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e &quot;harvested&quot; seals in recent years has been youn There are at least two big problems with stomach content analysis that I'm aware of. Basically, if you sample a bunch of seals and they don't have very much cod in them, does that mean that they don't prefer cod, or that there isn't much cod around in the first place? Alternatively, suppose you sample the stomachs of 50 seals, and half of them are full of cod, and half of them aren't. Does that mean that some seals choose cod, or that some seals tend to be in microhabitats with more cod? If some seals choose cod, it might be difficult or impossible to selectively cull these animals. So how can you design an experiment to tell you whether seals are eating a lot of cod? As I understand it, it's much more informative to get a long-term look at what they're eating, for instance over multiple seasons. This is the focus of Sara Iverson's lab at Dalhousie, who are looking at ways of determining diet from signature fatty acids in seal blubber samples. On a broader scale, I don't think that ideology is ruling the day here, just caution, because a lot of screwey stuff can happen if you take out a big chunk of a large predator population. And the uncertainty here is huge. On the other hand, in terms of potential negative outcomes, do you think Canadian people would be more comfortable not having a huge cull (with very slow fisheries recoveries), or having a huge cull that does something unexpected and harmful to the St. Lawrence ecology? This is a political question, not a scientific one, assuming the uncertainties about these outcomes are similar. Incidentally, is a sexy paper came out recently suggesting evidence of Scotian Shelf (not Gulf of St. Lawrence) benthic fisheries (although not necessarily cod) recoveries: http://www.nature.com/nature/journal/v477/n7362/full/nature10285.html (see the "editor's summary" in the right column, too). So maybe patience is a virtue? This is not a clear-cut decision either way. As someone who's worked several winter seasons monitoring the seals on Sable, I can say with reasonable confidence that the 12.8% per annum seal population growth statistic is outdated. At this point, there is good evidence that these seals might be reaching their carrying capacity in the environment, which means that their population size is stabilizing, not growing. See http://icesjms.oxfordjournals.org/content/60/6/1265.short for the old state of things (exponential growth), and the more current research here ( http://bowenlab.biology.dal.ca/data/Bowen%20Hg%20pup%20prod%202004%20MMS%202007.pdf ) that suggests the population growth is leveling out (at last estimate, the rate was about 7% per annum). DFO did another aerial survey last winter; I'd imagine the latest population growth estimates are on their way out, too. Hope that stimulates some discussion. The hardest part for me is to be willing to change my mind if the evidence looks better one way. Incidentally, regarding Richard's consumption statistic: I don't think we can appreciate its significance until we put it into the perspective of the weight of our own fisheries landings in that ecosystem. Would you know the percentage relationship here? --Bob Farmer On Mon, Oct 10, 2011 at 16:12, Richard Stern <sternrichard@gmail.com> wrote: > Hi, > > With all the scientific observations, and data that has been collected, on > seals in recent years, by those who are both in favor of, and opposed to, a > seal cull, surely somewhere there must be a detailed analysis of the > contents of adult seals' stomachs? And surely there's someone on NatureNS > who knows this info? > For what it's worth, here's what seems to be a valid reference I found by > googling -- > > The single biggest island-breeding colony is on Sable Island (85,000, > increasing at almost 12% per annum). Other major sites in the western > Atlantic are in the Gulf of St. Lawrence (69,000). (and from Wikipedia > ----- The grey seal feeds on a wide variety of fish, mostly benthic or > demersal species, taken at depths down to 70 m (230 ft) or more. Sand eels > (Ammodytes spp) are important in its diet in many localities. Cod and other > gadids, flatfish, herring and skates are also important locally. However, > it is clear that the grey seal will eat whatever is available, including > octopus and lobsters. The average daily food requirement is estimated to be > 5 kg (11 lb), though the seal does not feed every day and it fasts during > the breeding season. > > Doing the math, therefore, it would seem that the Sable Island population > alone would eat up to 425,000 Kg of fish per annum - considerable > competition for Homo sapiens. > > Richard > > > > On Mon, Oct 10, 2011 at 3:31 PM, James W. Wolford <jimwolford@eastlink.ca> > wrote: >> >> Jeannie, I stand to be corrected, but I think a very large proportion of >> the "harvested" seals in recent years has been young pups only several weeks >> old and a bit post-weaning, and therefore would have no solid food yet in >> their guts. But if any cull that goes on consists of older seals that are >> shot, then it might make sense to sample their stomachs for foods consumed. >> >> Cheers from Jim in Wolfville. >> >> Begin forwarded message: >> >> From: jeannies@ns.sympatico.ca >> Date: October 10, 2011 10:26:54 AM ADT >> To: naturens@chebucto.ns.ca >> Cc: Gary Myers <gemyers@eastlink.ca> >> Subject: Re: [NatureNS] Seal Cull >> Reply-To: naturens@chebucto.ns.ca >> With all the seal slaughtering that's going on...did not ONE person think >> to open one up and see what type of fish they're consuming??? >> Jeannie Shermerhorn >> >> >> ---- Gary Myers <gemyers@eastlink.ca> wrote: >> >> The announcement that Fisheries and Oceans was proposing a 70,000 animal >> cull as an experiment followed by a further 70,000 experimentation kill the >> following year was made Sep 15 this year. Co-incidentally that date was the >> 40th anniversary of the founding of Greenpeace and CBC carried the two >> stories consecutively all day. My first reaction was to check to see if >> that was international prank day or some such. Surely someone needs to give >> their head a god shake. Gary Myers Morden NS > > > > -- > ################# > Richard Stern, > Port Williams, NS, Canada > sternrichard@gmail.com > ################### >
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