Sperm maturation and capacitation in the open thelycum shrimp Litopenaeus (Crustacea: Decapoda: Penaeoidea)

Transmission electron microscopy was applied to sperm removed from males and females belonging to Litopenaeus vannamei, L. stylirostris and L. occidentalis. It was discovered that a region named filamentous meshwork (FM), located between the nucleus and the hemispherical cap, develops differently in these three closely related species. In L. vannamei, the FM is synthesized in the male reproductive system, but seems to complete its formation after mating. In L. stylirostris, the FM region was not present in spermatophores collected from males or in sperm from the thelycum. In L. occidentalis, the FM region is fully developed in male sperm. It is suggested that completion of the FM is required for acrosome maturation, and the process continues after mating in some species of Litopenaeus. In vitro induction of the acrosome reaction in sperm from males and females of L. occidentalis demonstrated for the first time that reactivity is significantly superior in sperm cells that have been attached to the open thelycum for some hours, as compared to sperm in males (prior to transfer). This finding suggests that matured sperm cells of L. occidentalis become capacitated to react against egg water after mating.     

Experimental beam-trawling in Lanice conchilega reefs: Impact on the associated fauna

To study fisheries impact at the species level in temperate sandy bottom areas, a controlled field manipulation experiment was designed focusing on areas with high densities of the habitat-structuring, tube-dwelling polychaete Lanice conchilega (i.e. L. conchilega reefs). The hypothesis was that the impact on L. conchilega would be minimal, but that the fauna benefiting from the biogenically structured habitat would be impacted by beam-trawling. In this study, the impact of beam-trawl passage on intertidal L. conchilega reefs and its associated fauna was quantified. A treatment zone was exposed to a one-off experimental trawling. Subsequently, the impact on and recovery of the associated fauna was investigated for a period of 9 days post-impact. Community analysis showed a clear impact followed by a relatively quick recovery as apparent through MDS analysis (stress 0.06), a significant (p < 0.001) IMS of 0.61, through ANOSIM analysis: significant (p = 0.001) dissimilarities between treatment and control and through SIMPER analysis (decreasing dissimilarities over time). This impact and subsequent recovery was largely explained by two species: Eumida sanguinea and Urothoe poseidonis. Species analysis confirmed the beam-trawl passage significantly (p = 0.001) impacted E. sanguinea for the whole period of the experiment. The experiment confirmed that closely associated species of L. conchilega reefs are impacted by beam-trawl fisheries. This small-scale intertidal study provides some pointers which indicate that the tightly associated species will be impacted significantly when beam-trawling L. conchilega reefs in subtidal areas.     

东海区小黄鱼繁殖模型优化选择及其管理应用研究

根据 1999-2008 年东海区渔业资源底拖网大面定点调查获取的小黄鱼(Larimichthys polyactis)渔业生物学资料,利用AIC(Akaike Information Criterion)与BIC(Bayesian Information Criterion),对小黄鱼的Ricker、Beverton-Holt和Cushing繁殖模型进行了拟合优度检验.针对选择的繁殖模型,经单因子相关分析和逐步回归分析,筛选对繁殖模型有重要影响的环境因子,经模型的拟合和检验,确定东海区小黄鱼的适用繁殖模型.结果表明:3种繁殖模型中,Ricker繁殖模型更适合模拟小黄鱼亲体与补充量关系,但吕泗渔场海域3-4月平均海水表温、7月海水表温和5月长江径流量、7-8月长江平均径流量以及当年夏季风速对模型中的补充量有着重要的影响;优化后的Ricker繁殖模型不仅可以提高东海区小黄鱼亲鱼量与补充量的拟合精度,而且可参考该模型修正当年度小黄鱼的资源管理目标,提高资源管理的科学性.     

Breaking seasonal limitation: year-round sporogenesis in the brown alga Laminaria saccharina by blocking the transport of putative sporulation inhibitors

Year-round induction of sporogenesis of Laminaria saccharina was performed by mechanically blocking the transport of the putative sporulation inhibitors produced by the blade meristem and culturing the plants in constant short days. Sporogenesis was successfully induced by removal of the blade meristem, either by cultivating distal blade fragments or by performing a transverse cut in the frond. The earliest sorus formation after artificial induction was 10 days. The age of the sporophytes used for induction was 6–11 months or 2 years in tank-grown or field-collected sporophytes, respectively. Zoospores were successfully released in all cases. Thus, by year-round artificial induction of sporogenesis, (1) sporeling production of L. saccharina and thereafter sporophyte cultivation could be achieved without seasonal limitation, and (2) the life cycle of L. saccharina (from spore to spore) could be completed within 8 months under controlled conditions.     

