Introduction

1. Distribution and Drift Pathways of Larval and Juvenile Greenland halibut Dongwha Sohn1, Lorenzo Ciannelli1, Janet T. Duffy-Anderson2 , Ann Matarese2 and Kevin M. Bailey21Oregon State University, E-mail: dsohn@coas.oregonstate.edu, 2NOAA, NMFS, Alaska Fisheries Science Center (AFSC) A paradigm for slope spawning flatfish species? • Methods • - Historical data on GH adults and larvae were available from NMFS surveys conducted by scientists at the AFSC • Ichthyoplankton data (1982-2005): 60cm Bongo Net (60BON), Modified Bottom Trawl (MBT; samples the midwater), • Multiple Opening/Closing Net Environmental Sampling System (MOC) • - Groundfish survey data (1982-2006): Bottom trawl (BT) • Introduction • Greenland halibut (Reinhardtius hippoglossoides; GH) have declined significantly since the 1970’s in the eastern Bering Sea (EBS) . The reasons for the strong decline of GH in this region are unknown, and there is also very little information about the GH life history in the EBS. Objectives of this study are to examine transport pathways from spawning to potential nursery locations of GH egg, larvae, and early-juveniles in the EBS, and to determine what factors affect patterns of larval transport, dispersal and survival of the early life history stages. • Results – 1. Horizontal Distribution 2. Vertical Distribution by MOC Larvae from vertically stratified MOC tows were found throughout the water column between 0-500m, but highest concentrations were noted upper 45m vertical depth. Also, larvae length is bigger at shallower depths . Fig. 3. Schematic of mean circulation the upper 40 m. Aleutian North Slope Current (ANSC), Bering Slope Current (BSC) (Stabeno et al., 1999). Fig. 4. Mean (±SD) standard length (mm) related with vertical depth . • Conclusions • Potential spawning area (vertically and horizontally) is the continental slope (below 500m) near Bogoslof Is. and potential nursery area is the middle shelf (50-100m) near Pribilof Is. in the EBS. • GH spawn in deep water (below 500m), and it is likely that larvae slowly rise after hatching. The presence of larger larvae in the upper water column (<45 m depth) suggest some degree of diel migration of larger larvae, possiby associated with feeding. • GH larvae in the EBS have a long duration in the plankton and are subject to extended drift pathways. Larvae likely drift along the continental shelf edge, eventually crossing from the slope to the shelf to settle as age-0s. • Mechanisms of slope-shelf connectivity are still being investigated, though the larvae could be physically influenced by the ANSC and BSC. Eddies, transport through canyons, and/or wind-induced transport may all play a role in shelf-slope connectivity. • Patterns observed for GH may be indicative of strategies by other deep living flatfishes (arrowtooth flounder, Pacific halibut, Kamchatka flounder) which share a common goal of dispersing larvae toward nursery areas over the continental shelf. Fig. 1. Larval distribution and drift pathways by gear. 60BON: Early larvae (8.8-22.4mm SL) found on the continental slope (<500m) and drift northward during spring. MBT: Late larvae & early juveniles (18-54mm SL) found on the middle shelf (50m - 100m) near the Pribilof Is. during summer. BT: Age>0 (60-90mm SL) occurred on the middle shelf near St. Matthew Is. during summer. Fig. 2. Mean (±SD) standard length (mm) by gear . • Reference - Stabeno, P.J., Schumacher, J.D. and Ohtani, K., 1999. The physical oceanography • of the Bering Sea. In: Loughlin, T.R. and Ohtani, K., Editors, 1999. Dynamics of the Bering Sea, University of Alaska Sea Grant Press, Fairbanks, AK, pp. 1–28 AK-SG-99-03 .