The study of the early life history of large, open-ocean pelagic fishes such as tunas and billfish, and the identification of spawning and nursery habitats, has been extremely difficult as these animals are intrinsically rare, highly migratory, and difficult to study in captivity. Traditional methods such as the assembling of a developmental series of life stages, or the culturing of unknown eggs and larvae to a point where they can be identified, has not been easy or fruitful for many pelagic species. The discovery of a putative spawning 'hot spot' off the Kona coast of Hawaii, coupled with the development of shipboard approaches to real time identification and adaptive sampling of eggs, may provide new approaches and insights into the spawning ecology and reproductive biology of these highly valuable but poorly known species. Here we report the use of a shipboard PCR based assay to differentiate species of istiophorid billfish larvae and identify eggs of istiophorid and xiphiid billfish, coryphaenid dolphinfish, and wahoo. A species-specific multiplex PCR assay was designed to amplify a single, unique size fragment of the mitochondrial cytochrome b gene for all 6 species of Indo-Pacific billfish, both dolphinfish, and the monospecific wahoo. A boiling technique used to extract DNA from larval eye tissue or an individual egg, combined with a single-step PCR assay and agarose electrophoresis, allowed species identification within 3 h of sample acquisition. This nearly real-time identification method for morphologically indistinguishable eggs and larvae provides an opportunity to employ adaptive sampling methods to increase sampling efficiency and will help in determining the spatial and temporal dimensions of spawning and nursery habitats offshore. This study describes the occurrence of blue marlin, dolphinfish, shortbill spearfish, swordfish and wahoo off the Kona coast by molecular approaches, and it provides the first description of the eggs of blue marlin, shortbill spearfish and wahoo.

Armorhead (Pseudopentaceros wheeleri) occur in the subarctic, epipelagic habitats of the northern Pacific Ocean and are known to reproduce on seamounts in the central Pacific. Over the last few decades, overexploitation of seamount populations led to dramatic declines in abundances of reproductive populations. We undertook a study of the population genetics of armorhead to test whether distinct stocks exist in association with specific seamounts. We used the polymerase chain reaction (PCR) and a combination of DNA sequencing and restriction fragment length polymorphism (RFLP) analysis to analyze mtDNA variants for individuals collected from three localities: two seamounts and from the open ocean. We discovered that mtDNA haplotypes are not partitioned geographically, refuting the hypothesis that different seamounts harbor genetically distinct populations. Furthermore, genetic similarity of seamount and open-ocean fish supports the hypothesis that armorhead migrate between the central and northern Pacific Ocean for reproduction and feeding, respectively.

An investigation into armorhead Pseudopentaceros wheeleri recruitment variation at Southeast Hancock Seamount (in the central North Pacific) focused on the examination of recruit characteristics, primarily those derived from otolith-increment analysis. Otoliths from recruits were sampled from years representing relatively strong (509 metric tons [t] in 1980), moderate (58 t in 1986), and weak (1 t in 1989) recruitment biomass. Recruit body length was also examined among these 3 years and from 10 additional years, providing even higher recruitment contrast. Transverse sections of sagittal otoliths were prepared, and yielded information on the mean and variability in pre-recruit pelagic duration and increment-width profiles. Mean length of female recruits, and to a lesser extent of mean pelagic duration, decreased with increasing recruitment strength. Although generally similar in shape, the mean increment-width sequence spanning the first 1.8 yr of the 2+ yr pelagic phase differed among recruit years. Transitions in sequential increment-width (inflection points) were exhibited among all recruit years and occurred primarily within the first pelagic year interval. The weak 1989 recruit year was most distinct among recruit years in exhibiting lower increment widths at each of these inflection points.

Bluespine unicornfish (Naso unicornis) from Hawaii were aged to >50 years using cross-sectioned sagittal otoliths. Fish length was a poor indicator of age because of rapid and variable early growth, exemplified by fish aged to be 4 years near maximum length. Growth was deterministic with adult ages decoupled from body length. Otolith mass and thickness were evaluated as proxies for age and both were encouraging; thickness explained more variance but mass was easier to measure. An age estimation protocol was validated through ontogeny using bomb radiocarbon (14C) dating. Use of the postbomb 14C decline period from a regional reference chronology enabled age validation of young fish — a novel approach for the Pacific Ocean. A probabilistic procedure for assigning bomb 14C dates (CALIBomb) was used for the first time to determine fish birth years. The age-reading protocol was generally validated, and it was possible to describe length-at-age despite difficulties in counting otolith annuli beyond 30–40 years. Growth curves differed between the sexes, and a four-parameter generalized von Bertalanffy growth function provided the best fit.

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Specimens of the nominal rpeciea Pscudopcntacrror whcclcri Hardy and P. pectoralis Hardy were examined morphologically and electrophoretically to test the validity of the two speciea. Samples were collected primarily from the Hancock Seamountr of the muthem Emperor-northern H8waiian Ridge as well as from the North Pacific open ocean and northweatern Hawaiian Irlands. Morphometric resulta indicate continuity between P. wheelmi and P. pectoralis. No evidence of rpeciea aeparation waa revealed in analysea of meristic and electre phoretic data. W e conclude that the North Pacific pelagic armorhead conrists of a ringle, metamorphic rpecies, which we. aa firrt reviaerr. elect to a l l P. whcclm'. A hypothesir ir propoaed that attributa morphological variation to different l i f e history rtages.

Tropical deep-water snappers (Etelinae) support valuable fisheries across the Indo-Pacific, with stock assessments reliant on age-based information in the absence of reliable catch and effort statistics. These long-lived species have been considered notoriously difficult to age. However, nascent developments in ageing protocols, particularly thinner transverse sections of otoliths (∼180–200 µm), are providing improvements in growth zone clarity, interpretation and repeatability of annuli counts. At a recent international workshop, thin sectioned otoliths from three deep-water snappers were read under reflected light by eight fisheries scientists from across the Indo-Pacific, with various levels of fish-ageing experience. Precision and bias were assessed using traditional ageing precision metrics (index of average percent error, IAPE; and coefficient of variation, CV), and a novel approach using multivariate analyses (metric multidimensional scaling, mMDS) based on Euclidean dissimilarity among readers’ counts and subsequent von Bertalanffy (vB) growth parameter estimates. Annuli counts between the primary reader and all other readers were within two for 80% of estimates, with uniform variation across a wide age range for Etelis carbunculus (intraclass correlation coefficient (ICC) = 0.924, n = 20, 3–25 annuli) and Etelis sp. (ICC = 0.933, n = 15, 2–27 annuli). In contrast, annuli counts for Pristipomoides filamentosus (n = 14, 4–49) were less precise (i.e. ICC = 0.835, 66% of counts within two of primary reader) with a bias toward greater variation in younger, pre-maturational life stages (≤5 annuli). Traditionally accepted ageing precision (IAPE ≤ 5.5%, CV ≤ 7.6%) was achieved for each species, but was commensurate with reader experience. The multivariate mMDS ordination was more informative in identifying both distance (i.e. dissimilarity) and direction (i.e. form) of variations in annuli counts and vB growth parameter estimates among readers. The acceptable level of ageing precision and bias achieved among most readers indicated that deep-water snappers can be aged precisely when appropriate otolith preparation methods are used. This study contributes towards ageing protocols that can be used to (i) interrogate bias and precision of age data for stock assessments, and (ii) standardise comparisons of age-based life history characteristics across a species range.

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