Subject: Ecological role of menhaden
From: "Niels Moore" <
[email protected]>
Date: Sat, June 3, 2006 6:15 am
To:
[email protected]
Priority: Normal
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I would question the actual ecological "benefits" provided by menhaden in
the Bay for several reasons, and I would be interested in input from some of the
biological experts on FF.
First, while it is true that, as filter feeders, menhaden consume
phytoplankton and detritus, generally from the upper- to middle- water column, their
role is more accurately described as one of a "compactor" of these items. As
is likely the case with the majority of herbivores, menhaden simply digest,
then expel the vast majority of this plant-based food directly back into the
water in the form of urine and pelletized fecal matter. Past studies have
shown that the migration of large schools of menhaden into relatively confined
water bodies can result in significantly higher levels of ammonia within the
water column. Of even greater relevance to ongoing Bay problems, I believe
menhaden fecal matter is not bouyant, and therefore sinks to the bottom where it
subsequently decomposes. What effect would this have on dissolved oxygen
content in the deeper- to middle- levels of the Bay? Between excreting ammonia
and compacting N and P directly to the Bay bottom, would the immigration of
a large menhaden school reduce eutriphication or actually accelerate it?
Second, the absolute amount of nitrogen and phosphorus actually "removed" by
menhaden from the Bay system is likely relatively minute compared to the
total influx of these "pollutants". For starters, on a short term basis, it
would appear that N and P are actually removed from the Bay in one of three
ways:
(1) A menhaden emigrates out of the Bay and doesn't return;
(2) A menhaden is consumed by a predator (or scavenger) which itself, in
turn, is harvested and removed from the Bay; or
(3) A menhaden is directly harvested by man.
In sum, therfore, it could very well be that N and P levels in the Bay could
actually be higher (albeit likely marginally) than they are now, if the
various commercial menhaden fisheries (as well as recreational fisheries for
predators) did not ultimately extract them and their nutrients from this system.
Regardless, the dry weight of N and P actually contained in each pound of
menhaden harvest is relatively small, as with most critters, menhaden are
comprised mostly of water. In contrast, according to the Chesapeake Bay Program,
approximately 370 million pounds of N and 26 million pounds of P reached the
Bay during the 2005 water year.
Niels Moore
Menhaden Resource Council
_www.menhaden.org_ (http://www.menhaden.org)
__________________________
Almost the same lame rationalization he gave here just before I joked at how similar this was to the rationale Hitler gave for killing Jews. Personally I think Niels must be having a hard time looking at himself in the mirror to keep working this angle, but it doesn't matter...he's a prostitute for the industry.