Connections and Flows Update #6
In the vast expanse of the Gulf of Alaska, a team led by undergraduate student Ella Kelly is making significant strides in understanding the lives of juvenile Pacific cod. Ella, who is currently interning at Alaska Fisheries Science Center's Auke Bay Laboratories, is helping NOAA Fisheries with their juvenile Pacific cod habitat research survey.
The research primarily relies on fishery-independent sampling methods, such as beach seines and bottom trawl surveys. Beach seine sampling is a crucial part of the process, as it targets juveniles in nearshore habitats like shallow coastal areas and estuaries. Using a seine net, Ella and her team encircle and capture juvenile fish, which are then identified, counted, and measured.
The data collected includes species composition, juvenile cod size and numbers, and environmental parameters at the sampling sites. This method helps assess the presence and abundance of juveniles in habitat types that differ from deeper areas sampled by trawl nets.
Complementing beach seine sampling, NOAA Fisheries conducts bottom trawl surveys in the Gulf of Alaska. These surveys sample fish populations on the continental shelf and upper slope, capturing fish and other bottom-dwelling species, including juvenile and adult Pacific cod. The catches are sorted by species, weighed, and measured, with additional biological data such as age, sex, and stomach contents collected from sampled fish.
Data from beach seine and trawl sampling are recorded digitally on tablets and entered into databases to ensure accuracy. Environmental variables like temperature and habitat type are also recorded, which are used to model juvenile Pacific cod habitat and population distribution. This fishery-independent data supports stock assessments and management decisions for sustainable Pacific cod fisheries.
Ella, with her passion for marine life, enjoys the sound of fish splashing in the net when bringing the codend to shore. After the catch is sorted by species and age class, it is brought back to the lab in aerated 5-gallon buckets for further processing.
Genetic analysis will be used to trace juvenile Pacific cod back to their spawning grounds. A subsample of fish is brought back to Auke Bay Laboratories for direct analysis of body condition (fat content, calories) and correlation with Bioelectrical Impedance Analysis (BIA) measurements. The BIA sampler sends a small, harmless electrical current through the body, measuring how much it is impeded (resisted), to estimate the amount of fat mass, fat-free mass, and other body composition parameters.
Body condition data helps understand how habitat influences fish productivity, with higher body condition indicating favorable nursery areas for young Pacific cod. Different beaches have unique characteristics, with some having rocky terrains with kelp species and others supporting seagrass called eelgrass (Zostera marina). Juvenile Pacific cod find shelter and food in both kelp and eelgrass habitats.
In the rugged, 8 X 12 foot, lighted, and heated room on the deck of the mothership, the team works diligently to identify the caught fish, with Darcie focusing on young of the year Pacific cod, but also encountering saffron cod, walleye pollock, and Pacific tomcod.
The objective of this research is to increase our understanding of juvenile Pacific cod, their use of nearshore coastal areas, and their overwinter survival in the Gulf of Alaska. The findings from this research will contribute significantly to the conservation and management of Pacific cod fisheries.
- Ella, driven by her passion for marine life, shows excitement as she hears the sound of fish splashing in the net during beach seine sampling.
- In addition to the research on juvenile Pacific cod, the team also collects data on environmental parameters like temperature and habitat type, which are used in modeling the cod's habitat and population distribution.
- The data collected through fishery-independent sampling methods, such as beach seines and bottom trawl surveys, supports stock assessments and management decisions for sustainable Pacific cod fisheries.
- Not only do they study juvenile Pacific cod, but the team also encounters other species like saffron cod, walleye pollock, and Pacific tomcod during their research.
- In the home and garden of the mothership, the team works diligently to identify the caught fish, with Darcie focusing on young of the year Pacific cod, and the deck serves as a makeshift laboratory where further processing takes place.
