Is size at sex transition an indicator of growth or abundance in pandalid shrimp?

Growth and sexual development of northern shrimp Pandalus borealis was determined on the Scotian Shelf during two periods, one of low and one of high population abundance, using deviation and modal analysis. Growth rates were higher during the period of low abundance, probably due to density dependent effects and higher temperatures. Faster growth during the first period was associated with a smaller size at transition (L-t) from male to female and a smaller maximum size (L-max), while slower growth during the later period was associated with a larger L-t and L-max (and older age). Results are consistent with the theory of invariance in the ratio of pandalid L-t/L-max and its implications, i.e. that growth can be determined from measurements of L-t or L-max alone. L-t was not a good indicator of short-term changes in population abundance; consequently L-t or L-max should be used as measure of growth, not abundance. The theoretical and practical implications of the results are discussed. In particular, it is suggested that decreased fecundity resulting from an increased growth rate and decreased L-t and L-max is responsible for the negative lagged relationships between temperatures and abundance in stocks at the southern limit of their distribution. It is also suggested that measurements of L-t and/or L-max could be used in quantitative assessment models and to develop harvest limit reference points. (C) 2003 Elsevier B.V. All rights reserved.