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Surface temperature patterns in seals and sea lions: A validation of temporal and spatial consistency
Journal of Thermal Biology 35 (2010) 435–440
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Surface temperature patterns in seals and sea lions: A validation of temporal and spatial consistency Jeanette Nienaber a,b, Jamie Thomton a, Markus Horning c, Lori Polasek a,b, Jo-Ann Mellish a,b,n a
Alaska SeaLife Center, 301 Railway Avenue, Seward, AK 99664, USA School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775, USA c Department of Fisheries and Wildlife, Oregon State University, Marine Mammal Institute—Hatfield Marine Science Center, 2030 SE Marine Science Drive, Newport, OR 97365, USA b
a r t i c l e in fo
abstract
Article history: Received 8 April 2010 Accepted 20 September 2010
We assessed infrared thermography (IRT) as a tool for evaluating spatial and temporal surface temperature patterns in juvenile female harbor seals (Phoca vitulina, n ¼ 6) and adult female Steller sea lions (Eumetopias jubatus, n ¼ 2). Following a technical assessment of the influence of environmental parameters on the specific camera to be used, we identified regional and seasonal variability of surface temperatures. Variation was observed in several seasonal transitions (winter, reproductive, molt) in ten monitored body regions. Spatially and temporally consistent thermal patterns in the shoulder, axillae, foreflipper and hindflipper suggest thermal windows in both species. & 2010 Elsevier Ltd. All rights reserved.
Keywords: Thermoregulation Infrared thermography (IRT) Steller sea lions Harbor seals Eumetopias jubatus Phoca vitulina Thermal windows
Infrared thermography (IRT) is a non-invasive method increasingly used in veterinary and wildlife research applications as a diagnostic health tool (i.e., McCafferty, 2007; Spire et al., 1999; Eddy et al., 2001; Phillips and Heath, 2001; Dunbar and MacCarthy, 2006; Simon et al., 2006). In marine mammals, IRT has been applied to studies of heat flux (Williams et al., 1999; Willis and Horning, 2005), characterization of thermal windows (Cuyler et al., 1992; Mauck et al., 2003) and aerial surveys (Burn et al., 2006). Unfortunately, few IRT studies have the opportunity to perform a thorough validation of the method incorporating the capabilities of the particular equipment used and controlled conditions required to provide species-specific baseline surface heat patterns. Thermoregulation in pinnipeds has been used as a model for the understanding of how homeotherms function in mixed environments (e.g., aquatic and terrestrial, Bartholomew and Wilke, 1956; Irving et al., 1962). The physical processes of heat conduction, convection, radiation and evaporation influence an animal’s ability to maintain thermal homeostasis (Folkow and Mercer, 1986). Given that the thermal conductivity of water is 25 times higher than that of air (Bonner, 1984; Schmidt-Nielsen, 1997; Ryg et al., 1990; Rosen et al., 2007), pinnipeds require complex mechanisms to maintain a steady body temperature.
Passive heat loss occurs in areas of the body that have minimal insulation, such as the extremities or furless regions (Irving et al., 1962; Kvadsheim and Folkow, 1997), while active heat loss occurs in areas of vascularization (i.e., seal flippers; Bryden, 1978; Bryden and Molyneux, 1978; Molyneux and Bryden, 1978). However, even un-insulated extremities can conserve heat via counter-current heat exchangers (Scholander and Schevill, 1955). Fur and hair can also absorb or reflect solar radiation away from the skin surface (Cena and Monteith, 1976), although this effect is minimal in most pinnipeds. Thermal windows defined as sites of active heat management have been previously identified in marine mammals (Øritsland, 1968). These sites can be consistent in location (Noren et al., 1999; Meagher et al., 2002; Willis et al., 2005) or transient in nature (Mauck et al., 2003), but species-specific information is limited. Once the appropriate baselines are established, IRT has the potential to identify patterns of irregular heat loss, which may indicate infection, parasitism or inflammation. Due to the decline of harbor seals (mid-1970s) and endangered status of the western stock of Steller sea lions (1990) in Alaska, non-invasive tools for population monitoring are increasingly in demand. To help determine the viability of IRT as a potential diagnostic tool for these species, this study addressed four primary questions:
n Corresponding author at: Alaska SeaLife Center, 301 Railway Avenue, Seward, AK 99664, USA. Tel.: + 907 224 6324; fax: + 907 224 6320. E-mail address: [email protected] (J.-A. Mellish).
1. How does surface temperature of an object measured via IRT compare to the actual temperature of the object in a water bath as measured by a standard mercury thermometer?
1. Introduction
0306-4565/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jtherbio.2010.09.005
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2. What are the sensitivities of IRT-based surface temperature estimates to errors in parameters that are known to affect IRT (i.e., emissivity, relative humidity, ambient air temperature, reflected temperature and distance)? 3. How are seasonal baseline surface temperature variations as measured by IRT characterized in harbor seal and Steller sea lion body regions? 4. Can temporally and spatially consistent hot and cold spots be identified by IRT in harbor seals and Steller sea lions?
2. Materials and methods 2.1. Animals and equipment Six female juvenile Pacific harbor seals (Phoca vitulina) and two adult female Steller sea lions (Eumetopias jubatus) housed at the Alaska SeaLife Center (ASLC) in Seward, AK were the subjects for the year-long study. Six juvenile harbor seals, captured from central Prince William Sound and eastern Kenai Peninsula, AK, were brought to the ASLC as newly weaned pups in 2004 (PVAT, PVQI and PVSU) and 2005 (PVSH, PVSI and PVTI). The two adult female Steller sea lions, EJKI and EJSU were collected as pups from Maggott Island, Canada, in 1993. Due to a simultaneous long-term nutritional study, the harbor seals were on a lipid-regulated diet of either high fat Pacific herring (Clupea pallasii; PVAT, PVQI, PVSI) or low fat Atlantic herring (Clupea harengus; PVSU, PVSH, PVTI) mixed with pollock (Theragra chalcogramma), capelin (Mallotus villosus) and squid (Loligo opalescens) (L. Polasek, unpublished data). Steller sea lions were fed a daily diet of pollock and Pacific herring supplemented with pink salmon (Oncorhynchus gorbuscha) three days a week. All diets included a daily multivitamin dosage based on individual mass (Mazuri 5# Marine Mammal Tablet). In order to minimize error in data collection, only two investigators (JN, JT) collected thermal images during the yearlong study. All thermograms were taken with a FLIR P25 infrared camera (FLIR Systems, Danderyd, Sweden) using an uncooled focal plane array microbolometer sensor. The camera was factory calibrated to an absolute accuracy of 72 1C, with thermal sensitivity of o0.10 at 30 1C. Infrared images had a resolution of 320 240 pixels. Relative humidity (%) and atmospheric temperature (1C) were taken at each session with a Sper Scientific Ltd. #850070 Mini Environmental Quality Meter (Sper Scientific Ltd., Scottsdale, Arizona, USA), absolute accuracy of the parameters were 76% and 71.2 1C, respectively, while resolution was to the nearest 0.1 of a percentage point or degree. A standard mercury thermometer with an absolute accuracy of 72 1C and resolution to the nearest tenth of a degree, was used to collect the temperature of the control source (Comark USA, Beaverton, OR, USA). Habitat sea water temperature data were taken from daily husbandry staff records (Hach Model HQ30d, Hach Co., Loveland, CO, USA) with a resolution to the nearest tenth of a degree. Body
mass was collected on the day of the session by husbandry staff (Transcell Model TI-500-SL, Accurate Scales, Terre Haute, IN, USA) with a standard resolution of 5000 divisions available up to 50,000 divisions. Thermal image collection was attempted on at least two occasions per month per individual from February 2007 to February 2008. The number of samples for each individual varied from one to four images per month, and was dependent upon animal cooperation and concurrent research needs. The first image session per month was utilized for seasonal data analysis. Depending on the husbandry and research requirements of the captive animals, images were either taken indoors under artificial fluorescent lighting or in an outdoor exhibit under a concrete roof to minimize the effects of solar radiation. Indoor images were taken on either a concrete flooring covered with an epoxy coated paint or an aluminum surfacing. A typical session involved moving the animal approximately 15 m from a holding area to a working area for image collection. For standardization purposes, all thermograms were taken of wet animals, within 5–10 min of being trained to haul out. Animals were behaviorally controlled to station and moved between images while the thermographer stood in a fixed position. Eight images were taken per animal per session: right and left lateral, high and low anterior, high and low posterior, ventral and a reference image. Right and left lateral, low anterior and posterior, and ventral images were taken at an approximate 901 angle between camera lens and animal. High anterior and posterior images were taken at an approximate 451 angle between camera lens and animal. The reflected temperature image, used to account for the radiation reflecting at the object along the same angle plane, was taken at a 1801 angle from the animal. Distance between animal and camera was set such that the animal would fill the frame of the picture from tip of tail to tip of nose. Images were taken in gray color palette for ease of focus and increased contrast. The total session time was approximately 10 min per animal. No anesthesia or sedation was required.
