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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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Results of the length analysis of mature female blue whales.(A) Locations, lengths, and median predicted population (color) for all years. (B) The distribution of mean length differences for all bootstrap iterations. (C) The 95% percentiles (gray polygon) and median line for all bootstrap linear models fit to the predicted population versus lengths. The circles represent the median probability of being ENP and observed lengths and are plotted with a small amount of noise to prevent overplotting.
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pone-0098974-g014: Results of the length analysis of mature female blue whales.(A) Locations, lengths, and median predicted population (color) for all years. (B) The distribution of mean length differences for all bootstrap iterations. (C) The 95% percentiles (gray polygon) and median line for all bootstrap linear models fit to the predicted population versus lengths. The circles represent the median probability of being ENP and observed lengths and are plotted with a small amount of noise to prevent overplotting.

Mentions: We applied the length analysis to 258 mature females, compared to 252 from [15], which were distributed sufficiently across time and space for the statistical tests (Figure 14a). For the two-sample -tests, the median difference in mean lengths was 0.91 m (95% range 0.76–1.03 m, Figure 14b) and for all 1000 catch scenarios this difference was highly significant (). The slopes of the linear regressions were all significantly negative, demonstrating that the shorter a whale is, the more likely it from the ENP population (Figure 14c).


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)

Results of the length analysis of mature female blue whales.(A) Locations, lengths, and median predicted population (color) for all years. (B) The distribution of mean length differences for all bootstrap iterations. (C) The 95% percentiles (gray polygon) and median line for all bootstrap linear models fit to the predicted population versus lengths. The circles represent the median probability of being ENP and observed lengths and are plotted with a small amount of noise to prevent overplotting.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0098974-g014: Results of the length analysis of mature female blue whales.(A) Locations, lengths, and median predicted population (color) for all years. (B) The distribution of mean length differences for all bootstrap iterations. (C) The 95% percentiles (gray polygon) and median line for all bootstrap linear models fit to the predicted population versus lengths. The circles represent the median probability of being ENP and observed lengths and are plotted with a small amount of noise to prevent overplotting.
Mentions: We applied the length analysis to 258 mature females, compared to 252 from [15], which were distributed sufficiently across time and space for the statistical tests (Figure 14a). For the two-sample -tests, the median difference in mean lengths was 0.91 m (95% range 0.76–1.03 m, Figure 14b) and for all 1000 catch scenarios this difference was highly significant (). The slopes of the linear regressions were all significantly negative, demonstrating that the shorter a whale is, the more likely it from the ENP population (Figure 14c).

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