Species, sex, size and male maturity composition of previously unreported elasmobranch landings in Kuwait, Qatar and Abu Dhabi Emirate

This paper presents data from the first major survey of the diversity, biology and fisheries of elasmobranchs in the Persian (Arabian) Gulf. Substantial landings of elasmobranchs, usually as gillnet by-catch, were recorded in Kuwait, Qatar and the Emirate of Abu Dhabi (part of the United Arab Emirates), although larger elasmobranchs from targeted line fisheries were landed in Abu Dhabi. The elasmobranch fauna recorded was distinctive and included species that are undescribed, rare and have a highly restricted known distribution. Numerical abundance was dominated by sharks (c. 80%), of which carcharhinids were by far the most important. The milk shark Rhizoprionodon acutus and whitecheek shark Carcharhinus dussumieri together comprised just under half of all recorded individuals. Around 90% of recorded sharks were small (50-90 cm total length, L(T) ) individuals, most of which were mature individuals of species with a small maximum size (<100 cm L(T) ), although immature individuals of larger species (e.g. Carcharhinus sorrah and other Carcharhinus spp.) were also important. The most frequently recorded batoid taxa were cownose rays Rhinoptera spp., an undescribed whipray, and the granulated guitarfish Rhinobatos granulatus. The first size, sex and maturity data for a wide range of Gulf elasmobranch species are presented (including L(T) at 50% maturity for males of four shark species) and include some notable differences from other locations in the Indo-West Pacific Ocean. A number of concerns regarding the sustainability of the fishery were highlighted by this study, notably that most of the batoid species recorded are classed by the IUCN Red List as vulnerable, endangered, data deficient or not evaluated. Despite their considerable elasmobranch landings, none of the three countries sampled have developed a 'Shark Plan' as encouraged to do so under the FAO International Plan of Action: Sharks. Furthermore, Kuwait and Qatar currently report zero or no elasmobranch landings to the FAO.     

Temporal changes in allele frequencies but stable genetic diversity over the past 40 years in the Irish Sea population of thornback ray, Raja clavata

Rays and skates are an unavoidable part of the by-catch in demersal fisheries. Over the past 40 years, the thornback ray (Raja clavata) has decreased in numbers and even disappeared in some areas, leading to concerns about genetic risk. For this reason, the effective population size (N(e)), the migration rate (m) and temporal changes in the genetic diversity were estimated for the population of thornback rays in the Irish Sea and Bristol Channel. Using genotyped, archived and contemporary samples (1965 and 2003-2004), N(e) was estimated at 283 individuals (95% CI=145-857), m at 0.1 (95% CI=0.03-0.25) and the N(e)/N ratio between 9 x 10(-5) and 6 x 10(-4). Although these results must be treated with caution, due to the small sample sizes, this is the first attempt to estimate N(e) in an elasmobranch species. The low N(e)/N ratio suggests that relatively few individuals contribute to the next generation. The combined effect of sex bias, inbreeding, fluctuations in population size and, perhaps most important, the variance in reproductive success may explain the low N(e)/N ratio. In addition, the relatively high gene flow between Irish Sea population and other source populations is likely to have had an impact on our estimate, which may be more relevant at the metapopulation scale. No significant loss of genetic diversity was found over the 40-year timeframe and long-term maintenance of the genetic diversity could be due to gene flow.     

Shark and ray teeth from the Hauterivian (Lower Cretaceous) of north-east England

Sampling of hiatal horizons within the Hauterivian part of the Speeton Clay Formation of north-east England has produced teeth of several species of sharks and rays, four of which are previously unnamed. One species of shark, Cretorectolobus doylei sp. nov., and two species of rays, Spathobatis rugosus sp. nov. and Dasyatis speetonensis sp. nov., are named, whilst the presence of an indeterminate triakid shark is also noted. Synechodus dubrisiensis (Mackie) is shown to be a senior synonym of S. michaeli Thies. Although the dasyatid ray and triakid shark are by far the oldest representatives of their respective families, the overall composition of the fauna is considered to resemble more closely assemblages known from the Jurassic than those from upper parts of the Cretaceous.     

