assessing the status of demersal elasmobranchs in uk waters: a review

Author(s):  
j.r. ellis ◽  
n.k. dulvy ◽  
s. jennings ◽  
m. parker-humphreys ◽  
s.i. rogers

elasmobranch fish are susceptible to over-exploitation by commercial and recreational fisheries and an increasing focus of conservation initiatives. the lack of accurate species-specific landings data in many european fisheries and the paucity of biological data have restricted the types of stock assessment that can be undertaken. hence, other methods of determining the overall status of elasmobranch fish are required. for demersal elasmobranchs around the british isles, the most widely available biological data describe life histories and abundance from fishery-independent surveys. here, we examine the length-distribution of demersal elasmobranchs caught during groundfish surveys, to determine which life history stages are sampled effectively. for these stages, we report trends in abundance and relate the trends to knowledge of the species' biology and fisheries, and to the decline criteria that are used to assess species' status by nature conservation agencies. the analyses show that many large demersal elasmobranchs have been severely depleted in uk waters but that groundfish surveys still provide a good source of data for monitoring changes in status of the more abundant species. for rare and highly depleted species, groundfish surveys often provide good retrospective descriptions of declines, but the surveys have limited power to detect recent changes in status.

<em>Abstract</em>.—The objective of this study is to describe the distribution patterns of abundance and biomass, on a geographic and bathymetric basis, of the main macrourid species of Mozambique waters. Catch data from a demersal trawl survey (<EM>MOZAMBIQUE 07</EM>) were analyzed. The survey covered the continental shelf and upper-middle slope from 17°00’S to 26°50’S and from 100–700 m depth. Fourteen macrourid species were collected from 200 m and deeper. The most abundant species and the highest in biomass were <em>Coelorinchus braueri</em>, <em>C. trunovi, C. denticulatus</em>, <em>Ventrifossa nasuta</em>, and <em>Malacocephalus laevis</em>. Only those five species were analyzed in detail. The occurrence and yields by geographic and bathymetric range of these main species seem to reveal the existence of some species-specific preference for determinate depth ranges and/or geographic areas. Preanal length-weight relationships were estimated for <em>C. braueri, C. trunovi, </em>and <em>V. nasuta</em>: <em>a</em>= 0.00071; 0.00020; 0.00080; <em>b</em>= 2.50; 2.80; 2.76 and <em>r</em><sup>2</sup>= 0.93; 0.97; 0.78, respectively.


<em>Abstract.</em>—The principal aim of this study is to describe the distribution patterns of abundance and biomass, on a seasonal and bathymetric basis of the main macrourid species from the Spanish Gulf of Cadiz. The results from 23 bottom-trawl surveys carried out in the study area in spring and autumn of 1993–2006 were analyzed. The most abundant species captured were common Atlantic grenadier <em>Nezumia aequalis </em>and saddled grenadier <em>Coelorinchus coelorhincus. </em>In terms of biomass, softhead grenadier <em>Malacocephalus laevis </em>was the third most important species and bluntsnout grenadier <em>Nezumia sclerorhynchus </em>and glasshead grenadier <em>Hymenocephalus italicus </em>were the least abundant species. Of the five species caught in the surveys, only <em>N. aequalis</em>, <em>M. laevis </em>and <em>C. coelorhincus </em>were analyzed in detail; their yields expressed in number of individuals/h represented the higher values and showed higher yields in spring than in autumn, suggesting a seasonal pattern of abundance. However, <em>C. coelorhincus </em>did not show this pattern except between 1999 and 2004. <em>N. aequalis </em>showed the widest bathymetric range. The observed yields in the depth gradient for the three species revealed species-specific preferences for a determinate depth range. In relation to mean total size, larger individuals of <em>M. laevis </em>and <em>N. aequalis </em>were observed during the March surveys. <em>C. coelorhincus </em>was the only species that showed a slight increase in mean size with increasing depth.


