Annual changes in spatial aggregation of Atlantic cod, Gadus morhua, age classes in NAFO Divisions 2J3KL and 4RS (1978-1994)

• Main Author: Bennett, Elizabeth Jane
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2008
• Subjects: Northeast Newfoundland Shelf; atlantic cod; Gadus morhua; Newfoundland; Northwest Atlantic
• Online Access: https://research.library.mun.ca/10157/; https://research.library.mun.ca/10157/1/Bennett_ElizabethJ.pdf

Geographic contraction of range can be explained by using a basin model (MacCall 1990) which predicts that density-dependent populations will tend to contract toward the most favorable habitat as the population collapses. Literature has suggested that the distribution of demersal species such as Atlantic cod, Gadus morhua (Swain 1993) may be a product of the basin model phenomena. In this thesis I examine change in Atlantic cod aggregation during stock decline as it depends on age class, in order to better understand the spatial dynamics of the collapse of the Atlantic cod stocks in both NAFO (Northwest Atlantic Fisheries Organization) divisions 2J3KL (northeast Newfoundland Shelf) and 4RS (Northern Gulf of St. Lawrence), and explore how the basin model and density-dependent habitat selection relate to the change in aggregation into restricted areas during the collapse of Atlantic cod. -- I use research vessel data which was collected by Department of Fisheries and Oceans (1978-1994) in NAFO divisions 2J3KL, and 4RS to identify common characteristics of the spatial dynamics of the cod collapse. I explore the distributional shifts and change in aggregation of Atlantic cod age classes (≤2-12+ yrs) and age groups (ages ≤2, ages 3-4 ages, 5-6 and age 7-12+) from 1978 to 1994, by using distributional maps, the Gini index, the variance, the skewness of the frequency distribution, the exponent of power law, and the shape of cumulative frequency distribution. -- My results show that the most distinct measure of aggregation was the Gini index in combination with the distribution maps. These measures show that older cod peaked in aggregation while collapsing into fewer locations in the early 1990s and that the cod distribution collapse into reduced areas was specific to older age classes of Atlantic cod, with a lesser degree of spatial contraction in younger age classes and little or no contraction in the youngest age classes and variable rather than fixed locations of aggregation. Thus I offer an alternate explanation ...