An overview on the role of Hexanchiformes in marine ecosystems: biology, ecology and conservation status of a primitive order of modern sharks

The large size, high trophic level and wide distribution of Hexanchiformes (cow and frilled sharks) should position this order as important apex predators in coastal and deep-water ecosystems. This review synthesizes available information on Hexanchiformes, including information not yet published, with the purpose of evaluating their conservation status and assessing their ecological roles in the dynamics of marine ecosystems. Comprising six species, this group has a wide global distribution, with members occurring from shallow coastal areas to depths of c. 2500 m. The limited information available on their reproductive biology suggests that they could be vulnerable to overexploitation (e.g. small litter sizes for most species and suspected long gestation periods). Most of the fishing pressure exerted on Hexanchiformes is in the form of commercial by-catch or recreational fishing. Comprehensive stock and impact assessments are unavailable for most species in most regions due to limited information on life history and catch and abundance time series. When hexanchiform species have been commercially harvested, however, they have been unable to sustain targeted fisheries for long periods. The potentially high vulnerability to intense fishing pressure warrants a conservative exploitation of this order until thorough quantitative assessments are conducted. At least some species have been shown to be significant apex predators in the systems they inhabit. Should Hexanchiformes be removed from coastal and deep-water systems, the lack of sympatric shark species that share the same resources suggests no other species would be capable of fulfilling their apex predator role in the short term. This has potential ecosystem consequences such as meso-predator release or trophic cascades. This review proposes some hypotheses on the ecology of Hexanchiformes and their role in ecosystem dynamics, highlighting the areas where critical information is required to stimulate research directions.     

Aspects of reproduction and their implications for the conservation of the endangered limpet,Patella ferruginea

Summary

The protandric limpet, Patella ferruginea G., is the most endangered marine species in the Western Mediterranean and is at serious risk of extinction. Nevertheless, its biology and ecology are little known. In the present work, several reproductive aspects are studied. Recruitment take place in June and the largest individuals are the most scarce. The sex ratio is slanted towards the largest sizes, and the species seems to show sex change at sizes from 60 mm upwards, although males can be observed up to 80 mm. There is no correlation between size of oocytes and shell length; however, the larger females contribute greatly to the reproductive event, with high fecundity and GSI values. The mean diameter of oocytes was observed to be 149.78 μm, whereas the heads of spermatozoa were 3.78 μm long. The results of the present study increase the maximum length for males by double that cited in previous literature and highlight the importance of strictly protecting females (i.e., most of the largest individuals, >60 mm), since their population percentage is very low, in order to develop adequate strategies to preserve the species.     

Fisheries in the Southern Ocean: an ecosystem approach

The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is bound by its Article II, 3 to follow an ecosystem approach to management. This approach has been extended to the application of a precautionary approach in the late 1980s. In our review, we deal primarily with the science-related aspects of CCAMLR and its development towards an ecosystem approach to the management of the living resources of the Southern Ocean. To assist the Commission in meeting its objectives, as set out in Article II, 3, the Scientific Committee established the CCAMLR Ecosystem Monitoring Programme to detect possible effects of krill fishing on the performance of top-level predators, such as albatrosses, penguins, petrels and fur seals. Fisheries in the Southern Ocean followed the fate of other fisheries worldwide in which target species were depleted to low level one after the other. Currently, two types of fisheries are open: the longline fisheries on Patagonian toothfish (Dissostichus eleginoides) and Antarctic toothfish (Dissostichus mawsoni) and the trawl fisheries on mackerel icefish (Champsocephalus gunnari). Both fisheries are managed in a single-species context, however, with conservation measures in place to protect by-catch species, such as rattails (Macrouridae) and skates and rays (Rajidae). Two major problems still exist in fisheries in the Southern Ocean: the by-catch of birds in longline fisheries primarily in the Indian Ocean and the high level of IUU fishing again in the Indian Ocean. Both, the by-catch of birds and high IUU catches undermine the credibility of CCAMLR to safeguard the marine living resources in the Southern Ocean.     

