We applied temporal symmetry capture-recapture (TSCR) models to assess the strength of evidence f... more We applied temporal symmetry capture-recapture (TSCR) models to assess the strength of evidence for factors potentially responsible for population decline in bottlenose dolphins (Tursiops truncatus) in Doubtful Sound, New Zealand from 1995 to 2008. Model selection was conducted to estimate recruitment and population growth rates. There were similar levels of support for three different models, each reflecting distinct trends in recruitment. Modeling yielded low overall estimates of recruitment (0.0249, 95% CI: 0.0174-0.0324) and population growth rate (0.9642, 95% CI: 0.9546-0.9737). The TSCR rate of population decline was consistent with an estimate derived from trends in abundance (lambda = 0.9632, 95% CI: 0.9599-0.9665). The TSCR model selection confirmed the influence of a decline in the survival of calves (<1 yr old) since 2002 for population trends. However, TSCR population growth rates did not exceed 1 in any year between 1995 and 2008, indicating the population was declining prior to 2002. A separate reduction in juvenile survival (1-3 yr old) prior to 2002 was identified as a likely contributing factor in the population decline. Thus, TSCR modeling indicated the potential cause of the population decline in Doubtful Sound: cumulative impacts on individuals <3 yr old resulting in a reduced recruitment.
Remote biopsy sampling is a valuable technique to collect data on free-ranging cetaceans. Numerou... more Remote biopsy sampling is a valuable technique to collect data on free-ranging cetaceans. Numerous researchers have evaluated effects of biopsy darting on the target animal, but biopsy sampling may also have unintentional effects on nearby nontarget animals. We evaluated reactions of target and nontarget animals during remote biopsy sampling conducted on bottlenose dolphins (Tursiops truncatus) in . We examined external factors that might influence response of the target animal as well as other individuals in the group. Target animals reacted to biopsy attempts 90.9% (n ¼ 475) of the time. Of these, 97.5% (n ¼ 432) of reactions were to biopsy hits, and 84.4% (n ¼ 320) of all hits had reactions recorded as low. Nontarget animals reacted 21.9% (n ¼ 1,158) of the time; interanimal distance from target animal, season, sea state, and depth affected reactions of nontarget animals. Overall, however, biopsy effects appear to be minimal. We present a statistical tool for identifying factors that elicit greater reactions. This model could be adapted for species or locations, as needed, to identify factors that could influence effects of biopsy sampling. (JOURNAL OF WILDLIFE MANAGEMENT 72(4): 926-932; 2008)
Aquatic Conservation: Marine and Freshwater Ecosystems, 2009
1. The bottlenose dolphins of Doubtful Sound, New Zealand are a declining population at the south... more 1. The bottlenose dolphins of Doubtful Sound, New Zealand are a declining population at the southern limit of the species' range, exposed to impacts from tourism and habitat modification. Patterns in apparent annual survival were analysed from photographic resightings of naturally marked adults (1990 to 2008) and calves within the first year of life (1994 to 2008) using capture-recapture models.
More than 12 studies of different bottlenose dolphin populations, spanning from tropical to cold ... more More than 12 studies of different bottlenose dolphin populations, spanning from tropical to cold temperate waters, have shown that the species typically lives in societies in which relationships among individuals are predominantly fluid. In all cases dolphins lived in small groups characterised by fluid and dynamic interactions and some degree of dispersal from the natal group by both sexes. We describe a small, closed population of bottlenose dolphins living at the southern extreme of the species' range. Individuals live in large, mixed-sex groups in which no permanent emigration/immigration has been observed over the past 7 years. All members within the community are relatively closely associated (average halfweight index>0.4). Both male-male and female-female networks of preferred associates are present, as are longlasting associations across sexes. The community structure is temporally stable, compared to other bottlenose dolphin populations, and constant companionship seems to be prevalent in the temporal association pattern. Such high degrees of stability are unprecedented in studies of bottlenose dolphins and may be related to the ecological constraints of Doubtful Sound. Fjords are low-productivity systems in which survival may easily require a greater level of co-operation, and hence group stability. These conditions are also present in other cetacean populations forming stable groups. We therefore hypothesise that ecological constraints are important factors shaping social interactions within cetacean societies.
