Alejandro Acevedo-Gutiérrez

The diving behavior of blue and fin whales: is dive duration shorter than expected based on oxygen stores?

Many diving seabirds and marine mammals have been found to regularly exceed their theoretical aerobic dive limit (TADL). No animals have been found to dive for durations that are consistently shorter than their TADL. We attached time-depth recorders to 7 blue whales and 15 fin whales (family Balaenopteridae). The diving behavior of both species was similar, and we distinguished between foraging and traveling dives. Foraging dives in both species were deeper, longer in duration and distinguished by a series of vertical excursions where lunge feeding presumably occurred. Foraging blue whales lunged 2.4 (+/-1.13) times per dive, with a maximum of six times and average vertical excursion of 30.2 (+/-10.04) m. Foraging fin whales lunged 1.7 (+/-0.88) times per dive, with a maximum of eight times and average vertical excursion of 21.2 (+/-4.35) m. The maximum rate of ascent of lunges was higher than the maximum rate of descent in both species, indicating that feeding lunges occurred on ascent. Foraging dives were deeper and longer than non-feeding dives in both species. On average, blue whales dived to 140.0 (+/-46.01) m and 7.8 (+/-1.89) min when foraging, and 67.6 (+/-51.46) m and 4.9 (+/-2.53) min when not foraging. Fin whales dived to 97.9 (+/-32.59) m and 6.3 (+/-1.53) min when foraging and to 59.3 (+/-29.67) m and 4.2 (+/-1.67) min when not foraging. The longest dives recorded for both species, 14.7 min for blue whales and 16.9 min for fin whales, were considerably shorter than the TADL of 31.2 and 28.6 min, respectively. An allometric comparison of seven families diving to an average depth of 80-150 m showed a significant relationship between body mass and dive duration once Balaenopteridae whales, with a mean dive duration of 6.8 min, were excluded from the analysis. Thus, the short dive durations of blue whales and fin whales cannot be explained by the shallow distribution of their prey. We propose instead that short duration diving in large whales results from either: (1) dispersal behavior of prey; or (2) a high energetic cost of foraging.

Regulation compliance by vessels and disturbance of harbour seals (Phoca vitulina)

The US National Oceanic and Atmospheric Administration established a buffer zone around marine mammals to prevent harassment. The buffer zone varies by species listing status and by geographic area...

New insights into the diets of harbor seals (Phoca vitulina) in the Salish Sea revealed by analysis of fatty acid signatures

Harbor seals (Phoca fvitulina) are an abundant predator along the west coast of North America, and there is considerable interest in their diet composition, especially in regard to predation on valued fish stocks. Available informationon harbor seal diets, primarily derived from scat analysis, suggests that adult salmon (Oncorhynchus spp.), Pacific Herring (Clupea pallasii), and gadids predominate. Because diet assessments based on scat analysis may be biased, we investigated diet composition through quantitative analysis of fatty acid signatures. Blubber samples from 49 harbor seals captured in western North America from haul-outs within the area of the San Juan Islands and southern Strait of Georgia in the Salish Sea were analyzed for fatty acid composition, along with 269 fish and squid specimens representing 27 potential prey classes. Diet estimates varied spatially, demographically, and among individual harbor seals. Findings confirmed the prevalence of previously identified prey species in harbor seal diets, but other species also contributed significantly. In particular, Black (Sebastes melanops) and Yellowtail (S. flavidus) Rockfish were estimated to compose up to 50% of some individual seal diets. Specialization and high predation rates on Black and Yellowtail Rockfish by a subset of harbor seals may play a role in the population dynamics of these regional rockfish stocks that is greater than previously realized.

Long Distance Movements and Disjunct Spatial Use of Harbor Seals (Phoca vitulina) in the Inland Waters of the Pacific Northwest

