Environmental drivers of habitat use by common bottlenose dolphins (Tursiops truncatus) in the Indian River Lagoon, Florida, USA
Rachael Greller, Marilyn Mazzoli, Elizabeth Titcomb, Brandy Nelson, Richard Paperno, Scott H. Markwith
Human impacts in estuaries can influence the habitat use, health, and continued presence of marine mammals. Our objective was to examine the influences of variability in environmental factors and prey availability in 2003-2015 on habitat use of bottlenose dolphins living in Indian River Lagoon (IRL), Florida. We utilized photo-identification surveys to calculate dolphin density across the IRL in wet and dry seasons each year, and sampled prey and environmental factors monthly. Dolphin density was influenced by salinity and dissolved oxygen levels, which are associated with freshwater discharges of nutrient and algae laden waters from the region’s storm water management system.
A multidecadal Bayesian trend analysis of harbor porpoise (Phocoena phocoena) populations off California relative to past fishery bycatch
Karin A. Forney, Jeffrey E. Moore, Jay Barlow, James V. Carretta, Scott R. Benson
Bycatch – or accidental death in fishing gear – has affected dolphins and porpoises in many coastal regions worldwide. Off California, three harbor porpoise populations experienced substantial bycatch in nearshore gillnet fisheries during the 1970s-1980s. Our analysis of 1986-2017 aerial survey data reveals that all three populations are recovering after gillnets were eliminated. The southern-most Morro Bay population appears to have been affected to a much greater extent than previously recognized, growing from 570 porpoises to nearly 4,200 during our study. These results offer hope that other threatened dolphin and porpoise populations worldwide can also recover if bycatch is eliminated.
Age estimation and growth layer patterns in teeth of crabeater seals: A comparison of techniques
Julieta Cebuhar, Javier Negrete, Silvina Botta
Reading ages in teeth is a common technique that provides important information about ecological and life-history parameters. We applied and compared two techniques for age estimation in crabeater seals. We also evaluated the effects of cleaning teeth with H2O2 on GLG readings. Boiling with H2O2 affected cementum structure and thus resulted in underestimated ages, and must be avoided. Ages can be estimated regardless of which tooth/tissue or method is used for seals <13 years old. However, we recommend counting GLGs in the cementum of nontreated, stained thin sections of postcanine teeth for older animals.
Variation in trophic resources in female South American sea lions at a small geographic scale
M. Florencia Grandi, Damián G. Vales, Enrique A. Crespo, Rocío Loizaga
This study explores the isotopic niche of South American sea lion (SASL) females in the last period of the pregnancy from different colonies of northern Patagonia and considers whether the fine scale genetic spatial structuring is potentially related to variation in trophic resources. Differences among colonies revealed the plasticity of the species and support individual trophic specialization of SASL females at a small geographic scale. Also, significant differences were found between the north and south zones. Several hypotheses were proposed to explain the differences in SASL females’ isotope values (e.g., use of different foraging areas or prey, isotopic baseline variation).
Resting and swimming metabolic rates in juvenile walruses (Odobenus rosmarus)
David A. S. Rosen
Changes in Arctic ice conditions will likely impact the food requirements of walruses, but quantifying the effects requires accurate measures of the cost of different activities. This study measured the energy expended by two juvenile walruses while resting and while subsurface swimming. Energy expenditure was relatively low while the walruses were resting compared to other young pinnipeds. Energy expenditure doubled while swimming, and the costs of locomotion were generally higher than for other marine mammals, perhaps reflecting the fact that walruses are not pursuit predators. These estimates will be invaluable for quantifying the consequences environmental shifts of this unique species.
Abundance, survival, and annual rate of change of Cuvier’s beaked whales (Ziphius cavirostris) on a Navy sonar range
K. Alexandra Curtis, Erin A. Falcone, Gregory S. Schorr, Jeffrey E. Moore, David J. Moretti, Jay Barlow, Erin Keene
Cuvier’s beaked whales are sensitive to Navy sonar, yet a population of regularly occurring individuals uses a Navy training range off Southern California. We assessed the population growth rate, abundance, and survival of this group of animals with photo-identification data collected over 11 years. Our results support the existence of a small local resident population mixed with transients. We did not see evidence of a population decline, but our sample size remains limited and uncertainty high. Simulations of future sampling scenarios show that further monitoring and increased effort would substantially increase our ability to detect declines in the future.
