Effectiveness of bottom guarding nets in reducing bycatch in prawn (Penaeus spp.) trammel net fishery along the coast of Ban Nam Khem, Phang-Nga, Thailand

Evaluating dolphin damage in trammel net fisheries in the Valencia region: Insights to improve management

Discards remain among the main negative impacts of fishing activities, and their reductions are strengthened by the European Common Fisheries Policy (European Regulation 1380/2013). Trammel net fisheries appear more sustainable compared with other fishing techniques, especially from an ecological viewpoint. Despite this, reports show that trammel net fisheries deliver discard quantities between 10% and 43% of the total catch biomass. To supplement existing information, this current work attempts to address the discard reduction using guarding net in the small-scale fisheries of Egadi Islands MPA (Western Sicily, Central Mediterranean Sea). To assess the reduction of unwanted catches, 48 experimental fishing trials were conducted within a 6-month period. The experimental fishing trial employed a trammel net made up of 20 panels alternated with two different net configurations. The control panels (CN) held a large outer (180 mm) and small inner (31.25 mm) meshes. The test panels (GN) with guarding net constituted a three-mesh-high (50-mm mesh size) net placed between trammel net panels and a lead line. A total of 3,310 individuals belonging to 106 taxa and nine phyla were caught. Crustaceans were the most abundant unwanted catches in the control panels, whereas bioconstructions occurred in the guarding net panels. The discard ratios of CN and GN panels were statistically different (t-value = –2.55; p< 0.05). The analysis of catch per unit effort showed higher catches of CN panels for both commercial and discard fractions (p< 0.05). Moreover, the guarding net panels caught the main discarded species at 20% lower compared with the control. The overall value of the catch at the CN panels (€ 3,366.90) was higher than the total income (€ 2,043.70) generated using the GN panels, which suggests a significant commercial loss of 40% (p< 0.05).

This study aimed to determine the catch composition and compare the catch per unit effort (CPUE) of indigenous and non-indigenous species in longline and trammel net fisheries in the Mediterranean coasts of Türkiye. The data were collected weekly from May 2020 to September 2021 by commercial fishing vessels (n = 62 days for trammel nets, n = 75 days for longlines). The results of the study indicated that more than 90% of the catch composition consisted of non-indigenous species in trammel net fishery and Pterois miles (Bennett, 1828), Siganus rivulatus Forsskål et Niebuhr, 1775, Siganus luridus (Rüppell, 1829), and Scarus ghobban Forsskål, 1775 were the most commonly caught species. Although indigenous species were more common in longlines compared with trammel nets, non-indigenous species Lagocephalus sceleratus (Gmelin, 1789) and Lagocephalus suezensis Clark et Gohar, 1953 were represented by relatively high catch ratios. The results also revealed that the CPUE of non-indigenous species exhibited seasonal differences. Although some non-indigenous species caught within this study have a market value, some other highly invasive species do not. Therefore, it is critically important to develop effective management tools to control bio-invasion. This study provides the first comprehensive research by utilizing basic data with relatively long-term surveys in the small-scale fishery on the Mediterranean coasts of Türkiye. The outcomes of this study can provide guidance to decision-makers.

Summary Small-scale fisheries are generally promoted as a sustainable alternative to large-scale industrial fisheries. However, there is recent growing evidence that small-scale fisheries may be the largest threat to marine species of conservation concern. The objective of this study was to evaluate the potential impact of the trammel net fishery on elasmobranchs in the Gulf of Gabes, Southern Tunisia. Data are based on 191 shrimp trammel net set (40 mm stretched mesh size) surveys conducted aboard commercial fishing vessels from May to July 2009. Five species of the small coastal elasmobranchs (Mustelus mustelus (Linnaeus, 1758), Mustelus punctulatus Risso 1827, Dasyatis pastinaca (Linnaeus, 1758), Dasyatis marmorata (Steindachner, 1892) and Torpedo torpedo (Linnaeus, 1758)) and two species from the large coastal shark (Carcharhinus plumbeus (Nardo, 1827) and Carcharhinus brevipinna (Muller & Henle, 1839)) were recognized as by-catch in this fishery. Elasmobranch by-catch was dominated by sharks (90.3%), smoothhound sharks Mustelus sp. being by far the most important (88.9%) and reflecting their abundance in the area; 58% of the sets caught at least one specimen, with 4.8 ± 1.3 caught per set. Captures were composed essentially of neonate and juvenile sharks, while the batoids were dominated by mature individuals. This study shows that shrimp trammel nets represent a considerable source of mortality for early life stages of elasmobranch species in the Gulf of Gabes. Additionally, there was a high density of neonates and small juvenile M. mustelus in the Sfax zone, suggesting that these nearshore waters are a nursery grounds for smoothhound sharks. Further research should focus on the incidents of by-catch and evaluate the potential solutions to allow trammel net fisheries to coexist alongside the elasmobranch species.

