Synergism between cruising cod and ambush sculpin predators on 0-group gadoids is modified by daylight cycle and presence of aggressive wolffish

• Published in: Journal of Experimental Marine Biology and Ecology
• Main Authors: Strand, Hans Kristian, Pedersen, Torstein, Christie, Hartvig C, Moy, Frithjof Emil
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2020
• Subjects: VDP::Mathematics and natural science: 400::Zoology and botany: 480::Marine biology: 497; VDP::Matematikk og Naturvitenskap: 400::Zoologiske og botaniske fag: 480::Marinbiologi: 497; Norway; Gadus morhua; Northern Norway; Porsangerfjorden; midnight sun
• Online Access: https://hdl.handle.net/10037/18800; https://doi.org/10.1016/j.jembe.2020.151356

Shorthorn sculpin ( Myoxocephalus scorpius ) and large cod (300–400 g body weight) are important predators on newly settled 0-group cod ( Gadus morhua ) and saithe ( Pollachius virens ) in Porsangerfjorden in northern Norway. The Atlantic wolffish ( Anarhichas lupus ) used to be abundant but is now very rare in the fjord. Video recorded experiments showed that interactions between shorthorn sculpins, wolffish and large cod affected predation rates on small 0-group cod and saithe in tanks with a gravel, cobble and seaweed ( Fucus serratus ) substrate. We found that sculpins were unable to catch 0-group specimens when they were the only predatory species in the experimental tank and the lights were left on 24 h a day (to simulate the midnight sun), and that they did not even attempt to catch them. The addition of a large cod to the tank increased sculpin attack rates and predation success significantly. The “cod effect” was due to 0-group specimens avoiding attacks by escaping into the cobbles or vegetation, were they could be more easily reached by the sculpins. When tanks were supplemented with a wolffish in addition to the cod, both sculpin and cod predation success was lowered by approximately 50% in the 24-h light regime. When the experimental setup was changed to a day/night light cycle, however, the wolffish presence had no effect. Also, sculpins in tanks without cod and wolffish went from consuming zero to 29% of the 0-group specimens in the tank when the light regime went from 24-h light to day/night. Sculpins and cod were most effective predators on 0-group cod and saithe at dusk/night/dawn, and the presence of a cruising predator like cod increased sculpin predation success and probably vice versa . The experimental data indicate that rebuilding wolffish stocks in the fjord system may make the bottom substrate more protective for 0-group specimens of cod and saithe, by limiting the foraging volume of an effective bottom-dwelling 0-group predator like the sculpin. Further field and lab studies must be conducted before the reported findings optionally can be turned into a management advice.