Application of Gradient-Dependent Optimal Interpolation in Fishery Analysis of Neon Flying Squid (Ommastrephes bartramii) in the Kuroshio-Oyashio Confluence Region

A key issue in fishery forecasting is the collection of high-precision subsurface environmental data. A data assimilation method, named gradient-dependent optimal interpolation, was used to construct the near-real-time vertical temperature and salinity structure of a squid fishery ground based on Argo observations. The results were verified by truth-finding comparisons and applied to analyze the relationship between neon flying squid and the subsurface environment in the Kuroshio-Oyashio Confluence Region. The temperature and salinity differences between the constructed results and survey data were less than ±0.5 °C and ±0.02, respectively. Most of the relative analysis errors were less than the observational errors. Statistical analysis revealed that the most suitable temperature for squid was 18-24 °C at the near-surface (<5 m), although the squid can endure a temperature range from 11 to 12 °C at a depth of 300 m. There was an obvious thermocline in the fishery ground, with a thermocline depth of 65 m and a mean strength of approximately 0.10 °C/m. The regressive relationship between vertical temperature (thermocline parameters) and squid catch per unit effort (CPUE) followed the exponential (Gaussian) function. The most suitable salinity was 33.0-34.2 at depths shallower than 300 m.

Transient demographic dynamics of recovering fish populations shaped by past climate variability, harvest, and management

Large-scale commercial harvesting and climate-induced fluctuations in ocean properties shape the dynamics of marine populations as interdependent drivers at varied timescales. Persistent selective removals of larger, older members of a population can distort its demographic structure, eroding resilience to fluctuations in habitat conditions and thus amplifying volatility in transient dynamics. Many historically depleted marine fish stocks have begun showing signs of recovery in recent decades following the implementation of stricter management measures. But these interventions coincide with accelerated changes in the oceans triggered by increasingly warmer, more variable climates. Applying multilevel models to annual estimates of demographic metrics of 38 stocks comprising 11 species across seven northeast Atlantic ecoregions, this study explores how time-varying local and regional climates contributed to the transient dynamics of recovering populations exposed to variable fishing pressures moderated by management actions. Analyses reveal that progressive reductions in fishing pressure and shifting climate conditions discontinuously shaped rebuilding patterns of the stocks through restorations of maternal demographic structure (reversing age truncation) and reproductive capacity. As the survival rate and demographic structure of reproductive fish improved, transient growth became less sensitive to variability in recruitment and juvenile survival and more to that in adult survival. As the biomass of reproductive fish rose, recruitment success also became increasingly regulated by density-dependent processes involving higher numbers of older fish. When reductions in fishing pressure were insufficient or delayed, however, stocks became further depleted, with more eroded demographic structures. Although warmer local climates in spawning seasons promoted recruitment success in some ecoregions, changing climates in recent decades began adversely affecting reproductive performances overall, amplifying sensitivities to recruitment variability. These shared patterns underscore the value of demographic transients in developing robust strategies for managing marine resources. Such strategies could form the foundation for effective applications of adaptive measures resilient to future environmental change.

Trends in abundance indices derived from commercial fisheries for priority marine stocks in the Azores

Large-scale assessments of fish and shellfish populations may be valuable for identifying the impacts of fishing pressure on stocks, but they are rarely possible due to a lack of long-term datasets. In this study, a two-part mixed-effect model for lognormal data was used to obtain historical abundance indices for 16 priority fish and shellfish stocks in the Azores region derived from catch per unit effort (kg per day at sea per vessel) and landing per unit effort (kg per landing per vessel). This data was obtained over the past 30 years under the EC Data Collection Framework and, in addition to information on effort and catch, included details about the fishing operation such as quarter, vessel length and fishing gear. This information was analysed to investigate how abundance indices changed over the years, verify if trends from different data sources were different and, if possible, relate these results to the population and fishery dynamics. The abundance indices derived from both datasets were generally in agreement with each other. Declining trends have been observed for some commercially important species, such as forkbeard Phycis phycis, European conger Conger conger, parrotfish Sparisoma cretense, red scorpionfish Scorpaena scrofa, offshore rockfish Pontinus kuhlii, common spiny lobster Palinurus elephas, splendid alfonsino Beryx splendens and alfonsino B. decadactylus, which is concerning because they are particularly slow-growing, long-lived and have low natural mortality, making them susceptible to overfishing. The results of this study are very important and should help future stock assessment and management initiatives.

