Trawl Ban Research Articles

Determining demersal fisheries status in fisheries management arena (FMA) 712 under data limited situation

Abstract Demersal fisheries in FMA 712 have been established since the early 1950’s, industrialization in demersal fisheries was started on 1970’s with the operation of trawl fleets in Java Sea. The exploitation continued until the 1980s when the Trawl Ban regulation was enacted. According to historical statical data from 1980 the number of demersal fishing fleets are still dominating and endangered the sustainability of demersal fish stock in FMA 712. This study presented alternatives approaches to determining demersal fisheries status in FMA 712 using the Bayesian surplus production model (cMSY) and Length-Based Spawning Potential Ratio (LBSPR). The cMSY analysis was conducted using time series production data and known CPUE represent the area in FMA 712 and the LBSPR model was conducted using the life-history parameters and the length frequency data. The results show that current demersal fisheries condition is overexploited, points of estimation of the Biomass condition based on 1980-2022 data: B/BMSY 0,803, F/FMSY 1,75 and MSY 323.000 ton. Additionally, the spawning potential ratio (SPR) of the dominant demersal fish species (Lutjanus malabarius and Portunus pelagicus) was lower than the limit reference point (<0,20), indicating overexploited. This study demonstrates that alternatives approaches could be applied to limited data fisheries and provide useful and robust recommendations.

An investigation on the distribution dynamics of kiddi prawn, Parapenaeopsis stylifera (H. Milne Edwards, 1837) along southwest coast of India, using multi-dimensional approach

Along India's southwest coast, the kiddi prawn (Parapenaeopsis stylifera) supports a substantial fishery, known as "karikady fishery" due to its high demand in domestic and international markets. Following implementing "mechanised fishing prohibition," catch fluctuations observed in P. stylifera catches sparked widespread social unrest among stakeholders, who feared that unharvested prawns would be lost to the fishery when these prawns moved away from the coast during the monsoon season. The study derived scientific evidence for to distributional idiosyncrasy of the species with spatial distribution tracking, understanding the correlation of species movement and maturity with environmental parameters, and tracking the individual cohorts through population parameter analysis. Data for the study were collected from commercial vessels, experimental surveys, and analyses was supported by GIS software and SPSS foftware. 18 cruises in the RV Silver Pompano and 3 cruises in RV Matsyakumari at five depths (10, 30, 50, 70, 90 m) were conducted during 2016–2019 off Kerala, southwest coast of India and, and a spatial analysis of the experimental trawling data contributed to evaluating the impact of the environment on the distribution of the species. The study revealed that increased salinity has a statistically significant impact on the expansion of the species, as indicated by geographical data. P. stylifera prefers to settle in areas with high salinity and low temperatures, according to geographical studies. This study not only established that the perception that species migrate away from the coast is rational, but it also established that there is no resource loss as a result of the 'Monsoon trawl ban,' because current fishing methods are capable of catching the larger prawns that have migrated to deeper waters. The study reaffirmed the usefulness of "monsoon trawl ban" in ensuring the long-term viability of the "karikadi" fishery along the southwest coast by assisting in species recruitment during the monsoon season.

Fishing Production and Fishing Changes in Hong Kong after the Ground Trawl Ban of 31st December 2012: A Geospatial Evaluation

From data published by the Hong Kong SAR (HKSAR) government in their two sole fisheries surveys of 2006 and 2016/2017, the current authors produced regional maps using spatial interpolation to more accurately describe and estimate the geographic coverage of changes in fishing production in Hong Kong waters since the ground trawl ban of 2012 December 31st. These suggest the fishing industry has adapted to smaller craft, and that fishing production increased in several areas in the period after the ground trawl ban came into effect. In addition, the maps enable a smoother assessment to be made of the geospatial changes in fishing production which have occurred since the ground trawl ban and suggest a ‘workaround’ by fishermen. In particular, small fishing craft known as sampans are able to take advantage by being more suitable vessels for areas such as narrower or shallower bays. Marine plastics pollution is also a proxy indicator of these activities, as evidenced by discarded fishing gear that includes plastic nets, floats, and other fishing boat equipment.