Reproductive biology of Haemulon plumierii in the south‐western Atlantic Ocean's most extensive reefs: implications for fisheries management

The reproductive biology of the white grunt Haemulon plumierii was studied from 360 individuals obtained from artisanal fisheries landings in the Abrolhos Bank, Brazil, between August 2010 and March 2012. The overall sex‐ratio did not differ significantly from 1:1, although males predominated in larger size classes. β‐Binomial modelling of historical sex‐ratio data indicated that the catch rate of females has increased in recent years. Females reached maturity at a smaller total length (L_T; 214 mm) than males (235 mm L_T) and the L_T at which 50% of all individuals are mature (L₅₀) was 220 mm, corresponding to 41·5% of the maximum recorded L_T. Variation in the gonado‐somatic index and in the relative frequency of reproductive stages indicates that reproduction occurs year round, with increased activity during the austral spring and summer. Fecundity was not size dependent. The reproductive parameters provided here can support management measures focussed on seasonal closures during spawning peaks (September to November and February to March) and minimum sizes (>L₅₀) for the capture of this important artisanal fisheries resource in Abrolhos, the region with the largest and most biodiverse coralline reefs in the South Atlantic Ocean.     

Reproductive success in reindeer males in a herd with varying sex ratio

In polygynous species, male reproductive success is often correlated with dominance status of individual males and sex ratio in the population. Reindeer, Rangifer tarandus, is a polygynous species, and here we compared the variation in male reproductive success and dominance status during two successive years in a herd with a male:female sex ratio of 1:7 and 1:3. Copulations were recorded, together with data on male dominance hierarchy and size of mating groups. Male reproductive success was estimated by paternity analysis of calves using microsatellite DNA markers. The distribution of reproductive success among the males was highly skewed for both years with the most dominant male also being the most successful. The largest mating group was established in the herd with the least skew in sex ratio. In this herd some of the adult males present were less reproductively successful than some of the more subordinate younger males. Estimates of the mating group size of males, correcting for dominance status when more than one male is present in the groups, gave good prediction of individual males' reproductive success.     

Cory’s shearwater by-catch in the Mediterranean Spanish commercial longline fishery: implications for management

Cory’s shearwater Calonectris diomedea is the main seabird species by-caught by the Spanish longline fleet operating in the western Mediterranean Sea. Identification of the principal factors that determine this by-catch and understanding how they could be controlled is fundamental for improving the management of fisheries and so carry out a better conservation of Cory’s shearwater populations in the Mediterranean. The aim of this paper was to model the longline by-catch of Mediterranean Cory’s shearwater in the Spanish Mediterranean longline fishery as a function of time of the year, technical characteristics of the fishing operation, and geographical location. We used data recorded by an onboard observer program monitoring commercial longline fisheries. During the 10 years covered in this study, 80 birds were captured in 30 fishing operations out of a total of 2,587 observed fishing sets. We used favourability functions and Random Forest analyses to relate the presence of Cory’s shearwater in the by-catch with the explanatory factors. The most explanatory factor in relation to incidence of by-catch was the geographical location (longitude and fishing over the continental shelf) and then the technical characteristics of the fishing operation (number of hooks and fishing during non-working days). Our conclusion is clear, because seabirds are more likely to approach longline vessels when trawlers are not allowed to operate (i.e. non-working days), activity of longliners should be limited to working days, and closing longliners activity during the month of October could reduce greatly reducing seabird bycatch.     

