By most accounts, this has been a good year for eating Maryland blue crabs — just not by human beings. The Chesapeake Bay crab harvest is down, in part because of predators and cannibalism, but that's not the whole story.

In 2011, Maryland officials reported a record year for blue crab reproduction. It was such a successful spawn that most people in the seafood industry were licking their lips with anticipation. Surely, harvests would rise as those baby crabs matured into adulthood in late 2012 and the first half of 2013. That didn't happen.

Last year's crab harvest was mediocre at best (about 56 million pounds bay-wide) and down significantly from the previous year's catch. This year's will surely be worse. So what happened to all those baby crabs?

Scientists speculate that many of them were eaten long before they could grow big enough — five inches wide — to be legally caught by a Maryland or Virginia waterman and end up at a local restaurant or backyard crab feast. The suspects? Striped bass and red drum, which love to eat immature crabs. As it happens, both fish species had unusually good spawns themselves in recent years, and those youngsters showed up in the bay hungry.

But it's also likely that the young crabs started eating each other, too. That kind of cannibalism is not unusual among crabs, particularly when so many are bunched together in the same year class — it's a matter of survival of the fittest.

There are other factors, too. The amount of submerged aquatic vegetation in the Chesapeake Bay is down, so young crabs had fewer places to hide when they shed their shells and were more vulnerable to predation. Warm weather may have encouraged more predator fish to enter the bay as well. Even climate change may have been a factor as red drum, for instance, were rarely found north of New Jersey but have more recently been caught off Cape Cod.

All of which is not merely some interesting biology lesson but a sign that Maryland and Virginia need to take a second look at their approach to managing the blue crab population. While the two states have gotten more conservative over the last half-decade — relying on scientific models that consider the total crab population and particularly the number of female crabs before setting harvest limits — that approach may not be enough.

The fluctuations in the blue crab population are a little scary — like extreme stock market volatility before a crash. The Maryland Department of Natural Resources now estimates that there are about 300 million blue crab in the bay. Last year, the estimate was 764 million, more than twice as many.

As we've often noted before, a pollution-stressed Chesapeake probably can't produce the seafood bonanza it once did. Crabs are a hardy species, but even they have their limits. Weather plays a huge factor in crab reproduction — specifically, the wind and currents at the mouth of the Chesapeake in September and October decide whether the tiny larvae will end up in the bay or be swept out to the Atlantic Ocean.

The one thing that human beings can control is fishing pressure. Ensuring that there are enough crabs so that the species can reproduce in sufficient numbers has to be a top priority.

The DNR has already tightened rules to protect female crabs and reduce fishing pressure. But it may be time to look at quotas, too. If watermen were regulated by seasonal quota instead of daily harvest restrictions on where, when and how many crabs can be caught, they'd be more inclined to catch crabs when the prices are high and leave them alone when prices are down. That would likely reduce fishing pressure in the fall, allowing more mature crabs to survive into the following year, particularly migrating females.

This much is clear. Crabs are scarce this year and in danger of becoming scarcer, and their numbers might not rebound quite so quickly as they have in the past. Maryland won't see a harvest of any kind unless the species is protected — not just from pollution, loss of underwater plants, global warming, hungry red drum and their own cannibalistic instincts but from the threat of overfishing by commercial and recreational fisherman alike.