When the Trawl Ban Is a Good Option: Opportunities to Restore Fish Biomass and Size Structure in a Mediterranean Fisheries Restricted Area

This paper reports the results of a 15-year trawl ban imposed in 1990 in the Gulf of Castellammare (GCAST: NW Sicily, central Mediterranean Sea) and its effects on the biomass and size structure of demersal finfish and shellfish and on the proportion of different commercial categories of fish. Data were collected by experimental trawl surveys conducted in the GCAST and in two trawled areas before and after 1990. The biomass of the total assemblage and of a number of selected species was significantly higher in the GCAST after the ban. Highly commercial species had the largest increase in the same gulf after the ban, particularly at the depths used by artisanal fishermen. The results from size-based indicators were not as clear-cut as those from biomass though. Although the length frequency distributions obtained in the GCAST were significantly different from the other gulfs, in several cases, the values of the size indicators were higher in the trawled gulfs. Our results suggest that, at the temporal and spatial scale adopted, trawl bans may drive full biomass recovery but only partial size structure recovery of the fish populations subject to trawl exclusion, at least in the Mediterranean. The trawl ban in the Gulf of Castellammare provides an example of an effective ecosystem-based fisheries management tool that offers the potential for fish stock rebuilding and for the economic sustainability of artisanal, small-scale fisheries.

Effects of a trawling ban on the growth of young-of-the-year European hake, Merluccius merluccius in a Mediterranean fishing exclusion zone

This study evaluates the effects of a trawling ban on the growth of young-of-the-year (YOY) European hake, Merluccius merluccius (L., 1758) by comparing size structure, length–weight​ relationship, condition and growth in three gulfs along the coast of northern Sicily (central Mediterranean Sea), one of which has been subject to a trawl ban for 15 years. Hake ranging between 60 and 330 mm were collected from 50 to 200 m depth in May 2005. The length frequency distribution of YOY fish showed a higher modal length in the untrawled gulf and comparable densities in the three gulfs, while larger fish were more abundant in the untrawled gulf. Length–weight relationships and condition factors did not highlight any trend linked to the effects of fishing and suggested a large variability of the system. Growth curves had comparable slopes while different intercepts in both length–weight and growth curves suggest that the observed larger modal size of the first cohort in the untrawled gulf could be linked to better condition and growth during the initial life stage in the pelagic environment.

Initial recovery of demersal fish communities in coastal waters of Hong Kong, South China, following a trawl ban

Fisheries resources in Hong Kong have been overexploited since the 1970s due to intensive bottom trawling and other fishing activities that have depleted stocks and destroyed marine habitat. To rehabilitate depleted fisheries resources, a permanent ban on trawling in Hong Kong territorial waters came into force on December 31, 2012. In order to determine whether the trawl facilitated recovery of fish communities, trawl surveys were conducted at two sites in each of the eastern, southern and western (estuarine) coastal waters of Hong Kong before and three years after the trawl ban. A total of 315 species and 86 families of fishes in nine feeding groups were encountered during the surveys. Mean trophic level of the fish community, abundance and biomass of total fishes and of predatory fishes increased in eastern and western waters after the ban, but no changes or declines in these metrics were observed in southern waters. Although initial recovery in fish community were observed in eastern and western waters, anthropogenic disturbances might hinder the recovery process, including a large-scale reclamation for construction of coastal infrastructures in the west, illegal trawling, and expansion of non-trawling fishing efforts in the southern and eastern waters. Longer term monitoring is needed to evaluate the effects of the trawl ban, and determine whether recovery in the southern waters will continue to be constrained by the anthropogenic disturbances.Graphic abstract

Improvements of Population Fitness and Trophic Status of a Benthic Predatory Fish Following a Trawling Ban

Trawl fisheries have been shown to cause overfishing and destruction of benthic habitats in the seabed. To mitigate these impacts, a trawling ban has been enforced in Hong Kong waters since December 31, 2012 to rehabilitate the ecosystem and enhance fisheries resources. Previous studies demonstrated that reduced trawling activities would increase the heterogeneity of benthic habitats, thereby enhancing species richness and abundance of benthic fauna and providing more prey resources for predatory fishes. This study aimed to test a hypothesis that the population and trophic dynamics of the Bartail flatheadPlatycephalus indicus, a heavily fished benthic predatory fish, at inner and outer Tolo Channel of Hong Kong (i.e., EI and EO) improved with increases in their body size, abundance, biomass, trophic niche, and trophic position after the trawl ban. Samples were collected from trawl surveys before and after the trawl ban to compare the pre-ban and post-ban populations ofP. indicusfrom EI and EO. Body size, abundance, and biomass were assessed in 2004, 2013–2014, and 2015–2016, whereas trophic niche and trophic position were analyzed based on stable isotopes of fish samples collected in dry season of 2012, 2015, and 2018. Following the trawl ban, the abundance and biomass ofP. indicusincreased in EO, with body size increased in EI. Furthermore, as indicated by the results of stable isotope analysis (SIA) on their tissues and prey items, trophic niche, and trophic position ofP. indicusincreased in EI and EO, respectively. Our study demonstrated that the trawl ban had promoted the recovery of a predatory fish population through restoring size structure and trophic dynamics.

