The “Deep 7” fish species live near the seafloor in deep water off the coast of Hawai‘i: onaga, ‘ōpakapaka, ehu, kalekale, gindai, lehi, and hapu‘upu‘u. Pacific Islands Fisheries Science Center researchers provide information on the biology and population status for sustainable management of Hawaii’s largest domestic fishery. Scientists aboard the NOAA Ship Oscar Elton Sette will visit Penguin Bank (southwest Moloka‘i) and the Maui Nui area this spring to do exactly this. They will conduct four research projects in 5 days.
Project 1: Understanding ‘Ōpakapaka Recruitment Dynamics
Juvenile ‘ōpakapaka spend the first few years of their lives in shallow water before migrating to deeper water habitats. The big question is, how far are juvenile ‘ōpakapaka willing to swim to join their adult partners in deeper water? For this project, we will explore the origin of adult ‘ōpakapaka at Penguin Bank. Do they come from the area immediately surrounding Penguin Bank, from the other side of Moloka‘i, or do they cross the Kaiwi and Kalohi Channels? The key to these questions can be found in the fish’s otoliths (ear bones). The seawater in each ‘ōpakapaka “nursery” area has a unique chemical composition which each fish retains throughout its life. During this survey, teams will fish for juvenile and adult ‘ōpakapaka. We will compare the otolith microchemistry of juvenile fish from the different areas around Penguin Bank to that of adults at Penguin Bank to determine their natal origin.
Project 2: Fish Eye Lenses Help Validate Fish Ages
To understand the many aspects of fish biology (such as growth and age at maturity), we need to determine age. We do this by counting the annual growth zones deposited on fish otoliths, similar to counting rings on a tree. One method used to validate that these ages are correct is measuring the amount of Carbon-14 in the otolith. We compare that to the amount of Carbon-14 in a known age reference curve. The amount of Carbon-14 in an otolith reflects the depth that the fish lived during its first year. If it differs greatly from the reference curve, then the reference is not suitable to validate that species’ age. This is common in Hawai‘i because most of the Deep 7 live in deep water (except young ‘ōpakapaka), and the only reference curves available are from shallow water. One way to solve the problem of disparate Carbon-14 values is to measure the amount of Carbon-14 in fish eye lenses instead of otoliths. Eye lenses incorporate Carbon-14 that is more similar to Carbon-14 in shallow water reference curves and may be a more appropriate match.
During this survey, scientists will collect eye lenses and otoliths to compare their Carbon-14 values and determine which is a better match with the reference curve. They will also supplement regional Carbon-14 reference curves with modern Carbon-14 values from ‘ōpakapaka with known ages.
Project 3: Is This Fish Mature or Does it just Look Mature Because the Gonads were Poorly Preserved?
Researchers examine fish gonads (fish reproductive organs) to determine the size at which fish mature. This is important information for stock assessments because it allows scientists to determine the number of spawning fish in the population. Researchers collect the gonads from fish, preserve them in formalin, and then affix them to microscope slides. They then examine the slides to ascertain if the fish is mature or not. However, some of the characteristics of a mature fish also appear in juvenile fish whose gonads were poorly preserved (such as frozen or kept at room temperature too long). This can result in a misclassification of maturity and may potentially bias the size at maturity estimate. For this project, we will collect fish and preserve their gonads in several different ways that mimic poor preservation conditions to test how this impacts maturity estimates.
Project 4: Going Deeper with the Bottomfish Cameras
The Deep 7 inhabit waters as deep as 1,600 feet. The annual bottomfish survey uses advanced, low-light camera systems to help estimate fish abundance which improves our stock assessment. However, since the cameras currently use only ambient light, they are limited to a depth of about 650 feet. Below that, it is just too dark. During this project, scientists will test several prototype artificial lighting systems that can attach to the camera frame. We will use artificial lights to deploy cameras across the entire depth range of the Deep 7 as long as we can find a configuration that adequately illuminates the camera field of view without significantly affecting fish behavior.
The research includes scientists from NOAA Fisheries Pacific Islands Fisheries Science Center and the Cooperative Institute for Marine and Atmospheric Research.
