Thriving Oceans

Just a couple of recent fish/conservation related postings from JournOwl.com that I thought I would pass along…

The incredible shrinking reef fish

They say a picture is worth a thousand words and in the case of Loren McClenachan’s June 2009 publication in The Journal of the Society for Conservation Biology there is evidence of a major decline in the size of fish caught in the Florida Keys.  McClenachan used a unique method for quantitating the changes of reef fish size over the last 50 years by turning to photographic evidence and documented data of harvested trophy fish.

Read the post

Sea-cage pathogen factory: Salmon and Sea Lice

But the documentary is just a springboard into the real nuts and bolts of the fish farming issue that definitely has a marketable appeal to businessmen and everyday people concerned about overfishing alike.  Unfortunately the aquaculture solution has unintentional consequences including a decline in wild fish populations, perhaps to near extinction, in areas with high concentrations of fish farms.

According to Neil Frazer, Sea-Cage Aquaculture, Sea Lice, and Declines of Wild Fish, “The difference is that sea cages protect farm fish from the usual pathogen-control mechanisms of nature, such as predators, but not from the pathogens themselves. A sea cage thus becomes an unintended pathogen factory.”

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The California Department of Water Resources is experimenting with a new way to save salmon in the delta.  “Preliminary results show that an experimental, non-physical fish barrier is working to help keep young Chinook salmon and steelhead in a more direct path to the ocean and away from agricultural diversion and the state and federal pumping plants. The bubble curtain barrier project combines acoustics and a strobe-lit sheet of bubbles to create an underwater wall of light and sound at frequencies that repel juvenile Chinook salmon.”

Check out the video…

I came across a piece on Fish & Aquatic News this past Sunday in which authorities in Spain confiscated 11 tons of shark fins.  It simply reminded me that the Mediterranean Sea is a poster child for overfishing and already at the mercy of an irresponsible tuna industry. Yet, what I did not fully realize was that there has been an incredible decline in sharks over the last 200 years in this region alone.
In a 2008 publication in Conservation Biology, it was found that:

“Only 5 of the 20 large predatory sharks were detected at levels of abundance sufficient for analysis. Moreover, these 5 species showed rates of decline from >96 to >99.99%, which may classify them as critically endangered according to IUCN criteria.”

Even more disturbing is that the authors contend the depleted numbers may mean the large sharks are “functionally extinct” in the Northwestern Mediterranean. So, continued harvesting of sharks only for their fins is adding insult to injury on these cartilaginous ocean inhabitants.

After a rudimentary investigation on Spain’s fishing practices, I found that most of their longlines are actually set on the Atlantic ocean side, which may be compounding the dwindling Mediterranean shark populations. Because overharvesting (i.e. 11 tons of shark fins) is taking place, we are effectively limiting the ability for Atlantic and Mediterranean sharks to replenish falling populations and/or exchange individuals via the “critical migration corridor” in the Strait of Gibraltar.

With up to 2000+ pelagic longlining boats traversing the Mediterranean Sea, a considerable illegal fisheries industry continuing operations, and lackluster regulatory action, top predators responsible for structuring  ocean communities will continue to be at under threat of extinction.

photo credit: Erik Charlton

Reference:

Loss of Large Predatory Sharks from the Mediterranean Sea, Conservation Biology
Volume 22, Issue 4, Date: August 2008, Pages: 952-964

The S.F. Chronicle broke a story today in which the headline exclaims that the ‘U.S. extends disaster order for chinook salmon’, and I must say it is about time!  The writing on the wall has graced our oceans and rivers for the past few years so I think it is appropriate to start this off with a quote from JournOwl (‘Salmon by the numbers’) as it attests to the fact that chinook salmon are in trouble:

“At one time California’s Central Valley witnessed the return of adult Chinook salmon 3/4 of a million strong. By 2007, the returning population making the trek from the Pacific Ocean through the San Francisco Bay and spawning in the Sacramento River had declined to 90,000. And with the season ending in 2008, the numbers had managed to only reach 8.8% of their former number. Did I mention the Chinook salmon population of 750,000 I am referring to was a mere 6 years ago in 2002?”

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[Atlantic bluefin tuna]…the adult breeding population had declined to 10% of what it had been twenty years ago, when regulation of the taking of these great ocean rangers began.  The population as a whole had been reduced by more than half, and most of of what remained were immature.  Stunned, I blurted out, ‘Are we trying to exterminate them? If so, congratulations!  We’re making great progress.’

Sylvia Earle, NOAA’s Chief Scientist 1990-1992 (in Sea Change, 1995)