Short–beaked common dolphins (Delphinus delphis) are usually found in large social schools of doz... more Short–beaked common dolphins (Delphinus delphis) are usually found in large social schools of dozens to hundreds of individuals. Association patterns among individuals appear to be fluid with little evidence of intra-school sex segregation or kinship relationships. Short-beaked common dolphins are subject to by-catch mortality in purse-seine and gillnet fisheries in the coastal and shelf waters off South Australia. As common dolphins associate in large schools, such aggregations puts individuals at risk of simultaneous entanglements, which may result in a by-catch mortality that is gender or kinship biased. Such biased mortality may have a greater impact on the longterm viability of the common dolphin population. In the present study we use genetic markers to investigate sex segregation and the influence of maternal kinship and genetic relatedness of individual associations within schools of short-beaked common dolphins off South Australia. A total of 83 biopsy samples were obtained...
Delphinids show a wide range of social structures. However, studies investigating the influence o... more Delphinids show a wide range of social structures. However, studies investigating the influence of genetic relatedness and maternal kinship on school associations are limited to a small number of relatively well-studied delphinid species. This study investigated biparental genetic relatedness and potential maternal kinship structure in schools of short-beaked common dolphins Delphinus delphis from southern Australian waters. A total of 128 biopsy samples were obtained from free-ranging individuals within 62 schools of common dolphins. Each sample was genotyped at 13 nuclear microsatellite markers, sequenced at 438 bp of the mitochondrial DNA control region, and used for genetic sexing. Pairwise analyses within and between schools showed that the average genetic relatedness between males was greater within schools than between schools. Pairs of individuals within schools were also more likely to share mtDNA haplotypes, for both pairs of males and of females. The results suggest that both biparental relatedness and potentially maternal kinship have an impact on school associations of short-beaked common dolphins in southern Australia, similar to social traits reported of other dolphin species inhabiting shallow coastal environments. The information provided by this study contributes to our understanding of social evolution in delphinids. It also suggests that dolphin bycatch and deaths in fisheries from this region could lead to a reduction in the genetic diversity of this population, particularly if related individuals are simultaneously killed in the nets.
Worldwide, fisheries bycatch remains one of the greatest immediate threats to cetacean population... more Worldwide, fisheries bycatch remains one of the greatest immediate threats to cetacean populations. In Australia, short-beaked common dolphins are subject to bycatch mortality in 2 fisheries: the purse-seine fishery for sardines off central South Australia and the gillnet fishery for gummy sharks off southern Australia. The cumulative impact of bycatch from both fisheries on the dolphin population(s) in these regions are unknown. We used information from microsatellite markers and mitochondrial DNA to investigate population genetic structure and estimate contemporary migration rates in 332 biopsied and 15 stranded samples of common dolphins. Samples were collected from 11 locations along ~3500 km of coastline in southern and southeastern Australia. Bayesian and traditional analyses of population genetic structure revealed the presence of at least 6 management units of common dolphins, of which a minimum of 3 are potentially impacted by the 2 fisheries. These management units need to be managed separately for conservation purposes and for monitoring and mitigation of common dolphin fishery interactions off southern and southeastern Australia. We suggest that substructuring and migratory movements of common dolphins across these regions may be driven by spatial variations in oceanography, upwelling events and/or fish distribution. This study exemplifies how information on genetic substructuring in a neritic top predator can be valuable for fisheries bycatch management.
Short–beaked common dolphins (Delphinus delphis) are usually found in large social schools of doz... more Short–beaked common dolphins (Delphinus delphis) are usually found in large social schools of dozens to hundreds of individuals. Association patterns among individuals appear to be fluid with little evidence of intra-school sex segregation or kinship relationships. Short-beaked common dolphins are subject to by-catch mortality in purse-seine and gillnet fisheries in the coastal and shelf waters off South Australia. As common dolphins associate in large schools, such aggregations puts individuals at risk of simultaneous entanglements, which may result in a by-catch mortality that is gender or kinship biased. Such biased mortality may have a greater impact on the longterm viability of the common dolphin population. In the present study we use genetic markers to investigate sex segregation and the influence of maternal kinship and genetic relatedness of individual associations within schools of short-beaked common dolphins off South Australia. A total of 83 biopsy samples were obtained...
Delphinids show a wide range of social structures. However, studies investigating the influence o... more Delphinids show a wide range of social structures. However, studies investigating the influence of genetic relatedness and maternal kinship on school associations are limited to a small number of relatively well-studied delphinid species. This study investigated biparental genetic relatedness and potential maternal kinship structure in schools of short-beaked common dolphins Delphinus delphis from southern Australian waters. A total of 128 biopsy samples were obtained from free-ranging individuals within 62 schools of common dolphins. Each sample was genotyped at 13 nuclear microsatellite markers, sequenced at 438 bp of the mitochondrial DNA control region, and used for genetic sexing. Pairwise analyses within and between schools showed that the average genetic relatedness between males was greater within schools than between schools. Pairs of individuals within schools were also more likely to share mtDNA haplotypes, for both pairs of males and of females. The results suggest that both biparental relatedness and potentially maternal kinship have an impact on school associations of short-beaked common dolphins in southern Australia, similar to social traits reported of other dolphin species inhabiting shallow coastal environments. The information provided by this study contributes to our understanding of social evolution in delphinids. It also suggests that dolphin bycatch and deaths in fisheries from this region could lead to a reduction in the genetic diversity of this population, particularly if related individuals are simultaneously killed in the nets.
Worldwide, fisheries bycatch remains one of the greatest immediate threats to cetacean population... more Worldwide, fisheries bycatch remains one of the greatest immediate threats to cetacean populations. In Australia, short-beaked common dolphins are subject to bycatch mortality in 2 fisheries: the purse-seine fishery for sardines off central South Australia and the gillnet fishery for gummy sharks off southern Australia. The cumulative impact of bycatch from both fisheries on the dolphin population(s) in these regions are unknown. We used information from microsatellite markers and mitochondrial DNA to investigate population genetic structure and estimate contemporary migration rates in 332 biopsied and 15 stranded samples of common dolphins. Samples were collected from 11 locations along ~3500 km of coastline in southern and southeastern Australia. Bayesian and traditional analyses of population genetic structure revealed the presence of at least 6 management units of common dolphins, of which a minimum of 3 are potentially impacted by the 2 fisheries. These management units need to be managed separately for conservation purposes and for monitoring and mitigation of common dolphin fishery interactions off southern and southeastern Australia. We suggest that substructuring and migratory movements of common dolphins across these regions may be driven by spatial variations in oceanography, upwelling events and/or fish distribution. This study exemplifies how information on genetic substructuring in a neritic top predator can be valuable for fisheries bycatch management.
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