University Events

Description: The School for Marine Science and Technology
Department of Fisheries Oceanography
PhD Dissertation Defense

Spawning Dynamics, Seasonal Movements, and Population Structure of Atlantic Cod (Gadus morhua) in the Gulf of Maine


By
Douglas Zemeckis

Advisor
Steve Cadrin


Tuesday, February 16, 2016
1:00 pm

SMAST II, Room 157
200 Mill Road, Fairhaven, MA


Abstract:
Atlantic cod (Gadus morhua) have been a principal target species in New England's groundfish fishery since the 17th century. In recent decades, the Gulf of Maine cod stock has experienced substantial declines in abundance, and many historical spawning components have been depleted, reducing stock productivity and stability. Managing stock rebuilding has been difficult because of many uncertainties in population dynamics. Therefore, to support stock rebuilding efforts, the objective of this dissertation was to improve our understanding of the spawning dynamics, seasonal movements, and population structure of Atlantic cod in the Gulf of Maine. An interdisciplinary review of the scientific literature demonstrated that the cod population off New England can be described as a metapopulation that includes genetically-distinct spring- and winter-spawning subpopulations which are comprised of many finer-scale spawning components. Available information indicates that current management unit boundaries do not accurately represent the biological population structure. Therefore, a modification of current management units is recommended to provide a more accurate representation of the underlying biological population processes. Review of the cod spawning literature indicated that cod spawn in multiple locations and seasons, and the complex cod mating system can be described as a "lek". The aspects of cod spawning dynamics most important for consideration by fishery managers are the spatial and temporal extent of spawning, the behavior of spawners, and the reproductive contributions of older age-classes. The application of spawning closures as part of a multidisciplinary approach to fisheries management is recommended to prevent disruption of spawning and extirpation of semi-discrete spawning components. Spawning site fidelity contributes to the formation and maintenance of the observed metapopulation structure and delays the recolonization of abandoned spawning sites by limiting reproductive connectivity. Acoustic telemetry was used to document prevalent, fine-scale spawning site fidelity with respect to an inshore spawning site in the western Gulf of Maine. Movements away from the inshore spawning site were studied using conventional tags, acoustic telemetry, and geolocation utilizing data from archival data storage tags. Connectivity was documented among multiple inshore spawning sites, which is apparently sufficient to promote gene flow within the western subpopulation. Cod were primarily residential within the western Gulf of Maine. After spawning inshore, cod moved to offshore feeding grounds from summer to early winter. Deep offshore basins served as overwintering habitat before initiation of an inshore spring spawning migration. Results from this dissertation have been valuable for informing fishery managers in the development of regulations to protect cod spawning aggregations. Findings are contributing to ongoing processes to investigate cod population structure and reevaluate current management units. This dissertation provides a more holistic understanding of cod population dynamics, which is expected to contribute to the development of future fishery management plans and stock assessment models that work towards achieving stock rebuilding.

For additional information, please contact Sue Silva at s1silva@umassd.edu.