2.2. Validation of IRT Initial validation of the accuracy of the equipment used required two objects of known, but different emissivity (e). A glass jar filled with water (e ¼0.92) and a stomach temperature radio transmitter pill made of epoxy (e ¼0.84) were placed in a temperature controlled water bath (accuracy of 70.5 1C, VWR International, Inc., West Chester, PA, USA), for measurement at 5 1C temperature increments over a range of 0–30 1C. Once stabilized at each temperature, the object was temporarily removed from the water to allow for IRT image collection. A secondary assessment utilized software manipulations of environmental parameters (emissivity, reflected temperature, ambient air temperature, distance and relative humidity) to determine influence on calculated surface temperature. Each parameter was manipulated individually (with all other parameters constant) within the software on a single image (Table 1).
Table 1 Effect of manual parameter modification within the software analysis of infrared images of a reference surface temperature in a harbor seal (PVQI, 8.9 1C) and a Steller sea lion (EJSU, 12.1 1C). Each parameter was adjusted by 7 10% with all other parameters held constant. Parameter
PVQI (8.91C) standard setting
10% output
+ 10% output
EJSU (12.11C) standard setting
10% output
+ 10% output
Emissivity Relative humidity (%) Distance (m) Ambient air temperature (1C) Reflected temperature (1C)
0.98 62.6 3.0 19.6 10.6
8.9 8.9 8.9 9.0 9.0
9.0 8.9 8.9 8.9 8.9
0.98 62.9 7.6 19.7 15.6
12.0 12.1 12.1 12.2 12.1
12.2 12.1 12.1 12.1 12.1
J. Nienaber et al. / Journal of Thermal Biology 35 (2010) 435–440
Emissivity was adjusted by 70.02, as this is the common range of values used in living skin tissue studies (0.95–0.99; Best and Fowler, 1981; Speakman and Ward, 1998). All other parameters were modulated by 710%.
2.3. Surface temperature patterns All images were analyzed with FLIR ThermaCam Researcher Pro 2.8 SR-1 software (FLIR Systems, Danderyd, Sweden) in a rainbow color palette. Software corrected parameters included emissivity, relative humidity, ambient air temperature, reflected temperature and distance. One harbor seal (PVQI) and one sea lion (EJSU) image set was chosen at random to compare symmetry in surface temperature patterns among the eight image angles. With the exception of biopsy and/or injection sites, thermal patterns were symmetrical and equally visible from all positions, therefore the right lateral image was chosen for the analysis presented. The aim of this study was not to determine absolute surface temperatures and the size of specific areas of interest, but instead to define the relative surface temperature variation by region and season. Regions were selected for analysis based on physical landmarks and utility (e.g., ability to image in the field), including: whole body, torso, head, eye, muzzle, shoulder, axillae, hip, fore and hind flippers (Fig. 1). Whole body, torso and head were a composite of multiple regions and therefore are expressed as mean values. To test the widest range of difference among regions of the body, maximum (hot) and minimum (cold) temperatures were utilized for the remaining regions.
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2.4. Data analysis Seasonal trends were tested utilizing winter (October–April), reproductive (May–July) and molt (August–Sepember), as per Pitcher (1986) and Mellish et al. (2007), although it is likely that the harbor seals had not yet reached sexual maturity (4–9 years; Pitcher and Calkins, 1979). To avoid unequal sample replication, all individuals were represented using the first data point of each month for annual analyses. To avoid bias due to unequal length of seasons, results were reduced to four consecutive image sessions per animal closest to the center date for each season. Calculations and statistical analyses were completed using SYSTAT 10 (SYSTAT Inc., Chicago, IL, USA) and plots using SigmaStat 3.5 (Systat Software, Inc., Germany). A simple regression was used to describe the relationship between the known object surface temperature as measured via IRT and as measured via a mercury thermometer. Pearson correlation was used to compare whole body and torso regions. The coefficient of variation (COV) was used to determine variability between body regions during the winter season only utilizing six consecutive image sets per individual. COV was not calculated for reproductive and molt seasons due to reduced availability of the appropriate number of sequential image sets. Seasonal changes in mass and regional skin surface variation were analyzed by Mann–Whitney U-test. Discrete hot and cold regions (e.g., excluding the composite whole body, torso and head) were identified using a Wilcoxon signed rank test, followed by a manual ranking of means. Data are presented as mean 7standard deviation (SD) unless otherwise stated. Significance was set at the 95% confidence interval.
3. Results
24.3°C 3.1. Technical parameters
5
4
1
2
20
6
7 3
10 8 9 10
IRT temperatures were directly related to the temperature measured by the mercury thermometer for the glass jar (IRTglass¼0.962 water T+ 0.641, r2 ¼0.993, po0.001) and the stomach pill (IRTpill¼0.894 water T+1.249, r2 ¼0.999, po0.001) (Fig. 2). The difference measured was within the absolute accuracy indicated for both measurement techniques (IRT and mercury
35 5.3°C
Jar Pill
30 19.2°C
4
2
7 6 3
10 8
15
9
Water (°C)
1
5
25 20 15 10 10
9.6°C
5 0 0
Fig. 1. Surface temperatures measured through infrared thermography on a juvenile female harbor seal (Phoca vitulina, top panel), an adult female Steller sea lion (Eumetopias jubatus, bottom panel). Regions measured included: (1) whole body, (2) torso, (3) foreflipper, (4) hindflipper, (5) hip, (6) shoulder, (7) axillae, (8) eye, (9) muzzle and (10) head.
