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

Abstract

Simard, Y., and L. Savard. 1990. 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. Can. 1. Fish.Aquat. Sci. 47: 794-804.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 1984Data were collected in , 1985Data were collected in , and 1987 on the three main shrimp grounds: Sept-lles, 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.Les causes de la forte variabilite des distributions de frequence de longueur (DFLs) chez la crevette nordique du Golfe du Saint-Laurent sont etudikes 21 I'aide de statistique spatiales. Les DFLs sont considerees cornme une multivariable dont on 6tudie la structure spatiale au moyen de groupements hikrarchiques, de variogrammes de dissimilarit6 et de corr6logrammes multivariables. Les donnees ont 6t6 recoltees en 1984, 1985, et 1987 dans les trois principales regions de p@che: Sept-lles, Nord-Anticosti, et Esquiman. Les DFLs etaient toujours autocorrelkes suivant un large continuum d'echelles spatiales, et des assemblages homogPnes bien definis ont kt6 observees chaque annee dans chacune des trois regions. La forme d'autocorrelation indiquait que I'organisation spatiale provenait de large gradients, modules par la topographie des regions. Ces gradients resultaient vraisemblablernent de la migration ontogenique des crevettes vers les fonds plus profonds. Les longueur moyennes spkcifiques des cohortes ont montr6 un accroissement systkmatique le long des gradients spatiaux, representant jusqulA la moiti6 de la croissance annuelle. Ceci fut attribue au fait que les routes migratoires croisaient un gradient positif de temp&ature, qui accel&ait, directement ou indirectement, leur croissance. Des differences regionales et interannnuelles considerables de la proportion relative des modes composant les...

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Evidence of wind‐driyen upwelling in jacques‐cartier strait

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“…Fig.7). The above mentioned dissimilarity matrix between soundscape cubes can serve to compute a multivariate autocorrelogram or variogram (Mackas, 1984;Simard and Savard, 1990) to assess the autocorrelation range (i.e. the size of the soundscape) in different directions (e.g.…”