We are proud to have Nicole Peckham (Northeastern University PhD student) presenting a poster summarizing our NERR Science Collaborative Project at the 2019 Coastal and Estuarine Research Federation (CERF) meeting in Mobile, AL. This post has additional information about the project and the poster.
• Link to poster. “Stakeholder-driven modeling to understand oyster population sustainability.” J. W. White, L. Storch, N.E. Peckham, K. Dietz, D.L. Kimbro, N. Dix. This project is a collaboration with David Kimbro’s lab at Northeastern and the Guana Tolomato Matanzas NERR.
• The study system. The Guana Tolomato Matanzas National Estuarine Research Reserve is part of the nationwide NERR system. The GTM is an extensive estuarine system fed by multiple freshwater sources, and considerable spatial variability in tidal circulation, salinity, and oyster habitat. It supports both commercial and recreational harvest of oysters, but harvest is restricted to specific zones (see map on poster). The GTM NERR is a nexus for the Oyster Water Quality Task Force (OWQTF), a group of local harvesters, scientists, conservation workers, and interested members of the public. The OWQTF helps set research and management priorities for the GTM, and is a key end-user of the work.
This project was driven by questions arising in the OWQTF: what areas of the estuary support oyster reefs that contribute the most to population sustainability? What areas would be optimal for restoration (i.e., adding shell) or protection?
• Prior work. The Kimbro lab has been working in the GTM NERR since 2011, publishing studies on the role of increasing estuary salinity on oyster predators (Garland and Kimbro 2015) and fear-based interactions between oysters and their predators (Kimbro et al. 2014, Kimbro et al. 2017).
• Approach. Quantifying population sustainability fundamentally requires understanding the way individuals replace themselves via reproduction. However, lack of knowledge about the transport and connectivity of oyster larvae makes it impossible (at present) to describe the entire life cycle. Instead, we took an eggs-per-recruit (EPR) approach: if one new larval recruit settles in a site, how many eggs could it be expected to produce over its lifetime (on average)? Sites with higher EPR would be better suited for restoration (adding oyster shell substrate so that recruits can settle and survive) or protection (excluding harvest to promote larval production). More about this type of per-recruit analysis (and its history) can be found in Chapter 11 of our new book, Population Dynamics for Conservation.
• The model. We used a size-based integral projection model (IPM) to calculate EPR. An advantage of IPMs is that one can fit them to time series of size-abundance data to estimate unknown quantities, such as harvest rates (as opposed to age-based models, which can be harder to use because it is more difficult to age data from field surveys). Our group has published papers on fitting IPMs to time series to estimate parameters (White et al. 2016) and applying that approach to California oysters (Kimbro et al. 2019) and California marine protection areas (Nickols et al. 2019). The growth and mortality rates needed to parameterize the models were derived from field experiments conducted concurrently in our NSF-funded investigation of oyster predator-prey interactions in GTM NERR.
• Ongoing work. The results presented in this poster are preliminary; we are still working on additional analyses before the project ends. This will include a full population model, including reproduction and settlement, to investigate the effects of different harvest practices. Final model code will be made available in R for continued use by GTM NERR staff.
• Questions? Contact Will White.