Assessing the importance of Isle of Man waters for the basking shark Cetorhinus maximus

Dolton, Haley R.; Gell, Fiona; Hall, Jackie; Hawkes, Lucy A.; Witt, Matthew J.

doi:10.3354/esr01018

Cited by 12 publications

(6 citation statements)

References 63 publications

(57 reference statements)

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“…Basking sharks were tagged between the 26th of July and the 8th of August 2012 at Malin Head, Ireland (55.37 ○ N, 7.40 ○ W). This deployment time frame was chosen to maximise data recording across autumn and winter months when sharks are known to disperse from coastal seas around Great Britain and Ireland (Sims et al 2003;Doherty et al 2017a;Dolton et al 2019). The waters around Malin Head are a seasonal aggregation area (hotspot) for basking sharks in the North East Atlantic (Johnston et al 2019).…”

Section: Device Deployment Sitementioning

confidence: 99%

“…Seasonal shifts in environmental conditions have been proposed as dispersal cues for basking sharks (Cetorhinus maximus) that aggregate in coastal hotspots at temperate latitudes during summer months, moving typically into offshore areas with the onset of autumn (Sims et al 2003;Gore et al 2008;Skomal et al 2009;Doherty et al 2017aDoherty et al , 2017bBraun et al 2018;Dolton et al 2019). Oscillations in plankton abundance provide an intuitive explanation for this pattern (Sims and Reid 2002), but prey densities appear adequate for year-round foraging (Sims 1999) and residence in coastal seas (Doherty et al 2017a, b).…”

Section: Introductionmentioning

confidence: 99%

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Cool runnings: behavioural plasticity and the realised thermal niche of basking sharks

Johnston¹,

Houghton²,

Mayo³

et al. 2022

Environ Biol Fish

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Long-distance migrations by marine vertebrates are often triggered by pronounced environmental cues. For the endangered basking shark (Cetorhinus maximus), seasonal changes in water temperature are frequently proposed as a cue for aggregation within (and dispersal from) coastal hotspots. The inference is that such movements reflect year-round occupancy within a given thermal ‘envelope’. However, the marked variance in timing, direction and depth of dispersal movements hint at a more nuanced explanation for basking sharks. Here, using data from pop-off archival transmitters deployed on individuals in Irish waters, we explored whether autumnal decreases in water temperature triggered departure from coastal habitats and how depth and location shaped the sharks’ realised thermal environment over time. Temperature was not an apparent driver of dispersal from coastal seas, and variance in daily temperature ranges reflected occupancy of different habitats; coastal mixed/stratified and offshore subtropical/tropical waters. Furthermore, individuals that moved offshore and into more southern latitudes off Africa, exhibited a distinct daily cycle of deep dives (00:00–12:00, 200 m–700 m; 12:00–00:00, 0–300 m), experiencing a more extreme range of temperatures (6.8–27.4 °C), including cooler minimum temperatures, than those remaining in European coastal habitat (9.2–17.6 °C). Collectively, these findings challenge the supposition that temperature serves as a universal driver of seasonal dispersal from coastal seas and prompts further studies of deep-water forays in offshore areas.

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Section: Device Deployment Sitementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Cool runnings: behavioural plasticity and the realised thermal niche of basking sharks

Johnston¹,

Houghton²,

Mayo³

et al. 2022

Environ Biol Fish

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“…Based on our non-systematic data and other studies, basking shark sightings occurred primarily during summer months starting in the 1990s (Baduini, 1995;Dewar et al, 2018) with the majority of records from the late spring through early fall. This is also the season they are sighted in the temperate waters of the North Atlantic (e.g., Sims et al, 2003;Doherty et al, 2017;Johnston et al, 2019;Dolton et al, 2020). It is possible that these recent changes were biased to some degree by season; for example, more people may undertake recreational activities on the water during the summer.…”

