A preliminary appraisal of the contribution of recreational fishing to the fisheries sector in north-west Trinidad

Abstract An assessment of the recreational fishery in north-west Trinidad was made by questioning participants about the principal fishing methods used, location of activities, catches, effort and cost of fishing. Surface handline methods (live baiting [à la vive] and trolling) and rod and line (banking) were the most common methods used and were pursued mainly in the summer months (April to August). Total fish landings from the fishery were estimated at 1000 t year^-1, equivalent to about 10% of commercial catches for Trinidad. The principal species caught were kingfish, Scomberomorus cavalla (Cuv.), carite, Scomberomorus brasiliensis (Cuv.), cavalli, Caranx hippos (L.), snappers, Lutjanus spp., and groupers, Epinephelus spp. Many of the fishermen sold their catch to offset the costs of the fishing trip and thus competed with commercial fishermen. Recommendations for monitoring and possibly regulating the fishery through a licensing scheme are made.     

Dynamics of early life‐history stages of fish along an estuarine gradient

This study aimed to identify the spatial and temporal patterns of composition and distribution of early life‐history stages of fish along an estuarine gradient. Samples were collected quarterly between April 2010 and January 2011 using conical‐cylindrical plankton nets in the Vaza Barris estuarine river system (NE Brazil). A total of 38,781 fish eggs and 3,526 larvae, representing 20 families and 42 taxa, were caught. The most abundant larval taxa were Microgobius meeki, Ctenogobius gr. smaragdus/boleosoma, Gobionellus oceanicus, Ctenogobius gr. stigmaticus/saepepallens/shufeldti, Bairdiella ronchus, Achirus sp., Trinectes sp., Stellifer rastrifer and S. stellifer, accounting together for 34.5% of the total catch. Ichthyoplankton distributions were characterized by high seasonal and spatial variability mainly attributed to the environmental characteristics of the estuary. Overall, lower estuarine region served as important accumulation areas for ichthyoplankton, concentrating the greatest diversity and abundance. Salinity gradient, water temperature, and inorganic nutrients were the main variables that affected the larval fish assemblages, presumably influencing spawning, development and survival of individuals or through their effect on food supply. Moreover, this study reinforced the concept that hydrological variations may have a strong influence on estuarine species retention and marine species immigration. Finally, this study highlights the importance of estuaries for the growth and maintenance of stocks of fish species, and the development of strategies to protect these habitats is of utmost relevance.     

A synthesis of large-scale patterns in the planktonic prey of larval and juvenile cod (Gadus morhua)

Data from 40 published studies of the diet composition of larval and juvenile cod (Gadus morhua) from around the northern North Atlantic were summarized to assess generic patterns in ontogenetic and regional variability in the key prey. The results showed that larvae at the northern edge of the latitudinal range of cod depend primarily on development stages of the copepod Calanus finmarchicus, whilst those at the southern edge depend on Para‐ and Pseudocalanus species. Juvenile cod preyed on a wider range of taxa than larvae, but euphausiids were the main target prey. Analysis of regional variations in the relative abundances of C. finmarchicus and Para/Pseudocalanus spp. in the plankton, as estimated by the continuous plankton recorder (CPR) surveys, showed a similar geographical pattern to the larval cod stomach contents. Comparison of CPR data from the 1960s and 70s with data from the 1990s showed that the boundary between C. finmarchicus and Para/Pseudocalanus spp. dominance has shifted northwards on both sides of the Atlantic, whilst the abundance of euphausiids in the southern cod stock regions has declined. The results are discussed in relation to regional differences in the response of cod stocks to climate variability.     

