Population structure and movement patterns of blackbelly rosefish in the NE Atlantic Ocean (Azores archipelago)

Blackbelly rosefish Helicolenus dactylopterus (Delaroche, 1809) is one of the most important species of the demersal/deep‐water assemblages fished in the NE Atlantic Ocean (Azores archipelago). However, there is insufficient information about the stock structure of this species to support analytical resource assessments and it is currently managed with a precautionary approach. Here, we examine the depth and temporal distribution, size composition, sex, and movement patterns of blackbelly rosefish in order to test the hypothesis that the stock structure in the Azores region comprises different local management units (MUs). We also evaluate annual abundance indices and size composition from scientific surveys and commercial landings over the past c. 25 years for an assessment of the species' vulnerability to bottom longline fishing pressure. The greatest abundance occurred in seamount areas at 350–800 m depth. Larger individuals were mainly found in deeper waters, and no sexual segregation by depth was observed. Tagging results indicated a strongly sedentary behavior and an intraregional separation among populations. Although the abundance pattern and size composition were very similar over time, this species is particularly vulnerable to overfishing due to its biological characteristics (long life, large size, late maturity, slow growth, and low mortality rate). Proper monitoring and management of its exploitation should be a priority. Exploratory analysis for analytical assessment should be performed under the assumption of local MUs. Further oceanographic research is needed to understand larval transport and mixing of populations.     

Fisheries resource management of the daggertooth pike conger,Muraenesox cinereus,using existing limited datasets in the western Seto Inland Sea,Japan

The daggertooth pike conger, Muraenesox cinereus (Forsskål), has become an important fish resource in the western Seto Inland Sea, Japan, since the 1990s. However, introducing sustainable fisheries resource management for this species is difficult in this region because stock assessments have not been performed, and official fisheries statistics for this stock were discontinued after 2007. This study used existing limited data sets to compile the first report for fisheries resource management for this M. cinereus stock. Yield‐per‐recruit analyses showed that increasing fishing pressure above current levels would provide only a minimal increase in expected catch levels. Hence, the current harvest level is considered to represent the upper limit of fishing pressure. Age composition in a given year could potentially be used to forecast landing abundance for the following 2 years. This study provides a basis for establishing effective fisheries resource management strategies for M. cinereus.     

The importance of environment and life stage on interpretation of silky shark relative abundance indices for the equatorial Pacific Ocean

Recent large fluctuations in an index of relative abundance for the silky shark in the eastern Pacific Ocean have called into question its reliability as a population indicator for management. To investigate whether these fluctuations were driven by environmental forcing rather than true changes in abundance, a Pacific‐wide approach was taken. Data collected by observers aboard purse‐seine vessels fishing in the equatorial Pacific were used to compute standardized trends in relative abundance by region, and where possible, by shark size category as a proxy for life stage. These indices were compared to the Pacific Decadal Oscillation (PDO), an index of Pacific Ocean climate variability. Correlation between silky indices and the PDO was found to differ by region and size category. The highest correlations by shark size category were for small (<90 cm total length [TL]) and medium (90–150 cm TL) sharks from the western region of the equatorial eastern Pacific (EP) and from the equatorial western Pacific. This correlation disappeared in the inshore EP. Throughout, correlations with the PDO were generally lower for large silky sharks (>150 cm TL). These results are suggestive of changes in the small and medium silky indices being driven by movement of juvenile silky sharks across the Pacific as the eastern edge of the Indo‐Pacific Warm Pool shifts location with ENSO events. Lower correlation of the PDO with large shark indices may indicate that those indices were less influenced by environmental forcing and therefore potentially less biased with respect to monitoring population trends.     

A size-based stock assessment model for invasive blue catfish in a Chesapeake Bay sub-estuary during 2001–2016

Stock assessment modeling provides a means to estimate the population dynamics of invasive fishes and may do so despite data limitations. Blue catfish (Ictalurus furcatus) were introduced to the Chesapeake Bay watershed to support recreational fisheries but also consume species of conservation need and economic importance. To assess management tradeoffs, managers need to understand the current status of the population and anticipate future population abundance and trends. A Bayesian size-based stock assessment model was used to estimate blue catfish abundance, fishing mortality, and size structure over time (2001–2016) in the tidal James River. The model estimated population size increases until around 2006, with declines in total abundance after 2011 and large blue catfish (≥80 cm total length) after 2001. These first estimates of blue catfish population dynamics in the Chesapeake Bay region provide inputs for projection models to evaluate prospective management actions and identify monitoring needs.     

