Spiny dogfish are one of the rare success stories in the management of shark fisheries, with the U.S. Atlantic population representing one of the few shark stocks ever to fully recover from overfishing. At first glance this doesn’t seem to make any sense: spiny dogfish are one of the longest-lived and slowest-growing of the sharks that regularly interact with human beings, and with a 2-year pregnancy it doesn’t seem as though they could replace their numbers in anything less than the decades that have gone by without successful recovery from several other heavily-fished sharks. So how have spiny dogfish been able to succeed in recovering from overfishing where so many other sharks struggle? The answer may very well be in adaptations related to that seemingly long reproductive cycle of theirs.
The essential book Biology of Sharks and Their Relatives has a good overview of the reproductive systems found in elasmobranchs, and that’s where we’ll lay the groundwork for the potential reproductive edge of dogfish. Carrier et al. (2004) summarize that there are two different basic reproductive cycles found in sharks and rays. Both involve two different processes, the development of pups and the development of eggs. Where these cycles differ is the timing of egg development.
In some sharks, including members of the large coastal shark complex like blacktip and sandbar sharks, pup development occurs, followed by the development of the eggs. Basically, only one reproductive stage happens at a time. The mother shark puts all her reproductive resources into developing the pups, then develops the eggs that will hopefully be fertilized to develop into the next pups. Factor in the “resting period” that usually immediately follows birth and you have a reproductive cycle that can be considerably longer than the length of pregancy.
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