The effect of white and green LED-lights on the catch efficiency of the Barents Sea snow crab (Chionoecetes opilio) pot fishery

In commercial snow crab (Chionoecetes opilio) fishery, the catch efficiency of the conical pots is important for increasing the profitability of the industry. This study evaluated the effect of adding green and white light emitting diodes (LED) on the catch efficiency of commercially used conical pots. The results from the field experiments showed that inserting artificial lights significantly increases the catch efficiency for snow crab over the minimum landing size of 95 mm carapace width of up to 76% when using green LED, and by 52–53% on average when using white LED. This study shows that it is possible to improve the catch efficiency of the snow crab fishery by applying artificial LED lights to the conical snow crab pots, potentially resulting in an important economic benefit to the snow crab fishery.

Portuguese Artisanal Fishers’ Knowledge About Elasmobranchs—A Case Study

The high economic value of fisheries was historically associated to commercial teleost fishes. Since the 1970s, despite some elasmobranchs becoming an important target or a bycatch, relatively little research has been carried out on this group because of their low economic value. Due to their specific life history characteristics, sharks and rays are particularly vulnerable to overexploitation, taking several decades to recover after reaching an overexploitation status. In Portugal elasmobranch fishery results mainly from targeted longlining and bycatch from different fishing gears. During the last decade, the Total Allowable Catches (TACs) of rays have been decreasing, the European Union (EU) banned the capture of some ray species, the Portuguese government implemented both a closed season and a minimum landing size for some rays, and the EU prohibited target fishing for sharks. All these measures may have been highly responsible for the national and local landings reduction. Official landings from the last decade were analyzed, the landed species conservation status was consulted, and structured interviews using a questionnaire were conducted in the most important fishing port in the Portuguese mainland, the port of Sesimbra. Results led us to conclude that fishers’ answers and landings data did not match. It also revealed a lack of awareness by fishers about the state of shark and ray populations, and about some aspects of their biology and ecology, like reproduction season and method. The present study highlights the need to fill in this existing gap in knowledge through the transfer of scientific knowledge and sharing of management responsibilities. Also, we aimed to demonstrate the necessity for awareness and education activities within fishing communities, an essential step to elasmobranch conservation.

Effects of six codend meshes on the size selection of juvenile white croaker (Pennahia argentata) in demersal trawl fishery of the South China Sea

White croaker (Pennahia argentata) is a commercially important but overexploited species that is often caught in trawl fishery of the South China Sea (SCS). The codend size selectivity for this species in the local commercial trawl fishery is of concern when considering the established minimum landing size (MLS). This study investigated the size selectivity of white croaker for six different diamond-mesh codends with mesh size from 25 to 54 mm. We paid special attention to two codends, made with meshes of 25 and 40 mm in size, which are currently used according to the regulations established in the SCS. The results demonstrated that the legal codends do not perform satisfactorily in the fishing grounds where juvenile white croaker is relatively abundant. This is because at a length similar to the minimum landing size of the species (MLS = 15.0 cm), all white croaker were retained, and the estimated discard ratio was >97% in both cases of legal codends. Our study showed that by increasing the mesh size, the size selection of tested codends could be improved for white croaker, and the retention rates for juvenile fish would decrease. However, none codend was proved efficient to release undersized white croaker suggesting that other gear design changes may be necessary.

Factors contributing to the disease ecology of brown crab (Cancer pagurus) in a temperate marine protected area.

Marine ecosystems are affected by multiple, well-known stressors like fishing and climate change, but a less documented concern is disease. Marine reserves have been successful in replenishing stocks and aiding recruitment but studies have shown that high population abundances in marine reserves may lead to unwanted secondary effects such as increase in predators and competition, altering trophic webs, and disease. Here, we investigate factors contributing to disease prevalence in a brown crab (Cancer pagurus) population around Lundy Island (the UK's first MPA) after 7 years of no-take protection. Population parameters (size, sex, and abundance), disease (shell disease, Hematodinium spp. infection) and injury presence (a known precursor to some disease conditions) were assessed over two years in both fished and unfished areas of the MPA. We found no significant difference in prevalence between the disease prevalence in fished and unfished areas, however overall, the number of injured crabs increased significantly over the two years (12%), as did the prevalence of shell disease (15%). The probability of crabs having shell disease increased significantly in male crabs, and in those missing limbs. The probability of crabs being injured increased significantly in crabs below the minimum landing size. In terms of population parameters, crabs were more prevalent in the fished area compared to the unfished area, thought to be a result of an increase in the predatory European lobster. The findings of the present study highlight potential secondary community changes as a result of MPA implementation. Therefore, surveillance for such changes, as part of MPA management, would provide useful information on the health and overall function of the protected ecosystem.

