Blue Crab Harvest
Chesapeake Bay watermen use crab pots to harvest crabs during the summer months. Image courtesy: Mike Land
It is estimated that more than one-third of the nation's blue crab catch comes from the Chesapeake Bay. Blue crabs—harvested as hard shell crabs, peeler crabs (just prior to molting) and soft shell crabs (immediately after molting)—have the highest value of any Chesapeake commercial fishery, bringing in more than $50 million per year. They also support a major recreational fishery in the Bay.
Since the early 1990s, blue crab catches have dropped to levels lower than recorded in previous decades. This decline has been linked to increased fishing effort, as well as habitat loss from degraded water quality.
How many blue crabs are in the Bay?
Bay scientists use the annual Bay-wide winter dredge survey as the main indicator of blue crab stock status in the Chesapeake. The winter dredge survey is the most comprehensive and statistically sound of the blue crab surveys conducted in the Bay.
According to the 2008 winter dredge survey, which took place just before the start of the 2008 commercial season, the abundance of adult (age 1 or older) blue crabs was estimated to be about 120 million crabs, low compared to historical levels. Since 2002, crab abundance has stabilized below the survey average; however, the blue crab stock remains above the “overfished” threshold of 86 million crabs age 1 or older.
Blue crab recruitment—the number of juveniles that grow to a “catchable” size—is also estimated by the winter dredge survey. A prolonged period of low recruitment has persisted since the 1998 survey.
The total abundance of crabs in the Bay during the 2008 winter dredge survey was estimated to be 283 million crabs. The blue crab population has fallen nearly 70 percent since 1990.
How is harvest a pressure on blue crabs?
Between 1968 and 2005, commercial blue crab harvest from the Bay averaged around 73 million pounds annually. In several of those years, commercial harvests yielded over 100 million pounds of crabs; a record of 113 million pounds was set in 1993.
Since the early 1990s, there has been a dramatic decrease in Bay-wide blue crab landings. Commercial crabbers have also increased their fishing effort, but are catching fewer crabs per amount of effort than in years past. These occurrences likely relate to recruitment overfishing, when large removals of adults from the stock result in fewer juveniles being produced.
The 2007 Chesapeake blue crab harvest of 44.2 million pounds was among the lowest recorded since 1945. The low harvest corresponds with low stock abundance, but also reflects restrictive management measures in place since 2001 and 2002. While the crab harvest remains near record lows, the percentage of Bay crabs harvested remains high: an estimated 60 percent of the Bay's available blue crabs were caught in 2007—considerably more than the target harvest of 46 percent.
How is habitat loss a pressure on blue crabs?
Reduced acreage of underwater bay grasses due to poor water quality and irregular weather conditions has also been linked to the decline of blue crabs. Bay grass beds provide important habitat for blue crabs by protecting juveniles, molting adults and feeding adults from predators. Field experiments have shown that underwater bay grasses substantially reduce predation on juvenile blue crabs, and also result in higher growth rates compared to crabs living in unvegetated areas.
In addition to habitat loss, debate has grown over the effect of increased predation on the blue crab stock. Predatory fish like striped bass and Atlantic croaker—whose populations are currently very high—may rely on juvenile blue crabs as part of their diet, affecting the abundance of blue crab recruits (age 0 crabs).