Dynamic regulation of larval fish self‐recruitment in a marine protected area

The factors that regulate the self‐recruitment of fish larvae were explored in Cabrera National Park (CNP), an insular Marine Protected Area (MPA) located off southern Mallorca (Western Mediterranean). Our study attributes the regulation of larval arrival to the MPA to a combination of retention by topographically generated circulation patterns around the island and shelf break frontal dynamics. Specifically, within the shelf, interaction of the wind‐induced oscillatory flow with the island was shown to generate ephemeral recirculation patterns that, over time, favor larval retention in the proximity of the MPA. According to our measurements, oscillatory flows produced by wind‐forced island‐trapped waves (ITWs) dominate the flow around CNP. ITW‐forced dispersion simulations were in agreement with the observed distributions of several typical fish species that breed in the CNP. A second regulator of environmental variability is the influence of boundary currents and open ocean mesoscale structures at the shelf break. These structures generate frontal zones that are comparatively more long‐lived than inner‐shelf circulation patterns, and they were shown to act as barriers to the offshore dispersion of coastal fish larval assemblages. Finally, inferences from larval size distributions around the MPA together with particle‐tracking model simulations suggested the relevance of behavioral processes for larval recruitment to the MPA. Based on these observations, the waters around the CNP can be viewed as a relatively stable system that allows breeding fish populations to rely on self‐recruitment for their long‐term persistence, independent of other source populations along the coast of Mallorca.     

Assessment of commercial and recreational fishing effects on trophic interactions in the Cap Roux area (north‐western Mediterranean)

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Breeding and larval development of Holothuria mammata,a new target species for aquaculture

Sea cucumber commercial fisheries in the North‐eastern Atlantic and Mediterranean Sea started in Turkey in the 1990s. Due to ineffective management practices, the sea cucumber resource was overexploited. Holothuria mammata is one of the sea cucumber species exploited from this geographical area, showing high potential for its aquaculture. This research was undertaken to develop the breeding, larval and juveniles rearing techniques for development of H. mammata aquaculture. Broodstocks collected from Ria Formosa (Faro, S Portugal) were successfully induced to spawn by thermal stimulation from July to October, yielding up to 6.95 million eggs/female. The eggs and larvae were reared and their development described. H. mammata showed the five typical larval stages of most aspidochirote holoturians. Juveniles stage was reached after 21 days post‐fertilization. This is the first work focused on the aquaculture biotechnology of H. mammata, however, further research is need to improve the survival of juveniles to ensure the future production of this species.     

Long-term catch trends and risk assessment of the Critically Endangered white-spotted wedgefish (Rhynchobatus djiddensis) from South Africa

1. The white-spotted wedgefish (Rhynchobatus djiddensis) is a Critically Endangered shark-like ray in the family Rhinidae. Throughout its Western Indian Ocean distribution, it is targeted for its valuable meat and fins and is reported to have undergone major population declines. However, there remains a need for species specific time-series data to accurately assess localized population declines.
2. This study used two independent long-term (37 and 40 years) time-series catch data from competitive shore angling and shark nets to investigate the size composition and catch per unit effort (CPUE) and conduct a risk assessment for the population on the east coast of South Africa.
3. From 1977 to 2017 the competitive shore fishery captured 7,703 individual R. djiddensis, whilst shark nets in the same region captured 2,856 individuals from 1981 to 2017. Individuals captured in the nets had a sex ratio of 1.8:1 females to males, and were larger than those caught by the anglers. Although the mean annual sizes of net-caught individuals were above the size of reported sexual maturity, there was little evidence to suggest that any individuals captured were reproductively active.
4. Both the competitive shore fishery and shark net catches exhibited strong seasonal trends with the majority of R. djiddensis catches occurring from October to May peaking in austral summer. Standardized CPUE from the competitive shore fishery declined substantially between 1977 and 2017 and shark net catches exhibited a significant (p < 0.05) fourfold decline in annual nominal CPUE from 1981 to 2017.
5. Ultimately, a risk assessment showed a 65.1% decline in abundance over a period of three generation lengths, which indicates that the sampled population of R. djiddensis in South Africa should be classified as Endangered according to the IUCN Red List using criterion A2b. The conservation implications of this are discussed.

     

Overview of loggerhead turtles coastal nets interactions in the Mediterranean Sea

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Lipid and amino acid metabolism during early development of Atlantic halibut (Hippoglossus hippoglossus)

Lipid classes, fatty acids, free amino acidsand protein content in captive Atlantic halibut(Hippoglossus hippoglossus) eggs weremeasured to investigate the changes in thebiochemical composition of eggs and larvae inboth the embryonic and early larval stages.Total free amino acids decreased continuously(p < 0.01) over the embryonic and larval stagesinvestigated. Triacylglycerol was significantlygreater at hatch than at all other stages(p < 0.05). When hatching occurred, there wasalso a significant increase in all phospholipidclasses. It is suggested that free amino acidsmay be the source of carbon skeletons for lipidsynthesis at hatching.     

