Management Considerations

Understanding the ability of a population to resist impacts has obvious and important implications for the successful management/conservation of that population. For instance, the practice of farming, be it agrior aquaculture, can tend to lead to a loss of genetic diversity in the farmed organisms. It is this genetic diversity that provides the basis not only for the plastic responses to density described above but also as the foundation for adaptation to new and changing environments and especially for disease resistance. Therefore, this loss represents a reduction in the buffering capacity of the population. Increasingly an ecosystem-based approach to resource management is being encouraged where the goal is to keep farmed systems more natural for the purpose of retaining as much ecological integrity and therefore, natural buffering capacity, as possible.

As with farmed systems, an understanding of the buffering capacity of populations of wild captured organisms is critical to their sustainable harvest. Because harvested populations are already at only a fraction of their natural densities, all other things being equal, it would be desirable to harvest from populations whose life-history characteristics give them stronger density-dependent growth. So for instance, a population of the short-lived (3-4 years) quickly maturing (4-5 months) dolphinfish (mahi-mahi, Coryphaena hippurus) would recover from a disturbance of some sort much more quickly than would a population of the long-lived (100 + years) late-maturing (20-30 years) fish, orange roughy (Hoplostethus atlanticus).

In many instances it is critical to identify the source of this buffering capacity. For example, the Caribbean spiny lobster (Panulirus pargus) is widely distributed throughout the Caribbean basin and is the basis of a large and valuable fishery throughout the region, yet management options are likely to be quite different from region to region due to alternatively structured connectivity patterns. P. pargus has a very long pelagic larval period of 4-9 months and thus is subject to potential large-scale dispersal during this life phase. Research has indicated that populations in the Florida Keys, USA are maintained largely by larvae from very distant sources such as the meso-American reef system. However, populations in the area of the Bahamas surrounding Exuma Sound are thought to be largely self-supplied with little if any exogenous input of larvae. Thus, while the biology of the benthic stages of the organism is unchanged, the buffering capacity of the Florida Keys population is likely to be higher due to its exogenous larval supply. Disturbance to the population within Exuma Sound on the other hand will directly interrupt the supply of larvae within the system. While the general management issues may be similar, knowledge of these factors would change the emphasis in each region. For instance, in the Florida Keys, it may not be as necessary to limit wild harvest of adults to the same level required in the Bahamas.

In addition to regulation of wild harvest, conservation and protection of organisms increasingly involves the use of protected areas. Such areas rely on the premise that the habitat set aside does currently and will continue to maintain populations with adequate buffering capacity and that they will remain intact despite continued extractive uses around them. However, in many cases, the fragmentation of habitat in such a manner can interfere with density-dependent processes such as migration which may be necessary for the population to respond to disturbance in a timely manner. Movement can also act as a buffer against changes in habitat caused by global climate change. Such range shifts have been observed and they pose a significant challenge to reserve design. For organisms with metapopulation dynamics, protected area design must also account for connectivity if it is to ensure adequate buffering capacity. The increase in harvest pressure outside protected areas, as is often seen in marine systems, can potentially impact the source of offspring for the population within the protected area, thereby reducing its ability to resist disturbance. It is clear that incorporation of variation among taxa in connectivity, density dependence, and individual resistance to environmental change will be required to fully manage wild populations and maximize effectiveness of protected areas.

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