Population‐level impacts of natural and anthropogenic causes‐of‐death for Hawaiian monk seals in the main Hawaiian Islands
Albert L. Harting, Michelle M. Barbieri, Jason D. Baker, Tracy A. Mercer, Thea C. Johanos, Stacie J. Robinson, Charles L. Littnan, Katie M. Colegrove, Dave S. Rotstein
The three causes-of-death that have had the greatest impact on monk seals in the Main Hawaiian Islands are human-caused trauma (clubbing, shooting, etc.), drowning in gillnets, and protozoal disease (nearly all cases involving toxoplasmosis). Researchers recently reviewed all of the known seal deaths that have occurred since 1992 to quantify both the frequency of deaths from each of 11 cause-of-death types, and also the age and sex of the affected seals. While many of the seals in the sample also died from natural causes, the impact of direct and indirect human-caused deaths is a major concern for monk seal recovery.
Sex ratios in blue whales from conception onward: effects of space, time, and body size
Trevor A. Branch and Cole C. Monnahan
Deviations from equal sex ratios can reveal insights into sex-specific growth, survival and movements. Blue whale sex ratios were examined from 311,901 whaling catches, including 21,542 fetuses. Males are slightly more common: 52.1% of catches and 51.3% of fetuses. Antarctic catches showed a shift from males to females in 1951, some evidence for higher male mortality before birth. Since females grow faster and longer, there were more males at intermediate lengths, and more females at the longest lengths. Overall, sex ratios are close to equality across time, space, and length; except for deviations from faster female growth and size-selective whaling.
Skin lesion prevalence of estuarine common bottlenose dolphins (Tursiops truncatus) in North Carolina, with comparisons to other east coast study sites
J. S. Taylor, L. B. Hart, J. Adams
Bottlenose dolphins are indicators of environmental health, and skin lesions can be used to infer population health. We estimated percentages of dolphins with lesions and characterized lesions on dolphins in Roanoke Sound, NC from April 2012-October 2014 using photo-identification. Dolphin percentages with lesions varied little between years, and most lesions were observed in spring. Pale lesions were most common. Annual lesion percentages were similar to published estimates for dolphins in Charleston, SC, Brunswick, GA, and Sarasota, FL, although varied seasonally. Future studies should examine relationships between lesions and environmental variables and use stranded dolphins to investigate skin lesion etiology.
The impact of temperature at depth on estimates of thermal habitat for short‐finned pilot whales
Stephanie K. Adamczak, William A. McLellan, Andrew J. Read, Christopher L. P. Wolfe, Lesley H. Thorne
Short-finned pilot whales forage at depths up to 1,500 m. While foraging, they experience a wide range of temperatures, yet most estimates of thermal habitat use only sea surface temperature (SST) measurements. We explored how temperature at depth influenced thermal habitat estimates for short-finned pilot whales in different seasons and at different latitudes along the northeastern US seaboard. To do this we used a metric, degree-hours, to calculate the time spent at different temperatures. We found the greatest difference between estimates of thermal habitat constructed using temperature at depth and SST when SST measurements greatly differed from bottom temperature measurements.
Distributional patterns of humpback whales (Megaptera novaeangliae) along the Newfoundland East Coast reflect their main prey, capelin (Mallotus villosus)
Kelsey F. Johnson and Gail K. Davoren
Humpback whales primarily consume capelin, a small forage fish, on their Newfoundland foraging ground. As capelin populations collapsed in the early 1990s, resulting in altered timing of spawning, we examined whether humpback whale movement/distribution match these prey changes. Combining citizen science and scientific monitoring, we found that northward coastal movements of whales were associated with the initial presence of spawning capelin. In one region, initiation of capelin spawning influenced the presence of whale aggregations and photo-identification revealed a 22% return rate to capelin spawning sites, indicating that these spawning sites are important foraging areas for humpback whales in coastal Newfoundland
Interannual differences in postrelease movements of rehabilitated harbor seal pups (Phoca vitulina richardii) in the Salish Sea
Samantha Sangster, Martin Haulena, Chad Nordstrom, Joseph K. Gaydos
We compared the movements of wild and rehabilitated harbor seals and the movements of harbor seals rehabilitated in different years. Rehabilitated pups travel farther daily and cumulatively than wild pups but transmission duration is similar suggesting similar survival. Movement patterns differed across years for rehabilitated seals suggesting that individual animal factors and local environmental pressures contribute to variability.