Ecological and eco‐social models for the introduction of the abalone Haliotis discus hannai into benthic systems of north‐central Chile: sustainability assessment

• 1. Loop models of ecological and socio‐economic systems were developed to analyse and predict the impact of a possible accidental introduction (escapes) of the abalone Haliotis discus hannai into a benthic community of north‐central Chile.
• 2. Although the ‘new’ ecological system resulting from a successful invasion of abalone would be locally stable, the establishment of a self‐enhanced dynamic of recruits would transform this into an unstable system.
• 3. The harvest of the kelp, Lessonia trabeculata and other macroalgae is not recommended because this destabilizes the system. The harvest of abalone adults is only sustainable if they do not exert a negative effect upon other native invertebrates.
• 4. The eco‐social model showed three important results: (1) if the variables ‘Price’ and ‘Farming’ are in expansion and stationary dynamics, then the models were found unstable; (2) a self‐enhanced dynamic of abalone recruits tends toward instability; and (3) the harvest of the kelp L. trabeculata and other macroalgae would be non‐sustainable.
• 5. Based on our results, the sustainable development of extensive farming of H. discus hannai in the sea would be not reached. If it is done, an intensive monitoring of the community after introduction into the system is strongly recommended. Likewise, the farming of macroalgal species (source of food for abalone) should be promoted in order to avoid harvesting of macroalgae from natural systems.

Copyright © 2006 John Wiley & Sons, Ltd.     

Effects of body weight, water temperature and ration size on ammonia excretion by the areolated grouper (Epinephelus areolatus) and mangrove snapper (Lutjanus argentimaculatus)

The effects of body weight, water temperature and ration size on ammonia excretion rates of the areolated grouper Epinephelus areolatus and the mangrove snapper Lutjanus argentimaculatus were investigated. Under given experimental conditions, L. argentimaculatus had a higher weight-specific ammonia excretion rate than E. areolatus. Weight-specific ammonia excretion rates of fasted individuals of both species showed an inverse relationship with body weight (W, g wet wt.), but a positive relationship with water temperature (t, °C). The relationships for total ammonia nitrogen (TAN) were: E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=21.4·exp^0.11t·W^−0.43 (r²=0.919, n=60); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=121.5·exp^0.12t·W^−0.55 (r²=0.931, n=60). Following feeding, the weight-specific ammonia excretion rate of E. areolatus increased, peaked at 2 to 12 h (depending on temperature), and returned to pre-feeding levels within 24 h. A similar pattern was observed for L. argentimaculatus, with a peak of TAN excretion being found 6 to 12 h after feeding. Stepwise multiple regression analysis indicated that weight-specific TAN excretion rates of both species increased with increasing temperature and ration (R, percent body wt. d⁻¹): E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=22.8·t−28.8·R−378.2 (r²=0.832, n=24); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=22.9·t−25.4·R−216.4 (r²=0.611, n=24). The effect of body weight on weight-specific postprandial TAN excretion was not significant in either species (p>0.05). This study provides empirical data for estimating ammonia excretion of these two species under varying conditions. This has application for culture management.     

Selective capture of blue cod Parapercis colias by potting: behavioural observations and effects of capture method on peri-mortem fatigue

Selective fishing is the successful capture of target species and size classes in a way that minimises bycatch, minimises damage to flesh, and maximises post-mortem (PM) value. We studied selective harvesting of blue cod Parapercis colias (Pinguipedidae) in central New Zealand, where it is captured mainly by commercial pot-fishing and recreational line-fishing. Potting with paua Haliotis iris (=abalone) guts selectively targeted large blue cod from localities that had six or more fish species and many small blue cod. Video observations of pot entries indicated that blue cod entered and left the pot throughout 30 min sets. Blue cod were observed by video to commence swimming when pot-hauling started. Observations of line-hooked fish indicated a characteristic spinning behaviour while hauling.

Fatigue during harvesting is a major factor in reducing the PM quality and shelf-life of fish muscle. Despite the relatively benign nature of capture via pot, it appears that burst exercise during hauling and a brief flurry of flapping as the pot leaves the water is sufficient to compromise flesh quality. Fish that were fatigued during harvesting had a poorer peri-mortem ‘ATP potential’ than fish that had been tank-rested for a year and then harvested using rested harvesting techniques. Modifying the potting method by providing a reservoir of water reduced peri-mortem fatigue during capture but by an insufficient amount to significantly improve PM flesh quality.

Blue cod flesh is compromised by pot capture, which is widely perceived as a benign harvesting method. In order to maximise value of blue cod, low-stress harvesting methods which take advantage of the behaviour of the fish are required.     