Section: Spatial and Temporal Trendsmentioning

confidence: 99%

Spatial Distribution, Temporal Changes, and Knowledge Gaps in Basking Shark (Cetorhinus maximus) Sightings in the California Current Ecosystem

et al. 2022

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Among the largest fish species, the basking shark (Cetorhinus maximus) is found circumglobally in temperate and tropical waters. Though historical documents have recorded their presence in the California Current Ecosystem (CCE), basking sharks are now only rarely observed in this part of their range. We compiled recent and historical data from systematic surveys (1962–1997) and other sources (1973–2018) to (i) examine temporal patterns of basking shark sightings in the CCE, and (ii) determine the spatial, temporal, and environmental drivers that have affected basking shark presence and distribution here for the last 50 years. We first calculated variation in basking shark sightings and school size over time. We then generated species distribution models using the systematic survey data and evaluated the performance of these models against the more recent non-systematic sightings data. The sightings records indicated that the number of shark sightings was variable across years, but the number and probability of sightings declined in the mid-1980s. The systematic survey data showed up to nearly 4,000 sharks sighted per year until the 1990s, after which there were no sightings reported. In parallel, there was more than a 50% decline in school size from the 1960s to the 1980s (57.2 to 24.0 individuals per group). During the subsequent decades in the non-systematic data (>1990), less than 60 sharks were sighted per year. There were no schools larger than 10 reported, and the mean school size in the last decade (2010s) was 3.53 individuals per group. Low sea surface temperature and high chlorophyll a concentration increased sightings probability, and prevailing climatic oscillations (El Nino-Southern Oscillation index, North Pacific Gyre Oscillation, Pacific Decadal Oscillation) were also correlated with basking shark presence. Lastly, we observed a significant shift in the seasonality of sightings, from the fall and spring during the systematic survey period to the summer months after the 2000s. We conclude by offering suggestions for future research and conservation efforts; specifically, coordinating the documentation of fisheries mortalities and sightings throughout the Pacific basin would facilitate more robust population estimates and identify sources of mortality. Additionally, monitoring shark fin markets and developing region-specific genetic markers would help ensure that convention on international trade in endangered species (CITES) regulations are being followed.

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Section: Biological Contextmentioning

confidence: 99%

“…Harbor seals and gray seals travel between Shetland and the Faroe Islands and found all the way to Norwegian fjords. One basking shark tagged in Isle of Man was inferred to move through the Bergen‐Shetland Corridor to a detection point off the coast of Sognefjord (Dolton et al, 2020). Satellite tracks of gray seals reveal traveling and foraging behavior in the Bergen‐Shetland Corridor hundreds of kilometers offshore (Russell et al, 2017).…”

Section: Biological Contextmentioning

confidence: 99%

Strategic importance of the Bergen‐Shetland Corridor to marine biology and oceanography of the Atlantic Ocean

Lennox

Junge

Reubens

et al. 2022

Fisheries Oceanography

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The North Sea is one of the busiest and most exploited marine areas on Earth and is home to many highly migratory and economically important species. At the northern boundary, a 300‐km corridor between Norway and Shetland forms a major egress point from the North Sea to the Norwegian Sea and broader Atlantic Ocean, which is known to be used by many focal species including Atlantic salmon, European eel, European sturgeon, Atlantic bluefin tuna, basking shark, Atlantic mackerel, spiny dogfish, among others. We argue that this relatively shallow 300‐km corridor is a critical area for ecological and oceanographic research in the North Sea to understand species distribution, migratory patterns, responses to climate, fisheries, and more. Instrumentation of the Bergen‐Shetland Corridor with a line of oceanographic and biological tracking infrastructure would help capture the spatiotemporal dynamics of the ocean and its major fauna between the North Sea and Norwegian Sea, a boundary between management areas from ICES and OSPAR.

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Assessing the importance of Isle of Man waters for the basking shark Cetorhinus maximus

Cited by 12 publications

References 63 publications

Cool runnings: behavioural plasticity and the realised thermal niche of basking sharks

Cool runnings: behavioural plasticity and the realised thermal niche of basking sharks

Spatial Distribution, Temporal Changes, and Knowledge Gaps in Basking Shark (Cetorhinus maximus) Sightings in the California Current Ecosystem

Strategic importance of the Bergen‐Shetland Corridor to marine biology and oceanography of the Atlantic Ocean

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