On April 29 the Quantitative Ecosystem Teams (Habitat Suitability, Stock Assessment, Socioeconomics, and Foodweb) will convene for the first time and begin their task of developing ecosystem based reference points to address the critical ecosystem issues for striped bass in Chesapeake Bay raised by the Striped Bass Species Team. This approach to Ecosystem Based Fisheries Management developed organically through the work of the Striped Bass Species Team and is the model the other species teams are currently following. Although reference points have been used for quite some time in fishery management, they have largely been focused on stock assessment issues and single species management. Utilizing reference points in a broader ecosystem context requires a shift not only in how we think about managing fish, but also a shift in assigning responsibility and accountability. EBFM acknowledges that human behaviors other than fishing must be managed to sustain healthy fish populations in the face of issues such as water quality, climate change, disease, and invasive species. Here, Dave Secor, Co-Chair of the Habitat Suitability QET, shares his insight on utilizing reference points in EBFM.

A Perspective on Reference Points in Ecosystem Based Fisheries Management

Dave Secor, UMCES-CBL, Co-Chair Habitat Suitability QET

During the past 50 years the adoption of reference points has played a key role in advancing the efficiency of fisheries management. Reference points inform managers on (1) what harvest levels should be considered as overfishing and (2) what levels of abundance should represent a depleted (overfished) population. Reference points are quantitative: they serve to formalize our best biological understanding of stock demographics (recruitment, growth, survival, reproductive schedule, longevity) into a tool that managers can readily understand and apply across diverse species and ecosystems. Could such an approach similarly apply to ecosystem issues such as: Has too much habitat been lost? Is fishing compromising an ecosystem role of the harvested species? How do we best manage multispecies fisheries and reduce destructive fishing practices?

Reference points evaluate what a population would look like absent fishing, but beyond looking at overfishing they have been used to address ecosystem issues such as power plant effects and degraded nursery habitats. The 1970s decline of Chesapeake Bay striped bass provides a useful example. Both scientists and managers wanted to know whether the cause of poor striped bass recruitment was overfishing or polluted nursery habitats. Dozens of scientific studies supported both hypotheses. To help resolve this issue, assessment scientist Phillip Goodyear estimated what an unstressed population should look like. He then compared how stresses due to fishing or habitat loss would affect this reference population. His principal finding was that the effects of the two stressors were equivalent in amplitude. Because action related to fisheries was likely to be more efficient, exploitation needed to be drastically reduced. This assessment was critical in justifying the Chesapeake Bay striped bass moratorium, which contributed to the strong recovery we are now enjoying.

Developing this type of reference point framework could be a fruitful direction for EBFM in the Chesapeake Bay. Granted, the approach is simplistic. The unstressed reference population is theoretically at carrying capacity, yet density-dependent effects are rarely considered in assigning reference points. Also problematic, reference points often assume constant levels of recruitment (i.e., a stationary environment). Still, as a starting point reference points related to an unstressed population "standard" would allow fisheries managers to evaluate lost habitat, lost ecosystem function, and socio-economic trade-offs in a manner similar to Goodyear's critical assessment of striped bass recovery tactics.

References

Goodyear, C. P. (1985). "Toxic materials, fishing, and environmental variation: simulated effects on striped bass population trends." Transactions of the American Fisheries Society 114: 107-113.

Hall, S. J. and B. Mainprize (2004). "Towards ecosystem-based fisheries management." Fish and Fisheries 5(1): 1-20.

Mace, P. M. (1994). "Relationships between Common Biological Reference Points Used as Thresholds and Targets of Fisheries Management Strategies." Canadian Journal of Fisheries and Aquatic Sciences 51(1): 110-122.

Please contact Shannon Green, Fisheries Ecosystem Coordinator for Maryland Sea Grant, for further information. Thank you!
sgreen@mdsg.umd.edu (301) 405-6372

www.mdsg.umd.edu/ebfm