Declining female size at onset of maturity in Nephrops norvegicus in long-term surveys (1997–2016)

Data on the demography and reproduction of marine species provide important information for a sustainable fisheries management. We show that the size at onset of maturity in female Nephrops norvegicus has been in decline for over 20 years and has always been above the established minimum landing size (MLS) in the Western Irish Sea. Determining the size at onset of maturity is one important factor to inform an effective MLS, such that individuals can reproduce at least once. The length at which half of females are sexually mature (L50) in the overall population declined by over 12% in two decades, from 23.6 mm in 1997 to 20.6 mm in 2016, while the MLS has remained at 20 mm. While L50 values differ among permanent sampling stations, the decline was observed at all stations. Current practice thus allows immature females to be landed before they reproduce and contribute to recruitment. While it is not always possible to identify the determining factors that drive the decline in SOM, we argue that it is appropriate to recognize this as an indicator of declining system productivity.

Out with the old and in with the new: T90 codends improve size selectivity in the Canadian redfish (Sebastes mentella) trawl fishery

The size selectivity of four codends were compared in the Gulf of St. Lawrence, Canada, redfish fishery (Sebastes mentella), including the regulated diamond mesh codend with a mesh opening of 90 mm (T0) and three experimental codends of different mesh openings (90, 100, 110 mm) in which the netting is turned 90° to the direction of tow (T90). Results for the regulated codend showed that there was little size selection, catching greater than 97% of redfish over all of the length classes observed. Considering the fished population, the smallest T90 codend would catch 30% fewer redfish under the minimum landing size (MLS) of 22 cm compared with the T0 codend, but would also lose 16% of catch above 22 cm. The T90 codend with 100 mm mesh opening had the same size selectivity as the smallest T90 codend. The 110 mm T90 codend would catch 50% less redfish below MLS but lose 40% of redfish above MLS. Overall, results show that T90 codends improve size selectivity in which large proportions of undersized fish are successfully released.

Evaluation on Minimum Landing Size Regulations in Turkish Marine Fisheries from Scientific Perspective

Crucial point of fishery management is to let the fish or other species reproduce at least once during their life. Therefore it is very important to determine the length at maturity (Lm) for given species before the first capture. Focus of this study is to determine the consistency between scientific results and minimum landing size (MLS) regulations in the marine fishery of Turkey. For this purpose, 4/1 communique on commercial fishery (2016/35) published by the Republic of Turkey Ministry of Agriculture and Forestry was investigated in order to expose the MLS of given species in Turkey. Literature survey on Lm was also conducted preferably on studies which were performed in Turkish waters or from the Mediterranean basin in order to avoid regional differences. While 86 marine species were reported to be landed in the official fishery statistics, only 49 of them were appointed with a MLS in the commercial fisheries regulation. It was determined that MLS of 27 species were below the Lm according to the selected literature, 7 of them require result on Lm, status of the 2 species couldn’t be decided due to different length types and 13 (27% of the decisions on MLS) of them were found to be in accordance with the scientific literature on Lm. This study shows that MLS regulation must be revised for most of the species in the surrounding waters of Turkey and comprehensive maturity studies are urgently needed in order to fulfill the scientific gap.

Comparison of selectivity of the trawl codends for whiting (Merlangius merlangus euxinus) in the Black Sea

A large part of the total whiting (Merlangius merlangus euxinus) fishing in the Black Sea is carried out with the traditional bottom trawl nets along the coast of Turkey. Diamond mesh shape with 40 mm mesh size (40D) has been used in the codends of these trawls. In this study, the traditional trawl codend (40D) and square-mesh codend with different size (36S and 40S) were compared for whiting size selectivity in August 2014. Selectivity data were collected by using a covered codend method and analysed taking between haul variations in to account. The selectivity parameters were estimated by using CC2000 software. Results showed that commercially used 40D trawl codend is not selective enough to release immature of whiting. However, the net change in square mesh (36S and 40S) instead of a diamond-shaped (40D) mesh significantly improved the mesh selectivity for whiting. The 40S trawl codend is even higher than the first maturity size (LM50) with a length at fifty percent retention (L50) of 15.74 cm. In conclusion all square mesh codends with different mesh size tested here supplied appropriate selection considering minimum landing size (MLS) of whiting.

Reproductive parameters of Atlantic chub mackerel Scomber colias in M'diq Bay, Morocco

Reproductive biology of Atlantic chub mackerel (Scomber colias) was studied based on samples from commercial catches in M'diq Bay, Morocco. Females predominated in the total catch (54%), their size at first maturity being 19.19 ± 0.43 cm TL. A minimum landing size (MLS) of 21 cm is suggested. The oocyte size frequency distribution and histological analysis confirmed that S. colias is a species with an indeterminate fecundity. The batch fecundity was estimated as 18,452–131,642, with a mean of 60,022 oocytes. The relative batch fecundity was 157–360, with a mean of 279 eggs g−1.