The telling of the classic fish tale always, at some point, involves the speaker spreading his arms wide and insisting: “It was this big.” In Key West, Florida, the phrase is more accurate with an adjusted emphasis: “It was this big.”

In “A 10 Percent World” (September 2010), author J.B. MacKinnon introduces Walrus readers to Dr. Loren McClenachan, a post-doctoral associate at Simon Fraser University whose research into humanity’s impact on marine life — ranging from goliath grouper to sea turtles to long-extinct seals — includes a 2009 study of Key West’s shrinking trophy fish. Walrusmagazine.com spoke with McClenachan about her work, the field, and the study’s troubling findings.

Can you describe your Key West study for our readers?

I found a bunch of photos that had been preserved in the local archives in Key West, showing the biggest fish that had been caught on any particular day. I measured and ID’d the fish and found that there had been a pretty significant change in the size of the fish that people had called “trophies” over the last half century or so.

I had been looking for any kind of information in the historical archive that would tell me about changes in the ocean over long timescales — looking at things that went back as far as the 1700s. I’d spent about three years, at that point, looking for archival information about the marine environment, including fish, but also including lots of different other types of organisms — turtles, monk seals, invertebrates, and even the coral and mangrove and seagrass itself. I had been looking for changes across the whole ecosystem, and this piece of information was particularly great because it was consistent over time.

What do you mean by “consistent over time”?

A lot of times with the historical record, we’re left with what people decided to write or take pictures of or make maps of. It’s not necessarily consistent over any period; it’s more like a snapshot. For example, another great piece of information I found was a map made in the 1700s that showed where the coral reefs were — it was actually written on the map where sailors could stop and get turtles and things like that. It was fantastic because it was so early. But that was just one piece of information, so it’s more difficult to compare that [time period] to what has happened since.

These photos were so great because they were all collected in the same way. It was [basically the same] picture taken in the same place with basically the same methods over fifty years, so it was a lot easier to compare and know that they were actually measuring changes in this particular place.

And there was a big reduction in the size of the fish?

Yes, a 90 percent reduction in terms of weight of the fish that were taken. These are photos of just the largest trophy fish, so we’re not talking about the whole suite of fish that are out there. These are the biggest fish, the “catch of the day” that people are showing off, not just some random fish that they caught.

In “A 10 Percent World,” MacKinnon notes that it’s telling how in each of the photos, even though the size of the fish changes, everyone looks equally proud of themselves.

It’s interesting. It’s a pretty obvious shifted baseline, in terms of what people hope to get out of going out fishing.

Can you explain this shifting baselines concept?

It is the idea that you expect the world to be what it was like when you first remember going out into it. But this shifts over time, so your grandparents’ idea of a place is much different than yours. [Between] that loss of memory and degradation of the environment, people start to expect less out of the environment, and start to think that degraded systems are natural, when in fact there’s been a lot of change that just happened before they had the opportunity to witness it.

So these degrading trends go back hundreds of years? How far back does this research extend?

I’ve tried to synthesize — and a lot of the historical research has tried to synthesize — going back as far as European contact, in the Caribbean. And some a little bit longer too; some studies have been able to incorporate archaeological information. Actually, a nice parallel to Key West’s fish photo board [which was unchanged for fifty years, allowing consistent measurement of fish pictured in front of it] is some really interesting research looking at the size of fish bones in archaeological middens, which showed changes in the size of the largest fish caught even before Europeans arrived. Other studies have looked at the effects of fishing and hunting on populations of marine turtles, and there are some really clear signals from the archaeological record for those big animals. But most of it has been more recent, looking at changes since European contact. As you move forward in time it’s easier to collect the information, so the resolution improves as you get more recent. The earliest that I’ve gone back is about 500 years.

And is this a growing trend, historical ecology?

It started about ten or fifteen years ago; there were a couple of established ecologists who had been doing research in the field and independently began to realize that things had changed a lot, and became interested in the field of incorporating historical data into ecological studies. In the last five years or so it’s really taken off. People have done studies all over the world, from the Caribbean to the Mediterranean to the Baltic to the Pacific to the Hawaiian Islands. There’s a lot of opportunity for it, too, because there’s a whole bunch of information out there that hasn’t really been analyzed in this way. People have been collecting and keeping historical information in archives, but looking at it with a biological lens is sort of a new way of doing it.

Are you working on any similar research right now?

This morning, I was working on a project looking at changes in sharks and monk seal populations in the Northwest Hawaiian Islands, another area with a fantastic historical record where a lot of other researchers are working. It seems to be that wherever people have looked at changes in marine animal populations, they’ve found a lot more than they expected to. There’s a lot of change that has yet to be documented.

Your research was funded by the Census of Marine Life. What’s that?

The History of Marine Animal Populations project, which is what our research fell under, is part of the Census of Marine Life. The census is concerned with documenting what was in the oceans, what is in the oceans now, and what will be in the oceans.

The Census is being released this year. Do you think that it’s going to impact policy, perhaps cause some actual changes to be made?

I would really hope so. In particular, with looking at baseline populations for recovery of endangered species and fisheries, there’s huge opportunity to integrate this sort of information because there is a mandate in a lot of different policies to recover species to some level of historical abundance. Obviously we’re not going to be able to recover populations to 100 percent of their historical abundance, but having a solid sense of how much things have changed can help make our recovery goals more biologically realistic.

MacKinnon writes about how we should move past a strict idea of conserving parcels of land, or species, in a “pristine” state — which would seem to demand that humans exist outside of the environment — and instead have an idea of integrating humans as part of an ecosystem that experiences constant change. Do you agree?

For sure... historians have known this for a really long time. They know that people are part of ecosystems, and that even the ecosystems that we think of as pristine still have some fingerprint of humans on them in some way. Understanding what that [means] is, I think, just interesting — and also useful for conservation.