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Dolphin Populations (dolphin + population)
Selected AbstractsAssessing the effectiveness of conservation management decisions: likely effects of new protection measures for Hector's dolphin (Cephalorhynchus hectori)AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2010Elisabeth Slooten Abstract 1.Fisheries bycatch affects many species of marine mammals, seabirds, turtles and other marine animals. 2.New Zealand's endemic Hector's dolphins overlap with gillnet and trawl fisheries throughout their geographic range. The species is listed as Endangered by the IUCN. In addition, the North Island subspecies has been listed as Critically Endangered. 3.Estimates of catch rates in commercial gillnets from an observer programme (there are no quantitative estimates of bycatch by amateur gillnetters or in trawl fisheries) were used in a simple population viability analysis to predict the impact of this fishery under three scenarios: Option (A) status-quo management, (B) new regulations announced by the Minister of Fisheries in 2008 and (C) total protection. 4.Uncertainty in estimates of population size and growth rate, number of dolphins caught and other model inputs are explicitly included in the analysis. Sensitivity analyses are carried out to examine the effect of variation in catch rate and the extent to which fishing effort is removed from protected areas but displaced to unprotected areas. 5.These methods are applicable to many other situations in which animals are removed from populations, whether deliberately (e.g. fishing) or not (e.g. bycatch). 6.The current Hector's dolphin population is clearly depleted, at an estimated 27% of the 1970 population. Population projections to 2050 under Options A and B predict that the total population is likely to continue declining. In the case of Option B this is driven mainly by continuing bycatch due to the much weaker protection measures on the South Island west coast. 7.Without fishing mortality (Option C) all populations are projected to increase, with the total population approximately doubling by 2050 and reaching half of its 1970 population size in just under 40 years. Copyright © 2009 John Wiley & Sons, Ltd. [source] Seasonal changes in distribution of Hector's dolphin at Banks Peninsula, New Zealand: implications for protected area designAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2010William Rayment Abstract 1.The efficacy of protected areas for wildlife management is largely dependent on appropriate design. It is therefore crucial that the distribution of target species is well understood. 2.The Banks Peninsula Marine Mammal Sanctuary (BPMMS) was designed to protect Hector's dolphins from bycatch in gillnets. However, the Banks Peninsula dolphin population is likely to be still declining, partly due to continued bycatch outside the boundaries of the BPMMS. 3.A three year series of aerial line-transect surveys around Banks Peninsula was carried out to investigate seasonal changes in distribution of Hector's dolphins out to 20 nautical miles (37,km) from the coast. 4.Dolphin sightings were concentrated close to shore in shallow water in summer, but were more evenly distributed throughout the study area in winter. A greater proportion of dolphins were sighted outside the 4 nautical miles (7.4,km) offshore boundary of the BPMMS in winter (mean=56%) than in summer (mean=19%) (G=88.25, df=1, P<0.001). 5.Partial Mantel tests revealed the effects of distance offshore and depth on dolphin occurrence while controlling for spatial autocorrelation and multicollinearity within the data. Distance offshore had the strongest and most consistent effect on dolphin presence, while depth had a strong effect in summer only. 6.It is proposed that restrictions on gillnetting around Banks Peninsula must be extended in order to reduce bycatch of Hector's dolphins to a sustainable level, and that a new offshore boundary of the BPMMS would be best defined by distance from the coast. Copyright © 2009 John Wiley & Sons, Ltd. [source] Probabilistic risk assessment of reproductive effects of polychlorinated biphenyls on bottlenose dolphins (Tursiops truncatus) from the Southeast United States coastENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2002Lori H. Schwacke Abstract High levels of polychlorinated biphenyls (PCBs) have been reported in the tissues of some species of marine mammals. The high concentrations are of concern because a growing body of experimental evidence links PCBs to deleterious effects on reproduction, endocrine homeostasis, and immune system function. Much of the recent research has focused on determining the exposure of marine mammal populations to PCBs, but very little effort has been devoted to the actual risk assessments that are needed to determine the expected impacts of the documented exposures. We describe a novel risk assessment approach that integrates measured tissue concentrations of PCBs with a surrogate dose-response relationship and leads to predictions of health risks for marine mammals as well as to the uncertainties associated with these predictions. Specifically, we use PCB tissue residue data from three populations of bottlenose dolphins (Tursiops truncatus), study the feasibility of published dose-response data from a