Using angling and electric fishing to estimate smallmouth bass abundance in a river

Estimating abundance is fundamental to effective fishery management but can be challenging in a river where spatial and temporal heterogeneity may preclude the consistent use of a single sampling gear and different gears have differing size selectivity and capture probabilities of fish. In this study, the number of smallmouth bass, Micropterus dolomieu Lacepède, was estimated based on mark–recapture data from angling and boat electric fishing in a 4.2‐km regulated section (mean width = 115 m) of the Broad River, South Carolina, USA. Closed‐population capture–mark–recapture models were fit in the Bayesian hierarchical modelling framework with an estimated number of 2,380 fish (95% credible interval: 1,578–3,693) over 200 mm TL, although simulations indicated that abundance would be slightly overestimated (<20%) when two gears selected for different individuals. Integrating two gear types into a mark–recapture study can provide a method for assessing abundance in spatially or temporally heterogeneous habitats.     

Estimation of production and long‐term changes in the population of European eel Anguilla anguilla (L.) in an Irish lake

Monitoring of yellow‐phase and silver‐phase Anguilla anguilla during their continental life history is necessary for evaluation of stock recovery measures. Eel population data for an Irish lake (Lough Sheelin) were compiled for the period 1993–2014. Catch data from 2009 to 2014 provided minimum estimates of recent silver eel production ranging annually from 0.79 to 1.84 kg/ha. Long‐term changes in yellow eel abundance and silver eel size structure were assessed as part of a fishery monitoring programme. Yellow eel catch per unit effort (CPUE) in the lake (from longline surveys) was considerably higher in the 1990s (52.2–62.1 eels/100 hooks) than 2002–2008 (1.9–15.8 eels/100 hooks). Conversely, during 1993–2014, the mean size of silver eels migrating from the lake increased significantly (p < .001), from 659 mm to 838 mm. The results suggest that in the absence of direct yellow eel abundance data, interannual variation in silver eel size structure may be a useful monitoring tool for local eel stocks as part of Eel Management Plans (EMP's).     

Biological and ecological aspects of the deep‐water red crab populations inhabiting isolated seamounts to the west of the Azores (Mid‐Atlantic Ridge)

Seamounts are common topographic features in the Mid‐Atlantic Ridge (MAR) including the Azores. However, the knowledge on the ecology of seamounts in this region remains scarce despite needs for assessment and management of seamount resources such as the developing fisheries for deep‐water crabs. We described here for the first time the biological characteristics of an unexploited virgin deep‐water red crab Chaceon affinis population on seamount areas of the MAR to test the hypothesis that its general life history characteristics are similar in different ecosystem types (coastal areas and seamounts) across Macaronesia. We used a randomly stratified design to prospect a layer between 600 and 900 m depth around the summit of two isolated seamounts off the Azores. Results were consistent with the literature information in relation to the patterns of depth distribution, size and sex structure, and reproductive aspects. On the other hand, seamounts showed higher abundances when compared to previously studied coastal areas. Abundance may be also different between seamount areas as a function of the suitable bottom type available and presence of hydrothermal vents. We recommend that the essential habitat of the species should be better mapped identifying vulnerable areas before the development of any fishery.     

Measuring copepod abundance in deep‐water winter habitats in the NE Norwegian Sea: intercomparison of results from laser optical plankton counter and multinet

The main purpose of this study was to assess the usefulness of the laser optical plankton counter (LOPC) as a Calanus finmarchicus monitoring tool in the NE Norwegian Sea in winter. To test this, a multinet and an LOPC were used simultaneously to sample overwintering copepods in the Lofoten basin in January 2007. Additional data from an LOPC laboratory experiment were also analyzed to help the interpretation of the field data. Both the laboratory data and the field data indicated that the presence of particles other than zooplankton generally contaminated the zooplankton signal in the LOPC data. However, reliable abundance estimates could be made from the LOPC data by choosing an appropriate size range in the LOPC size distribution. This size range was determined by comparing LOPC abundance estimates from systematically varying size ranges to multinet zooplankton abundance data. The average difference was smallest for a size range of about 900–1500 μm. As C. finmarchicus, stages IV and V, was by far the most abundant species in the NE Norwegian Sea, abundance estimates from the LOPC in this size range were in practice estimates of C. finmarchicus abundance, making the LOPC suitable as a tool for providing high resolution winter data in the NE Norwegian Sea.     

