Uncertainty associated with total bycatch estimates for rarely-encountered species varies substantially with observer coverage levels: Informing minimum requirements for statutory logbook validation
MetadataShow full item record
© 2018 Concerns regarding quantifying fishing impacts on rarely-encountered bycatch species in a demersal fish trawl fishery in north-western Australia have raised issues with, 1) uncertainty associated with extrapolated estimates from low levels of coverage by human observers, and 2) appropriate minimum levels of observer coverage. This study used data collected from a very high level of independent observations (85% coverage, n = 2127 trawls) using electronic monitoring (EM) to determine the uncertainty of extrapolated estimates of chondrichthyan, cetacean and reptile bycatch at different levels of observer coverage. The distribution of extrapolated estimates of total numbers for rarely-encountered bycatch (i.e. dolphins and hammerhead sharks) was asymmetric, with a higher tendency for overestimation at lower levels of observer coverage (= 25%). Conversely, the minimum level of observer coverage required to achieve a reasonable level of precision (± 30% or lower) for rarely-encountered species would need to be very high (=90%). Combining the interaction rates of rarely-encountered species (i.e. via statutory logbook validation) reduces the minimum level of observer coverage required to an achievable level (~64%), whilst maintaining relatively accurate (± 25%) quantitative bycatch estimates for management purposes. Future programs need to consider that, in contrast to the infrequent presence of human observers, EM with cameras installed to monitor all fishing activity will effectively negate the need to assume that fishing practices are equivalent between observed and unobserved events. Hence, analysis of data collected by human observers may need to account for additional biases and/or imprecision along with the marked increase in uncertainty associated with lower levels of observer coverage.
Showing items related by title, author, creator and subject.
Performance of bycatch reduction devices varies for chondrichthyan, reptile, and cetacean mitigation in demersal fish trawls: Assimilating subsurface interactions and unaccounted mortalityWakefield, Corey; Santana Garcon, Julia; Dorman, S.; Blight, S.; Denham, A.; Wakeford, J.; Molony, B.; Newman, Stephen (2017)To improve bycatch mitigation of chondrichthyans, reptiles and cetaceans for a tropical demersal fish-trawl fishery, species-specific responses to bycatch reduction devices (BRDs) were investigated using both in situ ...
Parsons, Miles James Gerard (2009)Techniques of single- and multi-beam active acoustics and the passive recording of fish vocalisations were employed to evaluate the benefits and limitations of each technique as a method for assessing and monitoring fish ...
Measuring routine childhood vaccination coverage in 204 countries and territories, 1980–2019: a systematic analysis for the Global Burden of Disease Study 2020, Release 1Alene, Kefyalew (2021)Background: Measuring routine childhood vaccination is crucial to inform global vaccine policies and programme implementation, and to track progress towards targets set by the Global Vaccine Action Plan (GVAP) and ...