Reproductive ecology and scientific inference of steepness: a fundamental metric of population dynamics and strategic fisheries management

The relationship between the biomass of reproductively mature individuals (spawning stock) and the resulting offspring added to the population (recruitment), the stock–recruitment relationship, is a fundamental and challenging problem in all of population biology. The steepness of this relationship is commonly defined as the fraction of recruitment from an unfished population obtained when the spawning stock biomass is 20% of its unfished level. Since its introduction about 20 years ago, steepness has become widely used in fishery management, where it is usually treated as a statistical quantity. Here, we investigate the reproductive ecology of steepness, using both unstructured and age-structured models. We show that if one has sufficient information to construct a density-independent population model (maximum per capita productivity and natural mortality for the unstructured case or maximum per capita productivity, natural mortality and schedules of size and maturity at age for the structured model) then one can construct a point estimate for steepness. Thus, steepness cannot be chosen arbitrarily. If one assumes that the survival of recruited individuals fluctuates within populations, it is possible, by considering the early life history, to construct a prior distribution for steepness from this same demographic information. We develop the ideas for both compensatory (Beverton–Holt) and over-compensatory (Ricker) stock–recruitment relationships. We illustrate our ideas with an example concerning bluefin tuna ( Thunnus thynnus/orientalis , Scombridae). We show that assuming that steepness is unity when recruitment is considered to be environmentally driven is not biologically consistent, is inconsistent with a precautionary approach, and leads to the wrong scientific inference (which also applies for assigning steepness any other single value).     

Using a macroalgae Ulva pertusa biofilter in a recirculating system for production of juvenile sea cucumber Apostichopus japonicus

A simple indoor recirculating system for production of juvenile sea cucumber (Apostichopus japonicus) was operated on a commercial scale for 90 days during winter. The system consists of three 70 m³ sea cucumber rearing tanks and one biofilter tank where macroalgae (Ulva pertusa) was used as a biofilter in order to reduce water requirements. Effluent from the sea cucumber tanks drained into the macroalgae biofilter tank and were then returned to the sea cucumber tanks by a discontinuous-flow recirculation system. Survival and growth rates in the sea cucumber culture tanks were similar to those in the control tank (with one water exchange per day). The survival rate averaged about 87%. The average body weight increased from 3.5 ± 0.3 g to 8.1 ± 0.8 g and total sea cucumber biomass production over the experimental period was 745 g m⁻² after initial stocking densities of 375 g m⁻². The growth rate of U. pertusa was 3.3% day⁻¹. U. pertusa was efficient in removing toxic ammonia and in maintaining the water quality within acceptable levels for sea cucumber culture; there were only small daily variations of temperature, pH and DO. The U. pertusa tank removed 68% of the TAN (total ammonia-nitrogen) and 26% of the orthophosphate from the sea cucumber culture effluent; the macroalgae biofilter removed ammonia at an average rate of 0.459 g N m⁻² day⁻¹. It would be efficient to use the U. pertusa biofilter in a recirculating system for production of A. japonicus juveniles in winter.     

Effect of variation in the protein value of the red macroalga Palmaria palmata on the feeding, growth and gonad composition of the sea urchins Psammechinus miliaris and Paracentrotus lividus (Echinodermata)

The sea urchins Psammechinus miliaris and Paracentrotus lividus were fed three macroalgal diets with varying protein content over a 90-day period. These diets were the red alga Palmaria palmata, which had been grown in seawater enriched with two levels of ammonia-N and contained a protein content of either 41% (High-N) or 32% (Low-N) and the brown alga Laminaria saccharina (23% protein). A significantly different response to the macroalgal diets by the two sea urchin species was found in terms of food consumption rate, food conversion efficiency, gonadal growth and gonad nutritional composition. P. miliaris was able to efficiently utilise the High-N P. palmata, whereas P. lividus exhibited a higher food conversion efficiency (FCE) and specific growth rate (SGR) when fed the Low-N compared with the High-N P. palmata. P. miliaris had a significantly higher food consumption rate and higher gonad index (GI) compared with P. lividus, irrespective of diet type. The lowest FCE, SGR and GI were shown by both species fed L. saccharina. No interspecific difference in gonadal nitrogen content was observed, although a positive relationship was shown between dietary and gonadal nitrogen content for both species. All three macroalgal diets produced bright orange or yellow orange gonad colour in P. lividus. High-N and Low-N P. palmata improved gonad colouration in P. miliaris compared with L. saccharina. The results suggest that P. miliaris can efficiently assimilate high protein plant-based diet, whereas P. lividus is less capable of benefiting from high dietary protein levels and this should be taken into consideration when culturing this species either in land-based or sea-based polyculture systems.     