Established and Emerging Research Trends in Norway Lobster, Nephrops norvegicus

The burrowing crustacean decapod Nephrops norvegicus is a significant species in European Atlantic and Mediterranean fisheries. Research over the decades has mainly focused on behavioral and physiological aspects related to the burrowing lifestyle, since animals can only be captured by trawls when engaged in emergence on the seabed. Here, we performed a global bibliographic survey of all the scientific literature retrieved in SCOPUS since 1965, and terminology maps were produced with the VOSviewer software to reveal established and emerging research areas. We produced three term-map plots: term clustering, term citation, and term year. The term clustering network showed three clusters: fishery performance, assessment, and management; biological cycles in growth, reproduction, and behavior; and finally, physiology and ecotoxicology, including food products. The term citation map showed that intense research is developed on ecotoxicology and fishery management. Finally, the term year map showed that the species was first studied in its morphological and physiological aspects and more recently in relation to fishery and as a food resource. Taken together, the results indicate scarce knowledge on how burrowing behavior and its environmental control can alter stock assessment, because of the poor use of current and advanced monitoring technologies.

Tradeoffs of managing cod as a sustainable resource in fluctuating environments

Sustainable human exploitation of living marine resources stems from a delicate balance between yield stability and population persistence to achieve socioeconomic and conservation goals. But our imperfect knowledge of how oceanic oscillations regulate temporal variation in an exploited species can obscure the risk of missing management targets. We illustrate how applying a management policy to suppress fluctuations in fishery yield in variable environments (prey density and regional climate) can present unintended outcomes in harvested predators and the sustainability of harvesting. Using Atlantic cod (Gadus morhua, an apex predatory fish) in the Barents Sea as a case study we simulate age-structured population and harvest dynamics through time-varying, density-dependent and density-independent processes with a stochastic, process-based model informed by 27-year monitoring data. In this model, capelin (Mallotus villosus, a pelagic forage fish), a primary prey of cod, fluctuations modulate the strength of density-dependent regulation primarily through cannibalistic pressure on juvenile cod survival; sea temperature fluctuations modulate thermal regulation of cod feeding, growth, maturation, and reproduction. We first explore how capelin and temperature fluctuations filtered through cod intrinsic dynamics modify catch stability and then evaluate how management to suppress short-term variability in catch targets alters overharvest risk. Analyses revealed that suppressing year-to-year catch variability impedes management responses to adjust fishing pressure, which becomes progressively out of sync with variations in cod abundance. This asynchrony becomes amplified in fluctuating environments, magnifying the amplitudes of both fishing pressure and cod abundance and then intensifying the density-dependent regulation of juvenile survival through cannibalism. Although these transient dynamics theoretically give higher average catches, emergent, quasicyclic behaviors of the population would increase long-term yield variability and elevate overharvest risk. Management strategies that overlook the interplay of extrinsic (fishing and environment) and intrinsic (life history and demography) fluctuations thus can inadvertently destabilize fish stocks, thereby jeopardizing the sustainability of harvesting. These policy implications underscore the value of ecosystem approaches to designing management measures to sustainably harvest ecologically connected resources while achieving socioeconomic security.

Sex matters: Otolith shape and genomic variation in deacon rockfish (Sebastes diaconus)

Little is known about intraspecific variation within the deacon rockfish (Sebastes diaconus), a recently described species found in the northeast Pacific Ocean. We investigated population structure among fish sampled from two nearshore reefs (Siletz Reef and Seal Rock) and one offshore site (Stonewall Bank) within a <50-km2 area off the Oregon coast. Fish from the three sample sites exhibited small but statistically significant differences based on genetic variation at >15,000 neutral loci, whether analyzed independently or classified into nearshore and offshore groups. Male and females were readily distinguished using genetic data and 92 outlier loci were associated with sex, potentially indicating differential selection between males and females. Morphometric results indicated that there was significant secondary sexual dimorphism in otolith shape, but further sampling is required to disentangle potential confounding influence of age. This study is the first step toward understanding intraspecific variation within the deacon rockfish and the potential management implications. Since differentiation among the three sample sites was small, we consider the results to be suggestive of a single stock. However, future studies should evaluate how the stock is affected by differences in sex, age, and gene flow between the nearshore and offshore environments.

