Spatial Distribution of Numerical Density of Pelagic Juveniles (0‐Group) of Broadcast Spawning Fish Stocks Follows a Common Statistical Pattern

Abstract

Statistical distributions of spatial abundance data of animal populations can be informative about underlying processes and mechanisms that govern the spatial distributions. Here, we examine a large data set from annual 0‐group fish surveys in the Barents Sea (1980–2017) collected with standardised trawl sampling from a regular grid with 30–35 nautical miles between stations. The primary data are expressed as swept‐area density of 0‐group individuals for six fish species. The annual data series are highly right‐skewed with a tail of high values on a linear scale but are close to lognormal with log‐transformed data. The 0‐group density spans typically 4–5 orders of magnitude for the annual series. When stations are ranked in order from highest to lowest density, they show a common pattern for the six species across the annual series. With log‐transformed data, this pattern is a near log‐linear relationship but with an upswing in the high‐density end revealing higher variability for the top stations. The cumulative version with linear‐scale data is approximated by a simple asymptotic model. Between 14 and 42% of the total number of sampled individuals of a year‐class were on average contained in the highest ranked station for the six species, while 50% of the sampled individuals were found in the first 2–7 highest ranked stations. The common and consistent pattern of the ranked distributions is interpreted to reflect the opposing forces of physical dispersion, on the one hand and aggregation by swimming and schooling, on the other.