Morphometics and Gonadal Development of the Hagfish Eptatretus cirrhatus in New Zealand

Hagfishes have been the target of commercial fisheries in many areas of the world, with the catch processed for leather and for human consumption. A fishery has been operating in New Zealand waters for the last six years, harvesting the bearded hagfish, Eptatretus cirrhatus. The fishery has thus far been unregulated. Based on samples collected dockside over a two-year period, this report expands the morphometric database for this species, provides information on the size and weight of the harvested animals, determines the sizes at the onset of gonadal development and the minimum sizes at sexual maturation for males and females, and indicates that E. cirrhatus, like most other hagfish species, has no specific breeding season. Although females appear in the population at smaller sizes, the sex ratio for mature animals is 1:1 and the sizes of the largest males and females are comparable. The changes observed in sex ratio as a function of TL suggest differences in the timing and rates of gonadal development in females versus males rather than protogyny. Based on the size of the eggs, the number of eggs per female, the proportion of the population that contains large eggs, and the number of postovulatory females, it is clear that E. cirrhatus, like other hagfish species, are potentially vulnerable to overexploitation.     

Reproductive versus ecological advantages to larger body size in female snakes, Vipera aspis

Body size can influence an organism's microevolutionary fitness either via ecological factors (ecological selection) or changes in reproductive output (sexual or fecundity selection). Published studies on sexual dimorphism in reptiles have generally focussed on sexual-selective forces on males, under the implicit assumption that the intensity of fecundity selection in females (and hence, overall selection on female body size) is likely to be relatively consistent among lineages. In this paper, we explore the degree to which larger body size enhances ecological attributes (e.g., food intake, growth, survival) and reproductive output (reproductive frequency, litter size, offspring size, offspring viability) in free-ranging female aspic vipers, Vipera aspis . The less-than-annual reproductive frequency of these animals allows us to make a direct comparison between females in years during which they concentrate on "ecological" challenges (especially building energy reserves) versus reproductive challenges (producing a litter). Because female snakes have limited abdominal space to hold the clutch (litter), we expect that fecundity should depend on body size. However, our data show that larger body size had a more consistent effect on ecological attributes (such as feeding rates and "costs of reproduction") than on reproductive output per se. Indeed, total reproductive output was maximised at intermediate body sizes. These results suggest that variation in female body size among and within species (and hence, in the degree of sexual dimorphism) may be driven by the ecological as well as reproductive consequences of body size variation in both sexes.     

Development of secondary sexual characters and their relationship to ontogeny and seasonal reproductive period in Hyphessobrycon igneus (Ostariophysi: Characiformes)

Sexual dimorphism in size, anal‐fin shape and coloration of Hyphessobrycon igneus, Characidae, were examined. Males were more frequent at larger body sizes, confirming body size as a sexually dimorphic trait. Anal‐fin shape and the colour of all fins were the same for females and juveniles, differing only in adult males. Likewise, only adult males had bony hooks on fin rays; larger and more sexually mature males had the most numerous and developed hooks and hooks were most developed in degree and number during peak reproductive periods. Fin hooks regressed in number and developmental degree after the reproductive period, but restarted development with the beginning of the new reproductive period without completely disappearing. Results show that bony hooks have a development and regression cycle related to reproductive seasonality.     

Relationship of cryptorchidism with sex ratios and litter sizes in 12 dog breeds

The aim of this study was to identify the influence of genetic carriership for cryptorchidism on litter sizes and sex ratios in the offspring. Weaning data of 11,230 litters in 12 purebred dog breeds were evaluated. Parents were classified as cryptorchidism 'carriers' (C) when at least one of their offspring was found cryptorchid. Subsequently the effects of 'carrier' and 'non-carrier' (NC) parents on their litters were studied. In litters from C x C parents we found an increased number of males per litter in all breeds, a reduced number of females per litter in 8 breeds and an increased litter size in 11 breeds in comparison with litters from NC x NC parents. Over all breeds the effects on litter size, on number of males per litter and on sex ratio were highly significant. Mixed litters from C x NC and NC x C did not show these effects and were not significantly different from the NC x NC offspring. Our results suggest a general mechanism in the dog species which causes cryptorchidism as well as increased male/female ratios and increased litter sizes. A consequence of such a mechanism is that selection in favor of increasing reproduction output frustrates selective efforts to eliminate cryptorchidism.     

