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Food Web and Ocean Fishieries: Held Together By Forage Fish

Posted by | March 18, 2013 | Ocean Solutions | 2 Comments
PuffinMouthful

The marine food web is a complicated beast; all organisms are connected in an intricate web of species feeding herring on each other. In the food web each group of species have a role to play. Plants create oxygen and form the base of most food webs; phytoplankton are the plants of the ocean. Zooplankton eat the phytoplankton who are themselves eaten by fish, who are eaten by larger fish, who are eaten by even larger fish etc., creating the marine food web.

We often hear that the stability of the marine food web is in jeopardy because top predators are declining. Recent studies have shown that the most notorious group of top predators, sharks, are declining – and no one is surprised to see cod or salmon in the news as examples of extreme population decline.

But what about all the species that make up the links between big predators (such as sharks, whales, tuna and salmon), and the wee phytoplankton? In fisheries science we call these species forage fish.

Forage fish are medium sized fish that provide a critical link in the food web; they consume plankton and are eaten by larger predators in the food web. Examples of forage fish include anchovies, herring, smelt and sardines. Forage fish often form dense groups, called schools, which attract a lot of predators. Schooling behaviour in fish is a very interesting topic and I could go on and on!!! Instead I’ll summarize the behaviour by saying it provides, “safety in numbers”.

Forage fish are prey to a large number of predators including seabirds, marine mammals, as well as recreationally and commercially important fish species like salmon, cod and tuna. (Not to mention sailfish!!)

As mentioned above, forage fish typically form large schools – making them easy prey for their natural predators. Commercial fisheries also exploit the schooling behaviour of forage fish. The Lenfest Forage Fish Task Force estimates that the direct capture of forage fish makes up more than one-third of the total annual marine harvest. For example, in 2006, the Peruvian anchovy was the top landed species in the world, bringing in 7 million tones! Forage fish, while often small, are a BIG DEAL for both the marine food web and commercial fisheries.

So, if there is a large commercial fishery, why don’t you see forage fish on your dinner plate? Well, most forage fish end up in animal feed. In 2006, 87% of the global forage fish harvest was consumed in the aquaculture sector.  In Australia, 2.5 million tones of forage fish were used to make cat food. You can think of it like corn. Up to 40% of the corn produced in the U.S. is used to feed cattle, and not people (another 40% is reduced to ethanol).

In economic terms, the Lenfest Forage Fish Task Force estimates that the direct commercial catch of forage fish translates into $5.6 billion dollars. In contrast, left in the ocean the forage fish would provide a supportive value of $11.3 billion to the commercial catch of predator species like salmon or tuna.

As we can see, everyone wants a forage fish or two. As forage fish abundance declines there will be an increase in competition between users:  humans who directly consume forage fish, humans who use forage fish in many non-direct-food industries (like aquaculture), and all those marine predators in the food web who rely on them as a major source of food.

Monitoring and Managing Forage Fish

Historically, forage fish were ignored by fisheries managers like the lonely middle child in a large family*. Harvest quotas were set at high levels and by-catch tallies were ignored or not incorporated into estimates of maximum sustainable yield. To complicate matters further, forage fish exhibit what fisheries managers call “boom and bust” population dynamics.

The “boom and bust” trend means in some years there are a lot of forage fish, and in other years there are few – irrespective of harvest pressure by natural or human predators. Forage fish are also very sensitive to changes in environmental conditions, which can have a large impact on the success of a year class (how many baby fish hatch and survive in a given year). These factors make it very hard to manage forage fish populations. * Many exceptions exist and a great list can be found in the last section of this article

When fish populations have limited management, or are not managed at all, we often see a decline in their abundance: especially in economically important forage fish species.

The Lenfest Forage Fish Task Force completed the most comprehensive assessment of global forage fish populations to date, and recommends:

 “ …cutting catch rates in half in many ecosystems and doubling the minimum biomass of forage fish that must be left in the  water, compared to conventional management targets.”

The Task Force used model simulations based on real catch data to show that at a catch level of 0.3, 60% of harvested forage fish species would collapse. Many forage fish species are currently managed at a catch level of 1.0; an arguably unsustainable level.

Protecting Forage Fish

In response to reports such as those of the Lenfest Task Group and direct observations of forage fish decline, many fisheries managers, conservationists and the fishing industry are pushing for change.  For instance, a  95% decline in river herring abundance was observed along the Atlantic coast. This decline led to the National Oceanic and Atmospheric Administration (NOAA) evaluating whether this species should be listed as a threatened species in the U.S. (See graph below – Pew Trust Herring Alliance River Herring Report).

herring decline

The Pew Charitable Trust supported monitoring of the Atlantic River Herring and produced a report outlining the potential causes of the population decline, conservation issues facing River Herring, and mitigation measures. Read the full report here!

What’s next?

Conservation organizations all over the world are pushing for an ecosystem based management approach to our natural resources. This framework would put forage fish in the spotlight and ensure that they are monitored, managed and conserved with the same vigor as the commercially important species they support. Here is a list of organizations mobilizing their efforts to save forage fish:

Pew Environmental Pacific Forage Fish Campaign

Northwest Straits Marine Conservation Initiative

Blue Ocean Institute

What are the most important things YOU can do to help the neglected forage fish?

1)  Avoid pet foods with ‘fish meal’ as the main ingredient

2)  Join local fisheries stakeholder committees and become a voice for forage fish!

3)  Eat certified sustainable fish species

Forage fish are not typically talked about when organizations call on support from the public. How do you think we can make forage fish a focus of Ocean Conservation in the eyes of the public? Let us know in the comments below!

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2 Comments

  • terese p collins says:

    Thank you for your article. Do you know what the migratin pattern is and the spawing habits are of the menhaden found in the Gulf of Mexico, and Mississippi Sound specifically.

  • Rebecca Dolson says:

    Hi Terese,
    Thank you for the note. Unfortunately, I am not knowledgeable about the menhaden species. If you would like a generic place to start your search with quality checked data I suggest Fishbase.org (http://www.fishbase.org/search.php). Type in the common name of your fish species of interest to start. It will provide you with preliminary information as well as references for further reading. Here is what the website had to say about the biology of the Gulf menhaden (Brevoortia patronus – is this the species you are looking at?).

    “Occur inshore in summer, but at least some moving into deeper waters from October (Mississippi Delta area). Feed in dense schools, filtering phytoplankton, but probably also feed at the bottom. Apparently breed in winter (October to February, with a peak in January). Salinity tolerance range from 0.1-60 ppt, but the commercial catch is mostly from 5.0-24 ppt. Marketed fresh, salted or canned. Mainly used as source of fish oil; also as fish meal (Ref. 188). Isopod is found in the mouth (Ref. 37032).”

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