Tracing Migratory Movements Of Breeding North Pacific Humpback Whales Using Stable Isotope Analysis

North Pacific humpback whales Megaptera novaeangliae are migratory animals with a complex population structure, segregating into geographically distinct aggregations on high-latitude feeding grounds. Several feeding aggregations may converge on a common breeding ground for mating and calving. Understanding how feeding and breeding habitats are linked is critical to understanding humpback whale life history and addressing management and conservation efforts. In a continued effort to explore the population structure of North Pacific humpback whales through the analysis of stable carbon (δ13C) and nitrogen (δ15N), the present study extends on a previous study of feeding animals to describe migratory linkages to breeding grounds (Witteveen et al. 2009). Skin samples (n = 597) collected from 4 known breeding regions were analyzed for δ13C and δ15N. Breeding regions differed in both δ13C (F3, 585 = 62.3, p \u3c 0.001) and δ15N (F3, 585 = 37.2, p \u3c 0.001). Breeding values reflected the foraging locations for 46 ind. sampled on both habitats; the relationship between the breeding and feeding stable isotope ratios was significant and positive for both δ13C (F 1, 44 = 10.3, r2 = 0.19, p = 0.002) and δ15N (F1, 44 = 40.9, r2 = 0.48, p \u3c 0.001). Furthermore, individual breeding and feeding values did not differ for δ15N (t45 = 1.41, p = 0.17) or δ13C (t45 = -1.15, p = 0.26) in pairwise comparisons. We used δ13C and δ15N in a classification tree analysis to describe probable migratory linkages to 6 previously described feeding groups. Stable isotope ratios predicted regional patterns of movement, and assignments of breeding individuals to feeding grounds differed by 12% on average from photographic matching. Our results indicate this technique can be used to help understand the population structure and ecology of North Pacific humpback whale populations, especially when used in combination with other research techniques. © 2009 Inter-Research

Modeling The Diet Of Humpback Whales: An Approach Using Stable Carbon And Nitrogen Isotopes In A Bayesian Mixing Model

Humpback whales are considered generalist predators, feeding on schooling fish, and zooplankton, but variability likely exists among regional feeding aggregations. We explored the diet of one feeding aggregation of humpback whales near Kodiak Island, Alaska, through analysis of the stable carbon (δ13C) and nitrogen (δ15N) isotope ratios of their skin and regional prey sources. Humpback whales were sampled during the summer feeding season over 3 yr (n= 93; 2004-2006). Prey samples were collected from the same region during trawl surveys conducted between 2003 and 2005. Isotope values of humpback whale skin and prey were entered into a Bayesian dietary mixing model to estimate feasible contributions of prey to humpback diets. Diet results indicated that humpbacks feed heavily on euphausiids, but also consume juvenile walleye pollock, capelin, and Pacific sand lance. The diet of humpback whales in 2004 was the most diverse, while diets in 2005 and 2006 showed a higher proportion of euphausiids. Our results reveal annual differences in humpback diets from the Kodiak region due to either individual prey preferences or prey availability. Application of a Bayesian mixing model to stable isotope analysis improves description of regional diets and comparison of these diets to resource availability and quality. © 2011 by the Society for Marine Mammalogy

Population Structure Of North Pacific Humpback Whales On Their Feeding Grounds Revealed By Stable Carbon And Nitrogen Isotope Ratios

Humpback whales Megaptera novaeangliae in the North Pacific Ocean are a migratory species known to have a complex population structure on both feeding and breeding grounds. We described the structure of this population using stable isotope analysis of skin samples (n = 1105) collected from free-ranging North Pacific humpback whales from 10 sampling regions in 2004 and 2005. We detected significant quadratic relationships between latitude and both δ13C (R2 = 0.29) and δ15N (R 2 = 0.23) as well as between longitude and δ15C (R2 = 0.43) and δ15N (R2 = 0.16). A weak negative linear relationship was seen between increasing distance from shore and both δ13C (R2 = 0.05) and δ15N (R2 = 0.02). Sampling regions were significantly different for both δ13C (ANOVA, F9,1094 = 136.4, p \u3c 0.001) and δ15N (F9,1095 = 71.5, p \u3c 0.001). We performed classification tree analyses using δ13C and δ15N as predictor variables to assign membership to sampling regions. Results of initial classification and ANOVAs supported combining the 10 sampling regions into 6 feeding groups. When applied to these feeding groups, the classification tree was able to predict 57% of group membership correctly, with accuracy rates for individual groups ranging from a low of 19% to a high of 78%. These results indicate that stable isotope analysis can be used to distinguish unique feeding aggregations of humpback whales within the North Pacific Ocean. Ultimately, isotopic characteristics of these aggregations can be applied to animals sampled on breeding grounds to assign them to a feeding aggregation, enhancing the ability to describe habitat linkages and migration patterns of humpback whales. © Inter-Research ch 2009

