Using geostatistics to quantify seasonal distribution and aggregation patterns of fishes: an example of Atlantic cod ( Gadus morhua)

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Mello, L GS, Rose, G A
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2005
• Subjects: atlantic cod; Gadus morhua
• Online Access: http://dx.doi.org/10.1139/f04-227; http://www.nrcresearchpress.com/doi/pdf/10.1139/f04-227

Geostatistical methods were used to (i) quantify fish aggregation patterns over a range of scales (100 m to 67 km) using both simulated and acoustic density data of Atlantic cod (Gadus morhua) and (ii) examine how changes in aggregation patterns influenced the precision of geostatistical density indices. Variogram parameters (range, sill, and nugget) reflected changes in distribution patterns. Variograms of dispersed and low-density aggregations had large range and small sill and nugget values. In contrast, when fish were aggregated in a small portion of the study area, the range was low and the sill and nugget large. The precision of density indices (coefficient of variation) was below 20% in all cases but at a maximum during summer when cod were broadly distributed in small, moderate to dense aggregations. Geostatistical modeling allowed us to describe and quantify distribution patterns of fish density over different scales of observation, comparisons of spatiotemporal changes in density distribution, and estimations of the precision of density indices while accounting for the effects of heterogeneous distributions, outliers and the typically large number of zero and low-density observations. Geostatistical methods have particular applicability to fishes exhibiting gregarious behaviour and seasonally variable distributions, which include many temperate and high-latitude fish species.