The Read Lab has several abstracts accepted for poster or spoken presentation at the upcoming 19th Biennial Conference on the Biology of Marine Mammals (November 28 to December 2, 2011 in Tampa, Florida). The theme of the conference is “Cumulative effects of threats to marine mammals: Challenges to animals, scientists, and managers.” The following abstracts have been accepted for poster or spoken presentations by Read Lab members and collaborators:
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The influence of variation in voltage-gated sodium channel genes on susceptibility of bottlenose dolphins to harmful algal blooms
Cammen, Kristina; Rosel, Patty; Wells, Randall; Read, Andrew
Harmful algal blooms of Karenia brevis frequently impact populations of bottlenose dolphins (Tursiops truncatus) in the eastern Gulf of Mexico. Interestingly, populations of dolphins appear to differ in their susceptibility to mortality associated with K. brevis as a result of their historical frequency of exposure. Harmful algal blooms occur almost annually along central-west Florida, but dolphin mortality from brevetoxin exposure, at least in Sarasota Bay, appears to be reduced as compared to other areas. In contrast, blooms are less frequent in the Florida Panhandle, where three bottlenose dolphin unusual mortality events since 1999 have been associated with K. brevis. Bottlenose dolphins in central-west Florida may have evolved resistance to brevetoxins over time while dolphins in the Florida Panhandle remain relatively naïve and susceptible. The objective of the present study is to investigate a potential genetic basis for this difference in susceptibility. Using a candidate gene approach and direct sequencing, we evaluated genetic variation at the biological binding site of brevetoxins within the voltage-gated sodium channels in skin samples collected from both live and stranded bottlenose dolphins in central-west Florida and the Florida Panhandle. Previous research in other systems identified mutations in sodium channel genes that greatly increase neurotoxin resistance. We found multiple variable regions within the bottlenose dolphin sodium channel genes, allowing us to compare sodium channel gene variants between dolphins from the Florida Panhandle and central-west Florida and, within each population, between dolphins that died due to brevetoxin exposure and those that survived the blooms. Variation in the sodium channel genes, a primarily conserved coding region of the genome, may be explained by differences in a neurotoxin selective pressure such as brevetoxin exposure. Our work attempts to identify genetic biomarkers of susceptibility to brevetoxins in bottlenose dolphins and determine the species’ potential for evolutionary adaptation to harmful algal blooms.
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Body orientation of foraging short finned pilot whales off Cape Hatteras, North Carolina, USA
Crain, Danielle; Ebert, Erik; Friedlaender, Ari; Johnston, David; Read, Andrew; Roberts, Bethany; Urian, Kim; Waples, Danielle; Nowacek, Douglas
Little is known of mechanisms of capture in wild odontocete cetaceans due to the difficulty in observing foraging behavior in the wild. However, digital acoustic tags (DTags) provide detailed information about the body orientation of free-ranging marine mammals, in addition to acoustic records of social and foraging sounds. We examined changes in body orientation of 11 short-finned pilot whales, Globicephala macrorhynchus, tagged with DTags off Cape Hatteras, North Carolina, in the summer of 2010. Seven of these whales produced echolocation buzzes during dives, indicating foraging attempts. We measured body orientation with three parameters: heading, pitch, and roll. Whales can swim on their sides and upside down, so we combined heading and pitch to form a ‘pointing angle.’ Pilot whales changed their body orientation at a higher rate during echolocation buzzes than during control periods before and after the buzzes. These observations are similar to those described for sperm whales by Miller et al (2004). In addition, pilot whales increased the change in their pointing angle and roll starting about 10 seconds before the end of the buzz, and returned to their baseline behavior a few seconds after the end of the buzz. Average buzz duration was 2.05 ± 1.51 seconds; however, buzz duration seems to have little effect on rate of change in pointing angle and roll. Finally, despite variation in depth of foraging, there was no significant difference in change of body orientation, suggesting that prey items at all depths require similar patterns in maneuverability. This information provides unique insights into the mechanism of prey capture and associated body orientation in pilot whales foraging at depth in a three-dimensional environment.