Trophic Levels Of North Pacific Humpback Whales (Megaptera Novaeangliae) Through Analysis Of Stable Isotopes: Implications On Prey And Resource Quality

Trophic levels of 1,105 humpback whales from six geographically and isotopically distinct North Pacific feeding groups were calculated using δ 15N of humpback whales and regional primary con-sumers. The overall mean trophic level for North Pacific humpback whales was 3.6 ± 0.02, indicating a diet of both fish and zooplankton, and, thus, supporting assumptions of humpback whales as generalist predators. The highest mean trophic level was calculated for the north Gulf of Alaska group (4.0 ± 0.03), while the lowest was found for the Russian and the western Aleutian Islands group (3.3 ± 0.08). Differences in mean trophic levels suggest that feeding groups differ in the proportion of fish and zooplankton in their diets

Trophic Levels of North Pacific Humpback Whales (Megaptera novaeangliae) Through Analysis of Stable Isotopes: Implications on Prey and Resource Quality

Trophic levels of 1,105 humpback whales from six geographically and isotopically distinct North Pacific feeding groups were calculated using δ15N of humpback whales and regional primary consumers. The overall mean trophic level for North Pacific humpback whales was 3.6 ± 0.02, indicating a diet of both fish and zooplankton, and, thus, supporting assumptions of humpback whales as generalist predators. The highest mean trophic level was calculated for the north Gulf of Alaska group (4.0 ± 0.03), while the lowest was found for the Russian and the western Aleutian Islands group (3.3 ± 0.08). Differences in mean trophic levels suggest that feeding groups differ in the proportion of fish and zooplankton in their diets

Humpback whale abundance in the North Pacific estimated by photographic capture-recapture with bias correction from simulation studies

We estimated the abundance of humpback whales in the North Pacific by capture recapture methods using over 18,000 fluke identification photographs collected in 2004–2006. Our best estimate of abundance was 21,808 (CV=0.04). We estimated the biases in this value using a simulation model. Births and deaths, which violate the assumption of a closed population, resulted in a bias of +5.2%, exclusion of calves in samples resulted in a bias of−10.5%, failure to achieve random geographic sampling resulted in a bias of −0.4%, and missed matches resulted in a bias of +9.3%. Known sex-biased sampling favoring males in breeding areas did not add significant bias if both sexes are proportionately sampled in the feeding areas. Our best estimate of abundance was 21,063 after accounting for a net bias of +3.5%. This estimate is likely to be lower than the true abundance due to two additional sources of bias: individual heterogeneity in the probability of being sampled (unquantified) and the likely existence of an unknown and unsampled breeding area (−8.7%). Results confirm that the overall humpback whale population in the North Pacific has continued to increase and is now greater than some prior estimates of prewhaling abundance

Baleen whales are not important as prey for killer whales Orcinus orca in high-latitude regions

Author Posting. © Inter-Research, 2007. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Marine Ecology Progress Series 348 (2007): 297-307, doi:10.3354/meps07015.Certain populations of killer whales Orcinus orca feed primarily or exclusively on marine mammals. However, whether or not baleen whales represent an important prey source for killer whales is debatable. A hypothesis by Springer et al. (2003) suggested that overexploitation of large whales by industrial whaling forced killer whales to prey-switch from baleen whales to pinnipeds and sea otters, resulting in population declines for these smaller marine mammals in the North Pacific and southern Bering Sea. This prey-switching hypothesis is in part contingent upon the idea that killer whales commonly attack mysticetes while they are in these high-latitude areas. In this study, we used photographic and sighting data from long-term studies of baleen whales in 24 regions worldwide to determine the proportion of whales that bear scars (rake marks) from killer whale attacks, and to examine the timing of scar acquisition. The results of this study show that there is considerable geographic variation in the proportion of whales with rake marks, ranging from 0% to >40% in different regions. In every region, the great majority of the scars seen were present on the whales’ bodies when the animals were first sighted. Less than 7% (9 of 132) of scarred humpback whales with multi-year sighting histories acquired new scars after the first sighting. This suggests that most killer whale attacks on baleen whales target young animals, probably calves on their first migration from low-latitude breeding and calving areas to high-latitude feeding grounds. Overall, our results imply that adult baleen whales are not an important prey source for killer whales in high latitudes, and therefore that one of the primary assumptions underlying the Springer et al. (2003) prey-switching hypothesis (and its purported link to industrial whaling) is invalid.This study was supported in part by funding from the Marine Mammal Commission