Evidence of clandestine harvest and failure of conservation policies for Argopecten purpuratus in the Rinconada Marine Reserve (Chile)

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Population age and sex structure of Aphanius fasciatus Nardo, 1827 (Pisces: Cyprinodontidae) in the Mesolongi and Etolikon lagoons (W. Greece)

The population structure of Aphanius fasciatus in the Mesolongi and Etolikon lagoonal system was studied, using 5794 fish. Significant differences were observed in the number of individuals of each sex, the age and size composition and survival. The overall males to females sex ratio was 1:2.44, although there was seasonal variation. During the reproductive period the percentage of males in the population decreased significantly, while after reproduction and during recruitment they increased. The females in each age class were larger than the males (40.33 mm and 36.72 mean total length for females and males, respectively). The survival rate of females was greater than males (0.73 for females and 0.60 for males). The strategy of this species is to invest in female individuals.     

Recreational fisheries in Portofino Marine Protected Area,Italy: Some implications for the management

Since the 1970s, recreational fishing has become a mass hobby in Italy, reaching a large number of people, who, using modern equipment, increased their harvesting capacity, provoking serious conflicts with the professional fisheries. Recreational fishing is strictly regulated inside Italian Marine Protected Areas (MPAs) and is generally allocated to local residents, mainly to reduce the tensions caused by limitations of access to the resources. The aim of this study was to provide an analysis of recreational fishing activities within the Portofino MPA (Mediterranean Sea), to assess the possible impact on the local fish stocks and to plan potential management actions. Furthermore, some serious inconsistencies on the minimum lengths of fish caught as defined by law relative to the minimum size of first reproduction are discussed. Since 2014, all anglers exploiting the Portofino MPA have been obliged to fill out a logbook. The compilation of these was not completely satisfactory, when compared with a group of reliable anglers whose catches were accurately monitored, but allowed for estimated yields of about 24 kg/angler/yr. After 15 years of protection, the fish biomass has increased within the Portofino MPA, generating a positive spillover effect. At the same time, it has attracted many anglers whose gross harvesting was estimated at about 8 t/year, representing about the 8% of the total yield of the local small‐scale fishery.     

Identifying key habitats for the conservation of Chilean dolphins in the fjords of southern Chile

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Spatial patterns in reproductive traits of the temperate parrotfish Sparisoma cretense

Reproductive biology and social behaviour of the parrotfish Sparisoma cretense was studied in the Azores Islands, northeast Atlantic, to characterize its spawning season and general reproductive biology in the region, to clarify the species mating system and associated spawning behaviours, and to evaluate the relationship between its reproductive traits and habitat features. S. cretense exhibits a dual mating system where males hold female harems within year-round territories or live in multi-male groups. Group behaviour predominates in smaller size classes, and territoriality in larger size classes. Males mature and become territorial earlier in life than females, and the best territories are held by larger males. The two behavioural modes are usually spatially segregated, with larger territorial fish preferring exposed and deeper reef ledges, and group fish occupying shallower, protected habitats. However, they frequently interact and overlap in space, especially during reproduction in the summer. Our findings indicate a highly competitive system and suggest that high quality spawning sites are important for the reproductive success of both types of fish. Patchiness of habitat along shorelines determines the relative distribution and equilibrium of territorial versus group fish. The complexity of this relationship between social structure and habitat might impact the populations’ productivity, and could influence the success of marine protected areas for this species.     

Per os challenge of Litopenaeus vannamei postlarvae and Farfantepenaeus duorarum juveniles with six geographic isolates of white spot syndrome virus

White spot syndrome virus (WSSV) is one of the most important pathogens of penaeid shrimp. It is widely distributed in most Asian countries where penaeid shrimp are cultured, as well as in the Gulf of Mexico and SE USA. The virulence of six geographic isolates of WSSV was compared using Litopenaeus vannamei postlarvae and Farfantepenaeus duorarum juveniles. The six geographic isolates of WSSV originated from China, India, Thailand, Texas, South Carolina, as well as from crayfish maintained at the USA National Zoo. For challenge studies, virus infected tissues were given per os to L. vannamei postlarvae and Fa. duorarum juveniles. Resultant WSSV infections were confirmed by histological examination. The cumulative mortality of L. vannamei postlarvae reached 100% after challenge with each of the six geographic isolates of WSSV. However, the Texas isolate caused mortalities more rapidly than did the other shrimp isolates; the crayfish WSSV isolate was the slowest. In marked contrast, cumulative mortalities of juvenile Fa. duorarum reached only 35–60%, and varied among the geographic isolates of WSSV. Interestingly, in Fa. duorarum, the Texas WSSV isolate was also the most virulent, while the crayfish WSSV was the least virulent. The findings suggest that slight differences in virulence exist among geographic isolates of WSSV, and that susceptibility may vary with species and lifestages of the host.     