Molecular evidence for cosmopolitan distribution of platyhelminth parasites of tunas (Thunnus spp.)

Global distribution of platyhelminth parasites and their host specificities are not well known. Our hypothesis was that platyhelminth parasites of large pelagic fishes are common around the world. We analysed molecular variation in three different taxa of platyhelminth parasites infecting four species of tunas: yellowfin tuna (Thunnus albacares, Scombridae) from Western Australia, southern bluefin tuna (Thunnus maccoyii, Scombridae) from South Australia, Pacific bluefin tuna (Thunnus orientalis, Scombridae) from Pacific Mexico and northern bluefin tuna (T. thynnus, Scombridae) from two localities in the Mediterranean (Spain and Croatia). Comparisons of ITS2 and partial 28S rDNA demonstrated two congeneric species of blood flukes (Digenea: Sanguinicolidae) from multiple hosts and localities: Cardicola forsteri from southern bluefin and northern bluefin tunas, and Cardicola sp. from Pacific bluefin and northern bluefin tunas; and a gill fluke, Hexostoma thynni (Polyopisthocotylea: Hexostomatidae), from yellowfin, southern bluefin and northern bluefin tunas. Partial 28S rDNA indicates that a second type of fluke on the gills, Capsala sp. (Monopisthocotylea: Capsalidae), occurs on both southern bluefin and Pacific bluefin tunas. This appears to be the first report of conspecific platyhelminth parasites of teleosts with a wide‐ranging geographical distribution that has been confirmed through molecular approaches. Given the brevity of the free‐living larval stage of both taxa of flukes on the gills (H. thynni and Capsala sp.), we conclude that the only feasible hypothesis for the cosmopolitan distribution of these flatworms is migrations of host tunas. Host migration also seems likely to be responsible for the widespread occurrence of the two species of blood flukes (Cardicola spp.), although it is also possible that these were translocated recently by the spread of infected intermediate hosts.     

南极磷虾生物量估算方法

南极磷虾是南大洋生态系统食物网中的关键种,在南大洋中上层生态系统中起着至关重要的连接作用,其资源的养护和持续利用受到国际社会日益关注。磷虾研究已有90多年的历史,其生物量及其分布一直是研究的重点。生物量评估方法也在不断发展,从早期的浮游动物干重法、生产量与生物量比例系数转换法,到网具采样法以及现在流行的声学法,评估手段也变得更为高效。本文通过系统梳理磷虾生物量的主要评估方法,分析其优缺点,并着重从磷虾目标强度模型(TS)参数的海上实测、声学数据中磷虾信号的提取,磷虾单位平方海里声学反射系数(NASC)的计算,基于渔船声学数据修正磷虾渔业单位捕捞努力量渔获量(CPUE),基于渔船声学数据的磷虾集群、洄游和渔场形成机制研究等5个方面对现行生物量声学评估法提出改进建议,提高资源评估的精度,以期为磷虾生物资源的开发与管理提供科学依据。     

Fishing and trade of devil rays (Mobula spp.) in the Bay of Bengal,Bangladesh: Insights from fishers’ knowledge

1. Devil rays (Mobula spp.) are globally threatened cartilaginous fishes that have attracted global conservation concern owing to their high extinction risk and lack of protection in many countries. Limited resources and data on threatened marine species, including devil rays, impede conservation actions, particularly in developing countries, many of which have high biodiversity.
2. Devil ray catch is a component of artisanal fisheries in Bangladesh, but data on their fisheries and trade are limited. To characterize devil ray fishing practices, fishers’ perception and trade, 230 fishers and traders were interviewed between 4 June 2018 and 22 June 2019, in four areas of south-east Bangladesh. Catch data were also opportunistically collected at landing sites.
3. Six devil ray species were documented, caught in an array of gill nets, set-bag nets and longlines. All interviewed fishers reported life-long devil ray bycatch in some numbers, and also noted a decline in catch over the last decade. Bottom trawling, increased bycatch levels, increased demand for devil ray products and, in some cases, ecosystem changes were identified by fishers as threats to devil ray populations.
4. Unregulated and undocumented trade and retained bycatch, especially by gill nets and set-bag nets, are fuelled by local consumption of devil ray meat and international trade in meat and gill rakers. Compliance with international trade control treaties for all Mobula spp. or the Bangladeshi law protecting Mobula mobular was low, with the majority of fishers (87%, n = 174) unaware of their existence.
5. To manage devil ray fisheries, and prevent possible population declines, we propose a combination of legally enforced gear modifications, and catch and trade control through community-owned implementation strategies. Additionally, we propose the simultaneous implementation of inclusive, community-based awareness and stewardship projects in conjunction with a coast-wide ray monitoring programme. Finally, we emphasize that more research and action rooted in a sustainable fishery model is urgently needed to protect Bangladeshi devil ray populations.