5
15 10 20 25 IRT Surface Temperature (°C)
30
35
Fig. 2. Linear regression of surface temperature of two objects of differing emissivity (glass jar e ¼0.92, stomach pill e ¼0.84) measured via infrared thermography versus a standard mercury thermometer.
J. Nienaber et al. / Journal of Thermal Biology 35 (2010) 435–440
20 15 10 5
All regions except eye, muzzle and hindflipper demonstrated seasonal surface temperature variation between the winter and reproductive seasons in harbor seals (U ¼84.5–191.0, p o0.05).
Hindflipper
Foreflipper
Hip
Axillae
Shoulder
Eye
30 Winter Reproductive Molt
25 20 15 10 5
Hindflipper
Foreflipper
Hip
Axillae
Shoulder
Muzzle
Eye
Head
0 Body
3.4. Hot and cold regions
Harbor seal (n = 6)
Surface Temperature (°C)
Surface temperatures for each region over the year were averaged by species (Fig. 3). Whole body and torso surface temperatures in harbor seals were 10.271.2 1C and 10.0 71.2 1C, respectively. Steller sea lion surface temperatures were 10.570.7 1C for whole body and 10.370.6 1C for torso. Both regions were highly correlated in each individual over the year (harbor seals, r Z0.790; Steller sea lions, r Z0.996). Surface temperature variability differed by body region and with species. Data from the middle of the longest season (winter) showed that in harbor seals, the hindflipper varied the least (COV¼5.8), while the shoulder was the most variable (COV¼12.3). Similarly in sea lions, the hindflipper was the least variable (COV¼ 2.7), whereas the head was the most variable (COV¼8.3). Seasonal fluctuations in surface temperature by region are shown in Fig. 4.
Muzzle
3.3. Surface temperature trends
Head
0 Torso
Harbor seal mass overall averaged 32.3 76.5 kg, with seals lighter at molt (29.876.1 kg) and the heaviest in winter (33.776.5 kg). Significant mass transitions occurred between winter and reproductive (U ¼423.0, p¼ 0.005), and winter to molt (U¼437.5, p¼ 0.002). There was no significant change from reproductive to molt (U ¼265.0, p 40.05). Average mass in Steller sea lions did not vary seasonally (215.076.4 kg).
Winter Reproductive Molt
25
Torso
3.2. Changes in body mass
30
Body
thermometer), therefore IRT estimates used in this study were not subject to temperature correction. Manipulation of environmental parameters within the software program changed average surface temperature output of the body image as a whole by no more than 70.1 1C (Table 1).
Surface Temperature (°C)
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Steller sea lion (n = 2) Fig. 4. Seasonal surface temperature as measured by infrared thermography in captive harbor seals (Phoca vitulina, HS) and Steller sea lions (Eumetopias jubatus, SSL).
Surface Temperature (°C)
30 Harbor seal (n = 6)
25
Steller sea lion (n = 2) 20 15 10
Hindflipper
Foreflipper
Hip
Axillae
Shoulder
Muzzle
Eye
Head
Torso
0
Body
5
Fig. 3. Regional surface temperature as measured by infrared thermography in captive harbor seals (Phoca vitulina, HS) and Steller sea lions (Eumetopias jubatus, SSL) averaged over the twelve month study period. To demonstrate the maximum range of temperature profiles, mean values are shown for composite regions (whole body, torso, head), maximum values are shown for hot spots (eye, muzzle, shoulder, axillae, hip) and minimum values are shown for cold spots (foreflipper, hindflipper).
Between reproductive and molt periods, only the muzzle changed significantly (U¼ 175.0, p ¼0.02). Between molt and winter, all regions varied (U ¼65.5–122.0, po0.001), except for the eye. Overall, the maximum temperature was in the eye (24.271.2 1C), and the minimum temperature was in the hindflipper (6.670.7 1C). Seasonal effects in Steller sea lions were less pronounced, with significant differences occurring only in the torso, shoulder, hip and foreflipper between the winter and reproductive seasons (U ¼8.5–12.0, po0.03). There were no regional temperature variations between reproductive and molt, and only the shoulder differed between molt and winter (U ¼13.0, po0.05). Similar to harbor seals, overall maximum temperatures were measured in the eye (25.170.3 1C); however, the minimum temperatures were recorded in the foreflipper (7.970.0 1C). Independent body regions (e.g., excluding the composite whole body, torso and head) were manually ranked within each season to determine whether hot and cold spots were consistent across seasons (Table 2). While there was a small amount of variation between seasons and species, the eye and muzzle were consistently the two hottest spots with and the foreflipper and hindflipper the two coldest spots.
J. Nienaber et al. / Journal of Thermal Biology 35 (2010) 435–440
Table 2 Manual rank (1¼ hot, 7 ¼cold) of mean surface temperatures as measured by infrared thermography in captive harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus). Significant differences between one column and the subsequent season (winter–reproductive–molt–winter) as identified by multiple runs of Mann–Whitney tests are noted. Harbor seal (n ¼6)
Steller sea lion (n ¼2)
Rank
Winter
Reproductive Molt Winter Reproductive Molt
1—Hot 2 3 4 5 6 7—Cold
Eye (E) Muzzle (M) Axillae (A)** Shoulder (S)*** Hip (H)*** Foreflipper (FF)** Hindflipper (HF)
E M* S H A FF HF
n
E M*** A*** S*** H*** FF*** HF***
M E A S* H HF* FF*
E M S H A HF FF
E M A S* H HF FF
p o 0.05. p o0.01 p o0.001.
nn
nnn
4. Discussion 4.1. Technical validation and field application Five environmental parameters are necessary for accurate IRT based surface temperature estimates: emissivity, relative humidity, ambient air temperature, reflected temperature and distance. In addition, one must also consider the curved nature of objects (i.e., glass jar, stomach pill, animal), which may result in incomplete and less accurate temperature imaging of the entire surface. It has been demonstrated (Ash et al., 1987) that peripheral surface temperatures of an isothermic balloon were 2–4 1C cooler than the perpendicular surface temperature from the camera lens to the object. As a result, it was concluded that the technique should be used to look at patterns of heat loss and not be used for absolute temperatures (Ash et al., 1987). While we demonstrated limited influence of environmental variables in our controlled setting with the ability to have the object filling the field of view (Table 2), field conditions with variable environmental parameters such as wind velocity (Moen and Jacobsen, 1974), and distance to the object may result in noise in the image collected. During field studies, data collection during similar weather conditions and consistent times of the day will help to minimize the error of environmental parameters (Ohman, 1981). This would be optimal for comparing physiological state of individuals (i.e., resting, foraging).
