Most humpback whale Megaptera novaeangliae populations partition their time between prey-rich feeding and prey-deficient breeding/calving regions. How these whales feed and optimize the consumption of prey resources prior to long-distance migrations and fasting is largely unknown. We deployed multi-sensor tags on humpback whales around the western Antarctic Peninsula to describe their daily activity patterns late in the feeding season to test the hypothesis that feeding behavior varies over the diel cycle so as to maximize energy intake and limit energy expenditure. Dives were assigned to a behavioral state (feeding, resting, traveling, exploring) to determine hourly rates and to build an ethogram of activity patterns. Our results show a distinct diel pattern of whales feeding exclusively at night. Feeding depth was deeper around sunrise/sunset and shallower (~50 m) at night, consistent with diel vertical prey movement. Shallow feeding dives typically contained a single feeding lunge, a strategy known to increase feeding efficiency and maximize intake rates by maintaining proximity to the surface and reducing the energetic costs of deep diving. The lack of feeding during daytime may indicate prey being too deep for efficient foraging. Our results add information where currently there is a paucity of data describing how baleen whales optimize feeding behavior, specifically in relation to prey distribution and movement, to fuel their extraordinary energetic requirements necessary for growth, migration, and reproduction. Understanding behavioral patterns and predator/prey dynamics in rapidly changing marine environments, like the Antarctic Peninsula, is critical for understanding how these changes will affect ecosystem structure and function.
Nonlinear phenomena or nonlinearities in animal vocalizations include features such as subharmonics, deterministic chaos, biphonation, and frequency jumps that until recently were generally ignored in acoustic analyses. Recent documentation of these phenomena in several species suggests that they may play a communicative role, though the exact function is still under investigation. Here, qualitative descriptions and quantitative analyses of nonlinearities in the vocalizations of killer whales (Orcinus orca) and North Atlantic right whales (Eubalaena glacialis) are provided. All four nonlinear features were present in both species, with at least one feature occurring in 92.4% of killer and 65.7% of right whale vocalizations analyzed. Occurrence of biphonation varied the most between species, being present in 89.0% of killer whale vocalizations and only 20.4% of right whale vocalizations. Because deterministic chaos is qualitatively and quantitatively different than random or Gaussian noise, a program (TISEAN) designed specifically to identify deterministic chaos to confirm the presence of this nonlinearity was used. All segments tested in this software indicate that both species do indeed exhibit deterministic chaos. The results of this study provide confirmation that such features are common in the vocalizations of cetacean species and lay the groundwork for future studies.
A capture-recapture survey of bottlenose dolphins (Tursiops truncatus) was conducted in the sounds, estuaries and near-shore waters of North Carolina during July 2006, using photographic identification techniques; 291 dolphins were identified from distinctive nicks and notches on their dorsal fins. The results of our photographic analyses were applied to several capture-recapture models. The best estimate of the number of bottlenose dolphins present in estuarine waters of North Carolina during July 2006 was 813 with a 95% Confidence Interval of 483–1,142. Previously in July 2000, 1,033 (95% CI: 860-1,266) dolphins were estimated to be present in the estuaries of North Carolina. When the analysis from the 2006 surveys was expanded to include adjacent coastal waters, then the estimate of abundance increased to 1,138. Therefore, the abundance of dolphins in this area remained relatively stable between the two studies. Most dolphins were found in the northern part of the study area and there was very little exchange between the northern and southern areas of the state. The recapture data was also used to identify a spatial boundary between two putative management units that may be useful for future stock delineations. Additionally, an unexpected potential bias was introduced with the transition from slide film to digital media in the evaluation of the distinctiveness scoring.
