Management of Horseshoe Crabs

In response to a question I asked Jane Brockmann (see below) about what she found to be one of the most interesting aspects of horseshoe crabs, she responded:         

          "A really interesting aspect of this whole issue is that the management of horseshoe crabs is actually very special and interesting. Horseshoe crabs are in no real danger, there are a lot of horseshoe crabs. What is in danger is this "bird/ horseshoe crab" phenomenon that you have in Delaware Bay and in some other places where there are so many horseshoe crabs that they dig up each other’s eggs and there are eggs strewn on the beach.  The migrating shorebirds feed on those excavated eggs. You just get these masses of birds on the beach and it is really something to see! In this system you are actually managing horseshoe crabs for the birds.  The management of nearly all other species is not like this. When you manage striped bass or blue crabs, or something like that, you’re managing blue crabs for blue crabs and you manage their harvest. You allow the harvesters to take the blue crabs up to a certain point.  Most populations of animals are density dependent, so if you get up to a certain population level and then they just don’t increase because all they’re doing is competing with each other, well, when a population is at that level then you can harvest out those extra ones and it actually doesn’t harm the population at all. This is a density dependant effect. So normally you manage a population, and an intelligent management of a population is right at this density dependant number. Well, with horseshoe crabs you have to manage them well beyond density dependence because that’s what creates the phenomenon of their digging up each other’s eggs. There’s so many of them, of course their numbers aren’t going to increase because they are digging up each other’s eggs, but that’s the resource that you’re actually managing for. I don’t know of any other management that’s like this. It’s a very special thing."