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Quantitative assessment of habitat use of Antillean Manatees in Caño Estero Hondo, Dominican Republic
Domínguez Tejo, Haydée María; Rivas, Diego Valentin
This study represents the first year-round site-specific analysis of manatee habitat use in the Dominican Republic. Field work was conducted from 2007-2008 at Caño Estero Hondo, a lagoon on the northwest coast, in an area where no prior information existed on habitat characteristics or patterns of manatee habitat use. Information was gathered via interviews with local residents (n=138), and boat-based 30 minute point-scans (n=183) at 22 stations in 6 zones. Generalized linear models and simulations were used to relate manatee presence to habitat variables, excluding opportunistic sightings. The area was characterized by shallow (x=1.99±1.27 m), warm waters (x=30.3±1.4˚C), abundant seagrass and little human disturbance. A total of 270 hours of effort resulted in 103 sightings: 27 during point-scans plus 76 opportunistic records. Manatees (adults, calves, possibly twins) were present throughout the year, and multiple behaviors were observed. Sighting probability did not vary with season; manatees were present even during the dry season (June-September), when surface salinity and temperature increased. Neither seagrass presence nor surface salinity (x=32±5‰) were significant predictors of manatee occurrence. Direct freshwater input from small creeks was confirmed in the field, but discharge volume was not quantified. Manatees may travel to nearby Bajabonico River to access freshwater. Statistically significant differences in depth, temperature and salinity were found inside versus outside the lagoon and across zones. However, sighting probabilities were spatially similar. As with temporal variation, spatial differences in habitat were small and unlikely to be of biological relevance to manatees. Notably, manatees were observed resting only at points inside the lagoon and primarily in the calm west arm of the lagoon. Our results indicate that Caño Estero Hondo is an important multi-use, year-round manatee activity center. Characterization of the seagrass beds, freshwater inputs and resting areas is needed to further understand manatee use of the study area.
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Occurrence and distribution of marine mammals in a proposed Undersea Warfare Training Range off Jacksonville, FL
Foley, Heather; Nilsson, Peter; Hardee, Rachel; Holt, Richard; McLellan, William; Pabst, D. Ann; Read, Andrew
The U.S. Navy has proposed establishing an Undersea Warfare Training Range (USWTR) in an area between 60 and 150 km off the coast of Jacksonville, Florida. To establish baseline information on the occurrence and distribution of marine mammals in this area we conducted aerial and shipboard line-transect surveys and a passive acoustic monitoring program. Here we report the results of aerial and shipboard line-transect surveys conducted between January 2009 and April 2011. During this period, we flew 42,895 km of aerial tracklines and recorded 477 sightings of ten cetacean species (n=5,736 individuals). Tursiops truncatus was encountered most commonly (202 sightings, n=1,699), followed by Stenella frontalis (184 sightings, n=3,213). Other species observed during aerial surveys include Grampus griseus (n=350), Globicephala macrorhynchus (n=174), Steno bredanensis (n=118), Balaenoptera acutorostrata (n=13), Eubalaena glacialis (n=3), Physeter macrocephalus (n=2), Kogia spp. (n=1), and Megaptera novaeangliae (n=1). In 35 vessel surveys totaling 2,486 km we encountered three cetacean species in 77 sightings (n=576). S. frontalis and T. truncatus were observed most often, followed by G. griseus (n=351, 160, and 43, respectively). T. truncatus was observed throughout the entire survey area, but S. frontalis and S. bredanensis were seen exclusively on the continental shelf. All E. glacialis sightings, including a rare observation of an offshore birth, occurred on the western edge of the survey area. All other species were detected only in pelagic waters. Stenella frontalis, T. truncatus, and G. griseus were observed throughout the year (12, 11, and 9 calendar months, respectively); G. macrorhynchus and S. bredanensis were detected from April to October, and all mysticete species were seen only between December and March. This monitoring program, combining a variety of survey modalities, is providing a rich picture of the cetacean fauna in these poorly studied offshore waters.
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Effects of Intrinsic and Extrinsic Factors on Fisheries Bycatch of Marine Mammals
McDonald, Sara Lynne; Lewison, Rebecca L.; Moore, Jeffrey; Read, Andrew J.; Crowder, Larry B.
