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

Abstract

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.

Spatio-temporal patterns in demersal elasmobranchs from trawl surveys in the eastern English Channel (1988–2008)

“…Variogram parameters can also be used to explore, identify and quantify the spatial structure of distributions (e.g. Petitgas 2001, Mello & Rose 2005, Vaz et al 2005, in relation to species habitat preferences and spatial behaviour (e.g. aggregation, segregation, seasonal variation, ontogenic shift).…”

Distribution, abundance, and feeding of a disjunct population of lady crab in the southern Gulf of St. Lawrence, Canada

“…Geographic distribution of lady crab was described using point Kriging to produce contour maps of lady crab distribution within the area surveyed during July-August for each of the five years (Comeau et al 1997;Smith and Papadopoulou 2003;Mello and Rose 2005 Seasonal and annual abundance indices were calculated as catch-per-unit effort (CPUE ha -1 ) in each survey, restricted to the 2,500-km 2 zone where lady crab was consistently captured during July-August surveys (Area A in Fig. 2).…”

Spatiotemporal patterns of the fish assemblages downstream of the Gezhouba Dam on the Yangtze River

“…A few studies have attempted to treat such uncertainties through various means [21,32,36,37], which generally result in new uncertainties. Thus, the process being followed is not completely clear [22].…”

“…Thus, instead of producing a single, average case estimate, geostatistical simulations provide several alternative realizations of the values of interest [20,21]. Geostatistical simulations also enable descriptions and quantifications of the distribution patterns of fish density over different scales of observation, as well as estimations of density precision while accounting for the effects of heterogeneous distribution [22].…”