And that is the difference between harvesting oceans and growing food on land.
Steven Palumbi, a pony-tailed marine ecologist and the Pew Fellow in Marine Conservation at Stanford University, gave a closing keynote at the conference, touching on this difference.
For oceans to be healthy, the entire eco-system of the ocean needs to be healthy. On land it may be easier to control all those variables -- making sure you have biodiversity in the crops you plant, taking into account water usage and quality, chemicals, mixed farming systems with animals, etc.
And yet, in our interactions with the oceans, we focus on only the species we're harvesting. One problem (alluded to earlier in the conference) of this focus is that it doesn't account for all the rippling effects of this harvest. By-catch, for example, is a huge problem (depleting juvenile red snapper when taking shrimp) or bottom trawling (that damages the seabed). If you simply look at the population you're fishing for you may miss these other effects.
Finally, since we're not actively living in the ocean, we might arguably have a greater impact than on the land. For these are still wild places, not like agriculture. We have to work within the diversity of the ocean, not create it anew on a farm.
Fred Kirschenmann, the Godfather of sustainability (and distinguished fellow at the Leopold Center of the University of Iowa) , talked about this interaction - that we shouldn't necessarily view nature as something apart from ourselves, off in the distance. That's true, we are nature too, but perhaps we're less attuned to a "whole systems" view of the sea than we are of the land.
How can we interact with it -- that is, take fish -- without screwing up? We can always plant more crops, if we care for the soil. We can't plant more fish. So, as Palumbi said, don't eat those "older than your grandmother."
Obviously this is an area that I'm just starting to think about. But I'm curious about it, looking wider, at distant impacts, rather than drilling down too narrowly.
- Samuel Fromartz

This ocean guy thinks you're making a good point, Sam. We rely on the productivity of wild ecosystems to produce fish to eat, and we should respect those ecosystems and treat them well if we want to have fish in the future.
We know that effects beyond species we're eating are common, and there are certainly many more effects that we don't know.
This doesn't mean we should avoid eating fish, only that we need to watch carefully for signs we're degrading ocean ecosystems when we catch (or farm) fish.
Mark
Posted by: Mark Powell | May 22, 2008 at 12:34 PM
Mark, Thanks for the comment. This is a very interesting point and I think one that's overlooked. The typical mindset is we look for "the problem" and then create "a solution." But if there are multiple interactions, as there are in any eco-system, both identifying the full nature of the problem and then coming up with a solution is tricky. But in linear systems, we don't usually think that way. I guess the point is the ocean is not linear...
Posted by: Sam Fromartz | May 27, 2008 at 11:22 AM