Nursery origin and population connectivity of swordfish Xiphias gladius in the North Pacific Ocean

Abstract

Element:Ca ratios in the otolith cores of young-of-the-year (YOY) swordfish, Xiphias gladius, were used as natural tracers to predict the nursery origin of subadult and adult swordfish from three foraging grounds in the North Pacific Ocean (NPO). First, the chemistry of otolith cores (proxy for nursery origin) was used to develop nurseryspecific elemental signatures in YOY swordfish. Sagittal otoliths of YOY swordfish were collected from four regional nurseries in the NPO between 2000 and 2005: (1) Central Equatorial North Pacific Ocean (CENPO), (2) Central North Pacific Ocean (CNPO),(3) Eastern Equatorial North Pacific Ocean (EENPO) and ( 4) Western North Pacific Ocean (WNPO). Calcium ( 43 Ca), magnesium ( 24 Mg), strontium ( 88 Sr) and barium ( 138 Ba) were quantified in the otolith cores of YOY swordfish using laser ablation inductively coupled plasma mass spectrometry. Univariate tests indicated that three element:Ca ratios (Mg:Ca, Sr:Ca and Ba:Ca) were significantly different among nurseries. Overall classification success of YOY swordfish to their nursery of collection was 72% based on quadratic discriminant analysis. Next, element:Ca ratios in the otolith cores of subadults and adults collected from three foraging grounds where targeted fisheries exist (Hawaii, California and Mexico) were examined to calculate nursery-specific contribution estimates. Mixed-stock analysis indicated that the CENPO nursery contributed the majority of individuals to all three foraging grounds (Hawaii 45.6 ± 13.2%, California 84.6 ± 10.8% and Mexico 64.5 ± 15.9%). The results from this study highlight the importance of the CENPO nursery and provide researchers and fisheries managers with new information on the connectivity of the swordfish population in the NPO.

Reading the biomineralized book of life: expanding otolith biogeochemical research and applications for fisheries and ecosystem-based management

“…In fully marine settings and for highly migratory fish species with ocean-wide or cosmopolitan distribution such as tunas and billfishes, otolith chemistry has also been used to investigate nursery area use and contribution rates as well as adult movements (Artetxe-Arrate et al 2021;Fraile et al 2016;Rooker et al 2008Rooker et al , 2021Wells et al 2021). These species regularly cross management boundaries, often migrating large distances to complete their life cycles and some exhibiting homing behaviour that further complicates stock assessment and management efforts (Collette et al 2011).…”