|Rasmus and Nancy|
|Fishing for copepods in the sea ice in the Artic Ocean|
|A lovely bluefin tuna (Thunnus thynnus) larvae collected during our survey|
This is the second cruise aimed at understanding what makes up a good habitat for larval Bluefin tuna (BFT) to survive and grow. We want to be able to tell where to find these habitats and how much will be available in the future ocean. Much of my research has focused on baby fishes, the larval period of a fish’s life. This is the time when fish, are the most vulnerable to starvation and predation. Therefore, it is also considered to be the period most critical to recruitment: which is the number of fish that make it to adulthood and reproduce themselves someday. Understanding what is needed for a larval fish to survive is of particularly importance to management of commercially exploited fish such as Bluefin tuna.
That’s where my expertise comes at play. I study what they eat. The more the larvae eat, the faster they can grow to improve their hunting capabilities and to avoid being eaten themselves. So, how do we determine a good larval tuna habitat? First, we need to know how much food is available to the larvae, and then which sources of nutrients are sustaining the food chain sustaining the larvae.
|Mike L. and Ramus recover and rinse the ring-net|
that has sampled the zooplankton (prey of BFT)
We are also studying their feeding habits by looking at their Nitrogen (N) signature. What is a Nitrogen signature? We look at the two naturally occurring isotopes of N (that is different variants of N). This is done in specific amino acids, the building blocks of proteins that make up the body tissues of the fish larvae. The less common 15N isotope is heavier than the common 14N. This weight difference means that 15N assimilated from the food is moved around the larval body and ultimately excreted as waste products at a slower speed relative to 14N. As a result there is a buildup of 15N compared to 14N in the larvae relative to their food.
Some larger zooplankton collected by our ring net
I am now back in the lab and I can’t wait to start analyzing all the tuna larvae we collected to unravel the secrets of their diet.