Background Worldwide, adult harbor seals (Phoca vitulina) typically limit their movements and activity to <50 km from their primary haul-out site. As a result, the ecological impact of harbor seals is viewed as limited to relatively small spatial scales. Harbor seals in the Pacific Northwest are believed to remain <30 km from their primary haul-out site, one of several contributing factors to the current stock designation. However, movement patterns within the region are not well understood because previous studies have used radio-telemetry, which has range limitations. Our objective was to use satellite-telemetry to determine the regional spatial scale of movements. Methodology/Principal Findings Satellite tags were deployed on 20 adult seals (n=16 males and 4 females) from two rocky reefs and a mudflat-bay during April–May 2007. Standard filtering algorithms were used to remove outliers, resulting in an average (± SD) of 693 (±377) locations per seal over 110 (±32) days. A particle filter was implemented to interpolate locations temporally and decrease erroneous locations on land. Minimum over-water distances were calculated between filtered locations and each seals capture site to show movement of seals over time relative to their capture site, and we estimated utilization distributions from kernel density analysis to reflect spatial use. Eight males moved >100 km from their capture site at least once, two of which traveled round trip to and from the Pacific coast, a total distance >400 km. Disjunct spatial use patterns observed provide new insight into general harbor seal behavior. Conclusions/Significance Long-distance movements and disjunct spatial use of adult harbor seals have not been reported for the study region and are rare worldwide in such a large proportion of tagged individuals. Thus, the ecological influence of individual seals may reach farther than previously assumed.

Aerial Behavior is Not a Social Facilitator in Bottlenose Dolphins Hunting in Small Groups

Two hypotheses that could explain the function of aerial behavior in dolphins feeding in large groups are: it is a social facilitator that establishes social bonds before or after a hunt, or it aids in capture of prey. To test which hypothesis best explains the function of aerial behavior in bottlenose dolphins ( Tursiops truncatus ) that hunt in small groups, I described the behavior of dolphins based on a set of predefined parameters, estimated occurrence of aerial behavior in groups, estimated frequency of aerial behavior per dolphin, described types of aerial behavior, and related these variables to size of group and behavioral contexts: before-feeding, feeding, after-feeding, and non-feeding. Data were collected from 111 groups. Behavioral parameters were significantly different during feeding, with dolphins moving faster and engaging in aerial behavior more often than in any other context. Aerial behavior per dolphin and occurrence of aerial behavior were highest during feeding. Results did not support the social-facilitation hypothesis. Although the aid-in-capture-of-prey hypothesis was favored, data showing a positive correlation between intake of food by individuals and aerial behavior per dolphin are required as conclusive evidence.

Fine-Scale Variability in Harbor Seal Foraging Behavior

Understanding the variability of foraging behavior within a population of predators is important for determining their role in the ecosystem and how they may respond to future ecosystem changes. However, such variability has seldom been studied in harbor seals on a fine spatial scale (<30 km). We used a combination of standard and Bayesian generalized linear mixed models to explore how environmental variables influenced the dive behavior of harbor seals. Time-depth recorders were deployed on harbor seals from two haul-out sites in the Salish Sea in 2007 (n = 18) and 2008 (n = 11). Three behavioral bout types were classified from six dive types within each bout; however, one of these bout types was related to haul-out activity and was excluded from analyses. Deep foraging bouts (Type I) were the predominant type used throughout the study; however, variation in the use of bout types was observed relative to haul-out site, season, sex, and light (day/night). The proportional use of Type I and Type II (shallow foraging/traveling) bouts differed dramatically between haul-out sites, seasons, sexes, and whether it was day or night; individual variability between seals also contributed to the observed differences. We hypothesize that this variation in dive behavior was related to habitat or prey specialization by seals from different haul-out sites, or individual variability between seals in the study area. The results highlight the potential influence of habitat and specialization on the foraging behavior of harbor seals, and may help explain the variability in diet that is observed between different haul-out site groups in this population.

Tidal Influence On the Haul-Out Behavior of Harbor Seals (Phoca vitulina) At A Site Available At All Tide Levels

Abstract Harbor Seals (Phoca vitulina) are the most abundant and widespread seal species in Washington State. Most seal haul-out sites are unavailable at high tide, hence abundance estimates are conducted at low tide when it is commonly accepted that most seals are hauled-out. On sites unaffected by tides, however, it is less clear whether tide level has an effect on seal abundance. We counted hauled-out Harbor Seals from sunrise to sunset on floating water-breakers at Semiahmoo Marina, Washington, to examine the effect of tides on haul-out behavior. Because haul-out behavior is affected by several factors, we conducted mixed-factor analyses that included tide level, tidal current, time of season, and time of day as fixed factors, and several meteorological variables as random factors. The number of hauled-out Harbor Seals was significantly associated with tide level, time of season, and time of day. Results suggest that seal counts in Semiahmoo Marina should be made late in the pupping season and early in the afternoon at moderately positive tide levels to achieve the highest counts. They also indicate that tide was associated with seal numbers unrelated to site availability because seal numbers were positively related to tide height, a finding opposite to studies at tidal haul-out sites.