Data from: Strong maternal fidelity and natal philopatry shape genetic structure in North Pacfic humpback whales

We quantified the relative influence of maternal fidelity to feeding grounds and natal fidelity to breeding grounds in humpback whales based on an ocean-wide survey of mitochondrial (mt) DNA diversity in the North Pacific. For 2,193 biopsy samples collected from whales in 10 feeding regions and 8 breeding regions during the winter and summer of 2004 to 2006, we first used microsatellite genotyping (average, 9.5 loci) to identify replicate samples. From sequences of the mtDNA control region (500 bp) we identified 28 unique haplotypes from 30 variable sites. Haplotype frequencies differed markedly among feeding regions (overall FST = 0.121, PhiST = 0.178, p < 0.0001), supporting previous evidence of strong maternal fidelity. Haplotype frequencies also differed markedly among breeding regions (overall FST = 0.093, PhiST = 0.106, p < 0.0001), providing evidence of strong natal fidelity. Although sex-biased dispersal was not evident, differentiation of microsatellite allele frequencies was weak compared to differentiation of mtDNA haplotypes, suggesting male-biased gene flow. Feeding and breeding regions showed significant differences in haplotype frequencies, even for regions known to be strongly connected by patterns of individual migration. Thus, the influence of migratory fidelity seems to operate somewhat independently on feeding and breeding grounds over an evolutionary time scale. This results in a complex population structure and the potential to define multiple units to conserve in either seasonal habitat

BakerCScottFisheriesWildlifeStrongMaternalFidelity.pdf

We quantified the relative influence of maternal fidelity to feeding grounds and natal fidelity to breeding grounds on the population structure of humpback whales Megaptera novae-angliae based on an ocean-wide survey of mitochondrial (mt) DNA diversity in the North Pacific. For 2193 biopsy samples collected from whales in 10 feeding regions and 8 breeding regions during the winter and summer of 2004 to 2006, we first used microsatellite genotyping (average, 9.5 loci) to identify replicate samples. From sequences of the mtDNA control region (500 bp) we identified 28 unique haplotypes from 30 variable sites. Haplotype frequencies differed markedly among feeding regions (overall F[subscript ST] = 0.121, Φ[subscript ST] = 0.178, p < 0.0001), supporting previous evidence of strong maternal fidelity. Haplotype frequencies also differed markedly among breeding regions (overall F[subscript ST] = 0.093, Φ[subscript ST] = 0.106, p < 0.0001), providing evidence of strong natal fidelity. Although sex-biased dispersal was not evident, differentiation of microsatellite allele frequencies was weak compared to differentiation of mtDNA haplotypes, suggesting male-biased gene flow. Feeding and breeding regions showed significant differences in haplotype frequencies, even for regions known to be strongly connected by patterns of individual migration. Thus, the influence of migratory fidelity seems to operate somewhat independently on feeding and breeding grounds over an evolutionary time scale. This results in a complex population structure and the potential to define multiple units to conserve in either seasonal habitat.Keywords: mtDNA, Genetic management units, Microsatellite genotypes, Migratio

BakerCScottFisheriesWildlifeStrongMaternalFidelitySupplementaryMaterial.pdf

We quantified the relative influence of maternal fidelity to feeding grounds and natal fidelity to breeding grounds on the population structure of humpback whales Megaptera novae-angliae based on an ocean-wide survey of mitochondrial (mt) DNA diversity in the North Pacific. For 2193 biopsy samples collected from whales in 10 feeding regions and 8 breeding regions during the winter and summer of 2004 to 2006, we first used microsatellite genotyping (average, 9.5 loci) to identify replicate samples. From sequences of the mtDNA control region (500 bp) we identified 28 unique haplotypes from 30 variable sites. Haplotype frequencies differed markedly among feeding regions (overall F[subscript ST] = 0.121, Φ[subscript ST] = 0.178, p < 0.0001), supporting previous evidence of strong maternal fidelity. Haplotype frequencies also differed markedly among breeding regions (overall F[subscript ST] = 0.093, Φ[subscript ST] = 0.106, p < 0.0001), providing evidence of strong natal fidelity. Although sex-biased dispersal was not evident, differentiation of microsatellite allele frequencies was weak compared to differentiation of mtDNA haplotypes, suggesting male-biased gene flow. Feeding and breeding regions showed significant differences in haplotype frequencies, even for regions known to be strongly connected by patterns of individual migration. Thus, the influence of migratory fidelity seems to operate somewhat independently on feeding and breeding grounds over an evolutionary time scale. This results in a complex population structure and the potential to define multiple units to conserve in either seasonal habitat.Keywords: Migration, Genetic management units, Microsatellite genotypes, mtDN