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"Feed the Fish"


Debbie MacKenzie <[log in to unmask]>


Scientific forum on fish and fisheries <[log in to unmask]>


Wed, 8 Mar 2000 19:13:49 -0400





text/plain (1 lines)

Dear Marine Scientists,

Thanks for all the comments. I'll try to address the main points you raised.

1. Terrestrial sources of nutrients enrich the ocean.

This question was also raised in my "guestbook" today - my reply:

The “threat of nutrient overload” is commonly described in marine
literature. It is, as you
point out, a very real problem in many coastal areas and is obviously the
result of
excessive run-off (sewage, agricultural, as you say). Also the problem of
the creation of
anoxic zones does exist. However, the fact that coastal waters in some
places are
positively fouled and sickened by an excess of nutrients, must not blind us
to the fact that
farther from shore the situation is essentially reversed - offshore areas
appear to be

The nearshore concentrations of nutrients are not effectively spread to the
offshore areas.
How this works appears to be poorly understood, but the mere fact of the
existence of the
huge dead zone in the Gulf of Mexico attests to the fact that
inshore-offshore mixing is
not effective. Part of the imbalance that we have created looks like this:
inshore nutrients
too concentrated, offshore too diluted.

One person wrote: "The oceanic energy cycle is not limited to the ocean
waters but also includes the terrestrial setting..." There seems to be
some confusion here between "energy" and "nutrients" - one chapter I wrote
and titled "Energy Flows, Nutrients Cycle" (Biochemistry 101)

2. Questions about Plankton levels - and their relationship to fish stock

John Gilbey wrote:

>They do have the potential for greater production, remove the fish which
>feed on them and there will be more production.

>I would like to see some references here, this is not my field but it would
>seem to me that if you remove too many fish, the plankton will increase
>giving more food for the remainder, BUT there may not be enough fish left
>for a viable fishery, and so we see a crash. These are two different things

>More rubbish. I have just been down the corridor to speak with the plankton
>people here at the marine laboratory in Scotland and they tell me there is
>no evidence for this. There may be a fall in calanus numbers but this is
>preliminary at the moment and further it is put down to changes in the seas
>circulation caused by global warming (unless you are suggesting that changes
>in the seas circulation are also due to overfishing?!) I still do not
>understand why phytoplankton numbers should fall if you remove the fish,
>surly the opposite would be the case?

And Patrick Schneider wrote:

>Also, I don't understand why plancton abundance should decline through
>fisheries. As the plancton is eaten by some fish (and whales), there
>should be an increase rather than a decline, when fish abundance
>decreases. On what findings do you base the opposite assumption?

This is how I see it: Plankton nourish fish and, in return, fish nourish
plankton. A sea with many fish swimming in it is fertilized by them in this
way - the living fish constantly excrete ammonia through their gills, and
some excrete urea...these bio-available nitrogen compounds directly
fertilize the phytoplankton. Removal of the living fish diminishes the
fertilizer and thereby undercuts the plankton. That is how fishing has
caused a decline in phytoplankton (fixed nitrogen is the limiting nutrient
for phytoplankton).

What data exists on plankton levels? Plankton recorders and satellite
pictures are quite recent so no really old data exists for comparison. One
would ideally need "historical" levels from a few centuries ago. I have
read that the standing crop of phytoplankton can double in a day depending
on conditions such as weather, etc...this is one factor that would make it
extremely difficult to know what is actually "normal" now let alone in the

If you read my material you will see that I think one useful plankton index
is the northern right whale, which has suffered a continuous decline
despite more than 60 years of protection from whaling. I just heard a news
headline on CBC today: "Scientists think that the right whales in the Bay
of Fundy are STARVING" (I've been trying to draw the attention of the media
to this point for quite a while with no problem is
that I am not a "scientist").

3. What do I mean by the "sum total of life?"

Patrick Schneider wrote:

>Just one example for one of your vague assumptions: What you call the
>"SUM TOTAL OF LIFE", do you have any measure for that? Or at least any
>definition? You can not talk about a decline of something, if this
>"something" is not defined. And even if you have a definition for it, I
>doubt very much you have a measure for this "SUM", in order to verify
>(to some extent), your argument.

