Effects of a fishing gear on an artisanal multispecific penaeid fishery in a coastal lagoon of Mexico: mesh size, selectivity and management implications

Abstract  The spatiotemporal effects of a bottom net used in an artisanal multispecific penaeid fishery at Celestun Lagoon, Mexico, were evaluated. Selectivity experiments, based on the covered codend method, were carried out with two bottom nets operating simultaneously but using different mesh size codends: 13 mm (MS13: currently used in the fishery) and 25 mm (MS25). Length at 50% retention, L ₅₀, was twice as high with MS25 (15.34 mm carapace length, CL) than with MS13 (6.95 mm CL); this global pattern was recurrent for all species, seasons and hydrological zones. These differences in selectivity determined that MS13 mainly retained recruits and juveniles, whereas MS25 mainly retained sub-adults. However, smaller shrimps were caught by both mesh sizes during the 'nortes' season (November to February) and at the outer zones of the lagoon. Thus, an increase in mesh size from 13 to 25 mm, together with fishery closures within specific area–season windows, is suggested to reduce risks of overfishing of these shrimp populations.     

Evaluation of a by-catch reduction device for glass eel fishing traps

Abstract  The effectiveness of a new design of glass eel, Anguilla anguilla (L.), fishing trap was tested in the Ebro River delta fishery (Eastern Mediterranean, Spain). The modified fishing trap incorporated a by-catch reduction device (BRD) to increase trap selectivity and minimise by-catch of non-targeted fish, without affecting glass eel captures. The BRD is inexpensive and easy to implement, consisting of a cylinder covered with a rigid square-mesh of 2.0–2.4 mm knot-to-knot, which is easily fitted to the fishing trap entrance. Testing of the BRD was made by paired comparisons between captures of targeted and non-targeted fish species from both conventional and BRD-modified traps. The use of a BRD in the glass eel traps resulted in a 68.9% reduction in the number of captured non-targeted fish specimens, while it did not reduce glass eel yields. The BRD implementation was fully effective for all species and individuals with sizes >40 mm total length, with the exception of the black-striped pipefish, Syngnathus abaster Risso. These results support the implementation of the BRD in glass eel fisheries along the Eastern coast of the Iberian Peninsula where these fishing traps are used.     

我国渔业节能减排基本情况研究报告

报告以水产科学为基础,以渔业装备与工程学科为专业背景,力图从我国渔业能耗与污染排放的基本状况分析入手,评价我国渔业能源消耗和污染排放的类型与规模,及其对渔业生产和社会发展的影响,围绕国家节能减排战略,提出技术措施与科技攻关的重点,以及建立稳定科研机制的建议,为行业管理部门的决策提供参考.     

Discards from the artisanal shrimp fishery in a tropical coastal lagoon of Mexico: spatio-temporal patterns and fishing gear effects

Abstract  Variability in community (richness, diversity and evenness) and population (size structure) attributes of discards was evaluated in a shrimp fishery in Celestun Lagoon, Mexico, in different climatic seasons and hydrological zones. Sampling was conducted using two bottom nets with different mesh size codends: 1.3 cm (used in the fishery) and 2.5 cm. Although the shrimp:discard ratio was 1:1 in both cases, total biomass and abundance with the 1.3-cm mesh size were, respectively, 4.6 and 1.8 times higher than with the 2.5-cm mesh size. This result was consistent in time and space. Discards were dominated by fishes [60% in 1.3-cm mesh size and 96% in 2.5-cm mesh size, mainly Cichlasoma urophthalmus (Günther), Eucinostomus gula (Quoy & Gaimard) and Lucania parva (Baird & Girard)] and shellfishes (40% in 1.3-cm mesh size and 4% in 2.5-cm mesh size, mainly Palaemonetes spp. and Callinectes spp.). The highest discards were registered the nortes season with both mesh sizes. The 1.3-cm mesh size retained significantly smaller sizes than the 2.5-cm mesh size in six of the eight most important species. An increase in mesh size, together with a fishery closure during the nortes season, are suggested to mitigate the impact of the fishery on the discarded fauna.     

Identification and evaluation of shark bycatch in Georgia’s commercial shrimp trawl fishery with implications for management

Abstract Many US states have recreational and commercial fisheries that occur in nursery areas occupied by subadult sharks and can potentially affect their survival. Georgia is one of few US states without a directed commercial shark fishery, but the state has a large, nearshore penaeid shrimp trawl fishery in which small sharks occur as bycatch. During our 1995–1998 investigation of bycatch in fishery‐dependent sampling events, 34% of 127 trawls contained sharks. This bycatch totalled 217 individuals from six species, with Atlantic sharpnose shark, Rhizoprionodon terraenovae (Richardson), the most common and finetooth shark, Carcharhinus isodon (Müller & Henle) and spinner shark, Carcharhinus brevipinna (Müller & Henle), the least common. The highest catch rates for sharks occurred during June and July and coincided with the peak months of the pupping season for many species. Trawl tow speed and tow time did not significantly influence catch rates for shark species. Gear configurations [net type, turtle excluder device (TED), bycatch reduction device] affected catch rates for shark species. Results of this study indicate gear restrictions, a delayed season opening, or reduced bar spacing on TEDs may reduce shark bycatch in this fishery.     

