary producers and apex predators in the ocean than there are forage fish.[2]
Ocean food webs
Forage fish occupy central positions in the ocean food webs. The position that a fish occupies in a food web is called its trophic level (Greek trophē = food). The organisms it eats are at a lower trophic level, and the organisms that eat it are at a higher trophic level. Forage fish occupy middle levels in the food web, serving as a dominant prey to higher level fish, seabirds and mammals.
Ecological pyramids are graphical representations, along the lines of the diagram at the right, which show how biomass or productivity changes at each trophic level in an ecosystem. The first or bottom level is occupied by primary producers or autotrophs (Greek autos = self and trophe = food). These are the names given to organisms that do not feed on other organisms, but produce biomass from inorganic compounds, mostly by a process of photosynthesis.
In oceans, most primary production is performed by
Thus, in ocean environments, the first bottom trophic level is occupied principally by
Phytoplankton | Dinoflagellate | Diatoms |
The most important groups of phytoplankton include the diatoms and dinoflagellates. Diatoms are especially important in oceans, where they are estimated to contribute up to 45% of the total ocean's primary production.[6] Diatoms are usually microscopic, although some species can reach up to 2 millimetres (0.079 in) in length.
The second trophic level (
Segmented worm | Tiny shrimp-like crustaceans | Juvenile planktonic squid |
Particularly important groups of zooplankton are the
Together, phytoplankton and zooplankton make up most of the plankton in the sea. Plankton is the term applied to any small drifting organisms that float in the sea (Greek planktos = wanderer or drifter). By definition, organisms classified as plankton are unable to swim against ocean currents; they cannot resist the ambient current and control their position. In ocean environments, the first two trophic levels are occupied mainly by plankton. Plankton are divided into producers and consumers. The producers are the phytoplankton (Greek phyton = plant) and the consumers, who eat the phytoplankton, are the zooplankton (Greek zoon = animal).
Diet
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Forage fish and the food web | |
Fishing down marine food webs |
Forage fish feed on plankton. When they are eaten by larger predators, they transfer this energy from the bottom of the food chain to the top and in this way are the central link between trophic levels.[8]
Forage fish are usually
Young forage fish, such as herring, mostly feed on
Ocean
Predators
Forage fish are the food that sustains larger predators above them in the ocean food chain. The superabundance they present in their schools make them ideal food sources for top predator fish such as tuna, striped bass, cod, salmon, barracuda and swordfish, as well as sharks, whales, dolphins, porpoises, seals, sea lions, and seabirds.[5]
Tuna | Shark | Striped bass |
Leopard seal | Dolphin | Gannet |
Schooling
Forage fish compensate for their small size by forming
Herring are among the most spectacular schooling fish. They aggregate together in huge numbers. Schools have been measured at over four cubic kilometres in size, containing about four billion fish.[12] These schools move along coastlines and traverse the open oceans. Herring schools in general have very precise arrangements which allow the school to maintain relatively constant cruising speeds. Herrings have excellent hearing, and their schools react very fast to a predator. The herrings keep a certain distance from a moving scuba diver or cruising predator like a killer whale, forming a vacuole which can look like a doughnut from a spotter plane.[13] The intricacies of schooling is far from fully understood, especially the swimming and feeding energetics. Many hypotheses to explain the function of schooling have been suggested, such as better orientation, synchronized hunting, predator confusion and reduced risk of being found. Schooling also has disadvantages, such as excretion buildup in the breathing media and oxygen and food depletion. The way the fish array in the school probably gives energy saving advantages, though this is controversial.[14]
On calm days, schools of herring can be detected at the surface a mile away by little waves they form, or from several meters at night when they trigger bioluminescence in surrounding plankton. Underwater recordings show herring constantly cruising at high speeds up to 108 cm per second, with much higher escape speeds.
They are fragile fish, and because of their adaptation to schooling behaviour they are rarely displayed in aquaria. Even with the best facilities aquaria can offer they become sluggish compared to their quivering energy in wild schools.
Hunting copepods
Copepods are usually the dominant zooplankton. Some scientists say they form the largest animal biomass on the planet. The other contender is the Antarctic krill. But copepods are smaller than krill, with faster growth rates, and they are more evenly distributed throughout the oceans. This means copepods almost certainly contribute more secondary production to the world's oceans than krill, and perhaps more than all other groups of marine organisms together. They are a major item on the forage fish menu.
Copepods are very alert and evasive. They have large antennae. When they spread their antennae they can sense the pressure wave from an approaching fish and jump with great speed over a few centimeters.