4.2. Biological parameters In the present study, thermograms of harbor seals and Steller sea lions were collected in air to determine patterns of surface temperature by season and region, with further definition of consistent hot and cold spots. At any given time, the surface temperature of an individual is determined by a combination of physiological (metabolic state), anatomical (insulation, vascularization) and environmental factors. In both species, temporal variations were most notable pre- and post-winter, but minimal variation was noted between the reproductive and molt periods. Higher surface temperatures were also noted between the reproductive and molt seasons and lowest during the winter. During the reproductive and molt seasons, seals and sea lions haul out of the water to facilitate pupping and promote circulation for new hair growth, activities which both require energy expenditure (Worthy, 2001). Insulation patterns (i.e., blubber depth) also
439
fluctuate similarly, thickest in the winter decreasing from reproductive to molt (harbor seals (Pitcher, 1986; Mellish et al., 2007), Steller sea lions (Mellish et al., 2007). In addition to monitoring overall patterns of surface temperature during an annual cycle, we specifically investigated the presence of consistent hot or cold spots for the identification of potential thermal windows (e.g., sites of active heat retention or dissipation; Table 2). The eye is consistently hot due to its uninsulated nature, and therefore cannot be considered a thermal window. However, eye temperature decreases with pain (Stewart et al., 2008), such that it may be a potential tool to reference physiological and/or metabolic state of the animal under very controlled conditions (e.g., long term captive animals). Similarly, high temperatures in the muzzle and hip are not likely due to active heat management. Instead, they are most likely a result of the high level of vascularization required to support a sensitive sensory tactile system (Dehnhardt et al., 1998), and a reduced blubber thickness (Willis et al., 2005; Mellish et al., 2007), respectively. However, our results suggest that the shoulder, axillae and flippers may be thermal windows. The extremities have been previously identified as areas likely to demonstrate the most day to day temperature fluctuation with changes in ambient air temperature (Cuyler et al., 1992; Choi et al., 1997). Prior attempts to identify thermal windows in pinnipeds in air have specifically looked at discrete areas visible via IRT in seals over the course of 2 h (Mauck et al., 2003). Within an individual session, no spatially or temporally consistent thermal windows were observed. The surface temperature of an animal tends to approach the temperature of the water when immersed (Hayward et al., 1981), though even small differences can result in a substantial heat exchange (Willis et al., 2005). There is evidence for spatially consistent heat flux patterns for swimming Steller sea lions (Willis et al., 2005). However, upon exit from the water, the surface of the animal will display varying patterns of heat dissipation and retention, mediated to some extent by physiological state and environmental conditions. Our study differed in design such that all animals were imaged in a similar state (e.g., within 5–10 min of hauling out). It should be taken into consideration at all times, however, that environmental factors such as evaporation, wind velocity or solar radiation, etc. may also lead to the appearance of inconsistent hot or cold areas. Blubber storage sites and tissue uniformity vary between harbor seals and Steller sea lions and may affect temporal variation seen in regional skin surface temperature. Harbor seal blubber is typically homogenous in both depth and composition, whereas Steller sea lion blubber includes interstitial tissue and varies in depth along the body (Mellish et al., 2007; Rosen and Renouf, 1997). Long-scale (i.e., seasonal) temporal skin temperature variations in regions were detected in both species, but were more prominent in harbor seals. Future study of the relationship between blubber depth and surface temperature would allow for a more precise interpretation of surface heat patterns and body condition in these species (i.e., anatomy versus physiological state).
Acknowledgements This research was conducted in partial fulfillment of the requirements for the degree of Master of Science at the University of Alaska, Fairbanks. All research was conducted under the ASLC’s Institutional Animal Care and Use Committee protocol no. 06-008 and the National Marine Fisheries Service’s (NMFS) permits 881-1745 and 881-1710. Funding was provided by the National Science Foundation (NSF) Major Research Instrumentation award #480431 (M. Horning and J. Mellish), NSF Polar Programs award
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#0440780 (J. Mellish and M. Horning), the Alaska SeaLife Center Transient Project #R2731 (J. Mellish), and the University of Alaska Fairbanks Thesis Fellowship Grant (J. Nienaber). We would like to thank the ASLC mammalogists B. Long, L. Hartman, E. DeCastro, H. Down, C. Phillips, and M. Peterson for their animal handling expertise, M. Castellini for his input on project and manuscript development, and A. Hindle and M. Keogh for comments on a prior version of this manuscript. J. Reese-Deyoe, G. Orlove, and J. Waldsmith, DVM, provided technological support. References Ash, C., Gotti, E., Haik, C., 1987. Thermography of the curved living skin surface. Miss. Med. 84, 702–708. Bartholomew, G., Wilke, F., 1956. Body temperature in the northern fur seal, Callorhinus ursinus. J. Mammal. 37, 327–337. Best, R., Fowler, R., 1981. Infrared emissivity and radiant surface temperatures of Canada and snow geese. J. Wildl. Manage. 45, 1026–1029. Bonner, W., 1984. Lactation strategies in pinnipeds: problems for a marine mammalian group. Symp. Zool. Soc. Lond 51, 253–272. Bryden, M., 1978. Arteriovenous anastomoses in the skin of seals. III. The harp seal Pacophilus groenlandicus and the hooded seal Cystophora cristata. Aquat. Mamm. 6, 67–75. Bryden, M., Molyneux, G., 1978. Arteriovenous anastomoses in the skin of seals. II. The California sea lion Zalophus californianus and the northern fur seal Callorhinus ursinus. Anat. Rec. 191, 253–260. Burn, D., Webber, M., Udevitz, M., 2006. Application of airborne thermal imagery to surveys of Pacific walrus. Wildl. Soc. Bull 34, 51–58. Cena, K., Monteith, J., 1976. Heat transfer through animal coats. Prog. Biometeorol. Div. B 1, 343–351. Choi, J., Miki, K., Sagawa, S., Shiraki, K., 1997. Evaluation of mean skin temperature formulas by infrared thermography. Int. J. Biometeorol. 41, 68–75. Cuyler, L., Wiulsrod, R., Øritsland, N., 1992. Thermal infrared radiation from free living whales. Mar. Mamm. Sci. 8, 120–134. Dehnhardt, G., Mauck, B., Hyvarinen, H., 1998. Ambient temperature does not affect the tactile sensitivity of mystacial vibrissae in harbor seals. J. Exp. Biol. 201, 3023–3029. Dunbar, M., MacCarthy, K., 2006. Use of infrared thermography to detect signs of rabies infection in raccoons (Procyon lotor). J. Zoo Wildl. Med. 37, 518–523. Eddy, A., Van Hoogmoed, L., Snyder, J., 2001. The role of thermography in the management of equine lameness. Vet. J. 162, 172–181. Folkow, L., Mercer, J., 1986. Partition of heat-loss in resting and exercising winterinsulated and summer-insulated reindeer. Am. J. Physiol. 251, R32–R40. Hayward, M., Keatinge, W., 1981. Roles of subcutaneous fat and thermoregulatory reflexes in determining ability to stabilize body-temperature in water. J. Physiol.-Lond 320 (1981), 229–251. Irving, L., Peyton, L., Bahn, C., Peterson, R., 1962. Regulation of temperature in fur seals. Physiol. Zool. 35, 275–284. Kvadsheim, P., Folkow, L., 1997. Blubber and flipper heat transfer in harp seals. Acta Physiol. Scand. 161, 385–395. Mauck, B., Bilgmann, K., Jones, D., Eysel, U., Dehnhardt, G., 2003. Thermal windows on the trunk of hauled-out seals: hot spots for thermoregulatory evaporation? J. Exp. Biol. 206 1727–1738. McCafferty, D., 2007. The value of infrared thermography for research on mammals: previous applications and future directions. Mamm. Rev. 37, 207–223.
