Dataset: Total mercury concentrations and size data for bigeye tuna, yellowfin tuna, and longnose lancetfish from the North Pacific Ocean

Lancetfish Sample Collection:

Whole lancetfish (n = 69) were collected by fisheries observers of the National Oceanic and Atmospheric Administration (NOAA) Pacific Islands Region and West Coast Region Observer Programs from 2018 to 2023 between 20 – 40° N and 115 – 160° W in the central and eastern North Pacific Ocean. Observers sampled lancetfish from the Hawaii-based shallow- and deep-set pelagic longline fisheries. Lancetfish were frozen whole at sea and capture location was recorded. In the lab, specimens were defrosted, measured to the nearest mm (FL), and weighed whole to the nearest 0.1 g. 

Dorsal muscle tissue from each lancetfish was sampled posterior to the operculum at the base of the dorsal fin insertion and anterior to the vent. Only white muscle tissue was sampled, and skin, bones, and cartilage were removed from white muscle tissues before analysis. Following dissection, all tissues were gently rinsed with Milli-Q to avoid contamination between samples, placed in pre-weighed Whirl-Paks, and weighed before and after drying to measure moisture content. Tissues were frozen at -80˚C before being freeze-dried and homogenized within the Whirl-Pak or using an electronic mill (IKA Tube Mill 100 Control). Milling vessels and tools were cleaned with 95% ethanol between samples. 

Tuna THg Data:

We used published size and THg data from muscle tissues of bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) collected in the central North Pacific ​(Brooks, 2004; Choy et al., 2009; Kaneko and Ralston, 2007; Kraepiel et al., 2003; Rivers et al., 1972; Thieleke, 1973​; as compiled in ​Drevnick and Brooks, 2017)​, along with data from ​Choy (2013)​. Life history, metabolism, and diet information for bigeye and yellowfin tuna are available in the literature and were used to explain changes in THg burden with size.