EcoHealth 1, 246–254, 2004 DOI: 10.1007/s10393-004-0094-6
2004 EcoHealth Journal Consortium
Bottlenose Dolphins as Marine Ecosystem Sentinels: Developing a Health Monitoring System Randall S. Wells,1 Howard L. Rhinehart,2 Larry J. Hansen,3 Jay C. Sweeney,4 Forrest I. Townsend,5 Rae Stone,4 David R. Casper,6 Michael D. Scott,7 Aleta A. Hohn,8 and Teri K. Rowles9 1
Sarasota Dolphin Research Program, Chicago Zoological Society, c/o Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236 Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236 3 US Fish and Wildlife Service, Stockton, CA 95205 4 Dolphin Quest, 4467 Saratoga Avenue, San Diego, CA 92107 5 Bayside Hospital for Animals, 251 N.E. Racetrack Road, Fort Walton Beach, FL 32547 6 Long Marine Laboratory, University of California, Santa Cruz, CA 95060 7 Inter-American Tropical Tuna Commission, c/o Scripps Institute of Oceanography, La Jolla, CA 92037 8 National Marine Fisheries Service, Beaufort, NC 28516 9 National Marine Fisheries Services, 1315 East-West Highway, Silver Spring, MD 20910 2
Abstract: Bottlenose dolphins (Tursiops truncatus), as long-lived, long-term residents of bays, sounds, and estuaries, can serve as important sentinels of the health of coastal marine ecosystems. As top-level predators on a wide variety of fishes and squids, they concentrate contaminants through bioaccumulation and integrate broadly across the ecosystem in terms of exposure to environmental impacts. A series of recent large-scale bottlenose dolphin mortality events prompted an effort to develop a proactive approach to evaluating risks by monitoring living dolphin populations rather than waiting for large numbers of carcasses to wash up on the beach. A team of marine mammal veterinarians and biologists worked together to develop an objective, quantitative, replicable means of scoring the health of dolphins, based on comparison of 19 clinically diagnostic blood parameters to normal baseline values. Though the scoring system appears to roughly reflect dolphin health, its general applicability is hampered by interlaboratory variability, a lack of independence between some of the variables, and the possible effects of weighting variables. High score variance seems to indicate that the approach may lack the sensitivity to identify trends over time at the population level. Potential solutions to this problem include adding or replacing health parameters, incorporating only the most sensitive measures, and supplementing these with additional measures of health, body condition, contaminant loads, or biomarkers of contaminants or their effects that can also be replicated from site to site. Other quantitative approaches are also being explored. Key words: bottlenose dolphin, ecosystem health, sentinel species, risk assessment
INTRODUCTION Published online: May 28, 2004 Correspondence to: Randall S. Wells, e-mail:
[email protected]
Bottlenose dolphins (Tursiops truncatus), can serve as important barometers of the health of marine ecosystems.
