Diel Reproductive Periodicity in Haddock in the Southwestern Gulf of Maine Katie A. Anderson, Francis Juanes and Rodney Rountree University of Massachusetts Amherst, USA Objective: Determine if haddock spawn at a particular time of day. The change in proportion of hydrated oocytes in the ovary was observed in spawning females across a twenty four hour period. The presence and condition of post-ovulatory follicles (POF’s) in histological prepared ovary tissues taken from fish caught across twenty four hours was also observed. METHODS: Commercial fishing vessels were chartered for 25 dedicated survey trips in the spring of 2006 (15) and 2007(10). Long lines were set and hauled in each of six time bins ( h, h, h, h, h or h) over a one to two week period to obtain representative 24 hour sampling. Sex, fork length and reproductive maturity of approximately 2000 haddock were recorded at sea. The presence and percentage of hydrated oocytes in each ovary was noted. (Fig.1). In the laboratory the ovaries of a subsample of female haddock selected from each haul were excised and weighed to determine the gonad somatic index (GSI = Gonad Weight/ (Body Weight-Gonad Weight) x 100). Preserved oocyte samples were sent to and independent laboratory of William Roumillat (South Carolina Department of Natural Resources) for histological examination to determine the accuracy and consistency of our field observations of ovarian macroscopic maturity stages. RESULTS: <>< Comparisons made between macroscopic predictions of maturity stage made in the field with histology analysis showed an 80% overall agreement. Thus our macroscopic field methods appear to reliably determine early and late final oocyte maturation (FOM). <>< GSI was very highly significantly influenced by time of day and appear to take the form of a quadratic polynomial response, indicating a decline in GSI in the early morning hours (Fig.2). Figure1. Hydration indices created and used in the field when determining the maturity stage of haddock ovaries. A) Developing ovary (no hydrated oocytes); B)Oocyte recruitment has seized, oocytes maturation has begun with 50% oocytes hydrated. ACKNOWLEDGEMENTS: Funding : MIT Sea Grant Program, Degree advisers :Francis Juanes and Rondey Rountree, Committee members: Cliff Goudey and Steve Cadrin. Fisherman:Tom Hill, Phil Powell and John Montgomery, Histology work: Wiilliam Roumillat. Many gracious field volunteers. Figure 2. The mean Square root of GSI for each time category pooled across the entire 2007 sampling season Figure 4. The mean CPUE for different female reproductive maturity stages for each time category pooled across 2006 and 2007 sampling season. Figure 3. Mean percentage of total female haddock caught in ripe and running maturity stage for each time category in 2006 and 2007 sampling season. <>< Percentage of female haddock in ripe and running reproductive maturity stage was significantly influenced by time of day in both years with a significant day/night difference (Fig.3). <>< Catch Per Unit Effort [CPUE=number of haddock caught/(number of hooks fished x length of time gear soaked)] of spawning female took a very different form then the remaining reproductive maturity stages. ABCD