2021 ◽  
Vol 14 ◽  
pp. 194008292110103
Author(s):  
Patrick Jules Atagana ◽  
Eric Moïse Bakwo Fils ◽  
Sevilor Kekeunou

We aimed to assess how bats are affected by habitat transformation by comparing bat assemblages in four habitat types: primary forest, secondary forest, cocoa plantations and human habitations in the Dja Biosphere Reserve of southern Cameroon. Bats were sampled in the four habitat types using mist nets. During 126 nights, a total of 413 bats were captured, belonging to four families, 16 genera and 24 species. Ninety three individuals (17 species) were captured in the primary forest, followed by plantations (105 individuals, 14 species), human habitations (159 individuals, 10 species), and secondary forest (55 individuals, eight species). Megaloglossus woermanni was recorded in all the four habitats, and was the most abundant species (105 individuals). The analysis of bat assemblage between habitat types showed a statistically significant difference in species composition. The distribution of the six most abundant species ( Epomops franqueti, Megaloglossus woermanni, Rousettus aegyptiacus, Dohyrina cyclops, Hipposideros cf. caffer and Hipposideros cf. ruber) was influenced by habitat types. Our results suggest that the decrease in species richness observed in disturbed habitats may be due to habitat perturbations of primary forest habitats. Therefore, it is important to examine the effects of habitat conversion at species level, as responses are often species-specific.


2019 ◽  
Vol 76 (7) ◽  
pp. 2125-2139 ◽  
Author(s):  
Tanja Miethe ◽  
Yves Reecht ◽  
Helen Dobby

Abstract In the absence of abundance indices from scientific surveys or commercial sources, reliable length frequency data from sampled commercial catches can be used to provide an indirect assessment of fishing mortality. Length-based indicators are simple metrics which describe length frequency distributions. The length-based indicator Lmax5%, the mean length of the largest 5% of individuals in the catch, combined with appropriately selected reference points, can be used to evaluate the presence of very large individuals in the catch and hence determine exploitation level. Using analytical per-recruit models, we derive reference points consistent with a spawning potential ratio of 40%. The reference points depend on the life history parameters for natural mortality, maturity, and growth (M, Lmat, L∞, k, CVL∞). Using available simulation tools, we investigate the sensitivity of the reference points to errors in these parameters and explore the usefulness of particular reference points for management purposes for stocks with different life histories. The proposed reference points are robust to uncertainty in length at first capture, Lc, and take into account the maturation schedule of a species. For those stocks with high M/k ratios (&gt;1), Lmax5%, combined with the appropriate reference point, can be used to provide a data-limited stock assessment.


Fisheries ◽  
2021 ◽  
Vol 2021 (3) ◽  
pp. 68-75
Author(s):  
Inna Kozobrod ◽  
M. Pyatinsky ◽  
Elena Vlasenko

Stock assessment of vimba population Vimba vimba (Linnaeus, 1758) in period 2015–2020 was performed by qualitative indicator method LBI (Length-Based Indicators) that allows to assess qualitative characteristics of the population and fisheries and MSY biological reference points. The indicator, qualitative approach to stock assessment was applied due to absence vimba population of stable stock-recruitment relationship (due to artificial reproduction exist), which makes impossible to apply surplus production approach to solve production equation dB/dt. LBI model was performed based on available length-weight vimba frequencies dynamics information, which allows to evaluate qualitative population characteristics and fisheries impact. Model results shows no overexploitation signals: in period 2015–2020 fisheries are carried out in maximum sustainable yield level. Indicator results according to reference points indicate no significant signals of reduction optimal length class (Lopt), small-size or large-size class. In 2016 and 2018 uncertain overexploitation of small-scale classes leads to no significant changes was underlined. In terms of biological and fisheries data lacking, LBI methods allow to perform stock assessment procedure more stable and robust then surplus or cohort approach, and output scientific advice to fisheries management.


