Thursday, December 3, 2009

Not good -- another study of drastically declining fish populations

A researcher from SUNY-ESF (next to Syracuse U.) -- a very nice campus; SUNY-ESF is just about literally in the shadow of the Carrier Dome -- has done another study of fish stocks in the North Atlantic...

...and guess what

(wait for it)

... they are severely depleted. WOW, I didn't see that coming.

Populations of numerous migratory fish species in the North Atlantic have declined by more than 95 percent, threatening not only food supplies and economic systems, but also the way humans perceive the health of the planet's ecosystems, according to a paper published today (Dec. 1) in the journal BioScience.

"It's shocking," said Dr. Karin Limburg, a fisheries ecologist at the SUNY College of Environmental Science and Forestry in Syracuse, N.Y., who is the paper's lead author.

Limburg and her co-author, Dr. John Waldman of Queens College of the City University of New York, report that a complex combination of habitat loss (caused largely by the construction of dams that prevent fish access to traditional spawning areas), urban sprawl, overfishing, pollution and climate change have led to the precipitous decline. Compounding the problem, they say, is the evolving knowledge of the humans who make decisions about how natural resources are managed.

(more)

As an example, Limburg pointed to a graph that depicts the status of the American shad between 1887 and 1997. It indicates the species was more than 10 times as plentiful during most of the early years of that period as it was during the middle of the 20th century. But a second chart shows that the levels in the 1880s were just 10 percent of what they had been 50 years earlier. (Ouch.)

"We can't envision salmon being a thing of the past," she said. "That was once the case with shad. It was the most important fish in U.S. fisheries, after cod." In fact, the shad's Latin name (Alosa sapidissima) reflects the species' high status as a food fish: "sapidissima" means "most delicious."

(more)

WHY should this be a surprise? Or is it (to you, at least)? As has been stated by others, numberous times, the fish in the ocean are the global example of the Tragedy of the Commons. Nobody owns the fish or the fisheries (particularly outsize the EEZs), everybody takes them, and nobody, but NOBODY, is trying to come up with ways to save them and allow them to return to somewhat sustainable populations -- albeit much, much smaller than the populations that once existed, as the article notes.


I was at the library today and discovered this; I emailed it to myself, so that I could bring it to my wide audience!!

Breaking news: Algal blooms increase where predatory fish decrease (due to overfishing)

And then I found online:

http://f1000biology.com/guardpages/evaluation/1168368//article/article.asp%253Fid%253D1168368%2526view%253D%2526style%253D

http://www.esajournals.org/doi/pdf/10.1890/08-0964.1

which is the study itself, but you've got to either subscribe or pay for it to read it.


Here's the discussion from Nature, edited a bit for length and fair-use:

by Matt Kaplan
Nitrogenous fertilizers and detergents have long been known to cause algal blooms that block sunlight and strangle ecosystems, but a study now reveals that overfishing of large predatory fish is also playing a key part.

Britas Klemens Eriksson at the University of Groningen in the Netherlands noticed that populations of predatory fish in the Baltic Sea seemed to be declining in areas where algal blooms subsequently tended to form. Curious as to whether there was a connection, Eriksson and a team of colleagues from the Swedish Board of Fisheries in Öregrund set up an investigation.

The team reviewed a year's worth of field data ...

"In areas where there were strong declines in perch and pike there were massive increases in smaller fish and large blooms of algae," comments Eriksson. Where perch and pike populations were intact, the surrounding waters had a 10% chance of experiencing an algal bloom; in areas where their populations had been substantially reduced, the chances of an algal bloom were 50%.

Intrigued by these trends, the researchers ran small-scale field experiments for 2 years ...

As expected, the nitrogenous pellets increased algal growth. But surprisingly, when predatory fish were prevented from accessing a given area, algae in that area became much more prevalent. The effect even proved to be true when nitrogenous pellets were not added to the system.

"This is the first study to show that top predators are linked to the formation of macroalgal blooms," says marine biologist Heike Lotze, at Dalhousie University in Nova Scotia, Canada.

Eriksson speculates that the effect results from the disruption in the food chain caused by excluding the large predator fish. Top-predatory fish feed on mid-level predatory fish, which in turn feed on invertebrate herbivores such as snails and crustaceans. These are the animals that control the algal community. Knock out the top predators, and mid-level predators develop huge populations which, in turn, reduce the numbers of algal-eating species, allowing blooms to grow unchecked, explains Eriksson.

The team report in Ecological Applications that, on the basis of their findings, fighting algal blooms by more tightly controlling nitrogenous materials in waste water and agricultural run-off is not the best approach. "If we want to manage algal blooms effectively, we need to start by taking an ecosystem perspective … we have to restore depleted fish communities," says Eriksson.

"That they are showing effects over four trophic [feeding] levels is really impressive," says Lotze. "We've tried to experimentally explore these sorts of interactions before, but with so many levels there is often too much noise to see trends. That they've managed to get clear results is exciting." (I'd actually use the terms "sobering" and "depressing", rather than "exciting", but scientists do get excited about clear research results, even when the implications are bad news.)

[a couple concluding paragraphs removed]

And here's yet another piece of sucky news about fish in the sea:

Warming drives off Cape Cod's namesake, other fish

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