[Show abstract][Hide abstract] ABSTRACT: Although most eastern North Pacific (ENP) gray whales feed in the Bering, Beaufort, and Chukchi Seas during summer and fall, a small number of individuals, referred to as the Pacific Coast Feeding Group (PCFG), show intra- and interseasonal fidelity to feeding areas from northern California through southeastern Alaska. We used both mitochondrial DNA (mtDNA) and 12 microsatellite markers to assess whether stock structure exists among feeding grounds used by ENP gray whales. Significant mtDNA differentiation was found when samples representing the PCFG (n = 71) were compared with samples (n = 103) collected from animals feeding further north (FST = 0.012, P = 0.0045). No significant nuclear differences were detected. These results indicate that matrilineal fidelity plays a role in creating structure among feeding grounds but suggests that individuals from different feeding areas may interbreed. Haplotype diversities were similar between strata (hPCFG = 0.945, hNorthern = 0.952), which, in combination with the low level of mtDNA differentiation identified, suggested that some immigration into the PCFG could be occurring. These results are important in evaluating the management of ENP gray whales, especially in light of the Makah Tribe's proposal to resume whaling in an area of the Washington coast utilized by both PCFG and migrating whales.
[Show abstract][Hide abstract] ABSTRACT: We examined the incidence of rake mark scars from killer whales Orcinus orca on the flukes of humpback whales Megaptera novaeangliae throughout the North Pacific to assess geo- graphic variation in predation pressure. We used 3650 identification photographs from 16 wintering or feeding areas collected during 1990 to 1993 to determine conservative estimates in the percentage of whales with rake mark scarring. Dramatic differences were seen in the incidence of rake marks among regions, with highest rates on wintering grounds off Mexico (26 vs. 14% at others) and feed- ing areas off California (20 vs. 6% at others), 2 areas between which humpback whales migrate. Although attacks are rarely witnessed, the prevalence of scars demonstrates that a substantial por- tion of animals are attacked, particularly those that migrate between California and Mexico. Our data also suggest that most attacks occur at or near the wintering grounds in the eastern North Pacific. The prevalence of attacks indicates that killer whale predation has the potential to be a major cause of mortality and a driving force in migratory behavior; however, the location of the attacks is inconsis- tent with the hypothesis that animals migrate to tropical waters to avoid predation. Our conclusion is that, at least in recent decades, attacks are made primarily on calves at the wintering grounds; this contradicts the hypothesis that killer whales historically preyed heavily on large whales in high- latitude feeding areas in the North Pacific.
Endangered Species Research 03/2008; · 2.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Springer et al. (2003) contend that sequential declines occurred in North Pacific populations of harbor and fur seals, Steller sea lions, and sea otters. They hypothesize that these were due to increased predation by killer whales, when industrial whaling's removal of large whales as a supposed primary food source precipitated a prey switch. Using a regional approach, we reexamined whale catch data, killer whale predation observations, and the current biomass and trends of potential prey, and found little support for the prey-switching hypothesis. Large whale biomass in the Bering Sea did not decline as much as suggested by Springer et al., and much of the reduction occurred 50–100 yr ago, well before the declines of pinnipeds and sea otters began; thus, the need to switch prey starting in the 1970s is doubtful. With the sole exception that the sea otter decline followed the decline of pinnipeds, the reported declines were not in fact sequential. Given this, it is unlikely that a sequential megafaunal collapse from whales to sea otters occurred. The spatial and temporal patterns of pinniped and sea otter population trends are more complex than Springer et al. suggest, and are often inconsistent with their hypothesis. Populations remained stable or increased in many areas, despite extensive historical whaling and high killer whale abundance. Furthermore, observed killer whale predation has largely involved pinnipeds and small cetaceans; there is little evidence that large whales were ever a major prey item in high latitudes. Small cetaceans (ignored by Springer et al.) were likely abundant throughout the period. Overall, we suggest that the Springer et al. hypothesis represents a misleading and simplistic view of events and trophic relationships within this complex marine ecosystem.
[Show abstract][Hide abstract] ABSTRACT: Mating system theory predicts that differences between the sexes in potential reproductive rate and an operational sex ratio skewed strongly towards males should result in intense male competition, polygynous mating and high variance in male reproductive success. Accordingly, humpback whales are thought to be polygynous with differences in reproduction among males related to alternative mating tactics. However, there is currently a lack of data on male reproductive success. We tested predictions regarding male reproductive success in humpback whales using molecular assessment of paternity in a population in the Mexican Pacific. Parentage analysis was conducted for 125 mother–calf pairs and a sample of 297 males using 13 microsatellite loci. Two separate analyses were conducted, based upon conservative and relaxed criteria for the assignment of paternity. In the conservative analysis, 40 paternities (32.5% of tested calves) were assigned among 33 males, whereas in the relaxed analysis, 62 paternities (49.6% of calves) were assigned among 51 males. Regardless of analysis, the distribution of male reproductive success deviated from a random mating model, with significantly larger than expected variance (conservative, P = 0.011; relaxed, P = 0.022), and significantly more than expected males siring three calves (conservative, P = 0.021; relaxed, P = 0.011). However, most successful males sired only one calf and no male was assigned more than three calves, so reproductive skew was not severe. Therefore we conclude that this population has a polygynous mating system, but without the large variation in male reproductive success expected by apparent skew in the operational sex ratio and degree of male competition for mates.
