We welcome back guest blogger, Ella Kelly, to Currents and Connections. Ella is an undergraduate student attending the University of Alaska Southeast in Juneau, Alaska. Ella is currently interning at Alaska Fisheries Science Center’s Auke Bay Laboratories. She is participating in the NOAA Fisheries juvenile Pacific cod research survey in the Gulf of Alaska. The objective of this research is to increase our understanding of how juvenile Pacific cod use nearshore coastal habitats and what factors influence their survival through winter. By collecting detailed data on the early life stages of Pacific cod, scientists are refining a computer model that predicts how larval cod disperse and where they settle. Incorporating these findings into stock assessments can improve estimates of Pacific cod population size, fishing pressure, and the number of young fish entering the fishery each year, ultimately leading to more accurate and sustainable fisheries management. Read on to learn more about Ella’s journey into the field of marine science and her adventures aboard the Lady Sea.
Sampling and Data Collection
The last couple of days have been a research intensive process, as well as a bodily intensive process. Pulling in beach seines is hard! I have been learning a lot about nearshore sampling and data collection – so that is what I will focus on during the next couple of blog posts.
My fellow interns were kind enough to let me strap Go-Pro’s to their heads to record beach seining and baited camera sampling. There is nothing quite like seeing the real thing! Today I’ll do a deep dive into beach seining.
Beach Seine Sampling
As I described in my previous post, we use a beach seine to sample nearshore marine nursery habitats used by our target species, Pacific cod. The video below shows what a typical beach seine set is like.
My favorite part about seining is right as we bring the codend to shore and are greeted with the sound of fish splashing in the net. We then look inside the net to see what we caught. It’s like my birthday every day, getting to open a new exciting present!
We empty the codend into buckets and totes of aerated seawater on shore. Larger, non-target fish are released back to the ocean. We then use hand-held sieves to sort the catch by species and age class.
Every beach is different. Some beaches are rocky and characterized by one or more kelp species, while others have a more mobile substratum that supports an important seagrass called eelgrass (Zostera marina). Juvenile Pacific cod find shelter and food in both kelp and eelgrass habitats.
Likewise, each seine catch is different. Sometimes we will end up with a single gadid, and other times we get hundreds or even thousands. When we get more than about 200, we take a subsample on the beach, by pouring everything into one bucket and swirling it up to get a totally randomized sample. With that sample, we usually take around 200 fish back to the ship’s lab to identify and process. The remaining fish are released back to the ocean.
Some of the cod we catch are brought back to the lab in aerated 5 gallon buckets for further processing.
The lab is a rugged, 8 X 12 foot, lighted, and heated room on the deck of our mothership where we have a fish assembly line to identify cod species, measure lengths, evaluate body condition, and collect samples to bring back to Auke Bay Laboratories for biochemical analysis of fat content.
Darcie identifies the cod which are difficult to differentiate at such a small size. We are focusing on young of the year Pacific cod, but we get some saffron cod, walleye pollock and Pacific tomcod as well. I have been learning to differentiate the little gadids (family of cods) from Darcie. Pacific cod have a long barbel on their chin, the pollock have less organized dots on their bellies and bigger eyes. I am learning how to identify the saffron cod and tomcod from Pacific cod – Thank you, Darcie!
Fionn measures the fish, then hands them to me. My task is to take a caudal fin clip from 10 fish and staple them to a card for genetic sampling that will occur back at Auke Bay Labs. Genetic analysis will be used to trace the juveniles back to their spawning grounds. After we have what we need for genetics, I check into the scribe role and write down Fionn’s fish length measurements.
Johanna then uses a Bioelectrical Impedance Analysis (BIA) sampler on each fish to measure lipid (fat) content. For juvenile fish, fat indicates healthy body condition and fish condition is thought to be a predictor of their survival and future productivity.
A BIA sampler sends a small, harmless electrical current through the body. The device measures how much the current is impeded (resisted) as it travels through the body. This resistance helps estimate the amount of fat mass, fat-free mass, and other body composition parameters. Body condition helps us understand how habitat influences fish productivity. In this case, body condition data tells us which bays have been the most favorable nursery areas for the young cod to live in. We also bring a subsample of fish back to our analytical laboratory at Auke Bay Laboratories in Juneau, Alaska, to directly analyze body condition (fat content, calories) and correlate with the BIA measurements.
Stay tuned for my next blog post, where I'll dive into the captivating world of underwater photography. Prepare to be amazed by sights you've always wondered about, from swaying beds of eelgrass to juvenile Pacific cod gracefully navigating their underwater world.