I mean the total "biomass" of every organism in the marine ecosystem. No, I
do not have the number, but it is still a valid concept and it is what I
believe has been in a steady decline. Definition: add up the "biomass
index" for every single organism in the sea, plankton, snail, seaweed to
shark, and everything in between (it can't be done of course...too many
missing numbers). Focusing on a single species and the trends experienced
by it in a changing system will probably never reveal the steady decline in
the system overall.

4. The "debt" - my comment about "all take and no give."

John Gilbey wrote:

>This sounds like a huge hole has been left which will not be refilled if
>fishing continues. You cannot just take a total figure for biomass for the
>last X years and say because so much has been removed there is a hole
>amounting to Y tonnes. As long as the amount taken is not above the stock
>recruitment levels (not always the case unfortunately), there is plenty of
>scope for stock replenishment. (i.e. you can sustainably remove biomass
>every year and the total standing crop will remain the same year on year).

"...a huge hole has been left which will not be refilled if fishing
continues." A very simplistic view but a useful one. What is supposed to be
filling in the hole from the other end? And can we rely on it to keep
filling in no matter how deep we dig it? What reassures you that there is
always "plenty of scope for stock replenishment?" I am not convinced. I see
many stocks in decline simultaneously.

5. The decline in the Atlantic and Pacific salmon stocks.

John Gilbey wrote:

>Yet in the last few years the amount caught at sea has dramatically
>declined, BUT the stocks returning are still generally down. If only it were
>as simple as a single cause for the fall in stocks, we could then do
>something about it easily! Talking about Atlantic salmon, NASCO have
>produced reduced quotas, NASF pay fisherman not to fish and the price of
>salmon has fallen through the floor, added together this has meant a drastic
>reduction in fishing effort and amount caught. If your arguments are true,
>this should have meant the salmon stocks returning to our rivers would
>increase, but, surprise surprise, they still continue to fall on many/most
>rivers. Perhaps this means that if you base all your arguments on a single
>piece of evidence or causal factor, your conclusions will be wrong. This is
>school level science, in the real world there a multitude or interacting
>factors all affecting stocks, and it these that fisheries scientists are
>trying to understand.

"If my arguments are true" salmon are starving at sea. Despite major
attempts to restore and preserve river habitat and hatchery programs
galore, salmon stocks are crashing (*only except pinks in Alaska...).
Scientific documents I have read on salmon constantly point to "marine
survival" as their main problem. Salmon range quite far offshore, there's
not much to eat out there, and they don't return.

6. Why do I discount the importance of "El Nino" and similar
environmental/usually "temperature" changes?

John Gilbey wrote:

>Again, more rubbish, if the change happen at the low end of the food chain
>this will effect everything 'upstream' of this.
>e.g. if El Nino means a drop in nutrients available to algae and plankton
>this will limit their production, fish which feed on these will in turn be
>limited, as will fish which feed on these fish etc etc. Thus the whole
>systems biomass will fall

Gary Sharp wrote:

>The consequences of environmental chnages on long-lived fishes is notable,
>has been studied and written about for several decades. My favorite
treatise on
>systems analysis and where and why the "good times' are misleading can be
>in a wonderfully thorough article penned by Lionel Johnson:The thermodynamic
>origin of ecosystems, Can. J. Fish.Aquat.Sci, 38(5):571-590. 1981. A "must
>for anyone wishing to understand the consequences of environmental
>on fish, and their related support systems.
>The ultimate question he answered was why all the older fish were in the
>of the size distributions of arcticc lakes with only one fish species? You
>the answer above, but would not know it, because of your preconceptions...

And the question was also raised in a "guestbook" entry, where I wrote back...