[Show abstract][Hide abstract] ABSTRACT: Townsend's shearwater (Puffinus auricularis auricularis) is an endangered seabird endemic to the Revillagigedo Archipelago. It nested on Socorro, Clarion, and San Benedicto Islands. It was extirpated by the Barcena volcano on San Benedicto in 1952, and there are no recent indications of nesting. Introduced mammals—pigs and rabbits—preyed on them and destroyed habitat at Clarion; shearwaters were extirpated by 1988, and no breeding attempts have been reported since. Our results confirm that Socorro holds the last breeding grounds. We found breeding colonies above 800 m and a minimum population of 1100 individuals. This represents a significant reduction in distribution and population size. Intensive cat predation at Socorro could potentially kill ca. 350 females per season, and sheep progressively destroy nesting areas. Population projections suggest that demographic instability could occur in less than 100 years under severe predation and habitat degradation. Only low predation rates would allow population persistence for more than 150 years in spite of a declining population. Thus, the immediate eradication of all introduced mammals is necessary to prevent the extinction of this seabird.
[Show abstract][Hide abstract] ABSTRACT: Despite the extensive use of photographic identification methods to investigate humpback whales in the North Pacific, few quantitative analyses have been conducted. We report on a comprehensive analysis of interchange in the North Pacific among three wintering regions (Mexico, Hawaii, and Japan) each with two to three subareas, and feeding areas that extended from southern California to the Aleutian Islands. Of the 6,413 identification photographs of humpback whales obtained by 16 independent research groups between 1990 and 1993 and examined for this study, 3,650 photographs were determined to be of suitable quality. A total of 1,241 matches was found by two independent matching teams, identifying 2,712 unique whales in the sample (seen one to five times). Site fidelity was greatest at feeding areas where there was a high rate of resightings in the same area in different years and a low rate of interchange among different areas. Migrations between winter regions and feeding areas did not follow a simple pattern, although highest match rates were found for whales that moved between Hawaii and southeastern Alaska, and between mainland and Baja Mexico and California. Interchange among subareas of the three primary wintering regions was extensive for Hawaii, variable (depending on subareas) for Mexico, and low for Japan and reflected the relative distances among subareas. Interchange among these primary wintering regions was rare. This study provides the first quantitative assessment of the migratory structure of humpback whales in the entire North Pacific basin.
[Show abstract][Hide abstract] ABSTRACT: Humpback whale song, a male breeding display, shows a remarkable degree of similarity among distant breeding assemblages, despite constant progressive change. It has been hypothesized that whales maintain continuity through cultural transmission via migratory movements of males. We examined songs of whales breeding off Hawaii and Mexico to determine whether they changed similarly in both areas during the course of a breeding season. Songs recorded off Kauai, Hawaii (11 individuals) and Isla Socorro, Mexico (13 individuals) during winter and spring of 1991, were compared qualitatively and quantitatively. We measured 44 acoustic variables describing all known levels of song structure for each singer and we grouped these variables into six categories. We used two-factor analyses of variance to assess change across the season in each area, comparing the two regions and two 3-week periods (January/February and April). Twenty-seven variables changed significantly during the 12-week study in at least one area. Variables within categories displayed similar trends of change. Time and frequency characteristics describing the structure of song elements (units and phrases) changed synchronously in each area, with 21 of 25 variables displaying significant differences between periods and no interaction with region. Structures of song patterns, as defined by frequency of occurrence and number of unit and phrase types, changed differently in each area, with five of 12 variables indicating a significant interaction between region and period. Our results may suggest cultural transmission during the season, since many variables changed in similar manners. We propose an alternative hypothesis, that whales may be predisposed to gradually change certain features of song independently of cultural influences; change of structural elements may be governed by a discrete set of rules, or according to an innate template. Therefore, continuity of song patterns across the ocean basin may be due to a combination of mechanisms, only partially involving cultural transmission. We assess these hypotheses in relation to humpback whale behaviour and population structure, and cultural transmission and evolution of avian song.
