Evaluation of Closed Areas: Cashes Ledge as Juvenile Cod Habitat

Mattie Thompson, Monhegan Island groundfisherman, hoists an adult cod captured on Cashes Ledge
Mattie Thompson, Monhegan Island groundfisherman, hoists an adult cod captured on Cashes Ledge, summer of 2007. Photo: By Julien Gaudette.
Project Summary:

This project is investigating whether habitats associated with Cashes Ledge are critical nursery and adult grounds for cod.

Significance

This project is making several significant contributions to knowledge required to underpin ecosystem approaches to management. First, we are developing innovative methodology that will result in highly accurate biological habitat maps. Second, we are investigating the effectiveness of a management action – in this case, the closure of an area to fishing activity. Third, we are establishing a dataset that may be compared with historical data and future observations to document change around this highly productive ledge in the Gulf of Maine.

  • Jonathan Grabowski, Gulf of Maine Research Institute, Portland, ME
  • Robert Tetrault, F/V Robert Michael, Portland, ME
  • Matthew Thompson, F/V Alice Rose, Monhegan Island, ME
  • Matthew Weber, F/V Griffin, Monhegan Island, ME
  • Tom Weber, University of New Hampshire, Durham, NH

Graduate Student involved in the project:

  • Chris McGonigle, PhD candidate, University of Ulster, Ulster, Northern Ireland
  • Technical Advisors: Jon Witman, Brown University; Bob Steneck, University of Maine-Orono; Craig Brown, University of Ulster; Sara Ellis, Gulf of Maine Mapping Initiative; Lew Incze, Census of Marine Life Gulf of Maine Area Program and University of Southern Maine; and Luciano Fonseca, University of New Hampshire’s Center for Coastal and Ocean Mapping
  • Funded by: Northeast Consortium, Gulf of Maine Mapping Initiative, and the Gulf of Maine Council. Contributed to Census of Marine Life Gulf of Maine Area Program.
Location:

Cashes Ledge, 2006-2008

Project Detail:

The effectiveness of fisheries management is limited by the paucity of information on how management tools, such as closed areas, impact key fisheries species. In the Gulf of Maine, more information is needed to determine how closed areas, such as around Cashes Ledge, influence fish population dynamics and subsequently the status of fishery stocks. This study will help managers determine to what degree the Cashes Ledge closed area is being used by juvenile and adult cod, thereby contributing to rebuilding cod populations in the Gulf of Maine.

First, we intend to create biological habitat maps of the Cashes Ledge Complex using multibeam acoustic data combined with information from previous studies conducted over the past two decades on the physical structure, oceanography, and biology of the Cashes Ledge Complex (Witman and Sebens, 1992; Steneck, 1997; Steneck, unpublished data). Second, we conducted seasonal surveys in 2006 and 2007 on the kelp, barren cobble, and mud habitats in the vicinity of Cashes Ledge using video, trap, and gill net sampling to quantify which habitats are used by juvenile and adult cod. These observations will be used to ground-truth the biological habitat map. We will also assess whether habitat characteristics such as the presence of Laminaria spp. on the pinnacles influences the abundance and distribution of cod. Third, we will compare our cod data with those collected by researchers in the 1980s (Witman and Sebens, 1992; Steneck, 1997; Steneck, unpublished data). This approach will determine if cod populations have changed since previous studies were conducted in the 1980’s.

The Gulf of Maine Mapping Initiative (GOMMI) arranged for a Ph.D. student from the University of Ulster, Northern Ireland to join this collaborative project to develop new methods for mapping benthic habitats using acoustic and biological data sets. Quantifying the extent to which Cashes Ledge supports spawning, juvenile and adult cod habitat will help managers to assess the effectiveness of current management schemes and refine the scope and timing of future management actions. Establishing habitat maps and quantifying important ecosystem functions such as the provision of nursery habitat for commercially important fish species will assist managers in selecting the most appropriate areas for management action. This study will also provide baseline information that will be of value to ongoing efforts to monitor the impact of the Cashes Ledge closure.

References:
  • Smith, F., and J. D. Witman. 1999. Species diversity in subtidal landscapes: maintenance by physical processes and larval recruitment. Ecology 80:51-69.
  • Steneck, R. S. 1997. Fisheries-induced biological changes to the structure and function of the Gulf of Maine Ecosystem. Plenary Paper. pages 151 – 165 in Wallace, G. T., and Braasch, E. F. (eds). Proceedings of the Gulf of Maine Ecosystem Dynamics Scientific Symposium and Workshop. RARGOM Report, 91 – 1. Regional Association for Research on the Gulf of Maine. Hanover, NH.
  • Witman, J. D., and K. P. Sebens. 1992. Regional variation in fish predation intensity: a historical perspective in the Gulf of Maine. Oecologia 909:305-315.