Aspects of the reproductive biology of two pelagic sharks in the eastern Atlantic Ocean

This study used data provided by the Chinese Longline Fishery Scientific Observer Programme from the tropical eastern Atlantic Ocean to estimate the reproductive parameters of the blue shark (Prionace glauca) and crocodile shark (Pseudocarcharias kamoharai). Sizes ranged from 80 to 298 cm fork length (FL) for blue sharks and from 48 to 99 cm FL for crocodile sharks. Sexual segregation was observed during different months for both sharks. The sex ratio for blue sharks was 1.38 F:1 M, and 1 F:2.79 M for crocodile sharks. The size of adult blue sharks ranged from 144 to 280 cm for males and from 174 to 298 cm for females; and that of crocodile sharks from 63 to 97 cm for males and 78–99 cm for females. The size at 50% of maturity for blue sharks was estimated at 191.7 cm FL for females and 197.5 cm FL for males, and that of crocodile sharks was assessed at 84.9 cm FL for females and 78.5 cm FL for males. Most sexually matured females were pregnant; their means were 207.2 ± 16.4 cm FL for blue sharks and 89.4 ± 4.3 cm FL for crocodile sharks. Mature sizes for both species were significantly different among months. Embryonic sizes also varied widely among months for crocodile sharks, but a slight change was recorded for those of blue sharks. The observed mean size at birth and litter size were 34.5 cm FL and 37 ± 12 for the blue sharks, and that of the crocodile sharks, 39.5 cm FL and a dominant four embryos in the uterus. Due to the observed increasing catch trend of blue sharks and the slow reproductive cycle of crocodile sharks, this study presents the need of implementing conservation measures to ensure the sustainability of both species in their habitat.     

Management implications of the biodiversity and socio-economic impacts of shrimp trawler by-catch in Bahía de Kino, Sonora, México

The shrimp fishery is the most economically important fishery in Mexico. The trawler-based portion of this fishery results in high rates of by-catch. This study quantifies and describes the biodiversity of by-catch associated with trawling in the Bahía de Kino region of Sonora, Mexico. Data were collected from 55 trawls, on six boats, over 14 nights, during November of 2003, 2004, 2006-2009. By-catch rates within trawl samples averaged 85.9% measured by weight. A total of 183 by-catch species were identified during the course of this study, including 97 species of bony fish from 43 families, 19 species of elasmobranchs from 12 families, 66 species of invertebrates from eight phyla, and one species of marine turtle; seven of the documented by-catch species are listed on the IUCN Red List, CITES, or the Mexican NOM-059-ECOL-2010; 35 species documented in the by-catch are also targeted by local artisanal fishers. Some of the species frequently captured as juveniles in the by-catch are economically important to small-scale fishers in the region, and are particularly sensitive to overexploitation due to their life histories. This study highlights the need for further research quantifying the impacts of high levels of by-catch upon small-scale fishing economies in the region and presents strong ecological and economic rationale for by-catch management within the shrimp fishery of the Gulf of California. Site-specific by-catch management plans should be piloted in the Bahía de Kino region to address the growing momentum in national and international fisheries policy regimes toward the reduction of by-catch in shrimp fisheries.     

Social media posts reveal the geographic range of the Critically Endangered clown wedgefish,Rhynchobatus cooki

The shark-like rays of the family Rhinidae (wedgefishes) are globally threatened with extinction. The poorly known clown wedgefish, Rhynchobatus cooki has historically been recorded only from fish markets in Singapore and Jakarta, Indonesia. Its natural geographic range has until now gone undocumented. Social media posts revealed the first wild records of this Critically Endangered species; six records were located between 2015 and 2020 from small-scale fisheries in Lingga and Singkep Islands, Indonesia. These results demonstrate the utility of social media searches to identify biogeographic records of cryptic and data-poor species.     