surrogate species, and combine this information to estimate the risk of detrimental reproductive effects in female dolphins. Our risk analyses for dolphin populations near Beaufort (NC, USA), Sarasota (FL, USA), and Matagorda Bay (TX, USA) indicate a high likelihood that reproductive success, primarily in primiparous females, is being severely impaired by chronic exposure to PCBs. Excess risk of reproductive failure, measured in terms of stillbirth or neonatal mortality, for primiparous females was estimated as 60% (Beaufort), 79% (Sarasota), and 78% (Matagorda Bay). Females of higher parity, which have previously off-loaded a majority of their PCB burden, exhibit a much lower risk. [source] COASTAL BOTTLENOSE DOLPHINS FROM SOUTHEASTERN AUSTRALIA ARE TURSIOPS ADUNCUS ACCORDING TO SEQUENCES OF THE MITOCHONDRIAL DNA CONTROL REGIONMARINE MAMMAL SCIENCE, Issue 2 2001Luciana M. Möller Abstract Sequence analysis of the mitochondrial DNA control region was used to clarify the taxonomic status of two coastal bottlenose dolphin populations from southeastern Australia currently classified as Tursiops truncatus. A 368-bp segment of the control region of 57 biopsy-sampled, photo-identified dolphins of Jervis Bay and Port Stephens was compared to published sequences of T. truncatus and T. aduncus from different oceanic regions. Sequence divergence between haplotypes from southeastern Australia and T. aduncus was much lower than that from T. truncatus. Analyses using two different methods of phylogenetic reconstruction unambiguously placed all haplotypes from southeastern Australia in a group composed exclusively of T. aduncus. The results strongly indicated that these two bottlenose dolphin populations belong to T. aduncus, extending the range of the species to subtropical waters of the Western South Pacific Ocean. [source] Social kin associations and genetic structuring of striped dolphin populations (Stenella coeruleoalba) in the Mediterranean SeaMOLECULAR ECOLOGY, Issue 14 2007STEFANIA GASPARI Abstract We investigated hierarchical patterns of genetic subdivision, and assessed kinship within and between social groups of striped dolphins (Stenella coeruleoalba) in the Tyrrhenian Sea. A total of 165 samples were analysed at eight microsatellite DNA loci, including outgroup samples from the Adriatic, Scotland and Spain for population-level comparisons. We found population genetic structure within the Mediterranean basin, including small but significant differentiation between the Adriatic and Tyrrhenian Seas (FST = 0.0047, P = 0.008), and between putative ,inshore' and ,offshore' (FST = 0.0217, P = 0.005) populations in the Tyrrhenian Sea. Assessment of kinship within and among 12 association groups showed higher average kinship for females within than between groups, and smaller groups showed higher average kinship. Comparisons of relatedness for both sexes showed a significant difference between males and females, with females more likely to associate with adult kin. Together these data emphasize the importance of the social cohesion of kin in small groups to the structuring of striped dolphin populations in this environment. [source] Biomass removal by dolphins and fisheries in a Mediterranean Sea coastal area: do dolphins have an ecological impact on fisheries?AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2010Giovanni Bearzi Abstract 1.Dolphins are often claimed to compete with fisheries, including through removal of substantial biomass. To calculate the biomass removed by fisheries and the degree of resource overlap with dolphins in a coastal area of Greece, estimates of dolphin abundance based on photographic capture,recapture were combined with an assessment of fishing effort and catch. 2.The estimated total biomass consumed annually by local dolphin populations , 15 short-beaked common dolphins and 42 common bottlenose dolphins , was 15.5 and 89.8 tonnes, respectively. The total biomass removed by the local fishing fleet (307 fishing boats) was 3469.2 tonnes, i.e. about 33 times greater than that removed by dolphins. 3.Dolphins removed 2.9% of the total biomass, fisheries 97.1%. Nine purse seiners (representing only 3% of the active fishing fleet) were responsible for 31.9% of biomass removal. Similarity of biomass composition between dolphins and fisheries was expressed by a Pianka index of 0.46 for common dolphins and 0.66 for bottlenose dolphins. 4.Overlap differed according to fishing gear. Common dolphin overlap was higher with purse seiners (0.82), and lower with beach seiners (0.31), bottom trawlers (0.11) and trammel boats (0.06). There was virtually no overlap with longliners (0.02). Bottlenose dolphin overlap was higher with trammel boats (0.89) and bottom trawlers (0.75), and lower with longliners (0.38), purse seiners (0.24) and beach seiners (0.18). There was minimal overlap (0.12) between the two dolphin species. 5.This study suggests that ecological interactions between dolphins and fisheries in this coastal area have minor effects on fisheries. Conversely, prey depletion resulting from overfishing can negatively affect dolphins. Fisheries management measures consistent with national and EU legislation are proposed to ensure sustainability and to protect marine biodiversity. Copyright © 2010 John Wiley & Sons, Ltd. [source] | ||||||||||