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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

Spectrogram showing the ENP and WNP blue whale song calls.These calls were recorded on a hydrophone in the Gulf of Alaska at different times; the blue box shows the ENP song call and the red box the WNP song call. The clear distinction between the two is used to differentiate the presence and absence of the two populations.
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pone-0098974-g001: Spectrogram showing the ENP and WNP blue whale song calls.These calls were recorded on a hydrophone in the Gulf of Alaska at different times; the blue box shows the ENP song call and the red box the WNP song call. The clear distinction between the two is used to differentiate the presence and absence of the two populations.

Mentions: A key step in separating catches is using vocalization occurrence data to estimate the migration pathways of the ENP and WNP populations over time and space. Analyses of these vocalizations observe two distinct NP blue whale ‘song call’ types (Figure 1) [4], [8]–[10], which are assumed to be produced by the ENP and WNP populations. The ENP song call is comprised of the rhythmic repetition of a two part vocalization known as the ‘AB call’ type [11]. The AB call type components are produced exclusively by males in a variety of behavioral states [6]. The AB song calls are observed only in lone, traveling males and are produced year-round and thus likely have some kind of reproductive function, although their exact purpose is unknown [6]. The WNP song call is a single part call repeated as song in a similar way as the AB song of the ENP population, but has a clearly identifiable and distinct form (Figure 1) [8]. No studies have examined the behavioral context of WNP song, but it is assumed to be similar in function to the ENP song. Another common call type observed in the ENP population (and other populations of blue whales) is the downswept ‘D’ produced by foraging groups of both sexes [6]. A recent study found a temporal separation in the production of the AB and D call types at a summer feeding area, and argued that both were necessary for an accurate assessment of the timing of fine-scale seasonal movements into foraging regions [12]. Unfortunately there is no evidence of population differences in D-like calls as there is with song calls, and so we focused exclusively on the song call occurrence patterns.


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)

Spectrogram showing the ENP and WNP blue whale song calls.These calls were recorded on a hydrophone in the Gulf of Alaska at different times; the blue box shows the ENP song call and the red box the WNP song call. The clear distinction between the two is used to differentiate the presence and absence of the two populations.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0098974-g001: Spectrogram showing the ENP and WNP blue whale song calls.These calls were recorded on a hydrophone in the Gulf of Alaska at different times; the blue box shows the ENP song call and the red box the WNP song call. The clear distinction between the two is used to differentiate the presence and absence of the two populations.
Mentions: A key step in separating catches is using vocalization occurrence data to estimate the migration pathways of the ENP and WNP populations over time and space. Analyses of these vocalizations observe two distinct NP blue whale ‘song call’ types (Figure 1) [4], [8]–[10], which are assumed to be produced by the ENP and WNP populations. The ENP song call is comprised of the rhythmic repetition of a two part vocalization known as the ‘AB call’ type [11]. The AB call type components are produced exclusively by males in a variety of behavioral states [6]. The AB song calls are observed only in lone, traveling males and are produced year-round and thus likely have some kind of reproductive function, although their exact purpose is unknown [6]. The WNP song call is a single part call repeated as song in a similar way as the AB song of the ENP population, but has a clearly identifiable and distinct form (Figure 1) [8]. No studies have examined the behavioral context of WNP song, but it is assumed to be similar in function to the ENP song. Another common call type observed in the ENP population (and other populations of blue whales) is the downswept ‘D’ produced by foraging groups of both sexes [6]. A recent study found a temporal separation in the production of the AB and D call types at a summer feeding area, and argued that both were necessary for an accurate assessment of the timing of fine-scale seasonal movements into foraging regions [12]. Unfortunately there is no evidence of population differences in D-like calls as there is with song calls, and so we focused exclusively on the song call occurrence patterns.

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