Fisheries sustainability assessment and sensitivity analysis: an illustration

Using a modified Ecologically Sustainable Development (ESD) framework, this paper assesses progress towards sustainability over time with a case study of the demersal trawl fishery of Oman, which has been transformed and turned into the coastal fishery after the trawl ban. A multi-criteria decision analysis method is used for ranking the years and deciding on the best performing year under five alternative scenarios related to the core components involving humans and the environment. Under the environment component, the year 2001 stood out as the best across all scenarios. The combined results also echoed the same in four out of five scenarios. With reference to progress towards sustainability during the study period, no clear positive year-to-year trend was observed from the overall results. The analysis of the S2 scenario revealed that the closed fishing season during 1998–2001 yielded a positive spill-over effect on the local economy. The results from a comparative analysis indicated that the strengths (weaknesses) of the year 2001 were predominantly associated with the environment (human) component, and thereby, reflecting a comparatively higher conservation outcome in the year 2001. The findings from the comparative analysis would guide fishery managers in designing appropriate strategies for improving weaknesses of the preferred option and reducing the inter-scenario risk by combining positive features of the second-best option. The framework outlined in the present paper can be used to guide the sustainability assessment of other local fisheries (for instance, the lobster, abalone, and shrimp fisheries) including the recently developed coastal fishery.

Deep-sea trawling off the Portuguese continental coast––Spatial patterns, target species and impact of a prospective EU-level ban

Following the implementation of the European Council EC Regulation 2016/2336, which restricts bottom trawling below 800 m for vessels capturing deep-sea fish species, the quantification and characterization of the fishing activities at those depths became essential to evaluate potential negative economic impacts. In this study, the activity of the Portuguese coastal trawlers operating at fishing grounds deeper than 800 m is characterized for the period 2005–2016, based on the analysis of VMS data and landing declarations in national ports. A total of 13 of 125 active trawlers in the coastal fleet were found to be partially engaged in deep-sea trawling, but only two units were entirely dedicated to this activity over the period in analysis. The scarlet shrimp Aristaeopsis edwardsiana was landed from 2006 onwards as the only target species at these depths. For each of these 13 vessels, the correspondence between VMS records of trajectories assigned to fishing trips, and landing registers, provided information on the spatio-temporal patterns of activity along the time period under analysis. Among fish by-catch, only in 2006 and 2007 were deep-sea species protected under Reg. 2016/2336 recorded, after which only small, occasional landings occurred. Results show that the implementation of the trawl ban does not affect the economic activity of the Portuguese coastal trawl fleet. Even if a full ban was to be implemented it would only impact the activity of two single vessels, which would have to completely redirect their fishing operations.

Recovery of tropical marine benthos after a trawl ban demonstrates linkage between abiotic and biotic changes

Bottom trawling, which is highly detrimental to seabed habitats, has been banned in some jurisdictions to mitigate the problems of habitat destruction and overfishing. However, most reports of ecosystem responses to trawling impacts originate from temperate latitudes, focusing on commercial species, and recovery of invertebrate macrobenthos from trawl ban has hardly ever been studied in the tropics. In Hong Kong (lat. 22.4°N), a history of intensive trawling with various types of gears has long degraded coastal ecosystems. To facilitate the recovery of fisheries resources and associated benthic ecosystems, the Government of the Hong Kong Special Administrative Region implemented a territory-wide trawl ban on December 31, 2012. Comparison of surveys conducted in June 2012 (before the trawl ban) and June 2015 (2.5 years after the ban) revealed higher organic contents in sediment and lower suspended-solid loads in water column, as well as a significant increase in site-based abundance, species richness, functional diversity and among-site similarity of macrobenthos after the trawl ban. Our results suggest that the imposition of a trawl ban can be an effective measure for biodiversity conservation in tropical coastal waters.