[Stock assessment methods on marine crustacean species: A review.]

Crustaceans, such as crab, lobster, prawn, and Antarctic krill, have formed a vast and commercially valuable fishery globally. Although the importance and scale of these crustacean fishe-ries are increasing, the suitable and effective methods for stock assessment and management of crustacean fisheries are urgent to be improved compared to other fisheries. We reviewed and evaluated four kinds of stock assessment methods for assessing crustacean fishery, including the surplus production model, delay-difference model, the depletion model, and size-structured model. We described the application of those models in stock assessment of crustacean fishery, and briefly summarized the assumptions and data needed in these models. We further compared the advantages and disadvantages of those models. In addition, the assumptions of the models, the estimation method of the parameters, and the general solution of uncertainty were analyzed. Finally, the future direction and prospect of crustacean stock assessment were discussed.

Effect of fish length and nutritional condition on the fecundity of distressed Atlantic cod Gadus morhua from the Baltic Sea

The disappearance of larger individuals and the decrease in individual body condition suffered by Atlantic cod Gadus morhua in the eastern Baltic during the past two decades can be expected to affect the stock reproductive output. To investigate this, female G. morhua were collected during the spawning and pre-spawning period in 2015-2016. The current individual potential fecundity (F_P ) of eastern Baltic G. morhua was estimated and analysed in relation to total length (L_T ) and indices of nutritional status such as body condition (K) and hepato-somatic index (I_H ) using generalized linear models. In addition, the current prevalence of atresia and its potential relation to K were investigated. Moreover, a calibration curve to estimate F_P from oocyte diameter, based on the autodiametric oocyte counting method, was established for the first time for eastern Baltic G. morhua and can be used for future fecundity studies on this stock. The results showed that F_P was mainly positively related to fish length, but K and I_H also contributed significantly to the variation in F_P . The model predicted that fish with K = 1·2 have a F_P 51% higher than fish of the same L_T with K = 0·8. The prevalence of fecundity regulation by atresia was 5·8%, but it was found only in fish in the pre-spawning maturity stage and with low K. Temporal changes in biological features such as the length composition and individual body condition of eastern Baltic G. morhua, should be accounted for when estimating stock reproductive potential.

Satellite telemetry reveals higher fishing mortality rates than previously estimated, suggesting overfishing of an apex marine predator

Overfishing is a primary cause of population declines for many shark species of conservation concern. However, means of obtaining information on fishery interactions and mortality, necessary for the development of successful conservation strategies, are often fisheries-dependent and of questionable quality for many species of commercially exploited pelagic sharks. We used satellite telemetry as a fisheries-independent tool to document fisheries interactions, and quantify fishing mortality of the highly migratory shortfin mako shark (Isurus oxyrinchus) in the western North Atlantic Ocean. Forty satellite-tagged shortfin mako sharks tracked over 3 years entered the Exclusive Economic Zones of 19 countries and were harvested in fisheries of five countries, with 30% of tagged sharks harvested. Our tagging-derived estimates of instantaneous fishing mortality rates (F = 0.19-0.56) were 10-fold higher than previous estimates from fisheries-dependent data (approx. 0.015-0.024), suggesting data used in stock assessments may considerably underestimate fishing mortality. Additionally, our estimates of F were greater than those associated with maximum sustainable yield, suggesting a state of overfishing. This information has direct application to evaluations of stock status and for effective management of populations, and thus satellite tagging studies have potential to provide more accurate estimates of fishing mortality and survival than traditional fisheries-dependent methodology.