Choosing best practices for managing impacts of trawl fishing on seabed habitats and biota

Bottom trawling accounts for almost one quarter of global fish landings but may also have significant and unwanted impacts on seabed habitats and biota. Management measures and voluntary industry actions can reduce these impacts, helping to meet sustainability objectives for fisheries, conservation and environmental management. These include changes in gear design and operation of trawls, spatial controls, impact quotas and effort controls. We review nine different measures and actions and use published studies and a simple conceptual model to evaluate and compare their performance. The risks and benefits of these management measures depend on the extent to which the fishery is already achieving management objectives for target stocks and the characteristics of the management system that is already in place. We offer guidance on identifying best practices for trawl‐fisheries management and show that best practices and their likelihood of reducing trawling impacts depend on local, national and regional management objectives and priorities, societal values and resources for implementation. There is no universal best practice, and multiple management measures and industry actions are required to meet sustainability objectives and improve trade‐offs between food production and environmental protection.     

Environmental factors influencing the reproduction of an estuarine penaeid population and implications for management

This study determined environmental factors influencing the reproductive dynamics of a recreationally fished penaeid Metapenaeus dalli Racek in the Swan–Canning Estuary, south‐western Australia, during a restocking programme. Prawns were collected from nearshore (<2 m deep) and offshore waters (>2 m deep) every lunar month from October 2013 to March 2016. Reproduction occurred between November and March, when water temperature was >17°C, salinity >25 and stratification (bottom–surface salinity) <3. Densities of gravid M. dalli were highest in November of each year when 0+ females matured (19 mm; ~56% asymptotic length) and were highest in the Lower Canning Estuary. Individual fecundity ranged from 34,000 (18.1 mm carapace length [CL]) to 132,000 ova (27.1 mm CL). Egg production peaked in December/January and differed among years, being greatest in 2015/2016. These results suggest that closing fishing between November and December would protect breeding aggregations of M. dalli in inshore waters.     

Long-term variation in the abundance of the brown shrimp Crangon crangon (L.) population of the German Bight and possible causes for its interannual variability

Time series on Crangon crangon densities in the German Wadden Sea show a considerable degree of interannual variability, for the entire region in spring and in autumn as well as for three subareas, North Frisia, East Frisia and Elbe estuary. Across the entire survey area C. crangon density was inversely related to water depth. In autumn after the recruitment, settlement shrimp densities are correlated across a larger spatial scale (>100 km longshore), whereas in spring the overwintering adult spawning stock is uncorrelated across subareas. Interannually, extreme density variations can develop even over a short time span of 1 yr. On a large spatial scale shrimp abundance in autumn was correlated with year‐to‐year changes in physical environmental and biological parameters, winter water temperature, autumn river runoff and the winter NAO index. On a regional scale (North Frisia), density of gadoid predators was an additional component affecting shrimp stock abundance. No correlations to such parameters could be detected for the C. crangon stock in spring. Possible causes for the spring situation and additional sources for variability are discussed.     

Bait worms: a valuable and important fishery with implications for fisheries and conservation management

Bait is an integral part of coastal life, but is perceived as a low‐value resource as fisheries are data‐limited, locally focussed and largely unregulated even though the ecological impacts of collection are considerable. An empirical assessment of three UK‐based ragworm fisheries combined with an analysis of published literature has produced the first global assessment of polychaete bait fisheries. The five most expensive (retail price per kg) marine species sold on the global fisheries market are polychaetes (Glycera dibranchiata, Diopatra aciculata, Nereis (Alitta) virens, Arenicola defodiens and Marphysa sanguinea). We estimate that 1600 t of N. virens per annum (worth £52 million) are landed in the UK with approximately 121 000 tonnes of polychaetes collected globally valued at £5.9 billion. Using remote closed circuit television (CCTV) cameras to monitor collectors, activity at local sites is considerable with a mean of 3.14 collectors per tide (day and night) at one site and individuals digging for up to 3 h per tide, although intensity differed seasonally and between sites. Collectors removed on average 1.4 kg of N. virens per person per hour, walking a considerable distance across the intertidal sediment to reach areas that were usually already dug. The implications of these human activity and biomass removal levels are explored in the context of fisheries and conservation management. At local, regional and national scales, polychaete bait fisheries are highly valuable, extract significant biomass and have considerable impacts; therefore, they urgently require governance equivalent to other fisheries.     

An assessment of catches of shore sport fishing competitions along the coast of the Maltese Islands: Implications for conservation and management

Competitive shore‐based sport fishing is a popular recreational activity in the Maltese Islands. However, prior to this study, no scientific research surveys had been carried out during sport fishing competitions to investigate catches. Collaboration with Maltese sports fishermen was developed to target sustainable management. Recreational fishing catches were recorded between July 2012 and December 2015 by means of 1,633 roving‐access creel surveys, conducted during 79 sport fishing competitions, totalling a fishing effort of 7,548 hr. A total of 29,916 fish belonging to 80 species from 26 different families were caught at a mean catch‐per‐unit‐effort (CPUE) of 4.16 fish angler/hr (SD ± 3.79) and 0.18 kg angler/hr (SD ± 0.17) but with seasonal variation. Catch‐and‐release practices were implemented by all Maltese sport fishing clubs, however, the mean mortality rate stood at 35.5% (SD ± 42.1), indicating that more effort is required to improve survival of fish. The study outcomes provide conservation recommendations.