Does cantrang trawl fishing become more efficient after the partial trawl ban? a case study of technical efficiency of cantrang fishery in the Java Sea – Indonesia

Cantrang- a modified Danish seine that targets demersal fish and squid in the Java Sea- has been banned partially in all Indonesian waters since 2015. The policy goal was to limit the ecological impact by reducing the number of the fleet. This study compares the technical efficiency (T.E.) of cantrang fishing before and after the ban and identifies input technology that affects fleet efficiency. A Data Envelopment Analysis (DEA) was used to calculate the Technical Efficiency of the cantrang. In this case, the T.E. measures the ability of cantrang to maximize catch using a given set of production inputs such as Goss Tonnage (G.T.), fishing duration, and the number of skippers using the time series daily landing data from 2007 to 2017. The results show pure and scale efficiency of the fleet increases considerably during the after-ban period compared to the before-ban period. This relatively high technical efficiency at post-ban occurred due to the meaningful reduction of fishing days while optimizing the number of onboard skippers per vessel. Although the portion of skippers per vessel increases substantially at post-ban, this growth minimizes the onboard fishshorting, packaging, and grading works. Therefore, these tasks can be done faster than before.

Does a Trawl Ban Benefit Commercially Important Decapoda and Stomatopoda in Hong Kong?

Crustaceans were among the most valuable fishery resources in Hong Kong. However, the unrestricted and intensive use of different fishing gears, especially bottom trawling, has led to the depletion of commercially important crustaceans in Hong Kong since the 1980s. This study investigated whether commercial crustaceans recovered after the implementation of a permanent Hong Kong-wide trawl ban that began on December 31, 2012. Standardized field surveys were conducted using a commercial shrimp trawler at two sites in eastern and western waters of Hong Kong before (2004) and after the trawl ban (2013–2014 and 2015–2016) and two sites in southern waters after the trawl ban. Diversity, mean size, abundance, biomass and level of disturbance of commercial crustaceans from the three periods were investigated. The eastern waters exhibited an increased diversity of crustacean assemblages in Inner Tolo, and a higher abundance and biomass of crabs were detected in Outer Tolo after the trawl ban. Reduced disturbance, higher diversity in crustacean assemblages and greater abundance and biomass of predatory crabs were observed after the trawl ban in the outer estuary of western waters, and increased abundance and biomass of shrimp were detected in the inner estuary of western waters. No temporal or negative changes were detected in the southeast and southern waters of Lamma Island. The various responses of crustacean assemblages in Hong Kong waters revealed the critical role of complex interactions among multiple stresses, such as ongoing reclamation works, illegal trawling activities and increased fishing efforts using other (legal) fishing methods.

Stable-isotope based trophic metrics reveal early recovery of tropical crustacean assemblages following a trawl ban

Abstract Trawl bans are relatively uncommon, particularly at the level of an entire coastal jurisdiction, and have seldom been studied in the tropics. A permanent territory-wide trawl ban has been implemented in Hong Kong coastal waters since the beginning of 2013. We used isotope-based metrics, in addition to traditional community measurements, to determine whether benthic crustacean assemblages had shown any signs of recovery three years after the trawl ban. We expected increases in species richness, abundance and biomass as well as shifts in trophic structure, including longer food-chain length (FCL) and greater trophic diversity after the ban. We further anticipated that carnivorous crustaceans would have higher mean trophic positions (MTPoC) at the assemblage level, and broader trophic niches at the species level. Sampling was undertaken at six sites in three regions (eastern, western and southern waters) before (in 2012) and after (in 2015) the ban. In general, there were no changes in assemblage total abundance or species richness after the trawl ban, but a decrease in biomass was observed. Isotope-based metrics showed that trophic niches of the crustacean assemblages were, however, broader at all sites after the ban. The FCLs at four sites in the eastern and western waters were longer after the ban, and three of them also showed increased MTPoC. In contrast, declines in FCL and other trophic metrics were recorded at the two southern sites. Among the five most abundant carnivorous crustaceans, all species at one eastern site, three at one western site, and four at three other sites expanded their trophic niches after the trawl ban; no changes were evident at the other eastern site where carnivores were scarce. By using isotope-based trophic metrics, we detected early functional recovery of the crustacean assemblages that cannot be revealed by traditional community analyses, implying that the effectiveness of the trawl ban would be underestimated if the assessment was based on community measurements only. We, therefore, advocate the use of isotope-based trophic metrics in tandem with the community measurements for more comprehensive assessments of ecosystem responses to anthropogenic disturbances and management interventions designed to alleviate them.

