9334

• UCREFRP Catalog Number: 9334
• Author: Stickney, R. R.
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1993
• Copyright Material: YES

Reviews in Fisheries Science, 1(3): 203-222 (1993)
Stock Density Indices: Development, Use,
and Limitations
David W. Willis,a Brian R. Murphyb and
Christopher S. Guya
°Wildlife and Fisheries Sciences, South Dakota State University, Brookings, SD 57007,• and
bWildlife and Fisheries Sciences, Texas ABM University, College Station, TX 77843
ABSTRACT: The purposes of this paper are to review the development and assess the utility
of stock density indices. Stock density indices, specifically proportional stock density (PSD)
and relative stock density (RSD), were developed to quantify length-frequency data. Length
categories for standardized determination of stock density indices were based on percentages
of world-record length for each fish species; five-cell length categories have been proposed
for many warm- and coolwater fishes, but few Coldwater fishes. Both seasonal patterns in
sampling data and gear-related biases can affect length-frequency data used to determine
stock density indices. Stock density indices have been correlated with population dynamics
(recruitment, growth, and mortality), relative abundance, and condition for many fish species;
coefficients of determination typically are low, and much of the variability in the relations is
unexplained. Stock density indices for predator and prey fish populations tend to be inversely
related; however, inverse relations are more likely to be present in small (<50 ha) impoundments.
We recommend that development of five-cell length categories for additional fish species
continue to be based on established percentages of world-record length.
KEY WORDS: Proportional stock density, relative stock density, population assessment.
1. INTRODUCTION
Stock density indices, specifically proportional stock density (PSD) and relative stock
density (RSD), quantify length-frequency data. Both PSD and RSD were introduced
to the fisheries profession during the 1970s, and their use has proliferated. For
example, in a 1985 survey undertaken by the Fisheries Management Section,
American Fisheries Society (Gabelhouse et al., 1992), 34 states and 1 Canadian
province reported using PSD/RSD as a standard assessment tool for at least one
species of fish (Table 1). In addition, two other states used their own fish quality
indices to document size structure. Despite widespread application, questions
remain as to the appropriate use of these indices. The purposes of this paper are
to review the history/development of stock density indices, document assessments
of the indices, discuss their use and limitations, and recommend research needs.
1064-1262 /93/$.50
©1993 by CRC Press 203