2017 ◽  
Vol 372 (1717) ◽  
pp. 20160071 ◽  
Author(s):  
Tamara M. Frank

For all visually competent organisms, the driving force behind the adaptation of photoreceptors involves obtaining the best balance of resolution to sensitivity in the prevailing light regime, as an increase in sensitivity often results in a decrease in resolution. A number of marine species have an additional problem to deal with, in that the juvenile stages live in relatively brightly lit shallow (100–200 m depth) waters, whereas the adult stages have daytime depths of more than 600 m, where little downwelling light remains. Here, I present the results of electrophysiological analyses of the temporal resolution and irradiance sensitivity of juvenile and adult stages of two species of ontogenetically migrating crustaceans ( Gnathophausia ingens and Systellaspis debilis ) that must deal with dramatically different light environments and temperatures during their life histories. The results demonstrate that there are significant effects of temperature on temporal resolution, which help to optimize the visual systems of the two life-history stages for their respective light environments. This article is part of the themed issue ‘Vision in dim light’.


Biologia ◽  
2020 ◽  
Vol 75 (10) ◽  
pp. 1631-1641
Author(s):  
Janina Bennewicz ◽  
Tadeusz Barczak

Abstract The aim of this study was to identify the role of field margin habitats in preserving the diversity and abundance of ground beetle assemblages, including potentially entomophagous species and those with conservation status in Poland. Research material was collected in 2006–2007 in four types of margin habitats – a forest, bushes, ditches and in two arable fields. Insects were captured into pitfalls, without preservation liquid or bait added to the traps. Traps were inspected twice a week, between May and August, and one sample was a weekly capture. In field margin habitats the most abundant species were Limodromus assimilis, Anchomenus dorsalis, Pterostichus melanarius and Carabus auratus. A lower abundance of species was noted on fields, with dominant Poecilus cupreus and P. melanarius. The group of zoophagous carabids found in our study includes 30 species from field margin habitats, i.e. 37.5% of all captured Carabidae taxa and 58.3% of all specimens. The share of aphidophagous species was 84.9% among bushes, 86.7% near ditches, and 88.0% in the forest habitat. Several species captured during the study are under protection in Poland. These include the partly protected Carabus convexus, which also has the status of near threatened species, the partly protected Calosoma auropunctatum, and Broscus cephalotes. Considering all the investigated field margin habitats, ground beetles were most numerous in the oak-hornbeam habitat, defined as bushes, formed predominantly by Prunus spinosa, Crataegus leavigata, Sambucus nigra and Rosa canina. Thus, this habitat was the most important reservoir/refugium for the ground beetles.


