Utilization of Otolith Chemistry to Examine Swordfish Xiphias gladius Connectivity throughout the North Pacific Ocean

Population structure and connectivity of swordfish (Xiphias gladius) throughout the North Pacific Ocean (NPO) was examined using otolith chemistry. First, juvenile swordfish otolith core chemistry (proxy of nursery origin) was used to evaluate nursery-specific signatures.  Sagittal otoliths from juvenile swordfish were collected and analyzed to evaluate trace element signatures amongst seven nurseries throughout the NPO.  Otolith core trace element concentrations were quantified using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).  Resulting elemental concentrations were used to evaluate the utility of otolith core chemistry in identifying nursery-specific signatures throughout the NPO.  Next, otolith core chemistry of sub-adults and adults collected from three foraging grounds where targeted fisheries exist was examined to calculate nursery-specific contribution rates using the identified nursery-specific signatures.  Lastly, otolith bulk chemistry (proxy for lifetime signature) of sub-adults and adults was collected from the three foraging grounds to investigate population structure using both trace element concentrations and stable isotopes of carbon (δ¹³C) and oxygen (δ¹⁸O).  Results from this study will inform researchers and fisheries management agencies on the population structure and connectivity of swordfish in the NPO.