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  • 1
    Publication Date: 2013-06-25
    Description: Hammond, C. F., Conquest, L. L., and Rose, C. S. 2013. Using reflex action mortality predictors (RAMP) to evaluate if trawl gear modifications reduce the unobserved mortality of Tanner crab (Chionoecetes bairdi) and snow crab (C. opilio). – ICES Journal of Marine Science, 70: . Management of Bering Sea crab and groundfish fisheries must account for the delayed (and hence unobserved) mortality of crab that encounter bottom trawls, but are not captured. A new approach to predicting the delayed mortality of crab uses a reflex action mortality predictor (RAMP) model to establish a relationship between mortality and reflex impairments. A 2007 pilot study of 649 crab established RAMP curves for both Tanner crab (Chionoecetes bairdi) and snow crab (C. opilio). Additional data (1775 crab) collected in 2008 allowed us to update the existing RAMP curves to more fully examine the effect of injury scores on the RAMP models and to determine the best method for estimating overall mortality. Results confirmed that the additional measurements did not significantly alter the original relationship between mortality and reflex impairment score. Additionally, the RAMP curves were used to predict unobserved mortality from observed reflex impairment scores of Chionoecetes spp. captured after encounters with different parts of bottom trawl gear (footrope and sweep) and alternative types of footrope and sweep. In addition to estimating mortality rates caused by each gear part, we tested whether the alternative footrope and sweep designs reduced the unobserved mortality rates of crab. Results showed that the alternative footrope (58 cm disk footrope) reduced mortality from 11.4 to 7.2% for Tanner crab and from 9.7 to 5.0% for snow crab. The alternative (off-bottom) sweep reduced mortality from 4.1 to 1.0% for Tanner crab and from 4.9 to 0.0% for snow crab. Thus, the use of the reflex impairment score through the RAMP model is a cost effective way to estimate delayed mortality and to assess the effect of gear types on delayed mortality for management purposes.
    Print ISSN: 1054-3139
    Electronic ISSN: 1095-9289
    Topics: Biology , Geosciences , Physics
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  • 2
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    In:  http://aquaticcommons.org/id/eprint/8816 | 403 | 2012-06-12 17:56:00 | 8816 | United States National Marine Fisheries Service
    Publication Date: 2021-06-28
    Description: Delayed mortality associated with discarded crabs andfishes has ordinarily been observed through tag and recovery studies or during prolonged holding in decktanks, and there is need for a more efficient assessment method. Chionoecetes bairdi (Tanner crab) and C. opilio (snow crab) collected with bottom trawls in Bering Sea waters off Alaska were evaluated for reflexes and injuries and held onboard to track mortality. Presence or absence of six reflex actions was determined and combined to calculate a reflex impairment index for each species. Logistic regression revealed that reflex impairment provided an excellent predictor of delayed mortality in C. opilio (91% correct predictions). For C. bairdi, reflex impairment, along with injury score, resulted in 82.7% correct predictions of mortality, and reflex impairment alone resulted in 79.5% correct predictions. The relationshipsbetween reflex impairment score and mortality were independent of crab gender, size, and shell condition, and predicted mortality in crabs with no obvious externaldamage. These relationships provide substantial improvement over earlier predictors of mortality and will help to increase the scope and replication of fishing and handling experiments. The general approach of using reflex actions to predict mortality should be equally valuable for a wide range of crustacean species.
    Keywords: Biology ; Ecology ; Fisheries
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 337-347
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  • 3
    Publication Date: 2021-06-26
    Description: Unobserved mortalities of nontarget species are among the most troubling and difficult issues associated with fishing, especially when those species are targeted by other fisheries. Of such concern are mortalities of crab species of the Bering Sea, which are exposed to bottom trawling from groundfish fisheries. Uncertainty in the management of these fisheries has been exacerbated by unknown mortality rates for crabs struck by trawls. In this study, the mortality rates for 3 species of commercially important crabs—red king crab, (Paralithodes camtschaticus), snow crab (Chionoecetes opilio) and southern Tanner crab (C. bairdi)—that encounter different components of bottom trawls were estimated through capture of crabs behind the bottom trawl and by evaluation of immediate and delayed mortalities. We used a reflex action mortality predictor to predict delayed mortalities. Estimated mortality rates varied by species and by the part of the trawl gear encountered. Red king crab were more vulnerable than snow or southern Tanner crabs. Crabs were more likely to die after encountering the footrope than the sweeps of the trawl, and higher death rates were noted for the side sections of the footrope than for the center footrope section. Mortality rates were ≤16%, except for red king crab that passed under the trawl wings (32%). Herding devices (sweeps) can expand greatly the area of seafloor from which flatfishes are captured, and they subject crabs in that additional area to lower (4–9%) mortality rates. Raising sweep cables off of the seafloor reduced red king crab mortality rates from 10% to 4%.
    Keywords: Biology ; Ecology ; Fisheries
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 42-53
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  • 4
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    In:  http://aquaticcommons.org/id/eprint/8752 | 403 | 2012-06-11 18:33:38 | 8752 | United States National Marine Fisheries Service
    Publication Date: 2021-06-26
    Description: Otter trawls are very effective at capturing flatfish, butthey can affect the seaf loor ecosystems where they are used. Alaska f latf ish trawlers have very long cables (called sweeps) between doors and net to herd fish into the path of the trawl. These sweeps, which ride on and can disturb the seaf loor, account for most of the area affectedby these trawls and hence a large proportion of the potential for damage to seaf loor organisms. We examinedmodifications to otter trawls, such that disk clusters were installed at 9-m intervals to raise trawl sweeps small distances above the seafloor, greatly reducing the area of direct seafloor contact. A critical consideration was whether flatfish would still be herded effectively by these sweeps. We compared conventional and modified sweeps using a twin trawl system and analyzed the volume and compositionof the resulting catches. We tested sweeps raised 5, 7.5, and 10 cm and observed no significant losses of flatfish catch until sweeps were raised 10 cm, and those losses wererelatively small (5–10%). No size composition changes were detected in the flatfish catches. Alaska pollock (Theragrachalcogramma) were captured at higher rates with two versions of the modified sweeps. Sonar observations of the sweeps in operation and the seaf loor after passage confirmed that the area of direct seafloor contact was greatly reduced by the modified sweep
    Keywords: Biology ; Ecology ; Fisheries
    Repository Name: AquaDocs
    Type: article , TRUE
    Format: application/pdf
    Format: application/pdf
    Format: 136-144
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