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Estimating historical eastern North Pacific blue whale catches using spatial calling patterns.

Monnahan CC, Branch TA, Stafford KM, Ivashchenko YV, Oleson EM - PLoS ONE (2014)

Bottom Line: Blue whales (Balaenoptera musculus) were exploited extensively around the world and remain endangered.In the North Pacific their population structure is unclear and current status unknown, with the exception of a well-studied eastern North Pacific (ENP) population.The results of this study provide information for future studies investigating the recovery of these populations and the impact of continuing and future sources of anthropogenic mortality.

View Article: PubMed Central - PubMed

Affiliation: Quantitative Ecology and Resource Management, University of Washington, Seattle, Washington, United States of America.

ABSTRACT
Blue whales (Balaenoptera musculus) were exploited extensively around the world and remain endangered. In the North Pacific their population structure is unclear and current status unknown, with the exception of a well-studied eastern North Pacific (ENP) population. Despite existing abundance estimates for the ENP population, it is difficult to estimate pre-exploitation abundance levels and gauge their recovery because historical catches of the ENP population are difficult to separate from catches of other populations in the North Pacific. We collated previously unreported Soviet catches and combined these with known catches to form the most current estimates of North Pacific blue whale catches. We split these conflated catches using recorded acoustic calls from throughout the North Pacific, the knowledge that the ENP population produces a different call than blue whales in the western North Pacific (WNP). The catches were split by estimating spatiotemporal occurrence of blue whales with generalized additive models fitted to acoustic call patterns, which predict the probability a catch belonged to the ENP population based on the proportion of calls of each population recorded by latitude, longitude, and month. When applied to the conflated historical catches, which totaled 9,773, we estimate that ENP blue whale catches totaled 3,411 (95% range 2,593 to 4,114) from 1905-1971, and amounted to 35% (95% range 27% to 42%) of all catches in the North Pacific. Thus most catches in the North Pacific were for WNP blue whales, totaling 6,362 (95% range 5,659 to 7,180). The uncertainty in the acoustic data influence the results substantially more than uncertainty in catch locations and dates, but the results are fairly insensitive to the ecological assumptions made in the analysis. The results of this study provide information for future studies investigating the recovery of these populations and the impact of continuing and future sources of anthropogenic mortality.

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Related in: MedlinePlus

Maps showing the statistical uncertainty arising from bootstrapping.Uncertainty in the base case probability of a catch being from the ENP population quantified using bootstrapping (i.e. resampling the acoustic data with replacement and refitting the models). The -axis is the range of the predictions (95th minus 5th percentile) across all 1000 bootstrapped models. A value of  indicates all bootstrap models predict the same value, while  indicates some bootstrap models predict 0 and others predict 1, so that there is high uncertainty at that location. There is higher uncertainty where overlap between the two populations exists (e.g. Gulf of Alaska) or there is limited data (e.g. Hawaii).
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pone-0098974-g010: Maps showing the statistical uncertainty arising from bootstrapping.Uncertainty in the base case probability of a catch being from the ENP population quantified using bootstrapping (i.e. resampling the acoustic data with replacement and refitting the models). The -axis is the range of the predictions (95th minus 5th percentile) across all 1000 bootstrapped models. A value of indicates all bootstrap models predict the same value, while indicates some bootstrap models predict 0 and others predict 1, so that there is high uncertainty at that location. There is higher uncertainty where overlap between the two populations exists (e.g. Gulf of Alaska) or there is limited data (e.g. Hawaii).

Mentions: The variance in the parameters' additive fits across bootstrapped models provided a measure of statistical uncertainty. There was more uncertainty in the months with fewer observed calls and regions with ENP and WNP overlap and limited hours with observed calls (Figure 10). For this study, the uncertainty only impacts the results where it coincides with historical catches. Thus, while there is high uncertainty around Hawaii for all months, this has little influence on the results and more acoustic data here would likely have a minimal impact. The statistical uncertainty in the GOA in the summer months (the peak of catches) has the greatest influence on the uncertainty in the results.


