[NatureNS] Seals and fish VERY LONG

Date: Tue, 11 Oct 2011 10:28:37 -0300
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All:

As a the former chair of a three-member Eminent Panel [it is to blush]  
on Seal Management that submitted a lengthy report the Minister of  
fisheries in 2001 I thought I?d weigh in on seals vs. fisheries.  We  
concluded then that evidence for then the efficacy of culls  
(essentially of Gray and Harp Seals) in restoring fisheries was  
inadequate. I?m not going to commit myself on current issues issue.  
I?d have to do a great deal of work and preferably get paid for it .
Inevitably, public at large and naturalists in particular want to and  
should speak out on issues of seals and fisheries. However, I think  
that as a group with some understanding of how things work in nature,  
it might be good if positions were based on some knowledge of the  
issues, data, and analyses. You can get a vast amount of scientific  
information from the web, Some of it is in the (correctly) vaunted  
form of refereed scientific papers.  It is also an unfortunate, but  
unavoidable feature of science, including fisheries science, that  
detailed studies supporting certain conclusions can be pretty opaque  
to the lay reader:  biological terminology, statistical analysis,  
mathematical modelling, etc.

It is perfectly valid to hold a moral view that animals (or wild  
animals, or animals like mammals with which we might claim some  
affinity) should not be killed in our interests. Another moral view  
might be that we should ?correct? consequences of our former  
mismanagement of wild animals by readjusting (culling) some  
populations; no thoughtful fisherman that we spoke to during our Panel  
enquiries blamed seals for the collapse of fisheries, but some argued  
that seals were preventing those devastated stocks from recovering.  
That is the argument made by the recent DFO panel for stocks of  
Atlantic Cod in the Gulf (White Hake, and others also in trouble).  
That report made the same kind of analysis that is routinely used to  
adjust (and sometimes to close) fisheries, but in this case concluded  
that cod were experiencing negligible fisheries mortality, but very  
high and increasing mortality natural mortality, and found no evidence  
for causes other than seal predation.

But, positions for or against a cull should not use false information.  
An example of is in the recent press statement by Rebecca Aldworth  
listed as executive director of Humane Society International/Canada  
(from the Can. Press site).  "A cull of 70 per cent of the population  
would not be sustainable and could lead to the extrication [sic] of  
this species off our east coast," Aldworth said Thursday. "The fact  
the FRCC would call for such a reckless move . . . speaks to the  
political motives of the FRCC . . . and is, in my opinion, the fishing  
industry attempting to divert attention from the irresponsible fishing  
practices that continue today."  ___ She insists there is a lack of  
scientific evidence to suggest that the grey seal population has a  
negative effect on the health of groundfish stocks and that  
overfishing remains the largest threat against cod and other fish in  
the region.

Her problem is that no-one has argued that 70% of the East Coast  
population would be removed and there is NO commercial fishing for cod  
?that continue[s] today? in the southern Gulf. It has been closed for  
some years.

There has also been some confusion about numbers seals, size of mooted  
culls, and between earlier talk of a large cull (or sterilization) of  
Gray Seals on Sable Island and the recent consideration of more  
focussed culls in the Gulf (perhaps even in a small area of northern  
Cape Breton in winter). Also, a recent study has been quoted  
indicating modest recent recovery of cod on the Scotian Shelf,  
possibly because pelagic fish (more important sad seal prey) have  
declined as predators of young cod (although I attended a recent talk  
that indicated a current downward turn of cod again). But the Gulf  
situation is not the same as that of the Scotian Shelf.

A balanced, evidence-based, and scientifically cautious statement has  
been made by Jeff Hutchings, a biology professor at Dalhousie  
University. (Again from Can. Press. I placed dashes between originally  
separate paragraphs.)___ He was part of the workshop that concluded  
grey seals may be hindering the recovery of groundfish in the southern  
Gulf. ___"There was some pretty careful analysis," he said in an  
interview. "It is a scientifically defensible position to say that the  
elevated levels of natural mortality may well be caused by predation  
by grey seals." However, he said more research needs to be done to  
justify a cull. The problem, he said, is that a crucial piece of  
evidence ? an analysis of grey seal stomach contents taken off the  
north coast of Cape Breton ? has yet to be repeated. ___"It's one year  
of data," Hutchings said. "Any scientist would tell you that you would  
want to repeat that sampling to see whether it holds up in other  
years." ___ "Even if you have all of these (monitoring) criteria in  
place, the suggestion that we will know precisely what the  
consequences of the removal will be is simply not a statement that  
would receive strong scientific support," he said."

The last statement is certainly true; nor can we know precisely the  
consequences, e.g., of restored populations of the World?s large  
sharks that are so badly in need of protection from shark-finning for  
soup ? all fisheries and wildlife management is like this.

For information on numbers of Gray Seals the following is informative.  
Again, Fig. 2 summarizes the results. The overall Atlantic Canada  
population is estimated currently (with 95% probability) to lie  
between about 405,000 and 445,000 (my approximations from Fig. 2).  
Note, that the largest fraction is found on the Scotian Shelf (and  
Sable Island). All populations are increasing, but now at a lower per  
capita rate than in the past.

  <http://www.dfo-mpo.gc.ca/CSAS/Csas/publications/sar-as/2010/2010_071_e.pdf>

For information on Gray Seal diets, a number of studies recently have  
used sophisticated analysis of ?fatty acid signatures? in blubber  
(sampled relatively unobtrusively on Sable Island). This integrates  
diets of seals that have fed over a wide range and for some time, and  
gives the best overall view of possible impacts. See, e.g., Fig. 2 and  
3 in:

<http://bowenlab.biology.dal.ca/data/Beck%20Hg%20diets%20JAE%202007.pdf>

Obviously cod only make up a relatively small proportion of their  
overall diets, although there are many seals, so it adds up.

Finally, the data, analyses, and conclusions on seals and fish in the  
Gulf are in this recent report.

    
<http://www.dfo-mpo.gc.ca/Csas-sccs/publications/resdocs-docrech/2011/2011_041-eng.pdf>

That?s the one to read for focus on the issues at hand.  The study  
uses stomach contents, which have their shortcomings, but, unlike  
fatty acid signatures, give information on what?s being eaten on the  
spot, at the time by a particular segment of the seal population ? for  
example off the northern coast of Cape Breton, where high predation on  
larger cod is supposed to occur.

Ian McLaren


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