Abundance estimates of three cetacean species in the coastal waters of Matang,Perak, Peninsular Malaysia

1. The paucity of baseline data on coastal cetaceans due to a lack of research in developing countries frequently precludes assessment of their status and informed management actions for conservation.
2. This study provides the first abundance estimates of Indo-Pacific humpback dolphins, Irrawaddy dolphins, and Indo-Pacific finless porpoises in the coastal waters of Matang, Peninsular Malaysia.
3. Boat-based surveys covering 1,152 km² of coastal waters with 4,108 km of survey effort were conducted between 2013 and 2016 to collect data for line transect analysis of Irrawaddy dolphins and finless porpoises. Photo-identification data of humpback dolphins were concurrently collected for mark–recapture analysis.
4. Estimates of abundance from four sampling strata totalled 763 Irrawaddy dolphins (CV = 13%, 95% confidence interval (CI) [588, 990]) and 600 Indo-Pacific finless porpoises (CV = 27%, 95% CI [354, 1,016]).
5. The annual abundance estimates of humpback dolphins ranged between 171 (95% CI [148, 208]) in 2014–2015 and 81 (95% CI [67, 98]) in 2015–2016, likely due to the presence of offshore individuals that moved in and out of the study area. The estuarine strata were inhabited by 68 (95% CI [63, 73]) inshore humpback dolphins in 2013–2014 to 87 (95% CI [78, 97]) dolphins in 2014–2015.
6. As an International Union for Conservation of Nature important marine mammal area, the productive coastal waters of Matang are shown to support a high density of small coastal cetaceans, and the results serve as an important baseline for future studies to identify population trends for conservation management plans.

     

Age, growth and reproductive biology of the European conger eel (Conger conger) from the Atlantic Iberian waters

The European conger eel, Conger conger, is a fish widely distributed in the north-eastern Atlantic, being an important commercial and recreational fish species. A total of 85 juvenile congers eels were used in this study. Seventy-three congers were captured mainly by hook and pots in inshore waters (10–15 m depth) of the Iberian Peninsula (North Portugal and Vigo), monthly from March 1998 to March 2000. Another twelve specimens have been captured during a research cruise (R.V. “Capricórnio”) in summer 1999 by trawl at depths about 400 m in south Portugal. The length and weight of the congers eels ranged from 38 to 173 cm and 125 to 14,553 g, respectively. The observation of burnt otoliths under UV light proved to be a useful method for ageing conger eels. Marginal increment analysis was used to validate the annual pattern in the deposition of bright zones in the otoliths. Age for the congers ranged from 2 to 12 years. The VBF population growth curve estimates from the otoliths of the females gave results of L_∞ = 265 cm, k = 0.07 and t₀ = −1.20. Sex determination and gonadal development were obtained from histological analysis. All the specimens collected in the coastal shallow waters were females, either immature or in a developing stage. The ovaries contained oocytes in two main stages of development: a pre-vitellogenic stage and an early vitellogenic stage. The few males (n = 4) observed have been captured in the trawl fishery at deeper waters. The males possessed small cells spermatogonias and spermatocytes clustered in crypts in the testis scattered in a matrix of adipose tissue. The sexual steroids, 17β-oestradiol and testosterone, were measured in blood plasma samples by solid-phase radioimmunoassay. Both sexual steroids presented a high correlation with the sexual development stage in terms of maximum oocyte diameter and gonadosomatic index. This work presents for the first time, data on age, reproductive biology and endocrinology of conger eels captured in the west coast of the Iberian Peninsula.     

Southern right whale (Eubalaena australis), seasonal abundance and distribution at Head of Bight,South Australia

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Recreational anglers as citizen scientists can provide data to estimate population size of pike,Esox lucius

Catch‐per‐unit‐effort is often used as an approximation of population size. However, for the management and conservation of populations, information about the number of individuals is fundamental. Pike, Esox lucius L., is a popular fish species for recreational anglers. In this study, data in the form of journal keeping by anglers were used: date; place; and photographs of the captured fish; pike were identified based on their natural markings in combination with length measurements. The data were analysed by spatial capture–recapture (SCR) models. Results showed that a small and densely vegetated lake (6.7 ha) in south‐eastern Sweden had a population size of 91 (±22 SE) pike ≥60 cm. On one occasion, 10 individuals were caught, that is 11.1% of the population, highlighting that angling may potentially have a substantial impact on the population size. Hopefully, this study can inspire angler–manager collaborations for conservation of fish stocks.     