     

The effect of vertical migration strategy on retention and dispersion in the Irish Sea during spring–summer

A biophysical model of the Irish Sea was produced to predict net horizontal movement of key taxa including small copepods (Acartia, Pseudocalanus), large copepod species (Calanus finmarchicus and C. helgolandicus), the euphausiid Meganyctiphanes norvegica, and the larval stages of commercially important fish and Nephrops. The model coupled biological information on the vertical distribution and diel vertical migration (DVM) of these taxa with temporally resolved flow fields generated by a baroclinic hydrodynamic model. The DVM of Calanus spp. and Meganyctiphanes was parameterized empirically from data provided by a biophysical campaign carried out in the nearby Clyde Sea. Small copepods and larvae remained within the layers above the thermocline. Model organisms, programmed with particular behavioural patterns, were spaced at regular intervals (1/20° longitude × 1/30° latitude) in the model grid, which extended from 53 to 54.5°N and 4.5 to 6.4°W. The model was run over the months of April, May and June. Model simulations showed that the movement of model organisms followed one of four characteristic patterns: containment along the coast, advection to the north or south, stagnation in the centre of the gyre or circulation around the periphery of the gyre. The latter pattern was apparent even in April, when gyral circulation was not expected because of a lack of stratification in the water column. Thirty‐day model runs in April, May and June showed that the number of organisms retained within the model grid varied between 23 and 49%. Those seeded close to the Irish coast had the highest probability of being retained within the model grid at the end of 90 days. DVM increased the probability of retention through improving the chances of organisms becoming entrained within the gyre circulation. This was especially true for Calanus spp., with those performing midnight sinking being the most likely to be retained out of any model organism. Meganyctiphanes showed comparatively lower levels of retention in deep regions, which suggests that they may have to swim against currents during certain phases of their DVM to avoid displacement. Overall, model results supported a number of hypotheses on the origin and fate of various taxa in the Irish Sea, as well as revealing some less expected distribution patterns.     

Morphological and genetic characterization of Hysterothylacium Ward & Magath, 1917 (Nematoda: Raphidascarididae) larvae in horse mackerel,blue whiting and anchovy from Spanish Atlantic and Mediterranean waters

The presence of zoonotic Hysterothylacium larvae in fish from Spanish Atlantic and Mediterranean waters, which can cause economic losses for commercial fisheries, has been reported in several studies; however, little is known about species identity in this region. The aim of this study was to identify at species level the Hysterothylacium morphotypes detected in three commonly consumed fish: horse mackerel (Trachurus trachurus), blue whiting (Micromesistius poutassou) and anchovy (Engraulis encrasicolus). Third‐ and fourth‐stage Hysterothylacium larvae, as well as adults obtained from larval in vitro culture, were morphologically and molecularly identified by ITS1/ITS2 rDNA sequencing. Four Hysterothylacium morphotypes were detected. Genetic analysis showed that morphotypes VIII and IX were different larval stages of Hysterothylacium aduncum, which was supported by cultured adult species identification. Morphotypes III and IV were found to correspond to different developmental stages of another species of Hysterothylacium. As all larval types detected were morphologically indistinguishable from others previously reported yet showed clear genetic differences, they are referred here as new genotypes. This is the first time that ITS‐sequence data of various developmental stages of the same species, including adults, have been studied and compared, providing crucial knowledge for future studies on Hysterothylacium identification and biology.     