Meagher, E., McLellan, W., Westgate, A., Wells, R., Frierson, D., Pabst, D., 2002. The relationship between heat flow and vasculature in the dorsal fin of wild bottlenose dolphins Tursiops truncatus. J. Exp. Biol. 205, 3475–3486. Mellish, J., Horning, M., York, A., 2007. Seasonal and spatial blubber depth changes in captive harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus). J. Mammal 88, 408–414. Moen, A., Jacobsen, F., 1974. Changes in radiant temperature of animal surfaces with wind and radiation. J. Wildl. Manage 38, 366–368. Molyneux, G., Bryden, M., 1978. Arteriovenous anastomoses in the skin of seals. I. The Weddell seal Leptonychotes weddelli and the elephant seal Mirounga leonina. Anat. Rec. 191, 239–252. Noren, D., Williams, T., Berry, P., Butler, E., 1999. Thermoregulation during swimming and diving in bottlenose dolphins, Tursiops truncatus. J. Comp. Physiol. B-Biochem. Syst. Env. Physiol. 169, 93–99. Ohman, C., 1981. Practical methods for improving thermal measurements. Proc. Soc. Ph.-Opt. Instr. Eng. 313, 204–212. Phillips, P., Heath, J., 2001. An infrared thermographic study of surface temperature in the euthermic woodchuck (Marmota monax). Comp. Biochem. Physiol. 129, 557–562. Pitcher, K., 1986. Variation in blubber thickness of harbor seals in southern Alaska. J. Wildl. Manage. 50, 463–466. Pitcher, K., Calkins, D.,1979. Biology of the harbor seal, Phoca vitulina richardsi, in the Gulf of Alaska. U.S. Department of Commerce (NOAA/OCSEAP), pp. 231–310. Rosen, D., Renouf, D., 1997. Seasonal changes in blubber distribution in Atlantic harbor seals: indications of thermodynamic considerations. Mar. Mamm. Sci 13, 229–240. Rosen, D., Winship, A., Hoopes, L., 2007. Thermal and digestive constraints to foraging behaviour in marine mammals Phil. Trans. R. Soc. Biol. Sci. 362, 2151–2168. Ryg, M., Lydersen, C., Markussen, N., Smith, T., Øritsland, N., 1990. Estimating the blubber content of phocid seals. Can. J. Fish. Aquat. Sci. 47, 1223–1227. Schmidt-Nielsen, K., 1997. Animal Physiology: Adaptation and environment, fifth ed. Cambridge University Press, Cambridge, U.K. Scholander, P., Schevill, W., 1955. Counter-current vascular heat exchange in the fins of whales. J. Appl. Physiol. 8, 279–282. Simon, E., Gaughan, E., Epp, T., Spire, M., 2006. Influence of exercise on thermographically determined surface temperatures of thoracic and pelvic limbs in horses. J. Am. Vet. Med. Ass. 229, 1940–1944. Speakman, J., Ward, S., 1998. Infrared thermography: principles and applications. Zool. Anal. Comp. Syst 101, 224–232. Spire, M., Drouillard, J., Galland, J., Sargeant, J., 1999. Use of infrared thermography to detect inflammation caused by contaminated growth promotant ear implants in cattle. J. Am. Vet. Med. Ass. 215, 1320–1324. Stewart, M., Stafford, K., Dowling, S., Schaefer, A., Webster, J., 2008. Eye temperature and heart rate variability of calves disbudded with or without local anaesthetic. Physiol. Behav. 93, 789–797. Williams, T., Noren, D., Berry, P., Estes, J., Allison, C., Kirtland, J., 1999. The diving physiology of bottlenose dolphins (Tursiops truncatus). III. Thermoregulation at depth. J. Exp. Biol. 202, 2763–2769. Willis, K., Horning, M., 2005. A novel approach to measuring heat flux in swimming animals. J. Exp. Mar. Biol. Ecol. 315, 147–162. Willis, K., Horning, M., Rosen, D., Trites, A., 2005. Spatial variation of heat flux in Steller sea lions: evidence for consistent avenues of heat exchange along the body trunk. J. Exp. Mar. Biol. Ecol 315, 163–175. Worthy, G., 2001. Nutrition and energetics. In: Dierauf, L., Gulland, F. (Eds.), CRC Handbook to Marine Mammal Medicine. CRC Press, New York, pp. 791–827. Øritsland, N., 1968. Variation in the body surface temperature of the harp seal. Acta Physiol. Scand 73, 35A–36A.
Contents lists available at ScienceDirect
Journal of Thermal Biology journal homepage: www.elsevier.com/locate/jtherbio
Surface temperature patterns in seals and sea lions: A validation of temporal and spatial consistency Jeanette Nienaber a,b, Jamie Thomton a, Markus Horning c, Lori Polasek a,b, Jo-Ann Mellish a,b,n a
Alaska SeaLife Center, 301 Railway Avenue, Seward, AK 99664, USA School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775, USA c Department of Fisheries and Wildlife, Oregon State University, Marine Mammal Institute—Hatfield Marine Science Center, 2030 SE Marine Science Drive, Newport, OR 97365, USA b
a r t i c l e in fo
abstract
Article history: Received 8 April 2010 Accepted 20 September 2010
We assessed infrared thermography (IRT) as a tool for evaluating spatial and temporal surface temperature patterns in juvenile female harbor seals (Phoca vitulina, n ¼ 6) and adult female Steller sea lions (Eumetopias jubatus, n ¼ 2). Following a technical assessment of the influence of environmental parameters on the specific camera to be used, we identified regional and seasonal variability of surface temperatures. Variation was observed in several seasonal transitions (winter, reproductive, molt) in ten monitored body regions. Spatially and temporally consistent thermal patterns in the shoulder, axillae, foreflipper and hindflipper suggest thermal windows in both species. & 2010 Elsevier Ltd. All rights reserved.
Keywords: Thermoregulation Infrared thermography (IRT) Steller sea lions Harbor seals Eumetopias jubatus Phoca vitulina Thermal windows
Infrared thermography (IRT) is a non-invasive method increasingly used in veterinary and wildlife research applications as a diagnostic health tool (i.e., McCafferty, 2007; Spire et al., 1999; Eddy et al., 2001; Phillips and Heath, 2001; Dunbar and MacCarthy, 2006; Simon et al., 2006). In marine mammals, IRT has been applied to studies of heat flux (Williams et al., 1999; Willis and Horning, 2005), characterization of thermal windows (Cuyler et al., 1992; Mauck et al., 2003) and aerial surveys (Burn et al., 2006). Unfortunately, few IRT studies have the opportunity to perform a thorough validation of the method incorporating the capabilities of the particular equipment used and controlled conditions required to provide species-specific baseline surface heat patterns. Thermoregulation in pinnipeds has been used as a model for the understanding of how homeotherms function in mixed environments (e.g., aquatic and terrestrial, Bartholomew and Wilke, 1956; Irving et al., 1962). The physical processes of heat conduction, convection, radiation and evaporation influence an animal’s ability to maintain thermal homeostasis (Folkow and Mercer, 1986). Given that the thermal conductivity of water is 25 times higher than that of air (Bonner, 1984; Schmidt-Nielsen, 1997; Ryg et al., 1990; Rosen et al., 2007), pinnipeds require complex mechanisms to maintain a steady body temperature.
