Conservation
How Important Are Forage Fish?
In the last 10 years or so, fisheries science has been moving toward ecosystem-based management. In the simplest of terms, this means that all those flora and fauna in the ocean, and land as well, have some level of interrelationship. So, just as some movement has been made toward implementing this management philosophy, out comes a study that basically says hold your horses.
The study says we don’t think the interrelationship between predator and prey is as strong as it is being portrayed by fisheries managers.
Put another way, the study says there is not a strong correlation between the stock status of the prey and the stock status of the predator. This study was not done by any run-of-the-mill marine biologists, but by some of the most well-known scientists in the field. Drs. Chris Free, Olaf Jensen and Ray Hilborn have more marine-biology degrees than I have letters in my name, so who am I to challenge them?
But why am I having a hard time with this concept?
Likely, it has to do with the fact that there is some truth to both sides of the argument. That, of course, makes it a lot like the half-truths that are pushed on social media to support a certain point of view. Who is wrong and who is right? In many cases, it can only be determined by peeling back the onion and getting to the reason that a point of view is being pushed.
One of the layers is a well-known and accepted fact that big fish eat smaller fish. This happens right down the food chain, or the trophic pyramid in fish terms. The little fish at the base filterfeed on a variety of planktons. This has been a system of natural energy accumulation since life began on this planet. Almost everything has multiple uses within the system. A fish like menhaden is a filter feeder. In Chesapeake Bay, where menhaden is found in high
“Ecosystem-based management means all flora and fauna in the ocean and on land have some level of interrelationship.”
densities, it supplies food for a variety of predators: avian, fish and crustacean. What other biological services does it perform? Does its filter feeding have an impact on water quality, which has a positive impact on the bay habitat?
It is doubtful that over tens of thousands of years vast schools of these fish have survived for a single purpose. Menhaden are not the only forage fish taken to be ground up into products. Probably the largest reduction fishery in the world is for sardines off the west coast of South America, many times larger than the menhaden fishery on the East and Gulf coasts. It is highly questionable that those little fish were put there to be made into fish meal. Can we utilize forage fish? Sure. But the question is, how much?
Let’s peel down to the core. Ask any of the three scientists above, “If we eliminated forage altogether, would predators be able to sustain themselves?” A rhetorical question to which the answer is highly unlikely. So, we establish that there is some relationship between predator and prey. But how direct is that relationship?
Their study rightfully points out the natural cycles of boom and bust in every forage base, and these ups and downs statistically have minimal impact on the predators. There are also natural cycles in predators. One should point out that forage is short-lived and predators long-lived, a major difference in population dynamics. This makes understanding any relationship harder.
The study itself indicates that when one forage species is depleted, predators find other forage to feed on. But with a lot of predator species there is also a correlation between their migratory routes and their target forage.
The essence of the report is that, since there appears to be no correlation between the stock status of the forage base and the stock status of its predators, managers should feel free to allow forage harvest at maximum sustainable yield (MSY), and that whatever remains would be perfectly adequate for the other ecological uses. This is classic single-species management. Since the sustainable part of that equation usually has about a 50 percent chance of success, this might not be the best ecological use of the resource.
Perhaps a better way to manage would be to aim for optimal yield (OY), which takes into account all the uses of the resource while setting quotas. Managers and scientists are pretty darn good, but always allowing extraction right up to the maximum will not always provide the best long-term results.
If we eliminated forage altogether, would predators be able to sustain themselves?