Modelling the effects of reserve size and fishing mortality for Caribbean queen conch Strombus gigas

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Comparison of iodine and glutaraldehyde as surface disinfectants for red porgy (Pagrus pagrus) and white sea bream (Diplodus sargus sargus) eggs

The efficacy of iodine and glutaraldehyde as fish egg surface disinfectants were assessed in red porgy (Pagrus pagrus) and white sea bream (Diplodus sargus sargus) eggs, two species of interest for Mediterranean aquaculture. Iodine was effective in reducing the bacterial load of the 1-day-old eggs when applied at 50 mg L⁻¹ for 5 min. The same concentration did not cause any significant change in hatching success or survival of the larvae for the first 5 days. Glutaraldehyde failed to reduce the bacterial load of the fish eggs at concentrations that were safe for the eggs (100 mg L⁻¹ for 5 min), as it had a significant effect in preventing hatching of the developed embryo. Disinfecting 0-day-old eggs with iodine resulted in a significant reduction of hatching percentage, while larval survival thereafter was unaffected. The results of the present study suggest that iodine may be an appropriate egg disinfectant for both red porgy and white sea bream.     

Eggs of gilthead seabream Sparus aurata L. as a potential enrichment product of Brachionus sp. in the larval rearing of gilthead seabream Sparus aurata L.

The gilthead seabream Sparus aurata L. is a sequential spawner whose reproductive cycle can be manipulated to obtain year-round egg and fry production. Hence, there is an overproduction of eggs in commercial hatcheries that is normally wasted. Two feeding experiments were conducted with the purpose of investigating the potential use of fresh and freeze-dried gilthead seabream eggs for the enrichment of live preys. The first experiment was also designed to study the possibility of using freeze-drying as a conservation process for eggs in excess. Larvae were reared for 20 days after hatching (DAH),on a diet of Brachionus sp. As experimental controls, the commercial enrichment emulsion SUPER HUFA was used in the first experiment, and the microalgae Nannochloropsis sp. in the second. This study demonstrated the potential of gilthead seabream eggs as an enrichment product to be used in the feeding of the first larval stages of Sparus aurata L. The data obtained emphasize the need to have an overall perspective of the nutritional requirements of the organisms in culture.     

Growth of the hatchery-produced juveniles of commercial sea cucumber Holothuria (Theelothuria) spinifera Theel

The present study was conducted to develop the hatchery technology for seed production of the widely exploited commercial sea cucumber Holothuria spinifera Theel 1886, to facilitate an effective stock enhancement programme. Broodstock collected by skin divers were used for spawning trials. The embryonic and larval stages were similar to other aspidochirotes. The larval survival rate was 43.5% on day 9, which decreased to 18.3% nearing metamorphosis on day 13, the growth rate was 48 μm day⁻¹ and the settlement rate was 3.5%. Algamac^® used to induce settlement also served as the food source for the early settled juveniles, followed by Sargassum spp. extract (<40 μm) for the first month. Sargassum spp. powder along with fine sand (1:1) was given to juveniles >20 mm. Addition of Spirulina spp. along with Sargassum spp. powder and fine sand (0.5:1:2) enhanced the growth rate of the juveniles. In the hatchery, the juveniles attained an average size of 1, 30 and 48 on 20, 80 and 120 days respectively.     

High‐resolution modelling of ocean circulation can reveal retention spots important for biodiversity conservation

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On the sharks and fishes observed using underwater photography during a deep-water cruise in the eastern Mediterranean

An underwater photographic survey, in deep-sea waters of the eastern Mediterranean (280–1490 m), was carried out with a “free-fall camera” connected to a recovery buoy, a flood-light and a bait holder, at six stations between the Israeli coast and Cyprus.The behaviour of the sharks was observed at all stations. The two genera Etmopterus (about 30 cm total length) and Centrophorus (about 90 cm total length) were present on the same sites, close to the sea bed, without disturbing each other. Other species of sharks were less abundant. The Teleostei were represented by Triglidae spp., Epinephelus, Echelus and Conger. Decapoda Macrura and Brachyura, mainly Penaeidae, were also observed.The sea bed at depths of 500–1000 m in the Levantine Basin of the Mediterranean is inhabited by a characteristic fauna, which has a large potential for commercial fishery. Experimental fishing with long lines, based on the results of this study, indicated that a commercial fishery of the shark Centrophorus could be developed.