Population dynamics of fish juveniles and invertebrates in Icelandic waters

• Main Author: Jonasson, Jonas Pall
• Other Authors: Guðrún Marteinsdóttir, Líf- og umhverfisvísindadeild (HÍ), Faculty of Life and Environmental Sciences (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of Iceland, School of Engineering and Natural Sciences, Faculty of Life and Environmental Sciences 2021
• Subjects: Fiskifræði; Fiskirannsóknir; Hafstraumar; Sjávarvistfræði; Fiskistofnar; Doktorsritgerðir; Gadus morhua; Iceland; North Atlantic
• Online Access: https://hdl.handle.net/20.500.11815/2379

The marine ecosystem around Iceland is shaped by its position in one of the most hydrographically complicated regions of the North Atlantic. The response of marine populations to those diverse conditions is expected to be different across taxonomically distinct species but by comparing and analysing the differences we can better understand the system as a whole. In the present study, population dynamics of juvenile cod (Gadus morhua), juvenile plaice (Pleuronectes platessa), brown shrimp (Crangon crangon) and Iceland scallop (Chlamys islandica) were analysed with respect to recruitment patterns and fluctuations. The studies were carried out during a period of increased influx of Atlantic waters around Iceland and consequently higher temperatures. The studied species either have their core distributional areas in Iceland, like the cod, or are at their southern borders, like the Iceland scallop. We also analysed population trends at sheltered sandy beaches, which is an essential habitat for the juvenile plaice and also the brown shrimp, a newly found invasive species and important predator of juvenile plaice. Findings revealed the highest abundance of cod larvae within low-salinity waters, characteristic of the Icelandic coastal current (ICC). That is in line with previous studies that have demonstrated a potential link between the freshwater discharge or the strength of the ICC and recruitment of cod. The distribution of the cod juveniles within the boundaries of the ICC highlights the role of the freshwater driven coastal current in successfully transporting larvae from the spawning areas into the northern nursery grounds. The fluctuation in recruitment is relatively small in the Icelandic cod stock and likely dampened by the smaller northerly grounds. In an effort to establish the natal origins of juveniles of plaice around Iceland, settlement and growth patterns of juvenile plaice were estimated. There were differences in the size and age distribution around Iceland, which led to the conclusion that juvenile ...