Monday, June 11, 2007

Don't go a shellfishin' on George's Bank

My brother, who works for the federal fisheries observer program, sent me some info regarding a pretty impressive "red tide" event currently occurring on George's Bank. Both "Red tides" and George's Bank are rather interesting topics, so I thought I'd take the time to write something about them both. You probably won't find shellfish from George's Bank at your local fishmonger, but if you do, I wouldn't eat them at this point.

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George's Bank
George's Bank is a shallow shoal in the North Atlantic located approximately 100 km off the coast of Massachusetts. GB is a very productive area (or at least, used to be) and was one of the most important areas for New England and Canadian fishermen. Essentially, this area is so productive because it sits where the cold, nutrient-rich Labrador current meets the warmer Gulf stream. Combine this with its shallow waters and you end up with an ideal environment for phytoplankton, which in turns makes George's Bank an ideal breeding and feeding environment for cod, haddock, herring, flounder, lobster, scallops, and clams. Combine lots of fish and shellfish with proximity to land and you have an ideal environment for fishermen (not to mention a veritable cornucopia of seabirds and marine mammals). GB is so shallow and so close to the mainland that it was part of the mainland during the last glaciation event, then became "George's Island" as seas began to rise, before finally succumbing to the sea 6,000 yrs ago. Fishermen sometimes dreg up interesting fossils from GB.

(click image to enlarge)

In addition to the shallow waters and mixing of currents, GB has a rather complex and heterogeneous sea floor, including a number of small "canyons", which increases GB's appeal to an even greater range of biodiversity.

Verrazano discovered GB in the early 1500s (though Basque fishermen may have been fishing there since 1000 AD - there was a Basque fishing fleet stationed in Newfoundland) and the entire western North Atlantic become a hotbed of fishing, particularly for cod. You've probably heard the off-quoted aphorism that cod were so plentiful you could walk to shore on their backs.

GB and the western North Atlantic were so important (and profitable) that the U.S. and Canada had to appeal to the International Court in The Hague in 1984 to step in and set international boundaries where their EEZ's overlapped. Fishermen and officials from both countries still squabble over this "Hague Line", which cuts through GB (most of GB falls within the U.S. EEZ; only the eastern edge is in Canadian waters).

Over the years, increased fishing effort and increasingly efficient and technologically advanced fishing gear decimated the fisheries on GB, effectively causing their collapse in the late 80s and early 90s. in 1993 Canada placed a moratorium on cod fishing and placed strict regulations on other GB fisheries. In 1994 the U.S. closed most of GB to commercial fishing. In 1995, this ban was extended indefinitely.

Red Tides
First off, "red tides" are not tides, they're algal blooms. Second, not all "red tides" are harmful and not all harmful algae cause "red tides". So, the more appropriate and scientifically-acceptable term is not "red tide", but "harmful algal bloom", or HAB. HABs are defined as an event when toxic-producing algae populations increase to the point that they become hazardous. For some species of algae, this requires an enormous population explosion, but for other, more toxic species, even a few cells per liter would be considered an HAB.

In the western North Atlantic, most HABs are the result of the dinoflagellate Alexandrium fundyense - incidently, these HABs are also "red tides". These critters produce neurotoxins, such as saxitoxin. Saxitoxin selectively blocks cellular sodium channels, which are necessary for creating nerve impulses. Blocking sodium channels thus prevents nerve impulses. Since nerve impulses control our muscles, saxitoxin can, in severe cases, cause paralysis. Naturally then, HABs of Alexandrium fundyense are responsible for Paralytic Shellfish Poisoning (PSP).

PSP occurs because shellfish are natural filters. They take in seawater, pass it through their gills, trapping microscopic organisms that they then digest. During blooms of Alexandrium fundyense shellfish in the area eat the dinoflagellates, but end up storing the saxitoxins in their tissue. Luckily for shellfish, saxitoxins have no effect on them. Unluckily for us (and any other vertebrate that decides to dine on the "infected" shellfish), the toxins enter our bodies when we eat the shellfish, block our sodium channels, and cause PSP. Symptoms of PSP? How about "nausea, vomiting, diarrhea, abdominal pain, and tingling or burning lips, gums, tongue, face, neck, arms, legs, and toes. Shortness of breath, dry mouth, a choking feeling, confused or slurred speech, and lack of coordination are also possible."1 In the most severe cases paralysis sets in and respiratory failure and death may follow.

HABs on GB:
As if the fisheries on George's Bank haven't been hit hard enough by depleted stocks, it turn out that there is a rather severe Alexandrium bloom sitting right on top of the shoal. The R/V Endeavor has recently completed a survey of the Gulf of Maine and Georges Bank and has found an HAB only on GB.

(click image to enlarge)

Superimposing the survey data onto the North Atlantic chart, you can see how the HAB is right on top of GB (note thre lack of data from the eastern, Canadian end of GB):
(click image to enlarge)

The worst section of the HAB has over 13,000 Alexandrium cells per liter of seawater, more than enough to cause PSP.

So, ignore those "George's Bank Quahogs" on sale at your local neighborhood food mart. Unless of course you think your diet is lacking in saxitoxins. (Actually, if you do see "George's Bank Quahogs" for sale, you best notify your nearest employee of the National Marine Fisheries Service - shellfishing on GB has been closed for more than a decade).

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