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Dispatches from the field

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


 

larval sablefish on ice
Larval sablefish caught with a neuston net  Photo: Ali Deary, NOAA Fisheries

 
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Sablefish larvae in the research spotlight

May 30, 2017 -- We are now officially halfway done with the survey! The weather recently became rough so the ship is currently anchored in a cove protected from the wind. As we wait for the weather to improve, we have been busy checking our data, tending to the gear, and getting everything prepped for our last nine days at sea.

We have sampled more than 150 stations and are about to sample a second area between the Shumagin Islands and Kodiak Island for sablefish. After extensive fishing in the 1970s, the number of sablefish declined rapidly in the Gulf of Alaska. After regulations were put in place, the population began to recover and had a peak abundance in the 1990s, although the population was still smaller than it was before heavy fishing occurred. Now, the numbers are relatively lower than the peak, though the Gulf of Alaska stock is considered sustainable.

Scientists believe sablefish population size is related to survival in the early life stages. That is before the fish grow large enough to be caught, which highlights the value of early life history research. Unlike the adults, which live along the seafloor in depths up to 1,500 meters, sablefish larvae live in the very top layer of the ocean. While bongo nets effectively capture other larval fish, these nets alone arenít effective at the surface. To study the early stages of sablefish, we must use an additional device, known as a neuston net. The neuston net skims organisms from the surface by fishing half in and half out of the water.

 

scientist on deck using a special net to collect
Researcher monitors the neuston net collecting organisms that live near the ocean surface  Photo: Ali Deary, NOAA Fisheries

 

For larvae, life near the surface can be difficult. At the surface, larvae are exposed to predators like seabirds. Plus, larvae are subjected to variable temperatures, salinities, winds, solar radiation, and currents. At deeper depths, conditions often remain constant.

We are not sure how water conditions influence the growth and survival of sablefish during the first year of life. Sablefish can also grow very quickly, which means they need to eat copious amounts of nutritious zooplankton. To assess how these variables affect the survival of young sablefish, which will impact the number of individuals that survive into adulthood, we are collecting larvae from different parts of the Gulf of Alaska. Along with several other researchers, we are going to identify the regions where we caught the most sablefish larvae, examine what the larvae are eating, and then determine how healthy these individuals are. With these data, we can start to piece together how life at the surface influences the survival of sablefish larvae.

Post by: Ali Deary

 


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