Bottlenose Dolphins as Ecosystem Sentinels
They are long-lived, long-term coastal residents in tropical and temperate regions throughout the world (Wells and Scott, 1999; Reynolds et al., 2000). Long-term research on such a species allows one to document the history of exposure to ecosystem perturbations and their effects. They are top-level predators on a wide variety of fishes and squids, and thus concentrate contaminants through bioaccumulation and integrate broadly across the ecosystem in terms of exposure to environmental impacts. Dolphin health and population status not only reflect the effects of natural and anthropogenic stressors on the species, but they serve as sentinels of the health and status of lower trophic levels in the marine ecosystem. Over the last 17 years, another reason to monitor bottlenose dolphin health and population status has emerged due to the occurrence of large-scale dolphin mortality events. During 1987–1988, it was estimated that half of the putative coastal migratory stock of bottlenose dolphins died along the mid-Atlantic coast of the U.S. (Scott et al., 1988), leading to a designation of this stock as ‘‘depleted.’’ Other unusual dolphin mortality events occurred in the northern Gulf of Mexico in 1990, 1992, and 2000, in which hundreds of bottlenose dolphins died (Hansen, 1992). A variety of factors, such as environmental contaminants, natural biotoxins (Geraci, 1989), and morbillivirus (Duignan et al., 1996; Lipscomb et al., 1996), have been suggested as probable agents responsible for the mortalities. In each of these cases, conclusive determination of the cause of death was hampered by a shortage of fresh carcasses to allow all desired tests to be performed. Evaluation of the impacts of the mortalities was hampered by inadequate background information on dolphin stock structure, abundance, life history, and vital rates prior to the mortalities. The lesson reinforced by each subsequent investigation is that a proactive approach to evaluating risks by monitoring living dolphin populations would be preferable to waiting for large numbers of carcasses to wash up on the beach. The authors have been developing methods for assessing the population status and health of coastal bottlenose dolphins, not only to monitor the risks to the populations themselves, but also to be able to use them as sentinels of the health of marine ecosystems. Much of this work has occurred in Sarasota Bay, Florida, where research on the resident dolphin community has been ongoing since 1970, and where four generations of identifiable individuals of known gender, age, and genetic relationships are currently under study (Irvine and Wells, 1972; Irvine et al., 1981; Scott et al., 1990a; Wells, 1991). Population moni-
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toring efforts benefit from the fact that at least 60% of inshore dolphins on the west coast of Florida are individually identifiable from dorsal fin features, facilitating direct counts and mark-recapture estimates (Wells, 2002; Wells and Scott, 1990; Wells et al., 1996a, 1996b, 1997). Using photographic identification techniques (Scott et al., 1990b; Wu¨ rsig and Jefferson, 1990) it is possible to define individual ranges (e.g., relative to contaminant sources) and measure female reproductive success as well as monitor population-level trends in abundance, losses, and other vital rates (Wells and Scott, 1990). In addition, the shallow waters of much of the habitat of inshore bottlenose dolphins facilitate safe capture and release operations, in which dolphins can be examined by veterinarians and sampled for subsequent health-related analyses. This article focuses on the information for health assessment that can be derived from directly examining and sampling dolphins.
APPROACH Dolphins are captured for examination and sampling by encircling them with a 500 m · 4 m seine net in shallow waters where handlers can safely stand and support dolphins as necessary. One at a time, each dolphin is transferred to foam pads on the shaded deck of a boat, where it is weighed and a standard series of length and girth measurements is collected. Adult females are first given an ultrasound examination for pregnancy before a decision is made to bring them aboard the vessel. Throughout the examination, behavior and respiratory patterns are closely monitored, and water is sponged over the animals. Blubber depth is measured ultrasonically at standard sites. Abdominal and thoracic organs are evaluated via ultrasound examination. Core body temperature is measured through a colonic probe. Blood samples (up to 320 ml) are collected through venipuncture from a vessel in the fluke. Blood samples are: 1) analyzed for standard chemistry, hematology, and reproductive hormones; 2) used for immunological studies; 3) applied to genetic studies including paternity analyses; 4) examined for circulating levels of environmental contaminants; and 5) stored for retrospective investigations of disease processes. Urine is obtained through sterile catheterization. Milk is expressed into a custom suction collection system for compositional analyses and measurements of environmental contaminants. Samples for evaluation of the presence or absence of a suite of microorganisms are collected from the blowhole,