Herrings are pelagic feeders. Their prey consists of a wide spectrum of phytoplankton and zooplankton, amongst which copepods are the dominant prey. Young herring usually capture small copepods by hunting them individually— they approach them from below. The (half speed) video loop at the left shows a juvenile herring feeding on copepods. In the middle of the image a copepod escapes successfully to the left. The opercula (hard bony flaps covering the gills) are spread wide open to compensate the pressure wave which would alert the copepod to trigger a jump.[1]
If prey concentrations reach very high levels, the herrings adopt a method called "ram feeding". They swim with their mouth wide open and their opercula fully expanded. Every several feet, they close and clean their
In the animation, juvenile herring hunt the copepods in synchronization: The copepods sense with their antennae the pressure-wave of an approaching herring and react with a fast escape jump. The length of the jump is fairly constant. The fish align themselves in a grid with this characteristic jump length. A copepod can dart about 80 times before it tires out. After a jump, it takes it 60 milliseconds to spread its antennae again, and this time delay becomes its undoing, as the almost endless stream of herrings allows a herring to eventually snap the copepod. A single juvenile herring could never catch a large copepod.[1]
Migrations
Forage fish often make great migrations between their spawning, feeding and nursery grounds. Schools of a particular stock usually travel in a triangle between these grounds. For example, one stock of herrings have their spawning ground in southern Norway, their feeding ground in Iceland, and their nursery ground in northern Norway. Wide triangular journeys such as these may be important because forage fish, when feeding, cannot distinguish their own offspring.
Fertile feeding grounds for forage fish are provided by ocean upwellings.
Capelin are a forage fish of the smelt family found in the Atlantic and Arctic oceans. In summer, they graze on dense swarms of plankton at the edge of the ice shelf. Larger capelin also eat krill and other crustaceans. The capelin move inshore in large schools to spawn and migrate in spring and summer to feed in plankton rich areas between Iceland, Greenland, and Jan Mayen. The migration is affected by ocean currents. Around Iceland maturing capelin make large northward feeding migrations in spring and summer. The return migration takes place in September to November. The spawning migration starts north of Iceland in December or January.
The diagram on the right shows the main
Predator attacks
Schooling forage fish are subject to constant attacks by predators. An example is the attacks that take place during the African
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Dolphins herd sardines[18] | |
Gannets "divebomb" sardines[18] |
Sardines have a short life-cycle, living only two or three years. Adult sardines, about two years old, mass on the
When threatened, sardines instinctively group together and create massive bait balls. Bait balls can be up to 20 meters (66 feet) in diameter. They are short lived, seldom lasting longer than 20 minutes. As many as 18,000 dolphins, behaving like sheepdogs, round the sardines into these bait balls, or herd them to shallow water (corralling) where they are easier to catch. Once rounded up, the dolphins and other predators take turns plowing through the bait balls, gorging on the fish as they sweep through. Seabirds also attack them from above, flocks of gannets, cormorants, terns and gulls. Some of these seabirds plummet from heights of 30 metres (98 feet), plunging through the water leaving vapour-like trails behind like fighter planes.[18]
The eggs, left behind at the Agulhas Banks, drift northwest with the current into waters off the west coast, where the larvae develop into juvenile fish. When they are old enough, they aggregate into dense shoals and migrate southwards, returning to the Agulhas banks in order to restart the cycle. [18]
Forage fisheries
History
Herring has been known as a staple food source since 3000 B.C. In Roman times, anchovies were the base for the fermented fish sauce called garum. This staple of cuisine was produced in industrial quantities and transported over long distances.
