• Estimating movement with a spatially-explicit stock assessment model of eastern Bering Sea walleye pollock, Theragra chalcogramma

      Miller, Sara Elizabeth (2007-05)
      The standard Eastern Bering Sea (EBS) walleye pollock (Theragra chalcogramma) stock assessment model has no spatial dimension. To advance the understanding of EBS walleye pollock movements and spatial structure on finer temporal and spatial scales, a spatially explicit migration model of EBS walleye pollock was developed. However, there are no estimates of movement rates for this population. Using standard sample size formulae in a Petersen-type experiment, we showed that only a moderate mark-recapture program [minimum number of tags for ages-1 + was 9,475 (all sectors included) and 20,924 (only catcher-vessel shoreside sector included)] is needed to estimate abundance. Given these sample size requirements determined for abundance estimation, the Darroch method was used to estimate movement parameters between two regions, the northwest (NW) and southeast (SE) EBS in a simple compartment model. Directed movement could be reasonably estimated with Monte Carlo simulation. To develop the EBS walleye pollock age-structured movement model, the standard stock assessment model was extended into a two-region (NW and SE EBS), two-season, age-specific movement model. Movement could be estimated from disaggregated data without mark-recapture information, but with low precision. However, the uncertainty indicates that a mark-recapture study is needed before such a model could be applied for management applications.
    • Physical Mechanisms For Variation In Pink Salmon (Oncorhynchus Gorbuscha) Survival Within The Upwelling And Downwelling Domains Of The Northeast Pacific

      Miller, Sara Elizabeth; Adkison, Milo; Criddle, Keith; Cokelet, Edward D. (Ned); Haldorson, Lewis J. (2011)
      Regional coastal conditions have a strong influence on juvenile salmon (genus Oncorhynchus) survival during their critical first months in the marine environment. Salmon survival has been thought to be favored within the downwelling domain if water column stabilities increase, whereas stability may have the opposite effect at lower latitudes. To explore this hypothesis at a local scale, we examined the relationship between stability and the characteristics of growth rate, condition, and marine survival of several stocks of pink salmon (O. gorbuscha) within Prince William Sound (PWS) and two water masses, Alaska Coastal Current and shelf, in the northern coastal Gulf of Alaska (GOA). While slower and weaker development of stratification with a deeper mixed layer depth may be more important for juvenile pink salmon survival in the Sound, earlier and stronger stratification with a shallower mixed layer depth may be more beneficial within the Gulf. As expected, stability within PWS did explain the growth rate of hatchery fish, although stability explained only a small amount of the variability and did not have the same relationship for each hatchery stock. Contrary to expectation, stability just prior to capture did not explain the variability in condition index for either hatchery or wild fish collected from within the Sound or from within either GOA water mass. When stability was below average just prior to capture within PWS, the relationship between condition index and year-class survival was positive; when stability was above-average just prior to capture, the relationship was negative. In a broader scale study, we explored the relationships between regional water column stabilities during early marine residence of pink salmon in both upwelling and downwelling domains of the northeast Pacific Ocean and marine survival rates the following year for hatchery stocks ranging from Vancouver Island, British Columbia, to Kodiak Island, Alaska. Contrary to expectation, our findings were similar between the upwelling and downwelling areas, but differed by the distance offshore. Marine survival rates of hatchery pink salmon from northern and southern stooks increased for salmon that experienced below-average stability on the inner shelf (luring early marine residence while stability effects from the outer shelf showed no consistent relationship to marine survival.