Spatio-temporal dynamics in maturation and spawning of Patagonian toothfish Dissostichus eleginoides on the sub-Antarctic Kerguelen Plateau

This study investigated maturation and spawning of Patagonian toothfish Dissostichus eleginoides in the Heard Island and McDonald Islands (HIMI) fishery on the Kerguelen Plateau in the Indian Sector of the Southern Ocean based on gonads and otoliths collected between 2004 and 2015 and using histological analyses and calibration of macroscopic staging criteria. Dissostichus eleginoides at HIMI spawn throughout the austral late autumn and winter months of May-August and spawning activity is concentrated on slopes along the west and south of the plateau around HIMI at depths of 1500-1900 m. Comparison between histological analyses and macroscopic gonad staging indicated that many fish that had spawned, as indicated by the presence of post-ovulatory follicles, returned to a resting stage which was macroscopically indistinguishable from maturing fish. Furthermore, the occurrence of females of all size classes with low gonado-somatic index and low macroscopic gonad stage during the spawning season suggested that a proportion of mature females did not spawn every year. Age-at-maturity estimates, based on the assumption that fish of macroscopic stages ≥2 were mature, decreased between the 2004-2009 and 2010-2015 periods for both sexes. The magnitude of this temporal variation in age at maturity, however, varied between gear types and fishing depths and variable sampling regimes probably influenced these variations. This study highlights the importance of correct interpretation of macroscopic gonad stages and understanding the influence of fishery operations on estimations of life-history parameters.

The Modular Optical Underwater Survey System

The Pacific Islands Fisheries Science Center deploys the Modular Optical Underwater Survey System (MOUSS) to estimate the species-specific, size-structured abundance of commercially-important fish species in Hawaii and the Pacific Islands. The MOUSS is an autonomous stereo-video camera system designed for the in situ visual sampling of fish assemblages. This system is rated to 500 m and its low-light, stereo-video cameras enable identification, counting, and sizing of individuals at a range of 0.5–10 m. The modular nature of MOUSS allows for the efficient and cost-effective use of various imaging sensors, power systems, and deployment platforms. The MOUSS is in use for surveys in Hawaii, the Gulf of Mexico, and Southern California. In Hawaiian waters, the system can effectively identify individuals to a depth of 250 m using only ambient light. In this paper, we describe the MOUSS’s application in fisheries research, including the design, calibration, analysis techniques, and deployment mechanism.

Fisheries management impacts on target species status

Fisheries management systems around the world are highly diverse in their design, operation, and effectiveness at meeting objectives. A variety of management institutions, strategies, and tactics are used across disparate regions, fishing fleets, and taxonomic groups. At a global level, it is unclear which particular management attributes have greatest influence on the status of fished populations, and also unclear which external factors affect the overall success of fisheries management systems. We used expert surveys to characterize the management systems by species of 28 major fishing nations and examined influences of economic, geographic, and fishery-related factors. A Fisheries Management Index, which integrated research, management, enforcement, and socioeconomic attributes, showed wide variation among countries and was strongly affected by per capita gross domestic product (positively) and capacity-enhancing subsidies (negatively). Among 13 management attributes considered, three were particularly influential in whether stock size and fishing mortality are currently in or trending toward desirable states: extensiveness of stock assessments, strength of fishing pressure limits, and comprehensiveness of enforcement programs. These results support arguments that the key to successful fisheries management is the implementation and enforcement of science-based catch or effort limits, and that monetary investment into fisheries can help achieve management objectives if used to limit fishing pressure rather than enhance fishing capacity. Countries with currently less-effective management systems have the greatest potential for improving long-term stock status outcomes and should be the focus of efforts to improve fisheries management globally.

Complete mitochondrial genome of Schizothorax gongshanensis (Cypriniformes: Cyprinidae)

In this study, the complete mitochondrial DNA of Schizothorax gongshanensis was determined. The complete genome is 16,591 bp in length which contains 13 protein-coding genes, 22 transfer RNA genes, 2 rRNA genes, an origin of light-strand replication (O_L) and a control region (D-Loop). The complete mtDNA sequence of S. gongshanensis provides a useful genetic marker for the studies on molecular systematics, population genetics and stock assessment.

Complete mitochondrial genome of Schizothorax nukiangensis Tsao (Cyprinidae: Schizothorax)

In this work, we reported the complete mitochondrial genome sequence of the Schizothorax nukiangensis Tsao for the first time. The complete mtDNA genome sequence of S. nukiangensis Tsao was 16 585 bp in length, which contains 22 transfer RNA genes, 2 rRNA genes, 13 protein-coding genes, an origin of light-strand replication (OL) and a control region (D-Loop). The overall base composition of the mitogenome was calculated to be 29.6% for A, 27.0% for C, 17.9% for G and 25.5% for T. The complete mitogenome of the S. nukiangensis Tsao can provide an important data set for further studies on population history, molecular systematics, phylogeography and stock assessment.