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feces, and genital tracts. Small blubber wedges (4-cm long · 3-cm wide · up to 1.5-cm deep) are obtained under local anesthesia from a standard location below the dorsal fin, for contaminant analyses. Most of the Sarasota Bay residents are of known age through observation, but a tooth is collected under local anesthesia from individuals of unknown age for sectioning and counting of growth layer groups (Hohn et al., 1989). A full examination and sampling program typically requires about 1 hour, and then the dolphin is returned to the water and released. More than 180 individuals have been examined in Sarasota Bay to date. Similar sampling was conducted by the National Marine Fisheries Service (NMFS) in Matagorda Bay, Texas in 1992 (n = 36 dolphins) and near Beaufort, North Carolina in 1995 (n = 31 dolphins) (Hansen and Wells, 1996). The bottlenose dolphin health assessment program initiated 17 years ago continues to evolve. Blood sampling for health assessment was begun in Sarasota Bay in 1987 in order to develop medical histories and track cases involving the well-known Sarasota Bay residents, and to develop a baseline for comparison with dolphins at other sites and held in zoological park settings. With the advent of large-scale dolphin mortalities in the late 1980s and early 1990s, the veterinary team developed a health evaluation system, assigning a grade to each dolphin based on a clinical assessment. This system was first applied in response to the Matagorda Bay mortality event in 1992. Building upon this concept, a NMFS-sponsored workshop was held in Sarasota in October 1993 to attempt to apply information on health parameters for free-ranging bottlenose dolphins to the development of a method for evaluating the health of dolphin populations. The specific goals of the workshop were as follows: 1. Develop and refine a ‘‘grading system’’ for the health of individual animals examined and sampled during the annual Sarasota bottlenose dolphin capture–release project, based on consideration of the full range of health and condition parameters measured. The grading system should be based on defensible, objective criteria; 2. Develop and refine a system to extrapolate the individual animal grades to a seasonal grade for the population as a whole based on the animals sampled during a given season; 3. Identify the indicators of greatest value in assessing the overall health of an individual or population; and 4. Relate trends in population health grades to trends in population parameters such as mortality or loss rates, natality, and fecundity.
Table 1. Data Sources for Development of Health Assessment Protocol of Bottlenose Dolphins (Tursiops truncatus) in Sarasota Bay, Florida
Data Blood chemistry and hematology Microbiology Results of physical examinations Sex, age, morphometrics, life history Body condition: weight, girth, blubber depth Diagnostic ultrasound examination Results of necropsies performed by Mote Marine Laboratory Population vital rates Behavior: ranging and social patterns Blubber biopsy wedges Blood/milk for contaminant analyses Urinalysis
Collected from Sarasota Bay dolphins since 1987 1990 1984 1984 1986 1990 1985 1980 1970 1997 1988 1993
The workshop participants, including marine mammal veterinarians, an epidemiologist, and biologists specializing in life history, behavioral ecology, physiological ecology, and microbiology considered and integrated the following kinds of data in their evaluation of the health of the individual dolphins and the Sarasota Bay dolphin community (Table 1). Records for each individual dolphin were compiled, sorted, summarized, and distributed to a set of experienced marine mammal veterinarians in advance of the workshop (Rhinehart et al., 1991, 1992). The veterinarians graded each of the dolphins based on all of the available information from each capture. The grading system evaluated each animal as if it were a captive dolphin with access to regular veterinary attention. At the workshop, the biologists worked with the veterinarians to evaluate their grading system, and to identify the most informative health parameters of those that have been or could be measured regularly and reliably in the field. The authors evaluated a variety of potential assessment parameters, including 56 blood hematology and chemistry measures, weight, girths, blubber depths, and the presence or absence of 80 microorganisms. These parameters were evaluated relative to the sex, age, and reproductive condition of each individual, and the type of sample (serum vs. plasma) and the analytical laboratory used (Specialty Veterinary Laboratory Services [SVLS],
Bottlenose Dolphins as Ecosystem Sentinels
Santa Cruz, CA vs. SmithKline-Beecham, locations throughout the US). From this list, we selected a set of the most indicative parameters that allowed us to develop a quantitative measure of the health of each individual. A mean annual health score for the population as a whole was calculated. The scores provided a set of tentative baseline values for comparison with other populations.