Science, subsidies and the politics of the pulse trawl ban in the European Union

The decision to ban the pulse trawl by the European Parliament in early 2019 was influenced by public debate over its scientific and political legitimacy. In their 2019 paper in Marine Policy, Le Manach et al. continued this debate by making three claims. First, that the pulse trawl has substantial negative social and environmental impacts. Second, that it received ‘illegal’ subsidies from the European Union amounting to €20.8 million. And third, that the Dutch government and industry did not provide adequate transparency in the allocation of subsidies. These claims are misleading and, in some instances, demonstrably false: the ongoing science on the effects of the pulse trawl shows relatively positive impacts; following the conventional definitions of “harmful” and “fisheries subsidies” in the economic literature, harmful subsidies provided to pulse trawling only amount to €0.3 million, or less than 2% of Le Manach et al.‘s estimate; and there is no evidence of intentional non-disclosure of information related to the distribution of subsidies by the Dutch government. Finally, we reflect on the consequences of the inaccuracies presented by Le Manach et al. in the governance of fishing gear innovation and their wider effect on the legitimacy of advocacy-based science.

Sizing up the role of predators on Mullus barbatus populations in Mediterranean trawl and no-trawl areas

Fishing leads to drastic changes in ecosystems with a net loss of predatory biomass. This issue has been evidenced from historical ecological studies and from the evaluation of the effects of effective and large marine protected areas. In two fishery reserves off the northern Sicily coast the red mullet Mullus barbatus underwent an impressive biomass increment and a few piscivores fish species recovered after a trawl ban. The red mullet, more than 20% of all demersal fish in the untrawled areas, represented a huge food resource to its potential predators. By contrasting two trawled and two untrawled gulfs we figured out predator - prey relationships through the use of a combined approach based on trophic niche, stable isotopes data and biomass. We show that the white grouper Epinephelus aeneus and the black-bellied anglerfish Lophius budegassa are the most important predators of the red mullet with higher biomass in the untrawled areas. We also found a potential re-establishment of the trophic role for white grouper inside the untrawled areas. Our study highlights some of the benefits obtained from the use of large offshore marine protected areas as a tool for ecosystem restoration.

Recovery of benthic communities from small-scale shrimp trawling: Evidence from using ecological indices over a short temporal scale

Mobile fishing gears are responsible of various direct effects on benthic communities. The most important (in volume and value) fishery in Saudi waters of the Arabian Gulf is the 6-month trawl season for the green tiger shrimp. The fleet is composed of hundreds of artisanal boats carrying out short-duration tows of small trawls. To study the impact of this trawl season on local benthic communities, two different methodologies were adopted in three areas of different trawling intensities. The first study design was aimed at the seasonal effect and the second design examined the immediate impact after the pass of a trawl. Both studies were evaluated using univariate ecological indicators (richness, diversity, AMBI, M-AMBI) and the multivariate species composition. The seasonal study revealed a cyclic dynamics of the benthic assemblages. Most of the univariate ecological descriptors decreased during the trawling season and increased during the off-season while species composition undertook a round trip in multivariate space, thus supporting the conclusion that the impact of trawling on the benthic ecosystem during the shrimp season is reverted during the trawl ban. Although our results confirm predictions of synthetic statistical models, they also show that the impact of trawling on benthic communities strongly depend on the existence of a trawl ban period.