Fishing for sardela or sardina (Sardina pilchardus) is an ongoing activity on the
Contemporary
This article is part of a series on |
Commercial fish |
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Large pelagic |
Forage |
Demersal |
Mixed |
Traditional
In former times, forage fish were more difficult to fish profitably, and were a small part of the global marine fisheries. But modern industrial fishing technologies have enabled the removal of increasing quantities. Industrial-scale forage fish fisheries need large scale landings of fish to return profits. They are dominated by a small number of corporate fishing and processing companies.[5]
Forage fish populations are very vulnerable when faced with modern fishing equipment. They swim near the surface in compacted schools, so they are relatively easy to locate at the surface with sophisticated electronic
Spawning patterns in forage fish are highly predictable. Some fisheries use knowledge of these patterns to harvest the forage species as they come together to spawn, removing the fish before they have actually spawned.[2] Fishing during spawning periods or at other times when forage fish amass in large numbers can also be a blow to predators. Many predators, such as whales, tuna and sharks, have evolved to migrate long distances to specific sites for feeding and breeding. Their survival hinges on their finding these forage schools at their feeding grounds. The great ocean predators find that, no matter how they are adapted for speed, size, endurance or stealth, they are on the losing side when faced with the machinery of contemporary industrial fishing.[2]
Altogether, forage fish account for 37 percent (31.5 million tonnes) of all fish taken from the world's oceans each year. However, because there are fewer species of forage fish compared to predator fish, forage species fisheries are the largest in the world. Seven of the top ten fisheries target forage fish.[5] The total world catch of herrings, sardines and anchovies alone in 2005 was 22.4 million tonnes, 24 percent of the total world catch.[19]
The Peruvian
Use as animal feed
Eighty percent of the forage fish caught are fed to animals, in large part due to the high content of beneficial long chain
According to Turchini and De Silva (2008), another 2.5 million tonnes of the annual forage fish catch is consumed by the global cat food industry. In Australia, pet cats eat 13.7 kilograms of fish a year compared to the 11 kilograms eaten by the average Australian. The pet food industry is increasingly marketing premium and super-premium products, when different raw materials, such as the by-products of the fish filleting industry, could be used instead.[25]
Environmental issues
In 2008 the
- The composition of landings of forage fish fisheries have changed over the past 50 years with the trophic level of fish used in fishmeal increasing over the past 20 years.
- Our understanding of the role of forage fish in marine ecosystem and the impact of fishing is still limited.
- Landing of forage fish peaked by the 1970s, and these high levels are highly unlikely in the future, even if fisheries are managed sustainably.
- The consumption of forage fish by seabirds and marine mammals is not likely to be onerous to fisheries, except in a few localized areas. By contrast, fisheries, by reducing the biomass of small pelagics, might pose a threat to these predators, particularly to those species for which stocks have been heavily depleted by human exploitation in the past.
- Some forage fish species are consumed by many people with consumption patterns changing over the last 20 years.
- Aquaculture continues to increase its consumption of fishmeal and fish oil.
In 2015 sardine populations crashed along the west coast of the United States, causing the fishery to close early and remain closed through the 2015–2016 season.[26] A key reason for the population crash, was overfishing due to the demand of fish meals and fish oil used in feed for aquaculture and for human nutritional supplements.[27] In an effort to provide some relief from the pressure put on forage fish populations, the World Bank along with the University of Arizona, Monterey Bay Aquarium and the New England Aquarium has sponsored a competition called the F3 (Fish-Free Feed) Challenge, which will award $200,000 to the most successful fish feed manufacturer who develops aquaculture feeds not made from fish.[28]
In lakes and rivers
Forage fish also inhabit freshwater habitats, such as lakes and rivers, where they serve as food for larger freshwater predators. Usually smaller than 15 centimetres (6 in) in length, these small
Golden shiner | Killifish | Southern redbelly dace |
Chinese minnow | Swarm of carp | Twaite shad |
In the context of human activity, within any fresh or saltwater ecosystem, there will always be both desirable and undesirable fishes, and this varies from country to country, and often from region to region within a country. Sport fishermen divide freshwater predators of forage fish into those:
- which have a good fighting ability and are good to eat, called sport (or game) fish.
- the other less desirable fish, called rough fish in North America and coarse fish in Britain
Rough or coarse fish usually refers to fish that are not commonly eaten, not sought after for sporting reasons, or have become invasive species reducing the populations of desirable fish. They compete for forage fish with the more popular sport fish. They are often regarded as a nuisance, and are not usually protected by game laws.[29] Forage fish generally are not considered rough or coarse fish because of their usefulness as bait.
The term rough fish is used by U.S. state agencies and anglers to describe undesirable predator fish. In North America, anglers fish for salmon, trout, bass, pike, catfish, walleye and muskellunge. The smallest fish are called panfish, because they can fit in a standard cooking pan. Some examples are crappies, rock bass, perch, bluegill and sunfish.
The term coarse fish originated in the United Kingdom in the early 19th century. Prior to that time, recreational fishing was the sport of the
Brook trout | Black crappie | Macquarie perch |
Rainbow trout | Pink salmon | Channel catfish |
Bait and feeder fish
Forage fish are sometimes referred to as bait fish or feeder fish.