HEALTH ASSESSMENT SCORING SYSTEM The workshop participants developed a dolphin health assessment scoring system. The ontogeny of the system involved several steps. In its initial form, the concept of an ‘‘expert system’’ in which health grades were assigned subjectively by the members of a team of marine mammal veterinarians was explored. The need for a replicable, objective system led to the integration of the clinical experience approach with a mathematical approach. As a result, an algorithm using a weighted scoring for values of a selected set of 19 blood parameters was derived (Table 2). The 19 blood parameters were selected on the basis of their stand-alone value as indicators of dolphin health and potential facility of replicable measurement across field sites. ‘‘Normal’’ baseline ranges were established for each parameter, based on the clinical experience of the veterinarians and on the values obtained from the free-ranging Sarasota dolphins. Values presented in the ‘‘0 Points’’ column of Table 2 were considered ‘‘normal.’’ Each parameter was scored on the basis of its deviation from ‘‘normal’’ range. Scores were weighted according to the relative medical importance of the particular parameter, as assigned by the veterinarians. Each animal then received a grade that was based on the sum of the point scores for each of the parameters. The four possible grades included: A (0–4 points)—The dolphin is apparently in good health, with no obvious medical problems or need for follow-up medical attention. B (5–9 points)—The dolphin would benefit from a followup veterinary examination. C (10–19 points)—The dolphin would benefit from medical treatment. D (>20 points)—The dolphin has a serious medical problem that requires treatment. Several parameters were considered to be duplicative and therefore interchangeable if necessary. For example,
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only one of alanine amino transferase (ALT), gamma glutamyl transferase (GGT), and aspartate aminotransferase (AST) was used for any given score (the highest value of the three was used), but in the absence of any two of these, the other was acceptable for scoring. The higher of the values for hemoglobin and hematocrit was selected. Similarly, the total leukocyte count (WBC) would have duplicated scoring of the leukocyte differential, so only the differential was scored. The reproductive condition, age class, and analytical laboratory affected some variables. Hemoglobin and hematocrit were scored differently for lactating vs. nonlactating females. Alkaline phosphatase (AP) was scored differently for calves/juveniles, subadults, and adults. Comparisons of health scores between age classes within genders found a significant difference (P < 0.01) only between adult and subadult females, with subadults exhibiting better health (mean = 3.0, SD = 2.70, n = 25 vs. adult female mean = 5.6, SD = 4.64, n = 38). Consistent differences between the two laboratories used prior to the workshop (SVLS and SmithKline-Beecham) led to different scoring for albumin, globulin, and bilirubin. SmithKline-Beecham was selected as our standard laboratory due to widespread availability of linked laboratories throughout the U.S. However, after 1995 SmithKline-Beecham no longer performed analyses on veterinary samples. Subsequent analyses were performed by a variety of laboratories (University of Miami, Sea World, Cornell University) in an attempt to find one that was both easily accessible and would perform reliably all 19 of the analyses required by the scoring system. For example, some laboratories would not perform analyses for iron or erythrocyte sedimentation rate. As a result, the data presented here reflect only the 1990–1995 period during which a consistent laboratory (SmithKline-Beecham) performed all 19 analyses.
EVALUATION SYSTEM
OF THE
HEALTH SCORING
The 1990–1995 dataset yielded 145 health scores from 80 different dolphins. These were collected during seven sampling sessions: June of 1990 (n = 20), 1991 (n = 29), 1992 (n = 27), 1993 (n = 17), 1994 (n = 24), and 1995 (n = 13), and during February of 1993 (n = 6) and 1994 (n = z9). In total, 130 scores were from summer samplings and 15 were from winter samplings. Sampled dolphins included
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Table 2. Baseline Blood Values, and Points Scored If Outside of the Baseline Values of Bottlenose Dolphins (Tursiops truncatus) in Sarasota Bay, Floridaa Points Parameterb
Units
0
2
5
10
1 2 3 4a 4b 5a 5b 6a 6b 7 7a 7b 7c 8a 8b 8c 9 10 11a 11b 11c 11d 12 13 14 15 16 17 18 19
mEq/L mEq/L mg/dl g/dl g/dl g/dl g/dl mg/dl mg/dl U/L U/L U/L U/L U/L U/L U/L mg/dl mg/dl g/dl g/dl % % /mm3 /mm3 /mm3 /mm3 /mm3 /mm3 lg/dl mm/hour
140–159 2.0–4.4