Global population genetic structure of the sequential hermaphrodite,dusky grouper (Epinephelus marginatus)

1. The dusky grouper Epinephelus marginatus is a large epinephelid species that occurs in the eastern and south-western Atlantic and western Indian Oceans. Late maturity, protogynous hermaphroditism, site fidelity, and overfishing have all contributed to its demographic decline.
2. Connectivity and demography within a broad sampling of dusky grouper populations throughout its distribution were assessed. To do so, genetic variation at 11 polymorphic microsatellite loci and a partial sequence of the mitochondrial control region (mtCR) were evaluated.
3. Two major mtCR lineages with a sequence divergence of 1.6% were found. The magnitude of genetic differentiation for mtCR among north and south Atlantic and Indian Ocean populations was high, with Φ_ST = 0.528.
4. D_EST and results of discriminant analysis of principal component revealed significant microsatellite genetic differentiation between all collection areas. Significant pairwise D_EST showed moderate (0.084) to very great (0.603) differentiation. The effective population size was low for all localities, ranging between 25 (Azores Archipelago) and 311 (Rio Grande do Sul). The overall effective population size was estimated as 299 (confidence interval = 215–412), and there was no evidence of strong or recent bottleneck effects.
5. Local and regional genetic structuring among dusky grouper populations is the consequence of the species' site fidelity, distribution across multiple oceanographic boundaries, and probably also of sequential hermaphroditism that contributes to the intensity of random genetic drift.
6. The spatial pattern of genetic structuring of dusky groupers is such that fisheries management and conservation of population genetic integrity will have to be pursued at the local and regional scales.

     

An investigation of the biological basis of recruitment,growth and adult survival rate variability of Pacific herring (Clupea pallasi) from British Columbia: a synthesis

I explored the biological basis of variation in recruitment (age 3 abundance), growth and age‐specific adult survival rate for the major populations [West Coast Vancouver Island (WCVI), Strait of Georgia, Central Coast, North Coast and Haida Gwaii] of Pacific herring (Clupea pallasi) that inhabit British Columbian waters. The analyses were based on a synthesis of time series of empirical observations of herring population characteristics (egg deposition, age‐specific abundance and size) and prey, competitor and predator biomass/abundance. Recruitment was not correlated among populations. Recruitment variability was explained for WCVI herring only, as a consequence of prey (the euphausiid Thysanoessa spinifera) biomass during August in each of the first 3 years of life, and the biomass of piscivorous Pacific hake (Merluccius productus) during the first year of life. Recruit mass and adult mass‐at‐age were correlated among populations and over ages within populations. Recruit mass was affected by T. spinifera biomass in August of the first and third years of life. Adult mass‐at‐age variability was determined mainly by size at the beginning of the growth season, but also by T. spinifera biomass in August. Age‐specific adult survival rates were not correlated among the five populations. Survival rates decreased with age; there were additional population‐specific effects of somatic mass and T. spinifera biomass in August. The analyses were repeated using physical oceanographic explanatory variables. Only recruit mass variation was explained significantly by physical oceanographic variables, and the biological‐based explanation of recruit mass variability accounted for more of the variation.     

Re‐evaluating the population size of South American fur seals and conservation implications

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Climate‐driven winter variations of Calanus sinicus abundance in the East China Sea

Global environmental changes threaten the sustainable use of resources and raise uncertainties regarding marine populations' responses in a changing Ocean. The pelagic copepods of the genus Calanus play a central role in shelf ecosystems transferring phytoplankton carbon to harvested populations, from boreal to temperate regions. Here we examined a 15‐yr time series of Calanus sinicus abundance in regards to climate forcing in the East China Sea. We identified a compound effect of the Pacific Decadal Oscillation (PDO) and the East Asian Winter Monsoon (EAWM) on environmental conditions in the East China Sea. Such climate influences not only a southward transport of C. sinicus from its population centres into the Taiwan area, but favours advantageous thermal conditions for the species as well. On the interannual scale, our results show that the population size of C. sinicus echoes climate‐driven temperature changes. Hence, the possibility of using the PDO and EAWM variability for assessing and predicting interannual abundance changes of C. sinicus in the East China Sea is considered. The observed close relationship between climate and C. sinicus may promote bottom‐up controls in the pelagic food web, further influencing the southern edge of the species' geographic distribution. Owing to the prominent role this species plays in food web dynamics these results might help integrative fisheries management policies in the heavily exploited East China Sea.     

Seasonal variability of cephalopod populations: a spatio‐temporal approach in the Western Mediterranean Sea

