Long-term changes in the role of threespine stickleback (Gasterosteus aculeatus) in the White Sea: predatory fish consumption reflects fluctuating stickleback abundance during the last century

Hypothesis: In the White Sea, predatory fish species have consumed higher proportions of stickleback during historical periods and seasons of high stickleback abundance. Organisms: Adults, juveniles, and eggs of threespine stickleback (Gasterosteus aculeatus), together with three species of predatory fishes: cod (Gadus morhua), saffron cod (Eleginus nawaga), and European sculpin (Myoxocephalus scorpius). Place and times: Kandalaksha Bay, White Sea, Russia; June to August 2011-2014. Analytical methods: Sampling with beach seine (stickleback) and gill nets (predatory fish). Analysis of predatory fish stomach contents (identification to the species level, counting, weighing), and in-depth survey of scientific literature on predatory fish diets over the last century. Results: Near the spawning grounds, stickleback comprise 60% of the summer food of sculpin (adult stickleback), 52% of the diet of cod (adults, juveniles, and eggs), and 15% of the diet of saffron cod (juvenile stickleback). These data resemble observations made during a period of high stickleback abundance in the White Sea (1930-1950s). During a period of low abundance (1960s to early 2000s), stickleback were absent from the stomachs of predatory fish.