Author(s):  
Francisco Andres Rivera-Quiroz ◽  
Jeremy Miller

Traditional taxonomic publications have served as a biological data repository accumulating vast amounts of data on species diversity, geographical and temporal distributions, ecological interactions, taxonomic relations, among many other types of information. However, the fragmented nature of taxonomic literature has made this data difficult to access and use to its full potential. Current anthropogenic impact on biodiversity demands faster knowledge generation, but also making better use of what we already have. This could help us make better-informed decisions about conservation and resources management. In past years, several efforts have been made to make taxonomic literature more mobilized and accessible. These include online publications, open access journals, the digitization of old paper literature and improved availability through online specialized repositories such as the Biodiversity Heritage Library (BHL) and the World Spider Catalog (WSC), among others. Although easy to share, PDF publications still have most of their biodiversity data embedded in strings of text making them less dynamic and more difficult or impossible to read and analyze without a human interpreter. Recently developed tools as GoldenGATE-Imagine (GGI) allow transforming PDFs in XML files that extract and categorize taxonomically relevant data. These data can then be aggregated in databases such as Plazi TreatmentBank, where it can be re-explored, queried and analyzed. Here we combined several of these cybertaxonomic tools to test the data extraction process for one potential application: the design and planning of an expedition to collect fresh material in the field. We targeted the ground spider Teutamus politus and other related species from the Teutamus group (TG) (Araneae; Liocranidae). These spiders are known from South East Asia and have been cataloged in the family Liocranidae; however, their relations, biology and evolution are still poorly understood. We marked-up 56 publications that contained taxonomic treatments with specimen records for the Liocranidae. Of these publications, 20 contained information on members of the TG. Geographical distributions and occurrences of 90 TG species were analyzed based on 1,309 specimen records. These data were used to design our field collection in a way that allowed us to optimize the collection of adult specimens of our target taxa. The TG genera were most common in Indonesia, Thailand and Malaysia. From these, Thailand was the second richest but had the most records of T. politus. Seasonal distribution of TG specimens in Thailand suggested June and July as the best time for collecting adults. Based on these analyses, we decided to sample from mid-July to mid-August 2018 in the three Thai provinces that combined most records of TG species and T. politus. Relying on the results of our literature analyses and using standard collection methods for ground spiders, we captured at least one specimen of every TG genus reported for Thailand. Our one-month expedition captured 231 TG spiders; from these, T. politus was the most abundant species with 188 specimens (95 adults). By comparison, a total of 196 specimens of the TG and 66 of T. politus had been reported for the same provinces in the last 40 years. Our sampling greatly increased the number of available specimens, especially for the genera Teutamus and Oedignatha. Also, we extended the known distribution of Oedignatha and Sesieutes within Thailand. These results illustrate the relevance of making biodiversity data contained within taxonomic treatments accessible and reusable. It also exemplifies one potential use of taxonomic legacy data: to more efficiently use existing biodiversity data to fill knowledge gaps. A similar approach can be used to study neglected or interesting taxa and geographic areas, generating a better biodiversity documentation that could aid in decision making, management and conservation.


2017 ◽  
Vol 15 (1) ◽  
pp. 87-102 ◽  
Author(s):  
Bijay Kumar Singh

  Covering about 13 per cent of the total land area of Nepal, Chure is an environmentally vulnerable, fragile and sensitive zone. Recognizing this, the Government of Nepal has declared it as “Chure Environmental Protection Area” and has formulated a high level board called “President Chure- Terai-Madhesh Conservation Board” to oversee the conservation activities in the region. Based on a review of literature and a decade long engagement of the author in the conservation in Chure, in this paper, I explore the status and issues related to the management of and land tenure in the Chure region. I find that land tenure is one of the most contested and challenging issues of conservation in Chure. With the presence of significant human settlements near to Chure Environmental Protection Area, the boundary is contested, particularly after the unilateral designation by the government; issues also remain around the rights to utilize forest resources. In fact, these factors have resulted in over exploitation of the resources, mainly by the upstream communities. I conclude the paper arguing for a broader, holistic approach that integrates upstream and downstream ecosystems in such a way that strengthens the historical socio-ecological links between the Chure region and the Terai so as to bring positive impacts for both.


2020 ◽  
Vol 77 (2) ◽  
pp. 295-313 ◽  
Author(s):  
Joseph Munyandorero

The recruitment compensation metrics, the stock–recruit steepness (h) and compensation ratio (κ), are difficult to estimate, yet they are integral components of contemporary fishery models. To aid in the estimation of κ and h, a hybrid method to construct their prior distributions for a species is developed. The method is hybrid because it integrates (i) a meta-analysis of the relationship between maximum rates of recruit production (α) and asymptotic lengths obtained across fish species of different life histories and (ii) species-specific unfished spawning biomass per recruit (Φ0). This method is applied to five finfish species found off the East Coast of the United States. Uncertainty is introduced by sampling growth parameters, α, and natural mortality and — through Monte Carlo simulations — propagated into Φ0, κ, and h for the Beverton–Holt and Ricker stock–recruit relationships. Descriptive statistics and parameters from probability density functions of the simulated distributions of κ and h are generated. The method developed requires fewer inputs than the reproductive ecology method while likewise allowing the development of species-specific statistics for κ and h. These statistics, rather than their counterparts generated from classical meta-analyses, are better suited for use in fishery models.


Sign in / Sign up

Export Citation Format

Share Document