“Marine Population Halved Since 1970”, Statistics to Set the Record Straight


  • Author: Lillian Pierson P.E.
  • Date: 01 Oct 2015
  • Copyright: Image appears courtesy of Getty Images

Marine population halved since 1970 is an article recently published by the BBC. This shocking and startling headline is sure to have many readers pouring onto the page to see more facts about the real damage we humans have done. Any reasonable person would be saddened, even despairing, to read and consider the facts claimed in this article. More specifically, claims saying “populations of marine mammals, birds, fish and reptiles have declined by 49% since 1970” and that there has been “a 74% drop in the populations of tuna and mackerel”.

Even as a trained and experienced environmental engineer, when I first read these statistics I went into a state of high alert. I wondered how things could have gone so wrong, so fast. I wondered about the vitality of the food chain, and how long our species could survive at this rate. I was sad and I was angry, but what made me sadder and angrier was yet to come.

thumbnail image: “Marine Population Halved Since 1970”, Statistics to Set the Record Straight

To ease my sense of despair, I decided to delve deeper into the data, to try to get a better grasp of what was actually happening in our seas. What I quickly discovered is that the statistics I had read in that article, the statistics that had me so concerned, had been reported to me out of context, in such a way to precipitate that exact response. In other words, I and other readers were directly misled.

I am in no position to say that the statistics that were reported in that article were right or wrong. I am not an oceanographer. The problem I have is not in the numbers themselves, but rather in the context or lack thereof. Without clarification and proper context, I was given no choice on what interpretation to make. I received the interpretation that the journalist fed me, and since I trusted the source, I earnestly thought there was reason for significant concern.

As a matter of opinion, I do think there are valid reasons for significant concern about our oceans… but my point is that, I was led to believe that a situation was irrevocably dismal, when the truth is that no one really knows the exact extent to which damage has been done. The problem is not the claim that ocean life is being adversely affected by human activities, the problem is that the journalist presenting the facts did not adhere to standard journalistic guidelines for ethics in reporting.

The issue of correct statistical interpretation is a matter of ethics, as much as it is of factual accuracy.

The issue of correct statistical interpretation is a matter of ethics, as much as it is of factual accuracy. Data journalists, or journalists using data to support a story, must be certain to look at their data and assess the following criteria:

• What is the size of the sample? Is the sample large enough to be considered representative?
• What is the context of the statistic? Does the interpretation make sense in light of that broader context?
• What is the source of the statistic? Is it credible?
• Are you comparing apples with apples?
• Is time and rate relevant to the statistic? What is the most relevant unit of temporal measure given what’s known about the broader context?

For credibility’s sake, a journalist must evaluate the context and validity of the assertions he or she makes, and the data used to support those assertions. Journalist have an ethical responsibility to understand and explain relevant caveats, so that readers are not misled. Ambiguity is the earmark of misrepresentation. It goes without saying that journalist should seek to deliver stories with clarity and accuracy, but this is not possible without carefully considering the nuances involved in correctly interpreting data.

So, let’s revisit the story about how “marine populations have halved since 1970”. When I went in and personally researched the topic for myself, here’s what I found:

Or in other words, the experts agree that they know what they don’t know. They know that there are a lot more (anywhere from 482,000 to 741,000) marine life species that are undiscovered than that have not been discovered (approximately 226,000 species discovered at this time) (8). For fish species, in particular, only 1% of fish species have been identified and correctly classified(1). Since there are more unknowns than knowns about see life, and since data on marine life is scanty at best, it’s safe to say that there would be no practicable method to determine the extent to which marine life populations have declined since 1970, if they declined at all. Perhaps this report was referring to a very specific and isolated set of sub-populations, but if so, that point needs to be made very clear and should be presented alongside the larger fact that experts agree that they have no idea about most marine species on Earth and are yet to even discover them, let alone measure their growth / death rates.

Have 74% of tuna populations been killed? It’s possible that 74% of one species (3) of tuna has declined to that extent, but the fact of the matter is that other tuna species aren’t even threatened (4)! So, no – the population of Tuna on Earth have not decreased by 74%. Again, clarity and context would have helped readers from making the wrong interpretation, but instead, readers got misrepresentation by omission.

What do we know about the ocean then? Well, we know that air pollution and runoff are polluting the ocean water. We know that there is a process called biomagnification, where the concentration of toxins increase by orders of magnitude (7) as they move up the food chain. We know that some marine species are more vulnerable than others. And we know that the mass of garbage dumped each year is three times greater than the mass of fish that are caught.

So what do we know about the ocean and its marine species? While there are countless isolated statistics, in general we can safely surmise that human activities are detrimental to the delicate balance of the seas and sea life. We can say for sure, that certain human activities are harmful, and that it is an excellent idea to adopt alternative, less detrimental practices. Not quite as fatalistic and dramatic as the BBC headline, but these facts are true and attention-worthy nonetheless.

[1] http://iss-foundation.org/2013/08/08/not-all-species-are-equally-vulnerable-to-fishing/  
[2] http://www.epa.gov/risk/expobox/populations/he-overview.htm  
[3] http://www.worldwildlife.org/species/bluefin-tuna  
[4] http://www.worldwildlife.org/species/yellowfin-tuna  
[5] http://www.marbef.org/wiki/Threats_to_Marine_Biodiversity  
[6] http://www.slideshare.net/sundaershkalal/fate-of-pesticides-in-environment-or-environmental-polution-by-pesticides  
[7] http://marinebio.org/
[8] http://www.ratical.org/radiation/Fukushima/StevenStarr.html  
[9] http://news.discovery.com/animals/whales-dolphins/marine-species-unknown-121115.htm

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