Posted by: leahbiery | September 24, 2010

Seafood Consumption Confusion

Hello from Vancouver, Sanibel Sea Schoolers! Now that I’m settled in this rainy but beautiful city I thought it would be nice to start blogging again.

This week, The Washington Post published an article about a project being undertaken by the University of British Columbia Fisheries Centre (a.k.a. my new home). The project aims to assign a “SeafoodPrint” to various types of fish based on the amount of primary production (energy from the bottom of the food web) they require. Kind of like a carbon footprint, but for fish consumption.

I was excited about the article because it presents an innovative way to begin standardizing the way we think about global seafood consumption. I shared it with some friends and family, and was surprised when most of them responded with confusion. As a “fisheries person,” the idea of a SeafoodPrint seems pretty straightforward to me, but now I realize that if you don’t have a background in biology, it’s probably like reading Chinese.

You can decide for yourself here.

I want to share an e-mail from my aunt in Washington, DC (a regular Washington Post reader), and my responses to her very insightful questions. Hopefully it will clear up some of the confusion.

Dear Leah,

Thank you for pointing out the article in this week’s Post referencing your professor’s study.  Fascinating.  I found the associated graphs, “who catches and who consumes”  and “what we eat makes a difference” both eye catching, mesmerizing, and even puzzling.  At some convenient time, I would appreciate brief explanations/opinions on the following:

Hey Aunt Marilyn,

It’s great to hear feedback from the “average” reader, although I’m sure you are above average. If you don’t understand it, we’re probably not explaining it well. I will share the feedback with my adviser.

1.  I’m foggy on the logic in the second graph explained as:  A single thousand-pound tuna might need to eat as many as 15,000 smaller fish in a year, for example, which means eating one pound of tuna is equivalent to 100 pounds of tilapia.

The concept of tuna vs. tilapia is about energy and biomass (the amount of living material in a system). It’s complicated, but I’ll give it my best try.

The basis of the marine food web is phytoplankton, which obtains its energy from the sun.

Think of a basic food chain: phytoplankton -> zooplankton -> anchovy -> mackerel -> tuna

The transfer efficiency of energy between each progressing trophic level in terms of biomass is only about 10%. That means if a zooplankton eats 1 pound of phytoplankton (unlikely), it will gain 0.1 pounds. It expends the other 0.9 pounds of zooplankton swimming around (think of it as burning calories).

In order to gain 1 pound of weight, a zooplankton would have to eat 10 pounds of phytoplankton.

If the zooplankton ate 10,000 pounds of phytoplankton, it would gain 1000 pounds. If the anchovy ate the 1000 pounds of zooplankton, it would gain 100 pounds. If the mackerel ate 100 pounds of anchovy, it would gain 10 pounds, and if the tuna ate that 10 pounds of mackerel, it would only gain 1 pound.

So, your one pound tuna steak required 10,000 pounds of phytoplankton to produce. That’s a ton of energy, and a ton of stress on the ocean.

A terrestrial example.

How would my not eating tuna keep the tuna from eating all those pounds of tilapia? Shouldn’t we be eating more tuna so there are less of them in the ocean to eat so many level 1 and 2 fish?  Just because I demand more tuna doesn’t mean the industry or nature will produce them.  Sorry, I don’t get it.

If you think of this as an entire system, we are very quickly depleting the ocean’s biomass by consuming so much predatory seafood (like tuna). In effect, by eating one pound of tuna, you are also eating the 10 pounds of mackerel, 100 pounds of anchovy, 1000 pounds of zooplankton, and 10,000 pounds of phytoplankton required to produce it. You’re not saving those smaller fish from being eaten, because by the time it reaches your plate, your 400 pound tuna already ate them.

You could have eaten the 100 pounds of anchovy for the exact same energy requirement. That much food would last a year, whereas your one pound tuna steak was only one meal. The anchovy is much more energy efficient – and much less demanding on the already pressured ocean. That’s why it’s better to eat lower on the food chain. Do you understand? If not, let me know and I’ll try again 🙂

In the long run, harvesting too many tuna will allow smaller fish populations to grow large. It is already happening, and it’s throwing ocean ecosystems way off balance. The term for it is “fishing down the food web.” We are taking too many predators out of the ocean, allowing smaller fish to thrive. Soon we might run out of large fish and be left with only jellyfish burgers.

Put simply, we need to eat more small fish and less large fish to keep the ocean in balance.

***Side Note***

This concept is also one of the main reasons why farming predatory fish is not sustainable – we are harvesting literally TONS of small fish from the ocean to produce only a few pounds of salmon/turbot/(insert predator here). It requires lots of energy (in terms of oil) to capture all those little fish, and they could be directly feeding hungry people instead of hungry captive salmon.

How do I get my grocer to stop purveying all that Level 4 seafood?   Is the idea for me to stop buying so they in turn reduce offerings?

I think you can certainly influence your grocer by avoiding “red” fish species, but if the demand exists among other customers, it will still be sold. In my opinion, the biggest way to make an impact is through positive reinforcement and through talking to others about the issue.

When your grocer makes sustainable species available, tell him how happy it makes you. Request that he continue to order that type of fish. Also, mention why you’re not buying the red list species. He may not realize you’re avoiding it for sustainability reasons unless you say so.

For the record I purchased a ‘green’ fish–tilapia, not hi in good omegas but tasty. We enjoyed it very much but I steer away from a regular diet because it is discovered to be not all that heart healthy.

If you’re looking for sustainable but still healthy fish options I would recommend wild Pacific salmon, troll-caught Spanish mackerel (avoid King mackerel, as it’s high in Mercury), or troll-caught – not longlined – mahi-mahi (predatory, but highly sustainable and reproduces amazingly fast). Sardines are also super heart healthy if you can stomach them.

3.  What do you think of the genetically altered Atlantic salmon issue that is being hotly debated? Scientists have figured out a way to turn on the growth hormone in this salmon so it matures in 1 yr instead of  3 yrs–more fish for the table, and they promise not to mix the altered salmon with the wild caught.   Do you approve?  I don’t think I do.  There is fall out any time you mess with mother nature.

I’m working on a blog about the Salmon issue – I’ll let you know when it’s finished.

Choosing what to eat is getting complicated.  I think we should figure how out how to evolve our stomachs into digesting grass.  This would end some of the misery.

You’re so right – choosing what to eat is SO complicated. That’s why I’m a vegetarian. Let me know when you figure out the meat maze and I will gladly convert.



Lost in the sea of debate.
Stay in touch and much love.

Aunt M

PS – If you’re on Sanibel, send me some sun!


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