Protecting pregnant and pupping porbeagle sharks
Porbeagle sharks have declined in the north-eastern Atlantic, their populations pressured by commercial fishing, and conservation intervention is needed where and when they are most vulnerable. Pregnant porbeagles need to move into shallower waters, which places them at high risk of contact with humans. Tom wants to understand how and where porbeagles are reproducing in this region. He is using ultrasonography and steroid hormone concentrations to assess whether females are pregnant, and then bio-logging to track their movement patterns. The information he obtains can help to advise how porbeagles in vulnerable life stages and areas could be best protected.
Thomas Horton
I grew up in a land-locked village in rural England and, perhaps oddly, have always had a fascination for water. Like others who didn’t have the ocean in their back garden, my intrigue was fuelled by fishing in local rivers and the wholesome pursuit of rock pooling when on family holidays. My father was, and still is, a keen fly fisherman and when my three brothers and I were young he taught us how to fish. Family holidays were spent in the Channel Islands off the UK, where rock pooling, jumping off the cliffs into the sea and...
A new reproductive hotspot for the critically endangered porbeagle shark
Our primary objective is to characterise the reproductive status and track the onward movements and habitat connectivity of mature porbeagle sharks from a putative reproductive hotspot off the UK coast.
Porbeagle shark populations in the north-eastern Atlantic have been depleted through commercial fishing, requiring urgent conservation action when and where the sharks’ most vulnerable life-history stages occur. Pregnant females often need to enter specific habitats, such as shallow coastal areas. Here they are more likely to interact with humans. This project aims to assess and characterise reproductive life-history traits for porbeagle sharks in the north-eastern Atlantic with a view to informing their conservation.
Reproductive performance in a species to a large extent determines its population growth and resilience to exploitation. Accurate information about the reproductive biology of fish species is therefore crucial to their conservation, and is even more pertinent for rebuilding populations such as those of porbeagle sharks in the north-eastern Atlantic. Porbeagle sharks mature late (8–13 years in the north-western Atlantic), have a long gestation period (9–12 months) and produce small litters (3–4 pups), resulting in a relatively low reproductive output, which makes their populations particularly susceptible to decline.
The North Atlantic porbeagle population is separated into two spatially discrete stocks: north-western and north-eastern. Comparatively little is known about the reproductive habits of the north-eastern stock, and no reproductive regions of importance have been identified. Tracking efforts in the region have focused largely on stock structure and migratory ecology and what little is known about the reproductive ecology in the region is inferred from the north-western Atlantic or catches occurring to the north-east of Scotland nearly 40 years ago.
It is estimated that mating occurs in December and January, gestation lasts longer than 12 months and that parturition occurs in summer/autumn. However, this information is both outdated and based on a very small and restricted sample size. Anecdotal records collected by recreational anglers indicate that generally large, potentially pregnant females occur off the northern coast of the UK, and young-of-the-year porbeagle sharks have been seen off the southern coast of south-western UK. More specifically, evidence from unpublished tracking records highlights that the area around south-western England may be a reproductive hotspot for porbeagle sharks in spring. Together, these observations may indicate that pups born off the north coast may move to juvenile habitat off the south coast, but to date there has been no dedicated research to address this knowledge gap.
We aim to assess and characterise reproductive life-history traits for porbeagle sharks in the north-eastern Atlantic, with a view to informing conservation measures.
- To determine reproductive state of large porbeagle sharks off the south-western UK via ultrasonography and steroid hormone concentrations.
- To use bio-logging methods to study the onward movements of mature females from the inferred reproductive area.
- To combine the data gathered by the methods above to advise on how vulnerable life stages and areas could be best protected, and how tangible conservation outcomes can be achieved.