POPULATION AND GENETIC EFFECTS OF SELECTIVE HARVEST STRATEGIES IN MOOSE: A MODELING APPROACH

Abstract

We evaluated the changes in population structure and frequencies of hypothetical alleles controlling antler growth of a simulated population of moose (Alces alces) subjected to a variety of harvest strategies based upon antler morphology. Legal bulls in the different selective harvest strategies were characterized by having at least one spike or forked antler (spike/fork), bulls having an antler spread of >91 cm, or >127 cm, and bulls with either a spike/fork antler of spread of >127 cm. In those strategies in which legal bulls were defined by spreads of a certain size, existence of at least one brow palm with three or more tines was considered as an alternative harvest criterion. A strategy allowing harvest of bulls with either a spike or fork antler or having antler spreads of >127 cm, but which ignored brow tines was also simulated, as was a strategy allowing hunters to harvest any bull, regardless of antler form. We assumed that antler growth is controlled by a polygenic two-allele (favorable/unfavorable) system and that brow palm formation is controlled by a two-allele monogenic locus and is independent of antler size. The strategies were evaluated based upon their ability to maximize the harvest, post-hunt bull:100 cow ratios, and frequency of favorable antler alleles. All harvest strategies, with the exception of any-bull hunting, yielded post-hunt bull:100 cow ratios of >20, but the population was regulated by the 91-cm legal threshold and was characterized by extremely low ratios of large-antlered (>127-cm spread) bulls:100 cows. Harvesting any bull produced the highest annual harvest,  followed in decreasing order by the strategy with the 91-cm threshold, the strategies with the 127-cm threshold, and the spike/fork strategy. Spike/fork hunting apparently increases the frequency of favorable antler alleles, but this is seemingly offset by harvesting bulls having antler spreads above a legal threshold, particularly the 91-cm threshold. Those strategies enabling harvest of bulls based on brow tines caused significant declines in favorable brow alleles. Frequency of alleles favoring antler growth is seemingly affected by hunting based on brow tine architecture, and frequency of alleles favoring growth of brow tines is similarly affected if hunting is based on antler spread even though loci controlling these traits are not linked. Of the strategies simulated, the one by which legal bulls are defined as those having either spike/fork antlers or antlers with a spread >127 cm best met the three management objectives although frequency of alleles favoring growth of brow tines declined. We propose that a strategy utilizing an open season on spike/fork bulls in combination with a limited-participation any-bull season is a suitable alternative to harvest strategies based upon antler spread and brow tines alone.