A Tope-less spring?

Spring in the United Kingdom heralds longer days, awakening plants and the return of migrating birds. Beneath the (somewhat murky) waters of Wales, spring also marks the arrival of another migratory animal, tope (Galeorhinus galeus) also known as soupfin or school sharks. These sharks are thought to winter near the Azores and North Africa before migrating to the shallow coastal waters of northern Europe each spring. Why they return to these areas and which habitats they use remains poorly understood. This is what Project SIARC is trying to find out, together with recreational fishers and charter skippers. Specifically, we aim to understand whether tope use the protected waters of the Pen Llŷn a’r Sarnau Special Area of Conservation (PLAS SAC) as a mating or pupping area. Identifying these critical locations is vital to inform management and ensure that conservation measures effectively protect tope during their most vulnerable life stages.

The trouble with tope

Tope grow to ~200 cm in length and are listed as Critically Endangered on the IUCN Red List of Endangered Species. In the UK, a ban on the commercial catch and landing of tope was implemented in 2008 and the species is now only permitted to be caught by recreational anglers on a catch-and-release basis. While the population appears to have stabilised, recovery of the population requires successful reproduction. Tope’s postulated triennial reproductive cycle and delayed maturity slow recovery, accentuating the importance of locating pupping and mating grounds.

Residents and anglers in PLAS SAC report catching pregnant females in May and June, with pups observed by late July. To test the hypothesis that the SAC functions as a pupping and nursery area, we aim to use blood samples from captured sharks to measure reproductive hormones and gauge reproductive status. In conjunction with a wider acoustic telemetry study, our goal was to catch 20 tope between May and June for tagging and sampling.

Heatwaves and hormones

Early fieldwork at the beginning of May was very successful – we caught 6 tope in the first three days (3 male and 3 female) with the body size of animals suggesting they were all mature (estimated length at maturity for tope is 140 cm). We fitted each shark with an acoustic transmitter, collected tissue samples for genetic analysis, and drew blood samples for hormone analysis. Warm weather, calm seas, and reports of large sharks caught by other anglers raised hopes of encountering pregnant females during subsequent weeks.

Left: Tope are caught by volunteer anglers using rod and line. Centre: Project leader Dr Daniel Montgomery tags a mature female tope. Left: A blood sample is taken from a tope for future analysis of reproductive hormones. All photos © Jake Davies

However, record breaking dry and warm weather in April and May warmed North Atlantic waters, leading to the development of a Marine Heatwave on the west coast of the UK and Ireland. Local fishers report that these conditions, settled weather with clear water and high temperatures, normally lead to a decrease in tope catches which might be linked to movements into deeper, cooler water. Our next two weeks of fishing, during theoretical peak tope fishing season, resulted in just three tope, and mature females remained elusive.

The charter vessel Highlander II while tope fishing during hot, calm conditions in Pen Llŷn a’r Sarnau Special Area of Conservation. Photo © Jake Davies

After rescheduling in June, we relocated south to Aberdyfi to work with one of our other charter skipper collaborators. A change in the weather in early June resulted in strong winds and a choppy sea, but fortunately the weather eased just enough for two days of fishing. The cooler weather seemed to have brought the tope back to the SAC as we had good catches on both days with a total of 23 tope caught! Interestingly, rather than the large females we were targeting, we instead caught several mature male tope. This included the largest animal for the project so far (a ~170cm male) which was fitted with a pop-up satellite tag. Fortunately, some female sharks were also caught, and as well as collecting blood samples from all animals, ultrasound data was obtained from 10 females.

Several further attempts to collect more samples in June and July were sadly thwarted by a combination of mechanical issues with charter boats and poor weather. As the field season concludes, our focus shifts to laboratory analysis of hormone profiles and movement data. We are excited to see what these data reveals about reproductive patterns of tope and clarify whether PLAS SAC serves as a mating or pupping ground.

Project SIARC’s 2025 tope tagging team. From Left to Right: Ben Wray (Natural Resources Wales), Charlie Bartlett (Skipper of charter vessel Mikatcha), Jake Davies (Project SIARC, ZSL), Dr David Curnick (Ocean Predator Lab, ZSL), Jake Lewis (volunteer angler), Sarah Davies (Project SIARC, ZSL), Dr Daniel Montgomery (Ocean Predator Lab, ZSL). Not pictured, our other wonderful skipper Tony Bruce of charter vessel Highlander II, additional members of Project SIARC who assisted with tope sampling, and the many volunteer anglers who helped with catching tope. Photo © Sarah Davies

Project SIARC is a collaborative programme led by the Zoological Society of London and Natural Resources Wales with funding from the Welsh Government Nature Networks Fund, On The Edge, The Moondance Foundation, The Fishmongers Company, and Save Our Seas Foundation. To hear more about our work, you can listen to the latest episode of the ZSL Wild Science Podcast