Each year, hundreds of thousands of marine mammals are taken as bycatch in the world’s fisheries. Inconsistent reporting of fishing effort and limited information on bycatch rates in many areas of the world, however, hamper assessment of bycatch at regional and local scales. Using a classification tree (CART), we conducted a meta-analysis of over 1,500 articles describing marine mammal bycatch between 1990 and 2008 to examine correlations of extrinsic variables (e.g. fishing gear and region), intrinsic variables (e.g. life-history and behavior) and bycatch intensity of marine mammals. Bycatch intensity represents a ranked classification of bycatch per unit effort (BPUE) based on expert opinion. The CART model had 157 unique records and the following independent variables: body length, age at first reproduction, foraging depth, latitudinal distribution, geographic distance from shore, region of interaction, and type of fishing gear. The categorical response variable was bycatch intensity. The strongest predictors of marine mammal bycatch intensity were region and type of fishing gear. Consistent with previous reviews, we found that bycatch in gillnets is ubiquitous. Bycatch in gillnets is especially intense in the Mediterranean, Southwestern Atlantic, and North Pacific Oceans. High bycatches also occurred in longline fisheries in the Eastern Tropical Pacific and North Atlantic Oceans. Intrinsic factors, including demographic attributes, behavioral ecology, and life-history traits, were not significant predictors of bycatch, but provided fine-scale details about bycatch interactions. For example, porpoises appear to be particularly susceptible to bycatch in gillnets, while larger delphinids interact more frequently with longlines. Using these findings, managers can plan assessments and consider mitigation measures using data that are commonly available (i.e. fishing gear and location). Consistent collection of fishing effort and bycatch data, however, are required to strengthen our understanding of marine mammal bycatch across regions and gear types.
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Integrating observations of diving behavior and prey fields to study the foraging ecology of short-finned pilot whales
Read, Andrew; Crain, Danielle; Ebert, Erik; Friedlaender, Ari; Johnston, Dave; Roberts, Bethany; Urian, Kim; Waples, Danielle; Nowacek, Douglas
Relatively little is known of the foraging behavior of deep diving odontocetes, but new research tools are providing important glimpses into the lives of these animals. We studied the foraging ecology of short-finned pilot whales Globicephala macrorhynchus along the shelf break near Cape Hatteras, North Carolina in the summers of 2008 and 2010 by deploying digital acoustic tags. We also made synoptic measurements of the acoustic volume backscatter of potential prey using calibrated EK-60 echosounders (38 and 120 kHz) and described the physical environment using an ADCP and CTD. We deployed 15 tags on adult whales for periods from 0.5 to 18.1h, with a total recording time of over 113h (mean 7.6h per whale). The sex of whales was determined from skin biopsy samples. We defined dives as submergences greater than 20m and deep dives as those greater than 500m. The whales made 181 dives, including 35 deep dives to over 1,044m, with a mean of 2.01 dives per hour. Echolocation buzzes, representing prey capture attempts, occurred 7.1 times per dive and 14.3 times per hour. Whales made deep foraging dives during both day and night, but five individuals tracked overnight made prey capture attempts more frequently during day (25.3h-1) than at night (13.2h-1). Overall, whales foraged at depths where biomass and/or single targets (-70 dB < TS < -35 dB) were greatest, but not all foraging decisions (e.g. deep followed by shallow dives) were based on vertical variation in biomass. In general, our results indicate that these whales consume a large number of relatively small prey, rather than the capture of large prey reported from the Canary Islands. We believe that quantitative descriptions of the distribution of prey are critical to interpreting such differences in foraging behavior.
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The effects of DMSO preservation on stable isotope signatures of short-finned pilot whales (Globicephala macrorhynchus)
Waples, Danielle; Zelnio, Kevin; Koopman, Heather; Read, Andrew
Considerable uncertainty surrounds how we treat cetacean tissue for stable isotope analysis and, in particular, how sample preservation and treatment affect tissue stable carbon and nitrogen isotope values. To address these issues we collected biopsy skin samples from ten short-finned pilot whales (Globicephala macrorhynchus) off Cape Hatteras, North Carolina in 2008. Each of the ten pilot whale samples was sub-sampled, with one portion preserved in DMSO and the other portion frozen; all samples were later homogenized and analyzed by isotope mass spectrometry. We used paired t-tests to examine differences in the preservation treatments. There was a significant depletion in δ13C values in samples preserved in DMSO compared to frozen samples (p= 0.001), but there was no difference in δ 15N values (p= 0.105). To further address questions of sample preservation and treatment, in 2011 we designed a matched sample experiment to address the effects of lipid extraction on preservation effects on δ13C and δ 15N values of 10 stranded short-finned pilot whales. Each sample of skin was sub-sampled, with one portion preserved in DMSO and the other portion re-frozen. The samples remained in DMSO for a minimum of 60 days, after which all samples were freeze-dried and further sub-sampled, with half of each sample receiving no further treatment and the other half subjected to lipid extraction. All samples were homogenized and analyzed by isotope mass spectrometry. Analysis of these results is in progress at the time of writing. We hope that these analyses will help provide insight into the effects of sample preservation and treatment on stable isotope analysis of cetacean tissues.
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