Recommendations for estimating mark rate of cetaceans in photo‐ID research: A critique of field sampling protocols and variance estimation
Lindsay Wickman, William Rayment, Elisabeth Slooten, Stephen M. Dawson
Estimating how many individuals are present in a population is a crucial, basic question when conserving a species. One way marine mammologists estimate population size is to photograph natural markings (e.g., nicks or scars on dolphins’ dorsal fins) to identify individuals. This method can be used to estimate population size, but it also requires an estimate of the proportion of the population that has these unique markings, or mark rate. In this study we investigate how to estimate mark rate as robustly as possible. By applying our recommendations for estimating mark rate, researchers can improve their final estimate of population size.
Developing protocols for in‐water morphometric measurements of cetaceans using stereo‐
Suzanne K. Hillcoat, Matthew I. Curnock, Naomi M. Gardiner, R. Alastair
Detailed knowledge of species’ body size and growth are imperative for successful conservation initiatives. Monitoring body condition can enable the detection of health declines ahead of significant mortality, thus potentially allowing time for a management response to prevent population decline. We trialed the use of a diver-operated stereo-video (SDOV) system for making body measurements of dwarf minke whales. We achieved significantly increased precision to previously used methods, which is desirable for monitoring growth rates and body condition. We also provide recommendations for field and analytical protocols, which may be applicable to other similarly-sized animals.
Common Bottlenose dolphins (Tursiops truncatus) in North Dalmatia, Croatia: Occurrence and demographic parameters
Grgur Pleslić, Nikolina Rako‐Gospić, Draško Holcer
The common bottlenose dolphin (Tursiops truncatus) population along the Croatian Adriatic coast is structured into discrete communities, yet many of them are unstudied. This study provides first insights into occurrence and demographic parameters of a community inhabiting the waters of North Dalmatia. Based on results, this area seems to host a mixture of resident and transient bottlenose dolphins, with the number of residents varying annually between 116 and 138 individuals. These results provide a baseline for informed management of two Sites of Community Importance, and a benchmark for future monitoring in North Dalmatian waters, an area under significant anthropogenic pressure.
Niche overlap and diet composition of three sympatric coastal dolphin species in the southwest Atlantic Ocean
Clarissa R. Teixeira, Silvina Botta, Fábio G. Daura‐Jorge, Luiza B. Pereira, Seth D. Newsome, Paulo C. Simões‐Lopes
We assess the feeding ecology of three coexisting dolphin species off southern Brazil using carbon and nitrogen stable isotopes collected from bone collagen. Specifically, we evaluated the contribution of prey sources to their diet, and temporal shifts in diet composition due to increased fishing pressure of their primary prey during the last three decades. Our results showed that the franciscana dolphin feeds mainly upon prey in the water column. In contrast, the Guiana and the Lahilles’s bottlenose dolphins feed primarily upon fish that live associated with the sea bottom and have been increasingly overexploited in southern Brazil.
Feeding ecology of the highly threatened common bottlenose dolphin of the Gulf of Ambracia, Greece, through stable isotope analysis
Asunción Borrell, Morgana Vighi, Tilen Genov, Ioannis Giovos, Joan Gonzalvo
The aim of this study was to determine the diet of bottlenose dolphins living in the Gulf of Ambracia (Greece) through the analyses of stable isotope analysis in 16 skin samples. Results suggested that the dolphin diet was based mainly on Atlantic horse mackerel, two species of sparids, and common cuttlefish, which represented together about 42% ± 15% of the biomass ingested, followed by clupeids and gobies (37% ± 17%). A better understanding of the feeding habits of these dolphins shows probable interactions with artisanal fisheries and is key for identifying adequate management measures consistent with an ecosystem-based approach.