British shark life: are spurdog siblings sticking together?
Fenella is studying Scotland’s spurdogs, a small shark found across the British Isles and in temperate regions around the world. While commercial targeting of spurdogs has been banned after major population declines, whole aggregations can be caught as bycatch. Fenella’s team is asking how related a population might be, if it’s caught in a single aggregation event off the Isles of Scilly. Her project’s work can look at relatedness of spurdogs across the British Isles, and also provide insights into the diet and movement of spurdogs within aggregations.
Fenella Wood
For as long as I can remember, I have felt an affinity with water. As a youngster, I spent every summer along the South Wales coast, exploring rock pools and swimming as much as I could. For the rest of the year, I would fill up on nature documentaries, longing to get back into the water the following summer. I was determined to turn my summer experience into my every day, instead of once a year. To do that, I moved to South Wales and started my BSc (Hons) in zoology at Cardiff University. Despite living relatively...
Social networks: how related are Scotland’s spurdogs?
To investigate the family relationships between individuals within a single spurdog aggregation and estimate their genetic connectivity with the wider north-eastern Atlantic population.
The spurdog is an aggregating species, which makes it particularly vulnerable to being taken as by-catch in large quantities by commercial fisheries. There has been limited research into this aggregating behaviour and the impact by-catch may have on the population. This project has the rare opportunity to assess genetic relatedness within a single aggregation and thus to reveal the impact that removing these aggregations may have on the gene pool in the north-eastern Atlantic.
The spurdog, also known as spiny dogfish, is a wide-ranging and highly mobile small shark that can be found in temperate seas around the globe. Like most elasmobranchs, it exhibits slow life-history traits, including a long generation time of 25–35 years and a gestation period lasting 18–24 months. Once a commercially important species, it is now categorised as Endangered in the north-eastern Atlantic by the IUCN Red List of Threatened Species due to a 77% decline in biomass between 1955 and 2010. The aggregating nature of the species means that when individuals are caught by commercial fisheries, they are caught in large numbers. Not only is this an issue in that the population size is reduced, but there could be unknown effects on genetic diversity. Previous research suggests these aggregations may contain a high proportion of closely related individuals (perhaps as siblings) and losing these family groups can decrease genetic diversity, reducing the species’ ability to adapt to environmental change. Understanding the genetic composition of spurdog aggregations is crucial to assessing the potential impact of by-catch on population sustainability in the north-eastern Atlantic. This is the first time family relations will have been assessed for an elasmobranch aggregation on such a scale. However, previous work using relatedness information has proven key in understanding the ecology and life history of elasmobranchs.
- To obtain the genetic profile of each individual from a single by-catch event.
- To identify relatives within the aggregation and assess the overall relatedness levels and genetic diversity.
- To compare the genetic diversity and connectivity between the aggregation samples with additional samples collected elsewhere in the north-eastern Atlantic.
Summary of main research results/outcomes
39 % of spurdog that were genotyped from a single aggregation were related to at least one other individual within the aggregation, with 43 % of these having more than one relative within the group. Comparatively, only 6 % of the other sampled populations
were related to another individual. This is likely due to smaller sample sizes of the other populations.
All populations showed high levels of genetic diversity, comparable with other studies. At a fine scale, spurdog sampled around the British Isles, showed similarity in genetic diversity, except for the aggregation, which had higher heterozygosity and lower
inbreeding coefficients. But spurdog sampled across three years from a West Scotland sea loch were significantly differentiated from all other populations, suggesting limited connectivity outwith the loch.