Re‐evaluating the effect of wind on recruitment in Gulf of Maine Atlantic Cod (Gadus morhua) using an environmentally‐explicit stock recruitment model

A previous study documented a correlation between Atlantic Cod (Gadus morhua) recruitment in the Gulf of Maine and an annual index of the north component of May winds. This correlation was supported by modeling studies that indicated strong recruitment of Gulf of Maine Atlantic Cod results from high retention of spring‐spawned larvae in years when winds were predominately out of the north, which favor downwelling. We re‐evaluated this relationship using updated recruitment estimates and found that the correlation decreased between recruitment and wind. The original relationship was largely driven by two recruitment estimates, one of which (2005 year‐class) was highly uncertain because it was near the terminal year of the assessment. With additional data, the updated assessment estimated lower recruitment for the 2005 year‐class, which consequently lowered the correlation between recruitment and wind. We then investigated whether an environmentally‐explicit stock recruit function that incorporated an annual wind index was supported by either the original or updated assessment output. Although incorporation of the annual wind index produced a better fitting model, the uncertainty in the estimated parameters and the implied unexploited conditions were not appropriate for providing management advice. These results suggest the need for caution in the development of environmentally‐explicit stock recruitment relationships, in particular when basing relationships and hypotheses on recruitment estimates from the terminal years of stock assessment models. More broadly, this study highlights a number of sources of uncertainty that should be considered when analyzes are performed on the output of stock assessment models.     

Persistence of submerged macrophytes in a drying world: Unravelling the timing and the environmental drivers to produce drought‐resistant propagules

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Response of Scotian Shelf silver hake (Merluccius bilinearis) to environmental variability

Commercially‐exploited fish populations are not only shaped by fishing pressure, but also by the dynamics of their environment. By quantifying the influence of environmental variability, fisheries management advice can be improved and uncertainties reduced. To this end, we developed statistical models of the response of Scotian Shelf silver hake stock metrics to variability in zooplankton community composition and phenology over the past 18 years and in the physical environment since 1985. Dominant modes of variability in these pelagic habitat indicators were characterized using principal component analysis, and the relationships of silver hake condition, abundance, and recruitment to pelagic habitat variability were assessed using generalized additive models. Condition was largely modulated by the onset and duration of the spring bloom, which controls food availability. In contrast, adult abundance was governed by composition of the zooplankton community and bottom‐water temperature, which dictates the distribution of silver hake. Finally, recruitment was affected by both thermal conditions and food availability. Our results presented here form the basis for qualitative assessment of ecosystem attributes and the influence on silver hake stock productivity.     

Fish and flows: Abiotic drivers influence the recruitment response of a freshwater fish community throughout a regulated lotic system of the Murray-Darling Basin,Australia

1. Fish assemblages in dryland rivers have life-history strategies that have evolved in response to environmental conditions and triggers, particularly water temperatures and flow regimes. The regulation of rivers through the construction of dams, weirs and other water diversion structures has altered natural flow regimes and the associated ecological processes of river systems worldwide.
2. Over a 3-year period, using standardized fish sampling and daily otolith ageing, the recruitment of eight freshwater fish species was monitored in response to various abiotic drivers, including hydrology and water temperatures, throughout the Macquarie River, a large regulated river system of the Australian Murray-Darling Basin.
3. A data-driven statistical classification system is provided that groups species into reproductive guilds, based on their recruitment response to hydrology and water temperature, specifically designed for use in environmental flow management.
4. The eight species were grouped into three distinct reproductive guilds that showed similar recruitment responses to the abiotic drivers. Murray-Darling rainbowfish, Murray cod, and eel-tailed catfish were considered as a single guild, characterized by seasonal recruitment during a relatively narrow thermal window under low to moderate stable discharges. The second group included common carp, bony herring, and golden perch, which recruited primarily in association with larger flow events. Un-specked hardyhead and Australian smelt formed a more differentiated guild, recruiting over a broad range of temperatures and discharges. Limitations associated with using a reproductive guild approach to simplify water management are discussed.
5. This study highlighted important relationships among hydrology, water temperatures, and successful recruitment that can, in turn, be used to inform development of adaptive flow management plans and effective use of environmental water for the conservation management of native fish communities. Important considerations in the design of studies that aim to examine relationships between recruitment and abiotic drivers are also discussed.