Papers by Briana Witteveen
Marine Mammal Science, 2015
ABSTRACT Knowledge of humpback whale (Megaptera novaeangliae) foraging on feeding grounds is beco... more ABSTRACT Knowledge of humpback whale (Megaptera novaeangliae) foraging on feeding grounds is becoming increasingly important as the growing North Pacific population recovers from commercial whaling and consumes more prey, including economically important fishes. We explored spatial and temporal (interannual, within-season) variability in summer foraging by humpback whales along the eastern side of the Kodiak Archipelago as described by stable carbon (δ13C) and nitrogen (δ15N) isotope ratios of humpback whale skin (n = 118; 2004–2013). The trophic level (TL) of individual whales was calculated using basal food web δ15N values collected within the study area. We found evidence for the existence of two subaggregations of humpback whales (“North,” “South”) on the feeding ground that fed at different TLs throughout the study period. Linear mixed models suggest that within an average year, Kodiak humpback whales forage at a consistent TL during the feeding season. TL estimates support mixed consumption of fish and zooplankton species in the “North” (mean ± SE; 3.3 ± 0.1) and predominant foraging on zooplankton in the “South” (3.0 ± 0.1). This trend appears to reflect spatial differences in prey availability, and thus, our results suggest North Pacific humpback whales may segregate on feeding aggregations and target discrete prey species.
Marine Mammal Science, 2008
Tags containing acoustic time-depth transmitters (ATDT) were attached to four humpback whales nea... more Tags containing acoustic time-depth transmitters (ATDT) were attached to four humpback whales near Kodiak, Alaska. Tags allowed for whale dive depths to be recorded in real time. Acoustic and mid-water trawl surveys were conducted concurrent with tagging efforts within the study area to quantify available fish resources and describe potential prey selection by humpback whales. Recorded dives were grouped through visual assessment and t-tests. Dives that indicated likely foraging occurred at a mean maximum depth of 106.2 m with 62% of dives occurring between 92 m and 120 m. Acoustic backscatter from fish surveys was attributed to potential humpback prey based on known target strength values and 10 net tows. Capelin comprised 84% of the total potential prey abundance in the region followed by age 0 (12%) and juvenile pollock (2%), and eulachon (<1%). Although horizontally segregated in the region, both capelin and age 0 pollock were distributed at depths exceeding 92 m with maximum abundance between 107 m and 120 m. The four-tagged humpbacks were found to forage in areas with greatest capelin 1 Current address: NOAA Fisheries, Kodiak Laboratory, Kodiak Fisheries Research Center, 301 Research Court, Kodiak, Alaska 99615, U.S.A. 516 WITTEVEEN ET AL.: HUMPBACK FORAGING HABITS 517
Marine Mammal Science, 2013
Humpback whales feed on a variety of prey, but significant differences likely occur between regio... more Humpback whales feed on a variety of prey, but significant differences likely occur between regional feeding grounds. In this study, the diets of humpback whales were analyzed by comparing stable isotope ratios in animal tissues at three humpback whale feeding grounds in the Russian Far East: Karaginsky Gulf, Anadyr Gulf, and the Commander Islands. Anadyr Gulf is a neritic zone far from a shelf break, Karaginsky Gulf is a neritic zone close to a shelf break, and the Commander Islands represent an open oceanic ecosystem where whales feed off the shelf break. Samples from the Commander Islands had the lowest mean d 13 C and d 15 N values (mean ± SE: d 13 C = −18.7 ± 0.1, d 15 N = 10.4 ± 0.1) compared to the samples from Karaginsky Gulf (d 13 C = −17.2 ± 0.1, d 15 N = 12.7 ± 0.2) and Anadyr Gulf (d 13 C= −17.8 ± 0.1, d 15 N = 14.0 ± 0.4). The samples from Anadyr Gulf had the highest d 15 N values, while the samples from Karaginsky Gulf had the highest d 13 C values. Both d 13 C and d 15 N values differed significantly among all three areas. Our data support the hypothesis that humpback whales tend to feed on fish in neritic areas and on plankton in deep oceanic waters.
Marine Ecology Progress Series, 2009
North Pacific humpback whales Megaptera novaeangliae are migratory animals with a complex populat... more 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 (δ 13 C) and nitrogen (δ 15 N), the present study extends on a previous study of feeding animals to describe migratory linkages to breeding grounds ). Skin samples (n = 597) collected from 4 known breeding regions were analyzed for δ 13 C and δ 15 N. Breeding regions differed in both δ 13 C (F 3, 585 = 62.3, p < 0.001) and δ 15 N (F 3, 585 = 37.2, p < 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 δ 13 C (F 1, 44 = 10.3, r 2 = 0.19, p = 0.002) and δ 15 N (F 1, 44 = 40.9, r 2 = 0.48, p < 0.001). Furthermore, individual breeding and feeding values did not differ for δ 15 N (t 45 = 1.41, p = 0.17) or δ 13 C (t 45 = -1.15, p = 0.26) in pairwise comparisons. We used δ 13 C and δ 15 N 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.
Marine Ecology Progress Series, 2013
We quantified the relative influence of maternal fidelity to feeding grounds and natal fidelity t... more 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 novaeangliae 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 ST = 0.121, Φ ST = 0.178, p < 0.0001), supporting previous evidence of strong maternal fidelity. Haplotype frequencies also differed markedly among breeding regions (overall F ST = 0.093, Φ 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.
Canadian Journal of Zoology, 2004
Despite extensive research on humpback whales (Megaptera novaeangliae (Borowski, 1781)) in parts ... more Despite extensive research on humpback whales (Megaptera novaeangliae (Borowski, 1781)) in parts of the North Pacific, little research has focused on the whales feeding in coastal waters west of Kodiak Island in the Gulf of Alaska. To extend research westward in the North Pacific, small-boat surveys were conducted near the Shumagin Islands during the summers of 1999-2002. Photographs of the natural markings of humpback whales were collected, representing 413 sightings of 171 individual whales. Small samples of skin tissue were collected from 20 individuals, including two mother-calf pairs, for sex identification and comparison of mtDNA haplogroups with previously published results from surveys in other regions of the North Pacific. Individual identification photographs were used in mark-recapture analysis to estimate abundance for the Shumagin Island region. The best estimate was given by a modified Jolly-Seber method: N = 410 (95% CI: 241-683) for 2002. Comparison of photographs with archived photographs from throughout the North Pacific revealed four migratory destinations for 13 of the Shumagin Islands whales: Hawai′i, Japan, offshore Mexico, and coastal Mexico. The frequencies of mtDNA haplogroups differed significantly from those in three other sampled feeding grounds: California, southeastern Alaska, and Prince William Sound. The haplogroup frequencies and migratory destinations of individuals suggested an affinity with the Hawaiian wintering ground but data are insufficient to associate whales off the Shumagin Islands with any surveyed breeding ground.
Aquatic Mammals, 2011
Trophic levels of 1,105 humpback whales from six geographically and isotopically distinct North P... more Trophic levels of 1,105 humpback whales from six geographically and isotopically distinct North Pacific feeding groups were calculated using δ 15 N 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.
A photo-identification, mark-recapture study was conducted on a feeding aggregation
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Papers by Briana Witteveen