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Seguam Pass Tanaga Pass Methods Fish were captured with a small trawl net, transferred into live tanks, tagged and released. Several months later fish were recaptured with commercial trawl nets and examined for tags. During the tag release cruise (June) and the tag recovery cruises (August and October), up to 150 sexed length frequencies were randomly collected from each trawl haul. During the tag release cruise in June, hauls weights and species composition were not determined per haul. The raw sexed length frequencies were summarized by stratum for the two areas Seguam and Tanaga pass. During the tag recovery cruises in August and October, haul weight was determined with a Marel flow scale and species composition was determined by subsampling the haul. Therefore sexed length frequencies were extrapolated to the total numbers of males and female fish per haul and then summarized by stratum for the two areas Seguam and Tanaga pass. Sex ratios per haul were determined from the sexed length frequency data. Discussion Tracking sex ratio and length frequency through time can help us understand the complexities of Atka mackerel spatial and temporal distributions throughout their spawning season. This study clearly shows the importance of incorporating changes in sex ratio and length frequency distributions into the design of a tag and release experiment. A sex specific tagging model that can incorporate length frequency data should be considered. The sex ratios and length frequency data from these tagging surveys can also provide useful information for the Atka mackerel stock assessment. Seasonal Changes in Atka Mackerel Sex Ratios in Seguam and Tanaga Passes during 2002 Results In Seguam Pass Sex ratios and length frequency distributions for Atka mackerel vary among strata throughout the spawning season. During August and October sex ratios were similar in strata 1 andamp; 2 whereas males dominated in strata 3 andamp; 4. However, size distribution of fish changed dramatically over time. During August a large influx of smaller fish (30-40 cm) was observed, which may represent a large year class of new recruits. Stratum 1 was still dominated by large females (40-50 cm) in August. In October the newly recruited year classes still dominate all 4 strata. Length frequency changes throughout the season. Results in Tanaga Pass In June males were slightly more abundant than females in all 4 strata. Length distributions peaked at 41 cm with females slightly larger than males. In October, a large influx of smaller fish (30-36 cm) was observed, similar to that in Seguam Pass. However, large fish were still present in strata 1-3 but disappeared completely in stratum 4 (Seamount). Collecting Length Frequencies Introduction Atka mackerel are an important prey item for Stellar sea lions . The National Marine Fisheries Service, Fisheries Interaction Team (FIT) has been conducting tag release-recovery studies on Atka mackerel in the Aleutian Islands since 1999. The primary objective of these studies is to estimate local abundance and movement rates relative to trawl exclusion zones. In order to construct the best tagging model, it is important to understand sex-specific differences in spatial and temporal distributions. We examined Atka mackerel sexed length frequency data from 3 research charters in 2002. Kimberly M. Rand and Susanne F. McDermott National Marine Fisheries Service, Alaska Fisheries Science Center, Fisheries Interaction Team, Seattle, WA, USA F/V Seafisher, charter vessel Atka mackerel tagging recovery cruise 2002 Atka mackerel ready for tagging…