We have made significant progress on our project goals to date and have achieved a number of important accomplishments and outcomes in the identification and modeling of alewife stock structure in Maine watersheds. These include:
- Sample selection for stock identification: Otoliths were selected from 14 key sites that are representative of the geographic length of the Maine coast and important spawning areas.
- Establishment of otolith processing protocols: We established a processing protocol specific to adult alewife otoliths to prepare them for microstructural analysis. This includes preparation and polishing of the otolith, digital photography and visualization of otolith microstructure, and image analysis of individual otoliths to measure growth increment widths.
- Processing samples: We have fully processed more than 420 otolith samples from selected sites.
- Data analysis: We have initiated analysis of the data to ascertain the appropriate statistical methods and summarize preliminary results.
- Model development: We have compiled relevant data on alewife runs and environmental conditions that will be used to inform the metapopulation model of alewife.
- Interaction with stakeholders: Through this research we have interacted with alewife harvesters, Maine Department of Natural Resources, National Marine Fisheries Service, and research scientists that participate in alewife research and stakeholders involved in alewife restoration efforts.
Initial analysis of measurements of otolith increment widths during the first 30 days of life of adult fish has revealed significant differences across watersheds. Fish from rivers east of Penobscot Bay tended to exhibit slower growth (tighter growth increments) compared to fish from west of Penobscot Bay (wider growth increments). Otolith microstructure shows promise in discriminating among discrete stocks of alewives. An understanding of population structure and a means to discriminate the source population of ocean-caught fish are needed to address mechanisms behind alewife population declines.