I could as easily say that “your presumption that the world oceanic biomass
is NOT unfounded.” I need to see solid evidence that refutes the
theory. The theory
that declining fish stocks are the result of temperature/climate change can
be challenged.
One inconsistency is this one: The severe decline in the northern cod stock
on the Grand
Banks of Newfoundland over the last decade, and their failure to rebuild
desite an 8 year
continuing fishing moratorium, has been explained on the basis that water
temps have
been a bit colder than normal (causing poor feeding behavior as a result of
temp). Over
the last 2 years, however, the water temp there has actually risen above
the long term
mean but the condition of the cod stock continues to decline (theoretically
they should be
feeding much better at current temp - but are not - in fact they continue
on their
downward slide...there is some important factor missing from the equation
temperature/climate variation).

Regarding "If El Nino means a drop in nutrients available to algae and
plankton..." - the nutrients in question being dissolved organic compounds:
phosphates, nitrates, CO2? I don't see how a water temperature change of a
couple of degrees could actually make these "unavailable" to algae. For
some reason many elaborate analyses of the marine ecosystem have been done
with models that seem not to really include food.

7. Fish stocks: which ones are collapsing, which are not, and why?

Gary Sharp wrote:

>Despite the groundfish collapses over George's Bank and off eastern Canada,
>the stocks of some less desireable species have not declined, but have
>Off Newfoundland some desirable species have bloomed, as their predators were
>removed (lesson #1). I have not stuck my nose into the NE Fisheries Center's
>annual assessments recently, but there were lots of Scomber scomber on the
>over the last decade, that noone wanted.

In Atlantic Canada all groundfish are in serious decline, and pelagics
appear to be as well, with the exception of one capelin stock. The
"desirable" species in Newfoundland are now shrimp and crab. Gary Sharp
also commented on California sardines which are apparently flourishing now.
"In fact the present range and status of the California sardine is very
likely what it would have looked like, if no over-fishing had taken place
at all, and the fisheries management were effective." Small fish like
capelin and sardines (and also shrimp and crab) are at a temporary
advantage since their natural predators are disappearing, and also because
they can feed on plankton - it's a rebound effect. "What it would have
looked like if no over-fishing had taken place" is sardines, capelin,
shrimp, etc., co-existing with healthy populations of their predators. That
is not what we have nos. Relatively large current populations of these
little, low trophic level creatures does not reassure me about the health
of the system. Where is there a robust population of one of the bigger
fish? Where are the fat swordfish?

8. Why are fish smaller for their age?

Gary Sharp described one common theory:

>example you use is a classic one: smaller fish at age is a symptom of
>induced increased
>meatbolism, resulting in individual fishes spending more of their consumed
>energy on respiration (running the engine faster, as in driving your car
>in 2nd gear), and having less available for somatic growth. (recommended
>Physiology 101).

No doubt there is truth in this. However, fish being unusually small for
their age is also consistent with the theory that they do not have enough
to eat - it hardly refutes it. (Physiology 101 - got A+ - I am in the habit
of describing things in simpler terms so that my fishermen neighbours, who
didn't take the course, can understand me.)

9. Solving the mystery.

Gary Sharp wrote:

>Fisheries physiological ecology was brought out of the Dark Ages by the
>folk following Fred Fry's teachings. Rollie Brett's works would clear the
>for you.

I have not read these two but have read a lot of the recent reports of
Canadian DFO marine biologists. It's still looking quite "misty" in a lot
of places. The research documents and stock status reports are FULL of
"uncertainties," "unexpected" findings and vague, hopeful statements like
"the stock will rebuild when recruitment improves."

10. What do I mean by "feed the fish?"

What I mean is that leftover food is not "rubbish." I think we should start
to scatter our food scraps in the offshore areas that previously supported
major fisheries (like the Grand Banks, for instance)...of course we can
argue the details of this.

John Gilbey wrote:

>Do you have any idea how much 'food' you would have to introduce to affect
>the feeding dynamics of the oceans!!!!!!

Yes. It would be an awesome undertaking.

Debbie MacKenzie

"Not everything that is faced can be changed, but nothing can be changed
until it is faced." - James Baldwin

.........and eventually I'll figure out how to draw one of those fish for you!

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