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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

Map of reported blue, fin, sei and common minke whale catch locations (1905–1971).These catch locations were used to infer potential locations for blue whale catches without known locations. 41% of catches are known only to broad, management-defined regions (shaded boxes) which are shown with their corresponding blue whale catches.
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pone-0098974-g003: Map of reported blue, fin, sei and common minke whale catch locations (1905–1971).These catch locations were used to infer potential locations for blue whale catches without known locations. 41% of catches are known only to broad, management-defined regions (shaded boxes) which are shown with their corresponding blue whale catches.

Mentions: In addition to missing data about Soviet catches, many other catches in the IWC catch databases are missing locations, dates or both (Table 1), and the original records are lost to history. This ‘catch uncertainty’ must be explicitly taken into account when separating catches to reliably quantify the uncertainty associated with the catch time series. We used a Monte Carlo method to integrate over all potential locations and months for each individual catch. Conceptually, possible sets of locations and months were determined for each catch, from which random samples could be generated. By generating and splitting many potential catch series, the catch uncertainty was propagated through into the uncertainty in the final results. The challenging part was to determine accurate sets of locations from which to draw randomly. We assigned catches into five categories ranging from the most uncertain location (IWC Region) to the most certain (exact position known), and treated each category as described below.


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)

Map of reported blue, fin, sei and common minke whale catch locations (1905–1971).These catch locations were used to infer potential locations for blue whale catches without known locations. 41% of catches are known only to broad, management-defined regions (shaded boxes) which are shown with their corresponding blue whale catches.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0098974-g003: Map of reported blue, fin, sei and common minke whale catch locations (1905–1971).These catch locations were used to infer potential locations for blue whale catches without known locations. 41% of catches are known only to broad, management-defined regions (shaded boxes) which are shown with their corresponding blue whale catches.
Mentions: In addition to missing data about Soviet catches, many other catches in the IWC catch databases are missing locations, dates or both (Table 1), and the original records are lost to history. This ‘catch uncertainty’ must be explicitly taken into account when separating catches to reliably quantify the uncertainty associated with the catch time series. We used a Monte Carlo method to integrate over all potential locations and months for each individual catch. Conceptually, possible sets of locations and months were determined for each catch, from which random samples could be generated. By generating and splitting many potential catch series, the catch uncertainty was propagated through into the uncertainty in the final results. The challenging part was to determine accurate sets of locations from which to draw randomly. We assigned catches into five categories ranging from the most uncertain location (IWC Region) to the most certain (exact position known), and treated each category as described below.

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