Variability, Spatial Patterns and Scales of Similarity in Size–Frequency Distributions of the Northern Shrimp ( Pandalus borealis ) and its Migrations in the Gulf of St. Lawrence

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Simard, Yvan, Savard, Louise
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1990
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Sept Iles; northern shrimp; Pandalus borealis
• Online Access: http://dx.doi.org/10.1139/f90-092; http://www.nrcresearchpress.com/doi/pdf/10.1139/f90-092

The causes of high variability of length–frequency distributions (LFDs) of the northern shrimp in the Gulf of St. Lawerence were investigated with spatial statistics. The LFD is considered as a multivariate whose spatial structure was analyzed with cluster analysis, dissimilarity variograms and multivariate correlograms. Data were collected in 1984, 1985, and 1987 on the three main shrimp grounds: Sept-Iles, North-Anticosti, and Esquiman. The LFDs were spatially autocorrelated over a wide range of scales, and well-defined homogeneous assemblages were observed in each region every year. The autocorrelation signature revealed that the spatial organization resulted from large gradients, partially related to the topography of the shrimp grounds, which probably resulted from the ontogenic depth-migration of the shrimps. The specific mean length of cohorts consistently increased along the spatial gradients, up to about one-half of the annual growth increment. This was attributed to the fact that the migration routes passed through an increasing temperature gradient, which, directly or indirectly, accelerated their growth. Significant regional and interannual differences in the relative proportion of the modal components of LFDs were noted, and were ascribed to fluctuations in the success and distribution of recruitment and survivorship.