Air-breathing marine animals face a complex set of physical challenges associated with diving that affect the decisions of how to optimize feeding. Baleen whales (Mysticeti) have evolved bulk-filter feeding mechanisms to efficiently feed on dense prey patches. Baleen whales are central place foragers where oxygen at the surface represents the central place and depth acts as the distance to prey. Although hypothesized that baleen whales will target the densest prey patches anywhere in the water column, how depth and density interact to influence foraging behaviour is poorly understood. We used multi-sensor archival tags and active acoustics to quantify Antarctic humpback whale foraging behaviour relative to prey. Our analyses reveal multi-stage foraging decisions driven by both krill depth and density. During daylight hours when whales did not feed, krill were found in deep high-density patches. As krill migrated vertically into larger and less dense patches near the surface, whales began to forage. During foraging bouts, we found that feeding rates (number of feeding lunges per hour) were greatest when prey was shallowest, and feeding rates decreased with increasing dive depth. This strategy is consistent with previous models of how air-breathing diving animals optimize foraging efficiency. Thus, humpback whales forage mainly when prey is more broadly distributed and shallower, presumably to minimize diving and searching costs and to increase feeding rates overall and thus foraging efficiency. Using direct measurements of feeding behaviour from animal-borne tags and prey availability from echosounders, our study demonstrates a multi-stage foraging process in a central place forager that we suggest acts to optimize overall efficiency by maximizing net energy gain over time. These data reveal a previously unrecognized level of complexity in predator–prey interactions and underscores the need to simultaneously measure prey distribution in marine central place forager studies.
Previously, all inferences regarding fine-scale baleen whale mother−calf relationships have come from surface observations, aerial surveys, or underwater video recordings. On May 19, 2010, we attached high-resolution digital acoustic recording tags (Dtags) to an adult female humpback whale Megaptera novaeangliae and her calf in Wilhelmina Bay (Western Antarctic Peninsula) to examine their concurrent diving and foraging behaviour. The Dtags logged ~20 h of concurrent recordings. We used cross-correlation analyses to quantify synchrony between the pair. Dive depth was positively correlated for the duration of the concurrent record and was highest when the calf's track lagged behind the mother's by 4.5 s, suggesting that the calf was 'following' its mother. Pitch and heading were positively correlated but to a lesser degree. Both animals executed feeding lunges; however, the mother foraged more intensively than the calf (792 and 118 lunges over 246 and 30 feeding dives, respectively). Also, the mother fed consistently once she initiated feeding at 16:22:00 h until the tag came off, whereas the calf executed 95.76% of its lunges between 17:00:08 and 19:28:21 h, local time. Correlation coefficients calculated per dive were highest when both animals were feeding and lowest when only the mother was feeding. In addition, 84.26 and 79.63% of the calf's lunges were performed within ± 20 s and ± 20 m of its mother's lunges, respectively. Our work describes the first record of a long-term continuous underwater relationship and foraging behaviour of a humpback mother−calf pair.
We examined bottlenose dolphin Tursiops truncatus community structure and abundance in the northeast Gulf of Mexico coastal waters stretching from St. Vincent Sound to Alligator Harbor, Florida, USA. Photographic-identification surveys were conducted between May 2004 and October 2006 to gain an understanding of dolphin distribution in this region. Dolphins were distributed year-round throughout the region; however, individual sighting records indicate that 2 parapatric dolphin communities exist. We conducted mark-recapture surveys using photographic-identification techniques to estimate the abundance of dolphins inhabiting the 2 areas these communities reside in: St. Vincent Sound/Apalachicola Bay, western; and St. George Sound/ Alligator Harbor, eastern. Sighting records of individual dolphins from 2004 to 2008 support the existence of 2 communities in these areas; only 3.5% of distinctive dolphins photographed were seen in both western and eastern areas. The 2 communities differ in their structure: the eastern area supports a more transient population with 45.7% of distinctive dolphins photo graphed only once compared with 28.3% in the west. Independent estimates of abundance (N, 95% CI = [low, high]) were calculated using the Chapman modification of the Lincoln-Petersen method for June 2007 and for January and February 2008 for the eastern area (242 [141−343], 395 [273−516]) and for the western survey area (197 [130−264], 111 [71−150]), respectively. Our results serve as a baseline that can be used by the US National Marine Fisheries Service to manage bottlenose dolphins in this region.KEY WORDS: Bottlenose dolphin · Photographic identification · Mark-recapture · Community structure · Abundance Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 438: [253][254][255][256][257][258][259][260][261][262][263][264][265] 2011 Bay, Florida ( Photo-identification (photo-ID) methods, which rely on obtaining a photograph of an individual dolphin's natural markings (such as nicks, notches, and/or scars found along the dorsal fin or peduncle), are widely used in the study of bottlenose dolphins. These natural markings are considered to be longlasting, and they have been used successfully to identify individuals and track them over time (Hammond 1990, Wilson et al. 1999. Using photo-ID methods, researchers have found that bottlenose dolphins are distributed relatively continuously in most parts of their range, although within this continuum range boundaries and discrete communities (i.e. resident dolphins that regularly share large portions of their ranges, exhibit similar distinct genetic profiles, and interact with each other to a much greater extent than with dolphins in adjacent waters; Wells et al. 1987) have been defined (Shane 1980, Irvine et al. 1981, Wells 1986, 1991, Wells et al. 1987, Hansen 1990, Shane 1990, Rossbach & Herzing 1999, Chilvers & Corkeron 2003, Lusseau et al. 2005, Fazioli et al. 2006, Balmer et al. 2008, Urian et al. 2009, 2004, and 2005/2...
