Theme B: Modelling and assessing the effectiveness of releases for fisheries management and conservation
Keynote: Comprehensive case studies
12 & 13. STRATEGIC MIXING OF FISHERY MANAGEMENT, AQUACULTURE AND STOCK ENHANCEMENT: CASE OF THE CHESAPEAKE BLUE CRAB.
Anson H. Hines1, Eric G. Johnson1, Romuald N. Lipcius2, Rochelle D. Seitz2, Oded Zmora3, Yonathan Zohar3, David Eggleston4, and Kenneth Leber5.
1Smithosonian Environmental Institute, 2Virginian Institute of Marine Science, 3University of Maryland,4North Carolina State University, 5Mote Marine Laboratory
Three main approaches are used in seafood production strategies: fishery management of wild stocks by regulating catch; aquaculture for directly consumable products; and stock enhancement or sea ranching that blends aquaculture with fishery management in open environments. How should these approaches be applied in strategic choices to meet increased demand for sustainable fishery production? This presentation is one of two case studies that examine major differences the strategic mix of these approaches for portunid crabs: the blue crab (Callinectes sapidus) in Chesapeake Bay USA compared with the swimming crab (Portunus trituberculatus) in Zejiang, Jiangshu and Sandong Provinces, China.
The Chesapeake blue crab fishery is complex, with independent fishermen using a diverse array of gear in differing combinations over the seasonal cycle to target separate stages of the migratory life cycle in spatially separate areas. The most important gear has been the crab pot for hard (intermolt) crabs during the warm season from April to November. However, trotlines have been locally important in catching intermolt crabs in tributaries of the upper estuary during summer; and a dredge fishery operated in the mainstem of the lower bay during winter. A small but lucrative output of soft (postmolt) crabs (2% of the weight; 11% of the value) are produced in summer by collecting premolt crabs from the wild and placing them in simple artisanal aquaculture facilities for short periods until molting. The fishery includes both male and female crabs, with males dominating the summer catch in the upper estuary, and females comprising 80% of the catch in the lower estuary.
Historically, the blue crab has supported a productive and valuable fishery. Total blue crab landings increased markedly during 1940 to 1990 from 45 to nearly 100 thousand metric tons per year, with peak values at US$175 million in the late 1990s. In early decades, 50-60% of the catch was derived from a single large estuary, the Chesapeake Bay; although the contribution from other regions increased in the 1980s. However, from 1991 to 2001 the Chesapeake stock declined markedly: fishery-independent surveys showed the spawning stock declined by 84%, and the total stock dropped by 70% to record low levels that were sustained through 2008. The cause of the rapid decline in the 1990s is not known, but stock assessment showed that the catch per unit effort dropped markedly and that the stock was overfished in 9 out of 11 years from 1998 to 2008.
In response to the marked decline in the Chesapeake stock, two separate approaches developed. First, fishery scientists and managers formed a blue crab advisory commission across management jurisdictions to develop improved management. Using an annual system-wide fishery-independent survey, the group repeatedly up-dated and improved the stock assessment. Attempts to recover the depressed stock resulted in fishery managers imposing numerous frequent changes in fishing regulations; however these changes neither reduced fishing pressure effectively nor increased the stock. One major regulatory change resulted in a greatly expanded sanctuary in the lower estuary that prohibited fishing on the spawning stock during the summer reproductive season; but since fishing of mature females was allowed to proceed in the winter, the spawning stock remained at record low levels through 2007.
In a second approach, the multi-institutional Blue Crab Advanced Research Consortium (BCARC) was formed in 2002 to test the feasibility of using hatchery-reared juveniles to replenish the spawning stock of mature females. BCARC emphasized integration of research on basic biology, hatchery technology, and experimental field releases of tagged juvniles for responsible stock enhancement. Over 8 years of funding totaling US$15million, BCARC significantly increased knowledge of basic physiology and ecology of blue crabs, and successfully developed hatchery technologies to complete the life cycle and produce cohorts of 20 mm juveniles for field experiments. From 2002-2010 we tagged and released 57 cohorts of 2,000-25,000 tagged hatchery-reared juveniles (378,000 crabs total) into nursery habitats of upper Chesapeake Bay plus nearly 150,000 juveniles in the lower bay. Releases resulted in averages of ~300% enhancement, ~15% survival, and production of ~300 adults ha-1; but these averages varied significantly among sites and years, allowing development of optimal release strategies.
By 2008, the fishery was declared in a state of emergency. Traditional fishery management approaches over 15 years had failed to restore the depressed stock. BCARC’s research demonstrated successful enhancement at small scale, and clearly showed that the stock was recruitment limited; but funding sources refused to commit additional support to scale up the enhancement approach. In a dramatic shift in management approach, fishing pressure on mature female crabs was greatly reduced by prohibiting fishing on the spawning stock in winter as well as summer. A major increase in juvenile recruitment occurred in 2009, which is now translating into significant recovery of the stock in 2010.
In summary, the BCARC researchers and the fishery managers took separate approaches that were not well coordinated. Each approach had major successes: (A) 8 years of research on stock enhancement provided an excellent example of integrating hatchery and field testing for successful enhancement strategy; (B) a major change in fishery management to reduced fishing pressure on females resulted in a recovery of the stock. However, research on aquaculture, stock enhancement, and fishery management is severely underfunded in the USA. In the blue crab case, the stock enhancement researchers and fishery managers did not cooperate enough, and have now lost the combined synergy to deal with future problems, as well as the momentum to build a stronger base of funding. Key recommendations resulting from this experience include: (1) the need for appropriate mutually agreed metrics of stock enhancement and for stock assessment; (2) the need for early incorporation of economic models into fishery management for regulatory, aquaculture and enhancement approaches; and (3) the need for much increased funding for all three approaches, commensurate with the value of the fishery.
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