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Dispatches from the field

Scientists seek out the tiniest catch, larval fish in the Gulf of Alaska


 

One of our researchers, Adam Spear, counting and identifying zooplankton for a rapid zooplankton analysis during the cruise.  Photo: Ali Deary, NOAA Fisheries

 
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Zooplankton- The food of larval fishes

June 7, 2017 -- We are now in the homestretch of our survey! Over 250 stations sampled and we are currently off the south eastern coast of Kodiak getting closer to the port. The past few days have been exciting! We collected more sablefish in our neuston net, and also saw Northern Fur Seals and orcas. Unfortunately, these animals moved too quickly to capture any decent pictures. The skies cleared over the past few days enabling us to witness some glorious sunsets and sunrises.

 

After rinsing plankton from the net, we preserve them in these jars that will be shipped back to Seattle after the survey is complete.  Photo: Ali Deary, NOAA Fisheries

 

Next step: analysis

As we near the end of the survey, we have collected over 300 samples. These samples will be offloaded from the vessel in Kodiak and sent to Seattle. It takes about a year to process and analyze all the samples collected. Given that we collect about 3,000 samples in total from all our surveys every year- this is a really fast turnaround time. Plankton samples are extremely labor intensive to process. For each sample, you must pick out all the larval fishes and identify them. Approximately half of the samples also are processed for zooplankton, which means we count and identify each zooplankton species. Although our primary focus is on larval fishes, we are also interested in zooplankton because they are prey for larval fishes. The number and nutritious value of the various zooplankton species influences the overall health and survival of the larval fishes eating them.

 

Unsorted plankton sample.  Photo: Ali Deary, NOAA Fisheries

 

Initial analysis

Rapid Zooplankton Analysis, or RZA, is a way for us to get a rough idea of the zooplankton species and their abundances at each station soon after leaving the ship. Until we have our final data, the RZA serves as an early indicator about the zooplankton community in the study area. It tells us if a given station has a favorable or unfavorable prey field for larval fishes, when combined with feeding preference information. The ability of larval fishes to find and feed on nutritious prey is crucial for their growth and survival. Larval fishes in regions with high numbers of nutritious zooplankton often have higher growth rates and more individuals will likely survive to adulthood.

 

A planktonic organism called a sea butterfly. This one is covered with some gelatinous organisms.  
Photo: Ali Deary, NOAA Fisheries

 

We also quickly count the number of larval walleye pollock collected at each station. This serves as an indicator of how many walleye pollock there are and where they are concentrated.

 

Another type of zooplankton, this is the larval form of a squid.  
Photo: Ali Deary, NOAA Fisheries

 

We provide these data to managers at the North Pacific Fisheries Management Council and the fishing industry. Knowing where the best environments are that enhance larval fish survival is essential to effective management of commercial fish species.

 

Sunrise as we approach our next sampling station offshore of Kodiak Island.  Photo: Ali Deary, NOAA Fisheries

 

Post by: Ali Deary

 


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