Assessment and bioeconomic analysis of the Majorca (NW Mediterranean) trammel net fishery

Long-term conservation of marine resources depends on the availability of data to adequately assess fish stocks, the environmental state and the impact of fishing activity on marine ecosystems. In recent years, electronic monitoring (EM) has developed significantly as a tool to provide data on fishing activity and catches. In this context, the question arises as to how these data can be utilized for scientific fisheries research, given the available EM systems and the wide variety of commercial fisheries. In our study, we tested four case studies in Spanish waters: otter bottom trawling targeting demersal fish, otter bottom trawling targeting mackerel, trammel net fishery and purse seining. To evaluate the utility of EM, in these case studies, we designed a comparative analysis based on two data sources: data from scientific human observers and data from an electronic camera system. Both methods were applied to the same hauls to assess the accuracy of the cameras, the system performance and the problems with adequate data collection for scientific purposes in each fishery studied. The results showed that the camera system recorded an average of 69% to 80% of the total captured species in trawling, full coverage (99%) in trammel nets, and 64% in purse seining. The number of detected individuals varied among the identified species. An 83% agreement was observed for retained Lepidorhombus spp. and 55% for retained Scomber scombrus in bottom trawl fisheries. Likewise, a 90% agreement was recorded for Sepia officinalis in the trammel net fishery. In terms of total estimated weight, a 75% agreement was achieved for retained Sardina pilchardus in the purse seine fishery. Additionally, the camera system was able to record bycatch species, including marine mammals and seabirds, and protected, endangered, and threatened (PET) species. This information provides an opportunity to gather more scientific data from small-scale fisheries, which are the most common type in Spain. Some possibilities are proposed to address several challenges to improve the accuracy of camera recordings in different fisheries so that they are useful for scientific data collection.

Environmental drivers of lionfish catch efficiency in trammel net fisheries in the Southwest coasts of Türkiye

Size selectivity of Korean flounder ( Glyptocephalus stelleri) by gillnets and trammel nets using an extension of SELECT for experiments with differing mesh sizes

For each Portuguese fleet component, landings of biogeographic groups of fish species were compared for the period of 1993–2009. Wide-distribution species were the most abundant in landings, but have shown a decreasing trend. Temperate species had higher landings in trawl fisheries, whereas subtropical species were most abundant and exhibiting an increasing trend in landings of multi-gear fisheries. A latitudinal gradient was observed, with landings of temperate species being more important in the North-western coast than in the South-western and South coasts. Although trawl fisheries were relatively more important in the North-western coast, there has been a recent increase in the relative importance of multi-gear fisheries and of subtropical species in this area. The increasing relative importance of subtropical species in Portuguese fisheries along with the fact that landings of subtropical species were higher in multi-gear fisheries could indicate an easier adaptation of Portuguese multi-gear fisheries to the effects of climate change. However, as multi-gear fisheries include a wide range of gears, techniques and target-species, they may not all respond in the same manner to changes in fish species’ distribution. Among multi-gear fisheries, trammel nets catch a wider variety of species and a wider size range than gill nets or longlines; thus, trammel net fishers can adapt to changes in abundance of the main target species more readily than those using more species- and size-specific gears. Therefore, trammel net fisheries could more easily adapt to the effects of climate change on fish distribution than gill net or longline fisheries.

Discarding is a significant problem due to net damage and labour loss in trammel net fisheries. In this study, the effects of 15, 25, and 35 cm high cloth tarpaulin rigged between the lead line and the net were investigated in reducing the discard amount of trammel nets for red mullet (Mullus barbatus) in the south-eastern Black Sea. During the study, twenty fishing trips were carried out on-board a commercial vessel between May 11 and June 20, 2018. Results showed that there were no significant differences in the amount of discards between the commercial and experimental nets (P>0.05) However, cloth tarpaulin mounted nets (CTMN) were found to be significantly successful to reduce the amount of shore crab (Liocarcinus depurator) and the veined rapa whelk (Rapana venosa) (P<0.05). Although it is insignificant, a decline of capture was also observed in the amount of target species in CTMN compared to the commercial net (CN). Finally, the advantages and concerns of this gear modification, and potential reasons for the reduction of target and discard species are discussed.

