Author: Gary Fitzhugh

National Marine Fisheries Service, 3500 Delwood Beach Road, Panama City , FL 32408, Tel. (850) 234-6541 ext. 214, Email: Gary.Fitzhugh@noaa.gov

Title: A few fuzzy things about fish reproduction and some possible ways to sharpen our focus

This presentation comes at the end of a summer rotation from the SE to NE Fisheries Science Center where an objective was to exchange ideas about ways to improve estimates of fish reproductive potential.  An assumption important to fisheries assessment is that mature stock biomass is directly proportional to egg production.  However, recent research has been pointing out that some aspects of what we believe about fish reproduction relative to this assumption are somewhat “fuzzy”.  Much of this work has centered on N. Atlantic fisheries, however these questions are also arising in lower latitude fisheries.  For example, groupers from the Gulf of Mexico; gag (Mycteroperca microlepis) and red grouper (Epinephelus morio), have exhibited evidence that many females, of an age and size that would be considered mature, are inactive and showing no signs of having entered into a vitellogenic phase during the spawning season.  Thus they appear to be skipping spawning.  This, among other examples, is leading workers to examine in more detail, the criteria used to assign the status of "maturity" and "activity" and to better evaluate measures of egg production (fecundity).   But it is recognized that measuring these attributes on annual basis, and across age structure, is not an easy or inexpensive thing to do.  So a common desire has been to seek more insight about energy allocation to reproduction, typically by examining fish condition (length-weight relationships).  Energy allocation tradeoffs have a rich theoretical treatment in the literature but much empirical information is lacking.  Bioelectrical impedance analysis (BIA) offers us an easy, cheap, and precise way to look at energy allocation by measuring body composition (e.g., lipids, protein, and total body water) under field settings.  BIA is new to fisheries applications, and is still in an R&D phase, but holds promise.