We applied temporal symmetry capture-recapture (TSCR) models to assess the strength of evidence f... more We applied temporal symmetry capture-recapture (TSCR) models to assess the strength of evidence for factors potentially responsible for population decline in bottlenose dolphins (Tursiops truncatus) in Doubtful Sound, New Zealand from 1995 to 2008. Model selection was conducted to estimate recruitment and population growth rates. There were similar levels of support for three different models, each reflecting distinct trends in recruitment. Modeling yielded low overall estimates of recruitment (0.0249, 95% CI: 0.0174-0.0324) and population growth rate (0.9642, 95% CI: 0.9546-0.9737). The TSCR rate of population decline was consistent with an estimate derived from trends in abundance (lambda = 0.9632, 95% CI: 0.9599-0.9665). The TSCR model selection confirmed the influence of a decline in the survival of calves (<1 yr old) since 2002 for population trends. However, TSCR population growth rates did not exceed 1 in any year between 1995 and 2008, indicating the population was declining prior to 2002. A separate reduction in juvenile survival (1-3 yr old) prior to 2002 was identified as a likely contributing factor in the population decline. Thus, TSCR modeling indicated the potential cause of the population decline in Doubtful Sound: cumulative impacts on individuals <3 yr old resulting in a reduced recruitment.
Remote biopsy sampling is a valuable technique to collect data on free-ranging cetaceans. Numerou... more Remote biopsy sampling is a valuable technique to collect data on free-ranging cetaceans. Numerous researchers have evaluated effects of biopsy darting on the target animal, but biopsy sampling may also have unintentional effects on nearby nontarget animals. We evaluated reactions of target and nontarget animals during remote biopsy sampling conducted on bottlenose dolphins (Tursiops truncatus) in . We examined external factors that might influence response of the target animal as well as other individuals in the group. Target animals reacted to biopsy attempts 90.9% (n ¼ 475) of the time. Of these, 97.5% (n ¼ 432) of reactions were to biopsy hits, and 84.4% (n ¼ 320) of all hits had reactions recorded as low. Nontarget animals reacted 21.9% (n ¼ 1,158) of the time; interanimal distance from target animal, season, sea state, and depth affected reactions of nontarget animals. Overall, however, biopsy effects appear to be minimal. We present a statistical tool for identifying factors that elicit greater reactions. This model could be adapted for species or locations, as needed, to identify factors that could influence effects of biopsy sampling. (JOURNAL OF WILDLIFE MANAGEMENT 72(4): 926-932; 2008)
Aquatic Conservation: Marine and Freshwater Ecosystems, 2009
1. The bottlenose dolphins of Doubtful Sound, New Zealand are a declining population at the south... more 1. The bottlenose dolphins of Doubtful Sound, New Zealand are a declining population at the southern limit of the species' range, exposed to impacts from tourism and habitat modification. Patterns in apparent annual survival were analysed from photographic resightings of naturally marked adults (1990 to 2008) and calves within the first year of life (1994 to 2008) using capture-recapture models.
More than 12 studies of different bottlenose dolphin populations, spanning from tropical to cold ... more More than 12 studies of different bottlenose dolphin populations, spanning from tropical to cold temperate waters, have shown that the species typically lives in societies in which relationships among individuals are predominantly fluid. In all cases dolphins lived in small groups characterised by fluid and dynamic interactions and some degree of dispersal from the natal group by both sexes. We describe a small, closed population of bottlenose dolphins living at the southern extreme of the species' range. Individuals live in large, mixed-sex groups in which no permanent emigration/immigration has been observed over the past 7 years. All members within the community are relatively closely associated (average halfweight index>0.4). Both male-male and female-female networks of preferred associates are present, as are longlasting associations across sexes. The community structure is temporally stable, compared to other bottlenose dolphin populations, and constant companionship seems to be prevalent in the temporal association pattern. Such high degrees of stability are unprecedented in studies of bottlenose dolphins and may be related to the ecological constraints of Doubtful Sound. Fjords are low-productivity systems in which survival may easily require a greater level of co-operation, and hence group stability. These conditions are also present in other cetacean populations forming stable groups. We therefore hypothesise that ecological constraints are important factors shaping social interactions within cetacean societies.
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