Food and initial size influence overwinter survival and condition of a juvenile marine fish (age-0 Atlantic cod)

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Geissinger, Emilie A., Gregory, Robert S., Laurel, Benjamin J., Snelgrove, Paul V.R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2021
• Subjects: atlantic cod; Gadus morhua; Newfoundland; Subarctic
• Online Access: http://dx.doi.org/10.1139/cjfas-2020-0142; https://cdnsciencepub.com/doi/full-xml/10.1139/cjfas-2020-0142; https://cdnsciencepub.com/doi/pdf/10.1139/cjfas-2020-0142

In subarctic Newfoundland, age-0 Atlantic cod (Gadus morhua) settle into coastal habitats in several summer–autumn pulses, resulting in broad length-frequency distributions before winter. Low winter temperatures and potential decreases in food availability pose challenges for young-of-year fish. To examine how size variation affects overwintering success under contrasting food scenarios, we conducted 114-day laboratory feeding trials at ambient overwinter sea temperatures, using demersal age-0 cod collected from Newman Sound, Newfoundland. We reared two size classes of juvenile cod under four daily ration levels (starvation, low, medium, high). We used Fulton’s K condition factor to interpret effects of food availability and fish size on survival over winter. We showed that small amounts of consumed food (<1% BW·day −1 ) maximized winter growth and condition potential of juvenile cod in Newfoundland waters. With no food, survival of small cod dropped below 80% on Day 47, whereas survival of large juveniles remained >80% until Day 74. Therefore, we expect higher survival of earlier settlers and increased size-selective mortality in age-0 cod during either unproductive or protracted winters, when food abundance is often low.