[Show abstract][Hide abstract] ABSTRACT: Sighting histories of individually identified female humpback whales (Megaptera novaeangliae) in their winter and summer ranges were used to investigate mortality of North Pacific humpback whale calves. We compiled records collected between 1979 and 1995 by eight independent research groups, which yielded 29 cases where 25 different mothers sighted in Hawai'i were identified later the same year in Alaska. In 7 of 29 cases, a calf sighted with its mother in Hawai'i was missing from its mother's Alaska sighting(s). After investigating many factors, we determined that the largest potential bias would occur in late-autumn observations, when calf absences might indicate weaning or temporary mothercalf separation rather than calf mortality. Our minimal and most robust estimate excluded all mortalities and survivals based on sightings of the mother after October 31; 3 of 20 cases or 0.150 (95% confidence intervals (CI) = 0.032, 0.378). The maximal calf mortality rate, derived from all the available data, was 7 of 29 cases or 0.241 (95% CI = 0.103, 0.434). An intermediate estimate that excluded all cases based on single Alaska sightings and omitted late-season sightings (2 of 11 cases or 0.182; 95% CI = 0.023, 0.518) is perhaps closest to the actual first-year mortality rate for humpback whale calves, although it is compromised by its small sample size. Our results demonstrate both the value and the limitations of using longitudinal data to determine the life-history parameters that are essential for documenting the recovery of endangered populations.L'observation suivie de Baleines à bosse (Megaptera novaeangliae) femelles identifiées individuellement dans leurs aires d'hiver et d'été a permis d'étudier la mortalité des petits dans la population du Pacifique Nord. Nous avons compilé des données obtenues de 1979 à 1995 par huit groupes indépendants de chercheurs et l'opération a révélé 29 cas où 25 mères différentes aperçues dans les eaux hawaïennes ont été observées de nouveau en Alaska plus tard la même année. Dans 7 des 29 cas, une mère aperçue à Hawaii avec son petit a été revue en Alaska sans son petit. Après avoir examiné plusieurs facteurs, nous avons déterminé que la cause la plus probable d'erreur potentielle était reliée aux observations de fin d'automne, alors que l'absence du petit pourrait s'expliquer par le sevrage ou par la séparation temporaire du petit d'avec sa mère, plutôt que par la mortalité. Notre estimation minimale la plus robuste ne tient pas compte des taux de mortalité et de survie basés sur les observations des mères après le 31 octobre; 3 cas sur 20 ou 0,150 (95 % IC = 0,032, 0,378). Le taux maximal de mortalité des petits, basé sur toutes les données, était de 7 cas sur 29 ou 0,241 (95 % IC = 0,103, 0,434). Une estimation moyenne excluant tous les cas d'observations uniques en Alaska et les observations de fin de saison (2 cas sur 11 ou 0,182; 95 % IC = 0,023, 0,518) est peut être plus près de la mortalité réelle des petits au cours de la première année, bien que les résultats soient compromis par la taille insuffisante des échantillons. Nos résultats démontrent la valeur et les limites des données longitudinales pour déterminer les paramètres démographiques essentiels à l'étude de la récupération d'espèces menacées.[Traduit par la Rédaction]
Canadian Journal of Zoology 03/2001; 79(4):589-600. · 1.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The known summer feeding range of the North Pacific humpback whale (Megaptera novaeangliae) extends from California, along the coasts of Oregon, Washington, and Alaska, into the Bering Sea, along the Aleutian Islands, the Sea of Okhotsk (Tomilin 1957), and to northern Japan (Rice 1977). In feeding areas of the northeastern Pacific Ocean, humpback whale photoidentification research has been concentrated off California (Calambokidis et al. 1993), southeastern Alaska (Darling and McSweeney 1985, Baker et al. 1986, 1992; Perry et al. 1990), Prince William Sound in Alaska (von Ziegesar 1992), the Oregon and Washington coasts (Calambokidis et al. 1993), and British Columbia (Darling and McSweeney 1985; Graerne Ellis, unpublished data). Results of these photoidentification studies have documented that individual whales tend to return to the same general areas in subsequent years (Darling and McSweeney 1985, Baker et al. 1986, Calambokidis et a(. 1996, von Ziegesar et al. 1994).
[Show abstract][Hide abstract] ABSTRACT: The humpback whale (Megaptera novaeangliae) is a cosmo- politan species whose stocks were dras- tically decreased by commercial whal- ing practices prior to 1967. The North Pacific population was estimated to be between 15,000 and 20,000 animals before the practice of whaling. At the time of the commencement of its inter- national protection in 1967, this popu- lation may have been reduced to fewer than 1000 individuals. The Pacific coast of Mexico and the Revillagigedo Archi- pelago constitute one of the main breed- ing and calving areas for North Pacific humpback whales. The objective of this paper is to present an estimation of abundance of humpback whales in this region based on photographic identifi- cation of individual animals. Estimates of population size were obtained by us- ing mark and recapture models for both closed and open populations, with each year representing a capture occasion. A total of 1184 humpback whales were identified in Mexican waters between 1986 and 1993. The best estimates of population size for the Mexican stocks were those provided by the modified Jolly-Seber method: 1813 (95% CI: 918- 2505) for the coastal stock in 1992, and 914 (95% CI: 590-1193) for the Revil- lagigedo stock in 1991.
Fishery Bulletin- National Oceanic and Atmospheric Administration 01/1999; 97(4):1017-1024. · 1.78 Impact Factor