Timeline
- 2006: The U.S. National Coalition for Marine Conservation asks U.S. fishery managers to put "Forage First!". Their campaign was launched with the publication of their report, Taking the Bait: Are America’s Fisheries Out-competing Predators for their Prey?,[31] available at cost to the U. S. fishing industry, encouraging fishery managers to protect predator–prey relationships as a first step toward an ecosystem based approach to fishery management.[2]
- 2009: The international Lenfest Forage Fish Task Force is established to develop workable management plans for tackling the depletion of forage fish.[32]
- 2015: sardine populations crashed along the west coast of the United States.[26]
Recent reports
- Pikitch E and 12 others (2012) Little Fish, Big Impact: Managing a Crucial Link in Ocean Food Webs Archived 2012-07-03 at the Wayback Machine Lenfest Ocean Program, Washington, DC. Summary and other materials available on the Lenfest Ocean Program website.
See also
Notes
- ^ a b c Kils, U (1992) The ecoSCOPE and dynIMAGE: Microscale tools for in situ studies of predator–prey interactions. Arch Hydrobiol Beih 36: 83–96
- ^ a b c d e f g National Coalition for Marine Conservation: Forage fish Archived 2008-12-17 at the Wayback Machine
- Alaska Science Center
- ^ .
- ^ a b c d Marine Fish Conservation Network: Forage fish: The Most Important Fish in the Sea Archived 2008-12-05 at the Wayback Machine
- .
- Carl von Ossietzky University of Oldenburg
- ^ Forage fish: The most important fish in the sea
- NOAA, 2004). Studies in Tropical Oceanography. 5: 665–847.
- doi:10.1071/MF04305.
- ^ Mahmoudi, B; McBride, R (2002). "A review of Florida's halfbeak bait fishery and halfbeak biology, and a preliminary stock assessment" (PDF). Florida Fish and Wildlife Conservation Commission. Archived from the original (PDF) on 2007-10-25.
- ISBN 9780706513516
- ^ Nøttestad, L and Axelsen, BE (1999) Herring schooling manoeuvres in response to killer whale attacks Canadian Journal of Zoology, 77: 1540–1546.
- ISBN 9780412429309
- ^ Wind Driven Surface Currents: Upwelling and Downwelling
- ^ Barbaro1 A, Einarsson B, Birnir1 B, Sigurðsson S, Valdimarsson S, Pálsson ÓK, Sveinbjörnsson S and Sigurðsson P (2009) "Modelling and simulations of the migration of pelagic fish" Journal of Marine Science, 66(5):826–838.
- ^ Marine Scientists Scratch Heads Over Sardines
- ^ a b c d e Sardine Run Shark Feeding Frenzy Phenomenon in Africa Archived 2008-12-02 at the Wayback Machine
- ISBN 92-5-105267-0
- ISBN 0-09-189780-7
- ^ Greenpeace: Rethinking sustainability: A new paradigm for fisheries management Archived 2009-03-25 at the Wayback Machine
- ^ World's Fish Catches Being Wasted As Animal Feed Terra Daily. Retrieved 1 December 2008.
- ^ New Study to Highlight Waste of Seafood The FishSite. Retrieved 1 December 2008
- ^ Michael B. Rust, et al., The Future of Aquafeeds, NOAA/USDA Alternative Feeds Initiative, NOAA Technical Memorandum NMFS F/SPO-124, December 2011, see http://docs.lib.noaa.gov/noaa_documents/NMFS/TM_NMFS_FSPO/NMFS_FSPO_tm124.pdf
- ^ Our pets’ gourmet tastes are putting pressure on dwindling fish stocks – Deakin University
- ^ a b Plunging sardine numbers spark quick management response Chinook Observer, 14 April 2015.
- ^ Fish Oil Market Analysis By Application (Aquaculture (Salmon & Trout, Marine Fish, Crustaceans, Tilapias), Direct Human Consumption) And Segment Forecasts To 2022 Grand View Research, February 2016.
- ^ The Race to Find Fish Feeds That Don’t Bankrupt the Ocean National Geographic, 24 May 2016.
- ^ ISBN 9780813117720
- ISBN 0719037778
- ^ National Coalition for Marine Conservation: Forage First! Archived 2008-05-11 at the Wayback Machine
- ^ "Lenfest Forage Fish Task Force Launched |". SBU News. 2009-05-29. Retrieved 2022-11-29.
References
- PMID 9452385. Archived from the original(PDF) on 2008-02-21. Retrieved 2009-04-11.
External links
- Herring Research: Using Acoustics to Count Fish
- Sanders, Michael (1995) Impacts of predator–prey relationships on harvesting strategies and management FAO.
- Skjoldal, Hein Rune (2011) "Ecological effects of fisheries on small pelagics" Background document for CBD Expert meeting, Bergen, 7–9 December 2011.
- Daniel Pauly at Fish Forever – YouTube: Pauly talks about his "epiphany" about directly eating anchovies.