Passive heat loss occurs in areas of the body that have minimal insulation, such as the extremities or furless regions (Irving et al., 1962; Kvadsheim and Folkow, 1997), while active heat loss occurs in areas of vascularization (i.e., seal flippers; Bryden, 1978; Bryden and Molyneux, 1978; Molyneux and Bryden, 1978). However, even un-insulated extremities can conserve heat via counter-current heat exchangers (Scholander and Schevill, 1955). Fur and hair can also absorb or reflect solar radiation away from the skin surface (Cena and Monteith, 1976), although this effect is minimal in most pinnipeds. Thermal windows defined as sites of active heat management have been previously identified in marine mammals (Øritsland, 1968). These sites can be consistent in location (Noren et al., 1999; Meagher et al., 2002; Willis et al., 2005) or transient in nature (Mauck et al., 2003), but species-specific information is limited. Once the appropriate baselines are established, IRT has the potential to identify patterns of irregular heat loss, which may indicate infection, parasitism or inflammation. Due to the decline of harbor seals (mid-1970s) and endangered status of the western stock of Steller sea lions (1990) in Alaska, non-invasive tools for population monitoring are increasingly in demand. To help determine the viability of IRT as a potential diagnostic tool for these species, this study addressed four primary questions:
n Corresponding author at: Alaska SeaLife Center, 301 Railway Avenue, Seward, AK 99664, USA. Tel.: + 907 224 6324; fax: + 907 224 6320. E-mail address: [email protected] (J.-A. Mellish).
1. How does surface temperature of an object measured via IRT compare to the actual temperature of the object in a water bath as measured by a standard mercury thermometer?
1. Introduction
0306-4565/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jtherbio.2010.09.005
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2. What are the sensitivities of IRT-based surface temperature estimates to errors in parameters that are known to affect IRT (i.e., emissivity, relative humidity, ambient air temperature, reflected temperature and distance)? 3. How are seasonal baseline surface temperature variations as measured by IRT characterized in harbor seal and Steller sea lion body regions? 4. Can temporally and spatially consistent hot and cold spots be identified by IRT in harbor seals and Steller sea lions?
2. Materials and methods 2.1. Animals and equipment Six female juvenile Pacific harbor seals (Phoca vitulina) and two adult female Steller sea lions (Eumetopias jubatus) housed at the Alaska SeaLife Center (ASLC) in Seward, AK were the subjects for the year-long study. Six juvenile harbor seals, captured from central Prince William Sound and eastern Kenai Peninsula, AK, were brought to the ASLC as newly weaned pups in 2004 (PVAT, PVQI and PVSU) and 2005 (PVSH, PVSI and PVTI). The two adult female Steller sea lions, EJKI and EJSU were collected as pups from Maggott Island, Canada, in 1993. Due to a simultaneous long-term nutritional study, the harbor seals were on a lipid-regulated diet of either high fat Pacific herring (Clupea pallasii; PVAT, PVQI, PVSI) or low fat Atlantic herring (Clupea harengus; PVSU, PVSH, PVTI) mixed with pollock (Theragra chalcogramma), capelin (Mallotus villosus) and squid (Loligo opalescens) (L. Polasek, unpublished data). Steller sea lions were fed a daily diet of pollock and Pacific herring supplemented with pink salmon (Oncorhynchus gorbuscha) three days a week. All diets included a daily multivitamin dosage based on individual mass (Mazuri 5# Marine Mammal Tablet). In order to minimize error in data collection, only two investigators (JN, JT) collected thermal images during the yearlong study. All thermograms were taken with a FLIR P25 infrared camera (FLIR Systems, Danderyd, Sweden) using an uncooled focal plane array microbolometer sensor. The camera was factory calibrated to an absolute accuracy of 72 1C, with thermal sensitivity of o0.10 at 30 1C. Infrared images had a resolution of 320 240 pixels. Relative humidity (%) and atmospheric temperature (1C) were taken at each session with a Sper Scientific Ltd. #850070 Mini Environmental Quality Meter (Sper Scientific Ltd., Scottsdale, Arizona, USA), absolute accuracy of the parameters were 76% and 71.2 1C, respectively, while resolution was to the nearest 0.1 of a percentage point or degree. A standard mercury thermometer with an absolute accuracy of 72 1C and resolution to the nearest tenth of a degree, was used to collect the temperature of the control source (Comark USA, Beaverton, OR, USA). Habitat sea water temperature data were taken from daily husbandry staff records (Hach Model HQ30d, Hach Co., Loveland, CO, USA) with a resolution to the nearest tenth of a degree. Body
mass was collected on the day of the session by husbandry staff (Transcell Model TI-500-SL, Accurate Scales, Terre Haute, IN, USA) with a standard resolution of 5000 divisions available up to 50,000 divisions. Thermal image collection was attempted on at least two occasions per month per individual from February 2007 to February 2008. The number of samples for each individual varied from one to four images per month, and was dependent upon animal cooperation and concurrent research needs. The first image session per month was utilized for seasonal data analysis. Depending on the husbandry and research requirements of the captive animals, images were either taken indoors under artificial fluorescent lighting or in an outdoor exhibit under a concrete roof to minimize the effects of solar radiation. Indoor images were taken on either a concrete flooring covered with an epoxy coated paint or an aluminum surfacing. A typical session involved moving the animal approximately 15 m from a holding area to a working area for image collection. For standardization purposes, all thermograms were taken of wet animals, within 5–10 min of being trained to haul out. Animals were behaviorally controlled to station and moved between images while the thermographer stood in a fixed position. Eight images were taken per animal per session: right and left lateral, high and low anterior, high and low posterior, ventral and a reference image. Right and left lateral, low anterior and posterior, and ventral images were taken at an approximate 901 angle between camera lens and animal. High anterior and posterior images were taken at an approximate 451 angle between camera lens and animal. The reflected temperature image, used to account for the radiation reflecting at the object along the same angle plane, was taken at a 1801 angle from the animal. Distance between animal and camera was set such that the animal would fill the frame of the picture from tip of tail to tip of nose. Images were taken in gray color palette for ease of focus and increased contrast. The total session time was approximately 10 min per animal. No anesthesia or sedation was required.
2.2. Validation of IRT Initial validation of the accuracy of the equipment used required two objects of known, but different emissivity (e). A glass jar filled with water (e ¼0.92) and a stomach temperature radio transmitter pill made of epoxy (e ¼0.84) were placed in a temperature controlled water bath (accuracy of 70.5 1C, VWR International, Inc., West Chester, PA, USA), for measurement at 5 1C temperature increments over a range of 0–30 1C. Once stabilized at each temperature, the object was temporarily removed from the water to allow for IRT image collection. A secondary assessment utilized software manipulations of environmental parameters (emissivity, reflected temperature, ambient air temperature, distance and relative humidity) to determine influence on calculated surface temperature. Each parameter was manipulated individually (with all other parameters constant) within the software on a single image (Table 1).
Table 1 Effect of manual parameter modification within the software analysis of infrared images of a reference surface temperature in a harbor seal (PVQI, 8.9 1C) and a Steller sea lion (EJSU, 12.1 1C). Each parameter was adjusted by 7 10% with all other parameters held constant. Parameter
PVQI (8.91C) standard setting
10% output
+ 10% output
EJSU (12.11C) standard setting
10% output
+ 10% output
Emissivity Relative humidity (%) Distance (m) Ambient air temperature (1C) Reflected temperature (1C)
0.98 62.6 3.0 19.6 10.6
8.9 8.9 8.9 9.0 9.0
9.0 8.9 8.9 8.9 8.9
0.98 62.9 7.6 19.7 15.6
12.0 12.1 12.1 12.2 12.1
12.2 12.1 12.1 12.1 12.1
J. Nienaber et al. / Journal of Thermal Biology 35 (2010) 435–440
Emissivity was adjusted by 70.02, as this is the common range of values used in living skin tissue studies (0.95–0.99; Best and Fowler, 1981; Speakman and Ward, 1998). All other parameters were modulated by 710%.