Different Sex Allocations in Two Related Species: The Case of the Extant Hippopotamus

Social and reproductive systems remain among the main predictors affecting mammalian birth sex ratio. The two extant hippopotamus species differ in their social and reproductive systems. While common hippopotamus (Hippopotamus amphibius) form herds and tend to be polygynous, solitary living pygmy hippopotamus (Choeropsis liberiensis) are promiscuous. Although it is one of the most studied topics, only few empirical studies using large sample sizes have reported distorted birth sex ratio. We examined the birth sex ratio in both hippopotamus species using international studbooks including large data sets exceeding a thousand individuals (1138 for common hippopotamus and 1161 for pygmy ones). In both species, the birth sex ratio differed from 1:1. Whereas more males than females were recorded in common hippopotamus (53.9% males), the opposite was found in pygmy hippopotamus (41.5% males). We also found that the birth sex ratio was affected by individual dams in common hippopotamus, and by individual sires in pygmy hippopotamus. The most plausible explanation for differentially skewed birth sex ratios in both species may be related to differences in social and reproductive systems. Whereas the polygynous, sexually dimorphic common hippopotamus biased the birth sex ratio towards males, the promiscuous and sexually monomorphic pygmy hippopotamus skewed the sex ratio in favour of females. Our results are in line with recent studies showing that not only manipulation by the mother (in common hippopotamus), but also by the father (in pygmy hippopotamus), may be responsible for the birth sex ratio in different species.     

A comparative study of litter size and sex composition in a large dataset of callitrichine monkeys

In many birds and mammals, the size and sex composition of litters can have important downstream effects for individual offspring. Primates are model organisms for questions of cooperation and conflict, but the factors shaping interactions among same‐age siblings have been less‐studied in primates because most species bear single young. However, callitrichines (marmosets, tamarins, and lion tamarins) frequently bear litters of two or more, thereby providing the opportunity to ask whether variation in the size and sex composition of litters affects development, survival, and reproduction. To investigate these questions, we compiled a large dataset of nine species of callitrichines (n = 27,080 individuals; Callithrix geoffroyi, Callithrix jacchus, Cebuella pygmaea, Saguinus imperator, Saguinus oedipus, Leontopithecus chrysomelas, Leontopithecus chrysopygus, Leontopithecus rosalia, and Callimico goeldii) from zoo and laboratory populations spanning 80 years (1938–2018). Through this comparative approach, we found several lines of evidence that litter size and sex composition may impact fitness. Singletons have higher survivorship than litter‐born peers and they significantly outperform litter‐born individuals on two measures of reproductive performance. Further, for some species, individuals born in a mixed‐sex litter outperform isosexually‐born individuals (i.e., those born in all‐male or all‐female litters), suggesting that same‐sex competition may limit reproductive performance. We also document several interesting demographic trends. All but one species (C. pygmaea) has a male‐biased birth sex ratio with higher survivorship from birth to sexual maturity among females (although this was significant in only two species). Isosexual litters occurred at the expected frequency (with one exception: C. pygmaea), unlike other animals, where isosexual litters are typically overrepresented. Taken together, our results indicate a modest negative effect of same‐age sibling competition on reproductive output in captive callitrichines. This study also serves to illustrate the value of zoo and laboratory records for biological inquiry.     

Reproductive biology of the Brazilian guitarfish,Pseudobatos horkelii (Müller & Henle, 1841) from southeastern Brazil,western South Atlantic

This study provides information on the seasonal occurrence, length‐width relationship, sexual development and size at first maturity of the critically endangered Brazilian guitarfish Pseudobatos horkelii in southeastern Brazil. Samples were obtained from September 2007 to August 2009 from commercial fisheries off São Paulo State coast at depths of 10–50 m, with net mesh sizes of 150 mm in the main net and 100 mm in the cod end. A total of 143 specimens (71 males, 72 females) were analyzed. Total length (TL), disc width (DW), sex and reproductive variables were recorded for each individual. Pseudobatos horkelii presents sexual dimorphism in length‐width relationships, with females attaining larger TL and DW. Females also mature at a larger TL, at 81.1% of the maximum TL, while males mature at 67.8% of the maximum TL. No specimens were captured in winter, and only a small sample size was observed in autumn. Males captured in spring and summer presented semen in the seminal vesicle, indicating that this species may reproduce in the warmer months, as already observed for other Rhinobatidae as well as for P. horkelii in southern Brazil.