posted on October 01, 1999 12:38
S. E. Wigley, J. M. Burnett, and P. J. Rago
National Marine Fisheries Service
Woods Hole, MA 02543 USA
Source - Journal of Northwest Atlantic Fishery Science, Volume 25: 133-140
Biological sampling of fish during research vessel survey cruises is often conducted using length-stratified age sampling schemes. Maturity-at-length or age may be affected by changes in sampling protocols, and may potentially result in biased estimates of maturation patterns. In such cases, these estimates may be artifacts of the sampling activities and not accurate estimators of stock dynamics.
In 1992, the Northeast Fisheries Science Center (NEFSC) modified the length-stratified age sampling protocol used during semi-annual research vessel bottom trawl surveys. While demonstrable gains in the precision of age-length keys for many species have been obtained with the new protocols, no systematic evaluation of the effects of the sampling protocol change upon maturity-at-length or age has been performed.
In this study, potential effects of changes in sampling protocol were assessed for two groundfish species, haddock (Melanogrammus aeglefinus) and American plaice (Hippoglossoides platessoides). Over the critical size range of maturity for both species, significantly different length frequency sampling was obtained from each sampling scheme during the 10-year study period. Analyses for American plaice were complicated by the sexually dimorphic growth. Simulation techniques were employed to assess whether the observed changes in maturity estimates were a result of the changed sampling protocols. The simulations suggested that these changes were real phenomena and not artifacts caused by changes in sampling.
Language - English
Publisher - Northwest Atlantic Fisheries Organization (NAFO), Dartmouth, N.S., Canada
Publication Date - October 1999
Publication Type - Journal Article
: Wigley, S.E., Burnett, J.M., and Rago, P.J. 1999. An Evaluation of Maturity Estimates Derived from Two Different Sampling Schemes: Are Observed Changes Fact or Artifact? J. Northw. Atl. Fish. Sci. 25: 133-140. doi.org/10.2960/J.v25.a12