This paper presents an estimation of growth curves and spatiotemporal distributions of juvenile shortfin mako shark (Isurus oxyrinchus) in the western and central North Pacific Ocean using port sampling data collected from 2005 to 2013. The monthly length compositions show a clear transition of three modes in the size range of smaller than 150-cm precaudal length (PCL), which were believed to represent the growth of age-0 to age-2 classes, and they were then decomposed into age groups by fitting a Gaussian mixture distribution. Simulation data of lengths at monthly ages were generated from the mean and standard deviation of each distribution, and fit with a von Bertalanffy growth function. Parameters of the estimated growth curves for males and females were 274.4 and 239.4 cm PCL for the asymptotic length and 0.19 and 0.25 year À1 for the growth coefficient indicating apparently faster growth than previously reported. Generalised linear models were applied to age-0 to explore the seasonal changes of PCL by area. They were born during late autumn and winter off the coast of north-eastern Japan, an area known to have relatively high productivity compared with other pelagic areas, and gradually expanded their habitat eastward and northward with the seasons as they grew. Journal compilation Ó CSIRO 2015 www.publish.csiro.au/journals/mfr B Marine and Freshwater Research M. Kai et al.
The taxonomy of the genus PennellaOken, 1815, a large parasitic copepod, is in a deplorable state. We performed morphological and genetic analyses on 52 Pennella individuals collected from 12 species of definitive hosts. Based on the morphological characteristics and their hosts, 29 individuals were determined or suggested to be large-size species (P. balaenoptera, P. filosa, P. instructa, and P. benzi), whereas 20 were considered intermediate- or small-size species. The remaining three small individuals, presumed to be newly attached, exhibited insufficient morphological characteristics for species identification or grouping. Mitochondrial DNA cytochrome c oxidase subunit 1 (COI) sequence analysis detected 154 haplotypes from 52 individuals classified into Groups I–IV. Sequences of Group IV were determined to be pseudogenes. Levels of divergence between all groups were significant (FST = 0.488–0.830, P < 0.001). All haplotypes of Group I were detected in intermediate- and small-size groups possessing large and well-branched antennary processes on the cephalothorax. Although Groups I and II exhibited the smallest difference in nucleotide sequence divergence (FST = 0.488 and K2P = 1.485 ± 0.355%), the morphological characteristics of Group I appeared to be distinct from those of the other groups. The substantial sequence divergence (FST = 0.830 and K2P = 4.123 ± 0.719%) between Groups II and III also supported their species status, but no characteristic morphological difference was observed between individuals in these groups. Results suggest that Pennella may contain only two or three species. and that some morphological characteristics and definitive host species previously used for species identification are not valid.
Longline surveys have been conducted in the Northwest Pacific Ocean from 2000 to 2014 using chartered commercial longline vessels. Each year, two cruises were conducted offshore of northeastern Japan from mid‐April to mid‐June. For each longline set during the surveys, onboard scientists collected detailed biological information about the species caught, such as the size and sex, and recorded the catch numbers for all species. Blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) have eurythermal distributions, but the application of a generalized additive model (GAM) showed that the sea surface temperatures (SSTs) at catch sites positive for shortfin mako were warmer than those for blue shark. On the basis of the GAM, the probabilities of occurrence of both sharks differed by size category: small sharks had a narrower SST range than that of large sharks. Most catches of both sharks were juveniles, and the nominal catch rate of blue shark was more than 10 times that of shortfin mako. The standardized catch per unit effort (CPUE) for both species was calculated using a generalized linear model (GLM) with negative binomial errors, or a delta‐lognormal GLM. The standardized CPUE for blue shark in the second quarter of the year peaked in the mid‐2000s and then decreased, but it has been increasing since 2012. The CPUE for shortfin mako in the second quarter generally increased, with fluctuations.
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