How many crabs are in the chesapeake bay
In , million adult female crabs were estimated to be living in the Bay, an increase from million in Harvest is a primary source of blue crab mortality in the Chesapeake Bay. But environmental conditions including water quality, weather patterns and habitat also cause the abundance of blue crabs to fluctuate from year to year. Loss of habitat, particularly of underwater grasses and marshes, is a primary concern for the blue crab population in the Bay.
Blue crabs—harvested as hard shell crabs, peeler crabs and soft shell crabs—are the most valuable commercial fishery in the Bay, earning millions of dollars of revenue each year. Blue crabs also support a large recreational fishery in the region. From the mids to the late s, there was a dramatic decline in the blue crab population.
Blue crabs use underwater grass beds and marshes as nurseries, feeding grounds and refuges from predators. A decline in underwater grass abundance —due to warming waters, irregular weather patterns and pollution—has been linked to declines in the blue crab population.
Because they are key feeding grounds and predator refuges, underwater grass beds and marshes increase juvenile blue crab survival and growth rates.
Research has also shown that denser underwater grass beds can hold more crabs, indicating both the quantity and quality of underwater grass habitat can affect blue crab populations. Striped bass, Atlantic croaker, red drum and other predatory fishes feed on juvenile blue crabs. A significant change in abundance of these fish populations could affect the abundance of juvenile blue crabs, and consequently the future of the blue crab population. Water quality improvements, underwater grass restoration and proper fishery management will help protect blue crab populations and maintain the resource.
Blue crabs are managed as a single species, using minimum catch size and seasonal harvest limits to meet target levels of fishing pressure. The annual winter dredge survey helps scientists determine where the current blue crab abundance and harvest levels fall in relation to the management targets and thresholds. Under this strategy, the fishing target is set to a level that should allow for sustainable harvest that allows the population to persist at an acceptable level of abundance over time.
As part of the Chesapeake Bay Watershed Agreement , Bay Program partners committed to two goals related to blue crabs. The first goal, Blue Crab Abundance , is to maintain a sustainable blue crab population based on the current target of million adult females and to refine the population targets based on the best available science.
In November , the three jurisdictions formally adopted a new abundance target of million adult females based on model results from a stock assessment update conducted in The survey is usually conducted December through March, and preliminary results are released around late April.
A comprehensive review of those results is completed annually by the Chesapeake Bay Stock Assessment Committee and released in early July. In , the winter dredge survey showed a drop in blue crab population from an estimated million to million. The number of adult females, the segment of the population we look at most closely to gauge the overall health of the population, increased from an estimated million to million, a number within the margins considered to be a healthy stock.
Juvenile crab numbers, however, decreased to their lowest level since the survey began in The blue crab population fluctuates annually based on a variety of factors, including reproductive success, weather, predation, and harvest. The extremely low estimate of the juvenile population in highlights the need to continue to protect spawning femailes and to consider precautionary measures to protect juveniles so they can grow to maturity and spawn. In general, the population has been more robust since a science-based Bay-wide management plan was agreed to in One of the best indicators of this increased abundance has been the fact that numbers have surpassed the target abundance for adult female blue crabs twice since , after exceeding it just once between and The long-term trend tells us that the blue crab population will respond positively to management actions.
This highlights the need to continue to ensure wise management of this valuable resource. The blue crab is one of the more resilient Chesapeake Bay species, but it faces constant challenges to survive: predators, dead zones of low oxygen, vanishing habitat, and at times cold winters, to name a few. Especially for young and female crabs, underwater grasses represent one of the most important habitats for foraging and protection. High flows of fresh water wash more pollution into the Bay, affecting water clarity and blocking sunlight that grasses need to survive, and warming water temperatures can create further stress.
Dead zones are caused by excessive nitrogen and phosphorus pollution in the water, which feeds large algal blooms. Dead zones form when the algae die, sink to the bottom, and are decomposed by bacteria—a process that strips dissolved oxygen from the surrounding water. Dense algal blooms also block sunlight, which prevents underwater grasses from growing. Fishing pressure also has an impact on the blue crab population. A decade or so later, the crab population had been cut in half to around million.
Not only was the blue crab population itself depleted, so too were the oyster reefs and underwater grasses that provide crabs with food, shelter, and oxygen. New science-based guidelines were established in , focusing on a reduction of the catch of female crabs in order to ensure sufficient spawning. The continuation of the annual Bay-wide Blue Crab Winter Dredge Survey will be essential in estimating the blue crab population and monitoring the stock.
As part of the Chesapeake Bay Program's partnership-wide implementation of adaptive management, progress toward this outcome was reviewed and discussed by the Management Board in November of Download Management Strategy.
Participating partners have committed to taking specific actions to achieve the approaches identified in the management strategy above. Loading Chart Loading Chart. In the Chesapeake Bay Watershed Agreement , the Chesapeake Bay Program set a population target and an overfishing threshold for adult female blue crabs. In , an estimated million adult female blue crabs lived in the Bay, compared with million in This number is above the