Linking physiological approaches to marine vertebrate conservation: using sex steroid hormone determinations in demographic assessments

Sex, age and sexual maturation are key biological parameters for aspects of life history and are fundamental information for assessing demographic changes and the reproductive viability and performance of natural populations under exploitation pressures or in response to environmental influences. Much of the information available on the reproductive condition, length at sexual maturity and sex determinations of endangered species has been derived from direct examination of the gonads in dead animals, either intentionally or incidentally caught, or from stranded individuals. However, morphological data, when used alone, do not provide accurate demographic information in sexually monomorphic marine vertebrate species (e.g. sharks, sea turtles, seabirds and cetaceans). Hormone determination is an accurate and non-destructive method that provides indirect information about sex, reproductive condition and sexual maturity of free-ranging individuals. Correlations between sex steroid concentrations and biochemical parameters, gonadal development and state, reproductive behaviour and secondary external features have been already demonstrated in many species. Different non-lethal approaches (e.g. surgical and mark-recapture procedures), with intrinsic advantages and disadvantages when applied on free-ranging organisms, have been proposed to asses sex, growth and reproductive condition. Hormone determination from blood samples will generate valuable additional demographic information needed for stock assessment and biological conservation.

Anguillids: conserving a global fishery

Concern has increased in recent years over the sustainability of anguillid populations worldwide in the face of sustained consumer demand. This is as true of the more numerous tropical species as it is for the better known temperate species. There are, however, critical gaps in knowledge of anguillid biology and ecology, and these hold back measures designed to conserve and enhance anguillid populations, including aquaculture. Developing a more integrated understanding of anguillid biology, and resolving challenges faced by stakeholders and policy makers, is now more urgent than ever. World experts from Japan, the U.S.A., Canada, the European Union and New Zealand led a 3 day event where >200 scientists drawn from >30 countries across the globe converged to share their experience and expert knowledge of anguillids. The session covered the full range of issues affecting anguillid stocks across the globe, and also highlighted advances in the understanding of fundamental aspects of anguillid biology. Overall, 49 oral presentations and 68 posters were presented and, while these were dominated by Anguilla anguilla, Anguilla rostrata and Anguilla japonica, a further eight anguillid species were represented. What was experienced by all was the facilitation of a more integrated understanding of anguillid biology, and how this understanding can interface with the challenges faced by fishermen, consumers, engineers, producers and managers. The highlights are reviewed, important trends in anguillid stocks and research identified and the consensus for future science and management direction reported.

Escaping paradise: Larval export from Hawaii in an Indo-Pacific reef fish, the Yellow Tang (Zebrasoma flavescens)

The depauperate marine ecosystems of the Hawaiian Archipelago share a high proportion of species with the southern and western Pacific, indicating historical and/or ongoing connections across the large oceanic expanse separating Hawaii from its nearest neighbors. The rate and direction of these interactions are, however, unknown. While previous biogeographic studies have consistently described Hawaii as a diversity sink, prevailing currents likely offer opportunities for larval export. To assess interactions between the remote reefs of the Hawaiian Archipelago and the species rich communities of the Central and West Pacific, we surveyed 14 nuclear microsatellite loci (nDNA; n = 857) and a 614 bp segment of mitochondrial cytochrome b (mtDNA; n = 654) in the Yellow Tang (Zebrasoma flavescens). Concordant frequency shifts in both nDNA and mtDNA reveal significant population differentiation among three West Pacific sites and Hawaii (nDNA F' _CT = 0.116, mtDNA ϕ _CT = 0.098, P < 0.001). SAMOVA analyses of microsatellite data additionally indicate fine scale differentiation within the 2600 km Hawaiian Archipelago (F' _SC = 0.026; P < 0.001), with implications for management of this heavily-exploited aquarium fish. Mismatch analyses indicate the oldest contemporary populations are in the Hawaiian Archipelago (circa 318,000 y), with younger populations in the West Pacific (91,000 - 175,000 y). Estimates of Yellow Tang historical demography contradict expectations of Hawaii as a population sink, and instead indicate asymmetrical gene flow, with Hawaii exporting rather than importing Yellow Tang larvae.