In the Balearic Islands, different trammel net designs have been adopted to promote fisheries sustainability and reduce discards. Here, we compare the catch performance of three trammel net designs targeting the spiny lobster Palinurus elephas in terms of biomass, species composition and revenue from commercial catches and discards. Designs differ in the netting fiber type (standard polyfilament, PMF, or a new polyethylene multi-monofilament, MMF) and the use of a guarding net or greca, a mesh piece intended to reduce discards. Catches were surveyed by an on-board observer from 1,550 netting walls corresponding to 70 nets. The number of marketable species captured indicated that the lobster trammel net fishery has multiple targets, which contribute significantly to the total revenue. The discarded species ranged from habitat-forming species to elasmobranches, but the magnitude of gear-habitat interactions on the long term dynamics of benthos remains unclear. No relevant differences in revenue and weight of discards were detected after Bayesian analyses. However, the species composition of discards was different when using greca. Interestingly, high immediate survival was found for discarded undersized lobsters, while a seven day survival assessment, using captive observation, gave an asymptotic estimate of survival probability as 0.64 (95% CI [0.54–0.76]). Therefore, it is recommended that it would be beneficial for this stock if an exemption from the EU landing obligation regulation was sought for undersized lobsters in the Balearic trammel net fishery.

Trammel nets are used with extended soaking times to increase the catching efficiency for demersal fish in commercial fishing. Long soaking time causes deterioration or damage to species caught in the first days. Effects of soaking time were investigated with 36‐mm, 42‐mm, and 46‐mm mesh sizes soaked over 1, 3, 5, and 7 days on target, non‐target, and other species. Only 26.3% (293 individual fish) of 1113 individual fish were not damaged of the target species. Total weight of non‐damaged individuals was 247.6 kg, of which 150.6 kg (60.8%) was the target species. Critically endangered and endangered Chondrichthyes species were negatively affected by soaking time and mesh size. Current and previous regulations did not restrict soaking time or mesh size of trammel‐net fisheries in Türkiye. Extended soaking times of trammel nets may cause more negative ecosystem effects than ghost fishing. Consequently, 42‐mm mesh‐size trammel nets soaked for 1 day should be used by fishers. If used for more than 1 day, 42‐mm or 46‐mm mesh sizes should be used.

Elasmobranch bycatch in a trammel net fishery in the Portuguese west coast

The scalloped spiny lobster Panulirus homarus supports numerous traditional diving,trap and trammel net fisheries in the Western Indian Ocean. Commercial catches made in 2003to 2005 in the Arabian Sea region of Oman (a coastline of ~1100 km, comprising Dhofar andAl-Wusta) were sampled for length and sex composition, and female reproductive condition.On average, lobsters caught in Dhofar were larger than in Al-Wusta, and length-based estimatesof growth parameters, size at maturity and natural mortality were consistent with fast-growingtropical lobsters. Compared to historical data from Oman dating from the late-1980’s (with peakcatches of >2000 t/yr) and mid-1990’s, recent landings, average lobster size and size at maturitywere considerably lower. A length-based cohort analysis suggested that fishing mortality does notimpact on lobsters 80 mm. The spawningbiomass ratio (Bsp/B) of

The size selectivity of a trammel net for herded oval squid Sepioteuthis lessoniana in Tateyama Bay, Chiba Prefecture, was estimated by comparison between the mantle length frequency distributions of oval squid caught by a trammel net and by a set net. The measured mesh sizes of the inner net of the trammel net and of the final section of the set net were 85.3 and 11.3 mm, respectively. In the trammel net fishery where oval squid are herded into the net, most of the oval squid are caught in the bag-shaped inner net. Hence, the logistic function was employed for the size selectivity curve of the trammel net. The ‘share each length's catch total’ (SELECT) model was implemented for the estimation of the selectivity curve. The size selectivity r(l) of the trammel net for the oval squid was expressed as a logistic function of the mantle length l: r(l)=exp (-18.57+0.88 l)/[1+exp (-18.57+0.88 l)]. From these logistic parameter estimates, the 50% selection mantle length and selection range (L75-L25) were calculated as 21.07 and 2.49 cm, respectively. The selection probability of oval squid whose mantle girth was equivalent to the mesh perimeter of the inner net was 0.09. Accordingly, oval squid of a girth smaller than the mesh perimeter were likely to pass through the mesh to escape from the net.