Trawl ban in a heavily exploited marine environment: Responses in population dynamics of four stomatopod species

Intensive trawling activities in Hong Kong waters have seriously depleted fishery resources and damaged marine benthic habitats over the last four decades. To minimize further destruction and rehabilitate fishery resources, the Hong Kong Government implemented a permanent territory-wide trawling closure on 31 December 2012. Such a trawl ban creates a unique opportunity to investigate recoveries in ecosystem structure and function following a major shift in disturbance regime by removing impacts from a major gear. This study was designed to test the hypothesis that dominant predatory mantis shrimps, including Harpiosquilla harpax, Miyakella nepa, Oratosquillina interrupta, and Oratosquilla oratoria would show signs of recovery following the trawl ban. Their population dynamics were investigated before and after the trawl ban. The results showed that their mean weight, mean carapace length and proportion of large-sized individuals increased significantly 3.5 years after the trawl ban, whilst their abundance, biomass and maximum length remained unchanged. This study suggests that the stomatopod assemblage in the human-dominated Hong Kong waters shows some initial signs of possible recovery following the trawl ban but also highlights the complexity of implementing fishery management and detecting changes resulted from management measures in a heavily urbanized seascape where many biotic and abiotic factors can influence their population dynamics.

Effects of reallocating fishing effort from trawling to creels in a Norway lobster fishery

The consequences of reallocating fishing effort from trawling to creels in an area off the West coast of Portugal for the operation of the trawl fleet, as well as on the population dynamics and the global catch value for a high-valued species, the Norway lobster (Nephrops norvegicus) are evaluated. The results suggest that only small portions of the area of interest are used by the trawl fleet, opening the possibility for a trawl ban without major disruption of the trawling activity. Economic benefits are expected, since predictions two scenarios tested, heavy and moderate exploitation, indicate no loss of catch value with much lower operational costs. Social benefits to local communities can also be expected since a much lower investment is needed for creel fishing, making this fishery attractive to small local companies already operating in the region. The proposed ban is consistent with the ecosystem approach to fisheries management and the Common Fisheries Policy (CFP) where the transition towards more responsible fishing practices is encouraged.

Socio economic impact of trawl ban on the livelihood of marine fishers' of Palk Bay, Tamil Nadu

Indian fisheries sector has witnessed phenomenal growth in marine fish production over the decades, with the modernization of fishing crafts and technology, thereby resulting in fluctuation of the same, thus rendering intense debate on growth and instability. To ease the production trend in a sustainable way and to conserve the dwindling marine resources, the monsoon trawl ban was introduced in 2001 in Tamil Nadu. The seasonal fishing ban has been one of the very few significant management measures for the sustenance of the marine resources since its preamble. Though remarkable upsurge in marine fish production was achieved post implementation of ban, yet, it had generated issues in employment, poverty and income generation of fishermen during the ban period and was always a matter of turbulence among mechanized and traditional sector of fishing. It is also alleged that the enhanced marine fish landings could also be a case of fishing in and out of the waters off Tamil Nadu coasts. We made an attempt to understand the social and economic impact of fishing ban on the livelihood of marine fisherfolk and to study the viability of different marine fishing units (Motorized and Mechanized) in Tamil Nadu. The overall employment loss and loss in labour income during the ban period was also assessed. The fishermen’s constraints during the ban has also been ranked and suggestions given to improve the livelihood security of the marine fishers’ in the Palk bay area.

Bottom shrimp trawling impacts on species distribution and fishery dynamics; Ungwana Bay fishery Kenya before and after the 2006 trawl ban

The Malindi–Ungwana Bay fishery Kenya is one of the most important marine fisheries of the Western Indian Ocean. There are two fishing grounds: Formosa and Malindi, with a designated 5-nM no-trawl zone offshore. However, the fishery was faced with numerous resource use conflicts and a decline in catches, culminating in a trawl ban in 2006. This study analyses catches and fishery dynamics before and after the 2006 trawl ban. Results show that artisanal landings declined before the ban, but rapidly recovered within 2 years after the ban was imposed. However, shrimp landings in the artisanal fishery remain low. Commercial shrimp landings gradually declined before the ban: ~550 t in 2001 to 250 t in 2006, and the shrimp: fish bycatch ratio was 1:1.5 compared to early reports of 1:7 in 1999. SIMPER analyses shows that 6 and 16 families (groups) accounted for 91.0 and 90.2% of the similarity in catch within the Formosa and Malindi fishing grounds, respectively. Formosa was important for Claridae, Cichlidae and Protopteridae, while Malindi recorded Carangidae, Siganidae, Carcharhinidae and Lethrinidae as the main families. Future studies should therefore embark on analyses of the factors driving the spatio-temporal distributions of the species and assess the impacts of bottom trawling on fishery dynamics before the trawl ban can be lifted.