What are fish nursery grounds?
Nursery grounds are places where young fish find food, favourable temperature and protection from predators during their early life stages. Different species of fish, including Atlantic cod (Gadus morhua) and saithe (Pollachius virens) juveniles, settle in nearshore areas at different times and depths, depending for example on the timing of spawning and oceanographic conditions. These nursery areas are important for helping young fish survive and grow so they can support future fish stocks.
What is the study about?
The study focused on the shallow coastal waters in the fjords of northwest Iceland. These areas have a variety of habitats, from gravel beaches to rocky and algae-covered zones. Traditionally, scientists have used beach seines—long nets pulled in from the shore—to catch small fish and measure their numbers. While useful, this method cannot cover areas that are deeper or very rocky. In this study, the researchers combined beach seining with scuba diving surveys. Divers swam along set paths underwater and counted the number of young cod and saithe they saw at different depths. This approach provided a clearer picture of where fish were living and how those patterns evolved throughout the summer.
What did they find?
Overall, the researchers observed clear differences in timing and depth use between cod and saithe.
- Saithe settled earlier in the summer. They were most common in shallow spots, especially where algae grew close to the shore. As the summer progressed, their numbers in these areas decreased.
- Cod settled later than saithe, but they stayed in shallow areas longer. They were seen both in dives and caught with beach seines in late summer, suggesting that cod rely on these nurseries for a longer time. Cod were also found across a wider depth range, although most stayed in waters shallower than 10 meters.
The study also showed that young cod often appeared in bigger groups earlier in the summer and later were seen as more scattered individuals. This change may reflect a shift in behavior from shoaling to more solitary living as they grow.
Importantly, both beach seining and diving revealed that during the study period, only cod and saithe utilized these shallow fjord nursery areas—no other closely related species were found.
Why is this important?
This research helps explain how two important commercial fish species utilize Iceland’s shallow waters during their early life stages. Cod and saithe are vital for Iceland’s fishing industry and local ecosystems. Understanding when and where these juvenile fish settle provides knowledge that can be used to manage fish stocks and protect key habitats.
Because beach seine nets are not effective in all places, dive surveys added new insights. For example, divers could record fish in rocky and algae-rich habitats where nets would not work. This filled a knowledge gap beyond what standard surveys usually capture.
Protecting nursery grounds is essential because survival at this stage significantly influences the number of fish that will reach adulthood and become part of the population that supports fishing.
What future research can be done?
While this study filled some important gaps, more work remains. Future studies could:
- Use genetic tools to separate different ecotypes of cod, since it is known that some live closer to shore while others are further offshore.
- Track changes over more years to see how climate and water temperature affect settlement patterns.
- Combine dive surveys with new tracking technology for a fuller picture of how small fish move.
By building on this work, scientists can better predict how young cod and saithe survive in their first year of life and how healthy populations for the future can be supported.
Access full scientific article here: https://doi.org/10.1002/ece3.71674