Chesapeake Bay Blue Crab Survey for Winter 2017 Shows 31-percent Increase in Spawning Females over 2016, But Declines in Juveniles and Total Population

On April 19, 2017, the Virginia Marine Resources Commission (VMRC), the Maryland Department of Natural Resources (Md. DNR), and the Virginia Institute of Marine Science (VIMS) reported the results of the latest winter dredge survey of Blue Crab populations in the Chesapeake Bay.  Since 1990, the survey has been conducted each year from December to March by VIMS and the Md. DNR.  The report for the 2016-17 survey showed increases over the previous year in spawning females but decreases in the number of juveniles and in the total population.  Despite the decreases, the population was the 11th highest recorded.   Survey results since 2008 are available online at http://www.vims.edu/research/units/programs/bc_winter_dredge/results/index3.php.

Following is an excerpt from the VMRC’s April 19, 2017, news release on the 2016-17 survey (see Sources, below, for the Internet link to the news release PDF):

“The Virginia Marine Resources Commission today released the results of the 2017 blue crab winter dredge survey, which shows a 31-percent increase in adult female crabs and forecasts another year of improved harvests.

“This is the highest level of adult, spawning age females recorded in the 28-year history of the Bay-wide crab winter dredge survey. …The results of the 2017 winter dredge survey show the total population of blue crabs in the Chesapeake Bay fell a bit, by 18 percent, due to a decline in the number of juvenile crabs, but remains at the 11th highest level ever recorded by the winter dredge survey.   This year’s female spawning stock increased by 31 percent, from 194 million to 254 million crabs, which surpassed the scientifically recommended target of 215 million spawning female crabs and remains well above the minimum safe threshold of 70 million crabs.  Spawning age female crabs are the cornerstone to maintaining a vibrant crab stock, and depend on conservative and cooperative fishery management efforts among the Bay jurisdictions.

“The adult male crab stock fell by 16 percent, from 91 million to a still-substantial 76 million.  However, the juvenile abundance plummeted by 54 percent, from 271 million to 125 million, which is the fourth lowest level on record.

“This was unfortunate but not unprecedented. Optimal spawning conditions do not occur every year.  Successful crab reproduction naturally fluctuates and can be affected by wind, currents, storms, temperature, and cannibalism. In recent years, post-reproduction predation events and environmental factors have caused at times dramatic downturns in crab stock abundance. For example, the level of juveniles fell from 581 million in 2012 to a mere 111 million in 2013.

“This reproductive variability highlights the need for fishery managers to continue to enhance resilience of the stock through adaptive management to compensate for unusual or extreme environmental conditions and the resulting impacts on reproductive success….

“A Bay-wide 10-percent crab harvest reduction was enacted in 2014 by VMRC, Maryland, and the Potomac River Fisheries Commission to combat low overall crab abundance and to boost a dangerously depleted female spawning stock.   Bay fishery managers have since refined their management regimen to focus on conserving juvenile crabs as well as spawning age female crabs. Each year’s juveniles become the next year’s spawning stock.  Adjusting catch regulations to conserve more of today’s juveniles from harvest when they reach market size in the fall and emerge in the spring after overwintering in the water bottom increases the likelihood they will survive to spawn another generation of abundant crabs in the summer. …

“The Bay-wide commercial harvest increased by 20 percent last year, from 50 million pounds to 60 million pounds, and remains at sustainable levels.  Since 2014, the Bay-wide commercial crab harvest has jumped 71 percent while overall crab abundance has increased by 53 percent.  The current low level of juvenile crabs appears to preclude the reopening of the winter crab dredge fishery, which has remained closed since 2008.

“The annual Bay-wide Winter Dredge Survey is the primary assessment of the Bay’s blue crab population, and has been conducted annually by the Virginia Institute of Marine Science and Maryland’s Department of Natural Resources since 1990.  The survey employs crab dredges to sample blue crabs at 1,500 sites throughout the Chesapeake Bay from December through March.  Sampling during winter when blue crabs are usually buried in the mud and stationary, allows scientists to develop, with good precision, estimates of the number of crabs present in the Bay.  The Chesapeake Bay Stock Assessment Committee (CBSAC), a subcommittee of the Sustainable Fisheries Goal Implementation Team,is reviewing the new survey results and will release their full analysis of the results in the 2017 Blue Crab Advisory Report this summer.  The annual advisory report is used by managers as they review and update fishery regulations. …”

Following are the lowest and highest estimates of key parts of the Bay crab population since 1990:
Total (both sexes and all ages) – low of 251 million in 2007; high of 852 million in 1993.
Spawning-age females – low of 53 million in 1999; high of 254 million in 2017.
Juvenile-age (both sexes): low of 105 million in 1992; high of 581 million in 2012.

A table of all the results since 1990 is available in the VMRC’s April 19, 2016, news release.

Sources:
Scientific Survey Shows Promising Blue Crab Stock Abundance with Boost to Adult Females (PDF), Virginia Marine Resources Commission News Release, 4/19/17.
Scientific survey shows highest-ever level of spawning-age female crabs, Virginia Institute of Marine Science News Release, 4/19/17.

Some news accounts on the winter 2016-17 survey are the following:
Survey finds Bay crab population strong, with record number of females, Bay Journal, 4/19/17.
The Chesapeake Bay was less crabby last winter, survey says, Virginian-Pilot, 4/19/17.

For previous News Grouper items on the Blue Crab winter dredge survey, please see this link: https://vawatercentralnewsgrouper.wordpress.com/?s=blue+crab+winter+dredge+survey.

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