Estimating historical eastern North Pacific blue whale catches using spatial calling patterns.

Monnahan CC, Branch TA, Stafford KM, Ivashchenko YV, Oleson EM - PLoS ONE (2014)

Maps showing the statistical uncertainty arising from bootstrapping.Uncertainty in the base case probability of a catch being from the ENP population quantified using bootstrapping (i.e. resampling the acoustic data with replacement and refitting the models). The -axis is the range of the predictions (95th minus 5th percentile) across all 1000 bootstrapped models. A value of  indicates all bootstrap models predict the same value, while  indicates some bootstrap models predict 0 and others predict 1, so that there is high uncertainty at that location. There is higher uncertainty where overlap between the two populations exists (e.g. Gulf of Alaska) or there is limited data (e.g. Hawaii).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4043989&req=5

pone-0098974-g010: Maps showing the statistical uncertainty arising from bootstrapping.Uncertainty in the base case probability of a catch being from the ENP population quantified using bootstrapping (i.e. resampling the acoustic data with replacement and refitting the models). The -axis is the range of the predictions (95th minus 5th percentile) across all 1000 bootstrapped models. A value of indicates all bootstrap models predict the same value, while indicates some bootstrap models predict 0 and others predict 1, so that there is high uncertainty at that location. There is higher uncertainty where overlap between the two populations exists (e.g. Gulf of Alaska) or there is limited data (e.g. Hawaii).
Mentions: The variance in the parameters' additive fits across bootstrapped models provided a measure of statistical uncertainty. There was more uncertainty in the months with fewer observed calls and regions with ENP and WNP overlap and limited hours with observed calls (Figure 10). For this study, the uncertainty only impacts the results where it coincides with historical catches. Thus, while there is high uncertainty around Hawaii for all months, this has little influence on the results and more acoustic data here would likely have a minimal impact. The statistical uncertainty in the GOA in the summer months (the peak of catches) has the greatest influence on the uncertainty in the results.

Bottom Line: Blue whales (Balaenoptera musculus) were exploited extensively around the world and remain endangered.In the North Pacific their population structure is unclear and current status unknown, with the exception of a well-studied eastern North Pacific (ENP) population.The results of this study provide information for future studies investigating the recovery of these populations and the impact of continuing and future sources of anthropogenic mortality.

View Article: PubMed Central - PubMed

Affiliation: Quantitative Ecology and Resource Management, University of Washington, Seattle, Washington, United States of America.

ABSTRACT
Blue whales (Balaenoptera musculus) were exploited extensively around the world and remain endangered. In the North Pacific their population structure is unclear and current status unknown, with the exception of a well-studied eastern North Pacific (ENP) population. Despite existing abundance estimates for the ENP population, it is difficult to estimate pre-exploitation abundance levels and gauge their recovery because historical catches of the ENP population are difficult to separate from catches of other populations in the North Pacific. We collated previously unreported Soviet catches and combined these with known catches to form the most current estimates of North Pacific blue whale catches. We split these conflated catches using recorded acoustic calls from throughout the North Pacific, the knowledge that the ENP population produces a different call than blue whales in the western North Pacific (WNP). The catches were split by estimating spatiotemporal occurrence of blue whales with generalized additive models fitted to acoustic call patterns, which predict the probability a catch belonged to the ENP population based on the proportion of calls of each population recorded by latitude, longitude, and month. When applied to the conflated historical catches, which totaled 9,773, we estimate that ENP blue whale catches totaled 3,411 (95% range 2,593 to 4,114) from 1905-1971, and amounted to 35% (95% range 27% to 42%) of all catches in the North Pacific. Thus most catches in the North Pacific were for WNP blue whales, totaling 6,362 (95% range 5,659 to 7,180). The uncertainty in the acoustic data influence the results substantially more than uncertainty in catch locations and dates, but the results are fairly insensitive to the ecological assumptions made in the analysis. The results of this study provide information for future studies investigating the recovery of these populations and the impact of continuing and future sources of anthropogenic mortality.

Show MeSH
Related in: MedlinePlus