Cephalopod populations show wide temporal fluctuations in abundance, which have usually been investigated at inter‐annual scales related to environmental variability. However, cephalopods are also strongly linked to seasonal environmental fluctuations owing to their short life cycles and single seasonal breeding. Therefore, population abundance critically depends on the success of breeding and recruitment from the previous year and the optimization of resources in a narrow period of favorable conditions. This adaptation of population dynamics is paramount in marked oligotrophic systems, such as the western Mediterranean Sea. We used monthly landings per unit effort (LPUE) to explore the spatio‐temporal variability in seasonal patterns of three cephalopod species (Illex coindetii, Eledone cirrhosa and Octopus vulgaris). Common trends across the study area were characterized for each species. In all cases, seasonal patterns were geographically aggregated in relation to differences in local environment (i.e., primary production and surface hydro‐climatology). Variability in the mean seasonal pattern over time was also investigated under contrasting environmental or population regimes. The mean seasonal trend was more pronounced in regimes of high‐population densities, suggesting a density‐dependent control that can modify the strength of the environmental forcing in the seasonal patterns. Our study also evidences a spatial synchrony in the seasonal fluctuations of LPUEs. Scales of synchrony ranged from 70 to 200 km, indicating a patchy‐aggregated spatial pattern as a part of complex population structures in the western Mediterranean. Improving our understanding of seasonal dynamics of cephalopods across temporal and spatial scales may lead to improved forecasts and management strategies.     

A comparative study of three different methods for assessing fish communities in a small eutrophic lake

Sound decisions on the management of fish stocks depend on knowledge about the species composition, number, biomass and size structure of existing populations. Accordingly, the ability to make solid population estimates is essential. In this study, a 2.15 ha lake was completely drained and the total number of fish was recorded and amounted to 180,915 individuals divided into seven species having a total weight of 1,395 kg. Before the draining, three commonly used methods in fish surveys were applied: multi‐mesh gillnets, point abundance sampling by electrofishing (PASE) and mark–recapture. Following the determination of the actual number and size distribution of each species, we evaluated the efficiency of the methods and found that gillnets caught a relatively high number of species (five out of seven) and thus proved to be the best tool for mapping species richness. However, gillnets were size selective towards larger individuals of perch (Perca fluviatilis) and did not catch roach (Rutilus rutilus) <5 cm. In contrast to gillnets, PASE was very effective at catching YOY fish in the shore zone but selected for larger‐sized roach. In sum, gillnetting proved to be the most accurate method for estimating species composition, PASE also being useful. Overall, mark–recapture provided relatively good estimates of population size but small‐sized (<11 cm) roach proved not to be well suited for mark–recapture surveys. We conclude that the best method(s) surveying fish stocks depends on various factors such as target species, size distribution and the purpose of the survey.     

Using mixed stock analysis to assess source populations for at‐sea bycaught juvenile and adult loggerhead turtles (Caretta caretta) in the north‐west Atlantic

Assessments of fisheries by‐catch on marine megafauna are important for developing effective management strategies. For sea turtles, impacts may be evident in nesting population trends, but generally only after a lag, as turtles are slow to mature. We examined 850 loggerhead turtle (Caretta caretta) by‐catch samples collected over 14 years throughout the western North Atlantic to identify source nesting populations. We identified proportions of turtles from 19 distinct management units (MUs), using mitochondrial DNA and mixed stock analysis, considering population size. We found a significant split in the distribution of small versus large loggerheads to the north and south of Cape Hatteras, North Carolina (latitude 35°N). North of Cape Hatteras, large turtles came from south‐east Florida (SEFL; 44% ± 15%) and the northern United States (33% ± 16%) MUs, while south of Cape Hatteras, the major contributors were Central East Florida (52% ± 20%) and south‐east Florida (SEFL; 41% ± 20%). Small turtles in the north came from Central East Florida (64% ± 14%), and in the south, south‐east Florida had the highest representation (56% ± 25%). There was little contribution from Mediterranean and Cape Verde populations, indicating low risk from western North Atlantic by‐catch to MUs in the Mediterranean. Understanding where threats may impact source populations is important, particularly for larger size turtles, as these individuals have the highest reproductive value. These findings allow more informed threat assessments to be conducted for loggerhead turtles considering spatial and demographic structure.     

Spatial distribution and abundance of the by‐catch coastal elasmobranch Raja undulata: Managing a fishery after moratorium

The undulate ray Raja undulata Lacepède is a coastal species common along the north‐eastern Atlantic Ocean and Mediterranean Sea and is highly accessible to coastal fisheries. Between 2009 and 2015, the species was under a European Union (EU) fisheries moratorium that hampered the collection of data to assess its stock status in Portuguese waters. After that period, a small experimental EU fishing quota was set for Portugal enabling collection of fishery data under a fishermen self‐sampling scenario. Based on the data collected, R. undulata abundance was estimated along the Portuguese continental coast through the application of a N‐mixture model and incorporating environmental factors. The results support the species coastal and patchy nature across the study area with higher abundances estimated in areas associated with shallow sandy bottoms as the Southwest region. The present work constitutes an important step for the management of this fishery resource, in particular concerns about its abundance trends over time and its spatial distribution and habitat requirements.