Two groups of common bottlenose dolphins (Tursiops truncatus) have been identified within St. George Sound, Florida, USA: high site-fidelity individuals (HSF) which are individuals sighted multiple times in the region (i.e., ≥2 months, ≥2 seasons, and ≥2 years), and low site-fidelity individuals (LSF), which are individuals sighted fewer than 2 months, in 2 different seasons among 2 different years. Our goal was to determine whether differences in foraging behaviors were correlated with differences in sighting frequency and overall usage of St. George Sound by the two groups. We used carbon, nitrogen, and sulfur stable isotopes and niche hypervolume metrics to model the foodweb of St. George Sound. Mixing model results indicated that croaker, mojarra, pigfish, pinfish, and silverperch were the most important prey items for dolphins. The hypervolume metrics demonstrate niche partitioning between HSFs and LSFs, with the HSFs relying more heavily on pinfish, pigfish, and mojarra, while the LSFs relied more on silverperch. Plankton, benthic diatoms, seagrass, and epiphytes all contributed to secondary production within St. George Sound. This diversity of source utilization by seagrass-associated consumers supported by a high rate of total production likely sustains high secondary productivity despite the potential for competition in this system. Zooplankton was the most important basal source to the system, followed by seagrass and benthic primary production (as indicated by a sanddollar proxy). The reliance of dolphins on seagrass-dependent prey indicates that alteration of seagrass habitat would significantly impact the dolphin community foraging in St. George Sound and suggests that preservation of seagrass habitat is an important component of an effective management strategy for dolphin populations in the region.
Antarctica bio-logging foraging behaviour humpback whale optimal foraging theory Optimal foraging theory (OFT) suggests that air-breathing diving animals should minimize costs associated with feeding under water (e.g. travel time, oxygen loss) while simultaneously maximizing benefits gained from doing so (e.g. foraging time, energy gain). Humpback whales, Megaptera novaeangliae, foraging along the Western Antarctic Peninsula appear to forage according to OFT, but the direct costs and benefits in terms of their behaviours (e.g. allocation of time) have not been examined. We compared the foraging behaviour of humpback whales in this region inferred from multisensor high-resolution recording tags to their behaviour predicted by OFT time allocation models assuming the following currencies were being maximized: (1) the proportion of time spent foraging, (2) the net rate of energetic gain and/or (3) the ratio of energy gained to energy expended (i.e. efficiency). Model predictions for all three currencies were similar, suggesting any of these OFT models were suitable for comparison with the observed data. However, agreement between observed and optimal behaviours varied widely depending on the physiological and behavioural values used to derive optimal predictions, highlighting the need for an improved understanding of cetacean physiology. Despite this, many of the theoretical OFT predictions were supported: shallow dives (i.e. <100 m), which were short and executed most frequently, yielded the highest proportions of foraging time, and the greatest net rates of energy gain and were the most efficient. In addition, dive and foraging times increased in duration rapidly with increasing maximum dive depths to approximately 100 m and then at lower rates with deeper dives. Our findings offer a thorough examination of the applicability of time allocation OFT models to the behaviours of a large, air-breathing, diving predator and provide insights into the foraging ecology and physiology of humpback whales in the Western Antarctic Peninsula.
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