2.3. Surface temperature patterns All images were analyzed with FLIR ThermaCam Researcher Pro 2.8 SR-1 software (FLIR Systems, Danderyd, Sweden) in a rainbow color palette. Software corrected parameters included emissivity, relative humidity, ambient air temperature, reflected temperature and distance. One harbor seal (PVQI) and one sea lion (EJSU) image set was chosen at random to compare symmetry in surface temperature patterns among the eight image angles. With the exception of biopsy and/or injection sites, thermal patterns were symmetrical and equally visible from all positions, therefore the right lateral image was chosen for the analysis presented. The aim of this study was not to determine absolute surface temperatures and the size of specific areas of interest, but instead to define the relative surface temperature variation by region and season. Regions were selected for analysis based on physical landmarks and utility (e.g., ability to image in the field), including: whole body, torso, head, eye, muzzle, shoulder, axillae, hip, fore and hind flippers (Fig. 1). Whole body, torso and head were a composite of multiple regions and therefore are expressed as mean values. To test the widest range of difference among regions of the body, maximum (hot) and minimum (cold) temperatures were utilized for the remaining regions.
437
2.4. Data analysis Seasonal trends were tested utilizing winter (October–April), reproductive (May–July) and molt (August–Sepember), as per Pitcher (1986) and Mellish et al. (2007), although it is likely that the harbor seals had not yet reached sexual maturity (4–9 years; Pitcher and Calkins, 1979). To avoid unequal sample replication, all individuals were represented using the first data point of each month for annual analyses. To avoid bias due to unequal length of seasons, results were reduced to four consecutive image sessions per animal closest to the center date for each season. Calculations and statistical analyses were completed using SYSTAT 10 (SYSTAT Inc., Chicago, IL, USA) and plots using SigmaStat 3.5 (Systat Software, Inc., Germany). A simple regression was used to describe the relationship between the known object surface temperature as measured via IRT and as measured via a mercury thermometer. Pearson correlation was used to compare whole body and torso regions. The coefficient of variation (COV) was used to determine variability between body regions during the winter season only utilizing six consecutive image sets per individual. COV was not calculated for reproductive and molt seasons due to reduced availability of the appropriate number of sequential image sets. Seasonal changes in mass and regional skin surface variation were analyzed by Mann–Whitney U-test. Discrete hot and cold regions (e.g., excluding the composite whole body, torso and head) were identified using a Wilcoxon signed rank test, followed by a manual ranking of means. Data are presented as mean 7standard deviation (SD) unless otherwise stated. Significance was set at the 95% confidence interval.
3. Results
24.3°C 3.1. Technical parameters
5
4
1
2
20
6
7 3
10 8 9 10
IRT temperatures were directly related to the temperature measured by the mercury thermometer for the glass jar (IRTglass¼0.962 water T+ 0.641, r2 ¼0.993, po0.001) and the stomach pill (IRTpill¼0.894 water T+1.249, r2 ¼0.999, po0.001) (Fig. 2). The difference measured was within the absolute accuracy indicated for both measurement techniques (IRT and mercury
35 5.3°C
Jar Pill
30 19.2°C
4
2
7 6 3
10 8
15
9
Water (°C)
1
5
25 20 15 10 10
9.6°C
5 0 0
Fig. 1. Surface temperatures measured through infrared thermography on a juvenile female harbor seal (Phoca vitulina, top panel), an adult female Steller sea lion (Eumetopias jubatus, bottom panel). Regions measured included: (1) whole body, (2) torso, (3) foreflipper, (4) hindflipper, (5) hip, (6) shoulder, (7) axillae, (8) eye, (9) muzzle and (10) head.
5
15 10 20 25 IRT Surface Temperature (°C)
30
35
Fig. 2. Linear regression of surface temperature of two objects of differing emissivity (glass jar e ¼0.92, stomach pill e ¼0.84) measured via infrared thermography versus a standard mercury thermometer.
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20 15 10 5
All regions except eye, muzzle and hindflipper demonstrated seasonal surface temperature variation between the winter and reproductive seasons in harbor seals (U ¼84.5–191.0, p o0.05).
Hindflipper
Foreflipper
Hip
Axillae
Shoulder
Eye
30 Winter Reproductive Molt
25 20 15 10 5
Hindflipper
Foreflipper
Hip
Axillae
Shoulder
Muzzle
Eye
Head
0 Body
3.4. Hot and cold regions
Harbor seal (n = 6)
Surface Temperature (°C)
Surface temperatures for each region over the year were averaged by species (Fig. 3). Whole body and torso surface temperatures in harbor seals were 10.271.2 1C and 10.0 71.2 1C, respectively. Steller sea lion surface temperatures were 10.570.7 1C for whole body and 10.370.6 1C for torso. Both regions were highly correlated in each individual over the year (harbor seals, r Z0.790; Steller sea lions, r Z0.996). Surface temperature variability differed by body region and with species. Data from the middle of the longest season (winter) showed that in harbor seals, the hindflipper varied the least (COV¼5.8), while the shoulder was the most variable (COV¼12.3). Similarly in sea lions, the hindflipper was the least variable (COV¼ 2.7), whereas the head was the most variable (COV¼8.3). Seasonal fluctuations in surface temperature by region are shown in Fig. 4.
Muzzle
3.3. Surface temperature trends
Head
0 Torso
Harbor seal mass overall averaged 32.3 76.5 kg, with seals lighter at molt (29.876.1 kg) and the heaviest in winter (33.776.5 kg). Significant mass transitions occurred between winter and reproductive (U ¼423.0, p¼ 0.005), and winter to molt (U¼437.5, p¼ 0.002). There was no significant change from reproductive to molt (U ¼265.0, p 40.05). Average mass in Steller sea lions did not vary seasonally (215.076.4 kg).
Winter Reproductive Molt
25
Torso
3.2. Changes in body mass
30
Body
thermometer), therefore IRT estimates used in this study were not subject to temperature correction. Manipulation of environmental parameters within the software program changed average surface temperature output of the body image as a whole by no more than 70.1 1C (Table 1).
Surface Temperature (°C)
438
Steller sea lion (n = 2) Fig. 4. Seasonal surface temperature as measured by infrared thermography in captive harbor seals (Phoca vitulina, HS) and Steller sea lions (Eumetopias jubatus, SSL).
Surface Temperature (°C)
30 Harbor seal (n = 6)
25
Steller sea lion (n = 2) 20 15 10
Hindflipper
Foreflipper
Hip
Axillae
Shoulder
Muzzle
Eye
Head
Torso
0
Body
5
Fig. 3. Regional surface temperature as measured by infrared thermography in captive harbor seals (Phoca vitulina, HS) and Steller sea lions (Eumetopias jubatus, SSL) averaged over the twelve month study period. To demonstrate the maximum range of temperature profiles, mean values are shown for composite regions (whole body, torso, head), maximum values are shown for hot spots (eye, muzzle, shoulder, axillae, hip) and minimum values are shown for cold spots (foreflipper, hindflipper).
