Quote:
Originally Posted by SLH
Yes, if you exceed carrying capacity. At some level animals will survive on reduced ranges but at the expense of reproductive rates and body condition, which would show itself in winter body condition, pregnancy rates, lamb and yearling growth rates, horn growth in sheep and degraded range conditions amongst other things.
Did he show any supporting evidence for this idea of 20% ewe reductions? Do we see range degradation, are we seeing lower pregnancy rates, body condition ect. it definitely is a real thing and Wishart did a long term study of this on Ram Mt., which is one of the reasons Coltman et al. got so much heat back in 2003 when they suggested that the declines they saw in horn growth at Ram Mt were due to hunters when at the same time of that conclusion the sheep population on Ram Mt. was somewhere around double.
With that would it not stand to reason that the provincial herd would also have to nearly double before we would see those types of effects?
Simply reducing the ewe herd by 20% will have no effect on the remaining herd if carrying capacity limits are not being exceeded. If range improvements are done it would allow herd expansion where carrying capacity is not limiting and would improve herd health (including horn growth) if carrying capacity is being exceeded. In a great deal of situations winter range is the limiting factor for carrying capacity.
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The herd may have already doubled. Population estimates from the 70's was around 3500. We are now in the 6500+ range. And then factor in habitat loss....
There is a significant challenge in conclusively determining carrying capacity at the meta-popluation level. Besides the huge volume of labour and time that would be required is the huge financial outlay required that is simply not available. We will have to work from other evidence. Fortunately there are other potential signs other than a population collapse that could signal that the herds are at carrying capacity. One of these being a flatlining of population growth, which we have seen since the mid-eighties.
Ewe harvest at the rate of 20% certainly can positively effect a herd at or below carrying capacity. This 20% harvest rate is generally not sufficient to induce a population reduction, the effects of this harvest rate is more likely to maintain a population while reducing the average age of the ewes. Research shows that younger ewes produce more and bigger/faster growing lambs. By increasing the ewe harvest we can impart a more vigorous herd age structure without reducing the population.
The current Sheep Management plan suggests a harvest of 500 ewes every year from a herd of 6900 sheep. Well, we have the 6900 sheep but the ewe harvest has been averaging about 50 ewes per year since 2004 , 10% of the management goal. Before that there were about 100 ewes taken each year from 1990-2002. From '82-'88 we killed over 400 ewes every year from a population a bit less than we have today.
Is it a coincidence that the period of high ewe harvest aligns itself with the years of high ram harvest?
I wonder where we would be today if the current Sheep Management Plan had been followed....