Kittiwake breeding success in the southern North Sea correlates with prior sandeel fishing mortality

Abstract

In the North Sea, sandeels provide a vital food source for breeding seabirds, but are also the target of an industrial fishery. GPS tracking suggests that the most productive fishing grounds overlap with foraging areas of black‐legged kittiwakes from eastern England, raising the prospect that the fishery could affect the birds. Rising sea temperatures also threaten sandeels, so kittiwake food supplies could be affected by local and larger‐scale processes. Drivers of kittiwake breeding success at Flamborough Head and Bempton Cliffs Special Protection Area, the UK's largest colony, and one of the closest to the sandeel fishing grounds, were examined. Relationships between sandeel stocks, sea surface temperature and kittiwake breeding success were analysed with generalized linear mixed models and generalized linear models, with model performance assessed using the Akaike Information Criterion and R2. Higher kittiwake breeding success was associated with higher sandeel spawning stock biomass (SSB; biomass of sexually mature fish) the preceding winter (R2 = 21.5%) and lower sandeel fishing mortality two years previously (R2 = 22.3%). After temporal trends were removed, only the fishing mortality effect remained. Models with multiple predictors supported the importance of fishing mortality. Higher sandeel SSB was associated with lower temperatures (R2 = 15.2–38.6%) and lower sandeel fishing mortality (R2 = 24.2–26.1%). Hence, lower temperatures and fishing mortality were positively associated with sandeel biomass, and higher sandeel biomass and lower fishing mortality were positively associated with kittiwake productivity. In light of worsening environmental conditions and declining sandeel and kittiwake populations, careful consideration should be given to the requirements of sandeel‐dependent predators when making fishery management decisions.

Combined bottom‐up and top‐down pressures drive catastrophic population declines of Arctic skuas in Scotland

“…Scotland's Arctic skuas are declining rapidly, with bottom‐up and top‐down pressures simultaneously reducing breeding success to unsustainably low levels. Recent observed changes at all trophic levels in the northeast Atlantic Ocean indicate significant restructuring of food webs, driven by fisheries management and climate change acting in combination (Carroll et al., ; Frederiksen et al., ; Régnier, Gibb, & Wright, ). Analogous examples in terrestrial ecosystems include interactions between humans, apex predators, land use and climate change affecting top‐down and bottom‐up pressures on mesopredators (Newsome & Ripple, ; Pasanen‐Mortensen et al., ; Ritchie & Johnson, ).…”

“…Type 2 (n = 9) Type 3 (n = 17) p-value (Carroll et al, 2017;Frederiksen et al, 2006;Régnier, Gibb, & Wright, 2017 Unfortunately, lack of data prevented our inclusion of other skua colonies in western Scotland.…”

“…Potentially, top-down pressures on sandeels also increased with population recovery of previously overexploited predatory fish such as herring Clupea harengus and mackerel Scomber scombrus (Frederiksen, Furness, & Wanless, 2007). Although human take impacts some North Sea sandeel stocks (Carroll et al, 2017;Cook, Dadam, Mitchell, Ross-Smith, & Robinson, 2014), this is considered unlikely in the closely regulated small-scale Shetland fishery (Poloczanska et al, 2004). More significantly, environmental conditions for sandeels appear to be worsening, with sea temperature increases and oceanographic changes affecting their physiology, food supply, phenology and survival, leading to trophic mismatch and less food for seabirds (Carroll et al, 2015;Frederiksen et al, 2006;Régnier et al, 2017).…”

“…Marine policies that could reduce bottom-up pressures on Arctic skuas and their hosts include restrictions or complete closure of sandeel fisheries (Carroll et al, 2017;Cook et al, 2014;Furness & Tasker, 2000), and protecting sea areas from damaging activities (Thaxter et al, 2012). Recent proposals for marine special protection areas and the designation of nature conservation marine protected areas for sandeels in Scottish waters are good examples (Scottish Government, 2016;Scottish Natural Heritage, 2016), although climate change impacts on marine food webs present major barriers to restoring food resources for seabirds (Carroll et al, 2015(Carroll et al, , 2017.…”

Comparing marine distribution maps for seabirds during the breeding season derived from different survey and analysis methods

“…Dogger Bank, Wee Bankie, Marr Bank, Smith Bank) which are known to be important sandeel spawning areas [ 37 , 38 ]. These areas are of particular conservation interest as they are subject to pressure from various human activities including an industrial sandeel fishery (Dogger Bank [ 39 ]), several operational or planned renewable energy developments [ 40 ], and have all been identified as being at relatively high risk to seabird bycatch from various types of fishing gear [ 29 ]. While our analysis was not designed to identify marine protected areas, some of the high use areas consistently identified across the datasets (parts of the Moray Firth, the Firth of Forth, and off the Northumberland coast) are being considered as marine Special Protection Areas, or have recently been designated as such [ 41 – 44 ].…”