Between reproductive and molt periods, only the muzzle changed significantly (U¼ 175.0, p ¼0.02). Between molt and winter, all regions varied (U ¼65.5–122.0, po0.001), except for the eye. Overall, the maximum temperature was in the eye (24.271.2 1C), and the minimum temperature was in the hindflipper (6.670.7 1C). Seasonal effects in Steller sea lions were less pronounced, with significant differences occurring only in the torso, shoulder, hip and foreflipper between the winter and reproductive seasons (U ¼8.5–12.0, po0.03). There were no regional temperature variations between reproductive and molt, and only the shoulder differed between molt and winter (U ¼13.0, po0.05). Similar to harbor seals, overall maximum temperatures were measured in the eye (25.170.3 1C); however, the minimum temperatures were recorded in the foreflipper (7.970.0 1C). Independent body regions (e.g., excluding the composite whole body, torso and head) were manually ranked within each season to determine whether hot and cold spots were consistent across seasons (Table 2). While there was a small amount of variation between seasons and species, the eye and muzzle were consistently the two hottest spots with and the foreflipper and hindflipper the two coldest spots.
J. Nienaber et al. / Journal of Thermal Biology 35 (2010) 435–440
Table 2 Manual rank (1¼ hot, 7 ¼cold) of mean surface temperatures as measured by infrared thermography in captive harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus). Significant differences between one column and the subsequent season (winter–reproductive–molt–winter) as identified by multiple runs of Mann–Whitney tests are noted. Harbor seal (n ¼6)
Steller sea lion (n ¼2)
Rank
Winter
Reproductive Molt Winter Reproductive Molt
1—Hot 2 3 4 5 6 7—Cold
Eye (E) Muzzle (M) Axillae (A)** Shoulder (S)*** Hip (H)*** Foreflipper (FF)** Hindflipper (HF)
E M* S H A FF HF
n
E M*** A*** S*** H*** FF*** HF***
M E A S* H HF* FF*
E M S H A HF FF
E M A S* H HF FF
p o 0.05. p o0.01 p o0.001.
nn
nnn
4. Discussion 4.1. Technical validation and field application Five environmental parameters are necessary for accurate IRT based surface temperature estimates: emissivity, relative humidity, ambient air temperature, reflected temperature and distance. In addition, one must also consider the curved nature of objects (i.e., glass jar, stomach pill, animal), which may result in incomplete and less accurate temperature imaging of the entire surface. It has been demonstrated (Ash et al., 1987) that peripheral surface temperatures of an isothermic balloon were 2–4 1C cooler than the perpendicular surface temperature from the camera lens to the object. As a result, it was concluded that the technique should be used to look at patterns of heat loss and not be used for absolute temperatures (Ash et al., 1987). While we demonstrated limited influence of environmental variables in our controlled setting with the ability to have the object filling the field of view (Table 2), field conditions with variable environmental parameters such as wind velocity (Moen and Jacobsen, 1974), and distance to the object may result in noise in the image collected. During field studies, data collection during similar weather conditions and consistent times of the day will help to minimize the error of environmental parameters (Ohman, 1981). This would be optimal for comparing physiological state of individuals (i.e., resting, foraging).
4.2. Biological parameters In the present study, thermograms of harbor seals and Steller sea lions were collected in air to determine patterns of surface temperature by season and region, with further definition of consistent hot and cold spots. At any given time, the surface temperature of an individual is determined by a combination of physiological (metabolic state), anatomical (insulation, vascularization) and environmental factors. In both species, temporal variations were most notable pre- and post-winter, but minimal variation was noted between the reproductive and molt periods. Higher surface temperatures were also noted between the reproductive and molt seasons and lowest during the winter. During the reproductive and molt seasons, seals and sea lions haul out of the water to facilitate pupping and promote circulation for new hair growth, activities which both require energy expenditure (Worthy, 2001). Insulation patterns (i.e., blubber depth) also
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fluctuate similarly, thickest in the winter decreasing from reproductive to molt (harbor seals (Pitcher, 1986; Mellish et al., 2007), Steller sea lions (Mellish et al., 2007). In addition to monitoring overall patterns of surface temperature during an annual cycle, we specifically investigated the presence of consistent hot or cold spots for the identification of potential thermal windows (e.g., sites of active heat retention or dissipation; Table 2). The eye is consistently hot due to its uninsulated nature, and therefore cannot be considered a thermal window. However, eye temperature decreases with pain (Stewart et al., 2008), such that it may be a potential tool to reference physiological and/or metabolic state of the animal under very controlled conditions (e.g., long term captive animals). Similarly, high temperatures in the muzzle and hip are not likely due to active heat management. Instead, they are most likely a result of the high level of vascularization required to support a sensitive sensory tactile system (Dehnhardt et al., 1998), and a reduced blubber thickness (Willis et al., 2005; Mellish et al., 2007), respectively. However, our results suggest that the shoulder, axillae and flippers may be thermal windows. The extremities have been previously identified as areas likely to demonstrate the most day to day temperature fluctuation with changes in ambient air temperature (Cuyler et al., 1992; Choi et al., 1997). Prior attempts to identify thermal windows in pinnipeds in air have specifically looked at discrete areas visible via IRT in seals over the course of 2 h (Mauck et al., 2003). Within an individual session, no spatially or temporally consistent thermal windows were observed. The surface temperature of an animal tends to approach the temperature of the water when immersed (Hayward et al., 1981), though even small differences can result in a substantial heat exchange (Willis et al., 2005). There is evidence for spatially consistent heat flux patterns for swimming Steller sea lions (Willis et al., 2005). However, upon exit from the water, the surface of the animal will display varying patterns of heat dissipation and retention, mediated to some extent by physiological state and environmental conditions. Our study differed in design such that all animals were imaged in a similar state (e.g., within 5–10 min of hauling out). It should be taken into consideration at all times, however, that environmental factors such as evaporation, wind velocity or solar radiation, etc. may also lead to the appearance of inconsistent hot or cold areas. Blubber storage sites and tissue uniformity vary between harbor seals and Steller sea lions and may affect temporal variation seen in regional skin surface temperature. Harbor seal blubber is typically homogenous in both depth and composition, whereas Steller sea lion blubber includes interstitial tissue and varies in depth along the body (Mellish et al., 2007; Rosen and Renouf, 1997). Long-scale (i.e., seasonal) temporal skin temperature variations in regions were detected in both species, but were more prominent in harbor seals. Future study of the relationship between blubber depth and surface temperature would allow for a more precise interpretation of surface heat patterns and body condition in these species (i.e., anatomy versus physiological state).
Acknowledgements This research was conducted in partial fulfillment of the requirements for the degree of Master of Science at the University of Alaska, Fairbanks. All research was conducted under the ASLC’s Institutional Animal Care and Use Committee protocol no. 06-008 and the National Marine Fisheries Service’s (NMFS) permits 881-1745 and 881-1710. Funding was provided by the National Science Foundation (NSF) Major Research Instrumentation award #480431 (M. Horning and J. Mellish), NSF Polar Programs award
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