Effects of the Presence of Official‐Looking Volunteers on Harassment of New Zealand Fur Seals

An increased number of tourists viewing animals in the wild have increased stress on these animals (hereafter wildlife). Many wildlife-viewing locations rely on voluntary compliance with posted regulations to protect animals from tourists because of the expense of employing on-site enforcement personnel. Voluntary compliance, however, is ineffective. The presence of official-looking volunteers may decrease the incidence of wildlife harassment by tourists. To test this possibility, we observed tourists interacting with 5- to 12-month-old New Zealand fur seals (Arctocephalus forsteri) at the popular Ohau Stream waterfall while in the absence or presence of a young woman in plain sight wearing a neon vest (i.e., observer) and when an observer was not present. We observed 254 tourist groups at the waterfall when young seals were present. The percentage of groups in which at least one person harassed (approached, touched, or threw objects) a young seal was two-thirds lower when the official-looking observer was present. Frequency of harassment was inversely related to observer presence. Programs in which volunteers work at tourist sites are popular in countries with high tourism rates, such as New Zealand. Our results show that a relatively inexpensive and effective tourism-management strategy may be to post such volunteers as observers at sites where tourists view wildlife.

Food Habits of Harbor Seals (Phoca vitulina) in Two Estuaries in the Central Salish Sea

This study describes the seasonal diet composition of the Pacific harbor seal (Phoca vitulina) in two estuaries, Padilla Bay and Drayton Harbor, in the central Salish Sea. Prey remains were recovered from harbor seal fecal samples (scats) collected at haul-out sites during spring and summer/ fall in 2006. Top prey taxa (≥ 25% frequency of occurrence) were compared between seasons, estuaries, and between estuarine and non-estuarine haul-out sites. Overall, prey from at least 26 taxonomic families were identified in 198 harbor seal scats. In Padilla Bay, the most common prey were gunnel (family Pholidae; 88.6%), snake prickleback (Lumpenus sagitta; 59.1%), Pacific staghorn sculpin (Leptocottus armatus; 50.0%), and shiner perch (Cymatogaster aggregata; 47.7%). Threespine stickleback (Gasterosteus aculeatus; 95.5%) and Pacific herring (Clupea pallasi; 83.1%) were the most frequently consumed species in Drayton Harbor; shiner perch, snake prickleback, mammal, and Pacific staghorn sculpin also each occurred in ≥ 50% of samples from at least one season. Occurrences of top prey taxa varied by season, estuary, and habitat type. Diet composition suggests that harbor seals in Padilla Bay and Drayton Harbor foraged primarily within estuarine habitats such as those found near the haul-out sites. Temporal and spatial variations in diet appeared to reflect differences in the availability of prey taxa. This study also identifies mammals as a potentially novel prey item for harbor seals in Drayton Harbor.

Nocturnal Haul-Out Patterns of Harbor Seals (Phoca vitulina) Related to Airborne Noise Levels in Bellingham, Washington, USA

Given their distribution, harbor seals (Phoca vitulina) are likely to interact with human activities and potentially be disturbed. However, it is unclear how human development affects the haul-out behavior of harbor seals near urban areas. Because disturbance related to human development may increase noise levels in air, one might expect seals to haul-out at times when airborne noise levels are low. This study examined the number of harbor seals hauled-out relative to time of day, noise levels in air, and tide level at two haul-out sites in the city of Bellingham, Washington, USA. Harbor seals were observed from May 2008 to April 2009. Two surveys were conducted every 1 to 2 wks—one during the day and one at night. Harbor seal counts and in-air noise levels were recorded approximately 100 m from each haulout site with binoculars and a sound level meter, respectively. Given the strong correlation between time of day and noise levels, one set of linear mixed effects models examined the interactive influence of time of day and tide level on harbor seal numbers. Another set of models examined the effect of noise level and tide level on harbor seal numbers. Despite fluctuations in harbor seal numbers in relation to time of year and haul-out site, more harbor seals hauled-out during the night than during the day. The best model for the number of harbor seals hauled-out included an interaction between time of day and tide level, and an interaction between noise level and tide level. This study indicated that numbers of harbor seals hauling-out in Bellingham were correlated with time of day and in-air noise levels. However, it is unclear if the nocturnal haul-out behavior of harbor seals was a consequence of human development. It is still possible that an unknown factor associated with time of day was responsible for the observed results. To tease out the correlation between time of day and in-air noise levels, a future comparative study between nearby haul-out sites—one close to human activities and one away from them—is recommended.