Trawl Closures Research Articles

Environmental drivers and the distribution of cold-water corals in the global ocean

Species distribution models (SDMs) are useful tools for describing and predicting the distribution of marine species in data-limited environments. Outputs from SDMs have been used to identify areas for spatial management, analyzing trawl closures, quantitatively measuring the risk of bottom trawling, and evaluating protected areas for improving conservation and management. Cold-water corals are globally distributed habitat-forming organisms that are vulnerable to anthropogenic impacts and climate change, but data deficiency remains an ongoing issue for the effective spatial management of these important ecosystem engineers. In this study, we constructed 11 environmental seabed variables at 500 m resolution based on the latest multi-depth global datasets and high-resolution bathymetry. An ensemble species distribution modeling method was used to predict the global habitat suitability for 10 widespread cold-water coral species, namely, 6 Scleractinian framework-forming species and 4 large gorgonian species. Temperature, depth, salinity, terrain ruggedness index, carbonate saturation state, and chlorophyll were the most important factors in determining the global distributions of these species. The Scleractinian Madrepora oculata showed the widest niche breadth, while most other species demonstrated somewhat limited niche breadth. The shallowest study species, Oculina varicosa, had the most distinctive niche of the group. The model outputs from this study represent the highest-resolution global predictions for these species to date and are valuable in aiding the management, conservation, and continued research into cold-water coral species.

Effects of spatial management of a penaeid fishery on other target fish species in eastern Australia

AbstractTemporal and spatial closures are often used to manage harvest by trawl fisheries. Trawl closures implemented to benefit a particular species may also benefit other species, but these indirect effects are rarely quantified. Using the New South Wales (Australia) Ocean Trawl Fishery as a case study, the potential unintended effects of trawl closures designed to protect juvenile eastern king prawn were explored for other quota managed Sillaginidae within the fishery (stout whiting Sillago robusta and eastern school whiting Sillago flindersii). Both species of whiting were more abundant within closed areas than adjacent areas, and spawning‐sized stout whiting were proportionally more abundant within closed areas. Thus, closures implemented to protect prawns also provided protection for exploited whiting species, including spawning‐sized individuals, enhancing their overall impact on the fishery. Spatial management of trawl fisheries elsewhere in the world may also similarly benefit other exploited species.

Adaptive Spatial Management to Deal with Postflood Inshore Bycatch in a Penaeid Trawl Fishery

AbstractAdaptive spatial management provides a way to balance the conservation of bycatch species and the potential economic effects of bycatch‐induced closures on a fishery, but implementation can be both data and resource intensive. We present a survey exploring a novel approach to adaptively manage an intermittent bycatch issue in an inshore trawl fishery where Sciaenidae bycatch species (including juvenile Mulloway Argyrosomus japonicus, a species of conservation concern) co‐occur with large aggregations of a valuable target species (eastern school prawn Metapenaeus macleayi), following flood‐induced egression from estuarine habitats. Diurnal sampling surveys followed three flood events and targeted permanent inshore closure zones (designed to protect the normally nocturnally harvested eastern king prawn Melicertus plebejus) and adjacent inshore nonclosure areas. Sciaenidae abundance was mostly <10 fish/ha trawled, but larger catches generally corresponded with larger catches of eastern school prawn, and these relationships appeared to be steeper within nonclosure zones. There were only minor differences in the size structure of eastern school prawn between zones, and patterns were event and location specific. Negligible eastern king prawn were encountered. The results show that temporarily allowing fishers access to permanent trawl closures following floods may support the exploitation of aggregated target species with reduced interaction with bycatch species of concern. The approach presented here is relevant to the consideration of adaptive spatial management in other trawl fisheries.

Biological evaluation of an existing spatial management network for an exploited penaeid species

Spatial management may be employed to achieve objectives aimed at maintaining or enhancing productivity and sustainability of exploited populations. Spatial management is used in penaeid fisheries to alter the spatiotemporal distribution of fishing effort to achieve outcomes such as avoidance of undesirable size-classes. Eastern King Prawn (Penaeus [melicertus] plebejus; EKP) is a valuable penaeid species for which harvest is supported by an extensive spatial management network, however these closures have never been evaluated. We examine temporal variation in biomass and size structures within three trawl closure areas spanning four degrees of latitude. There was substantial spatial variation in EKP biomass among locations, fished and non-fished zones and sampling periods, which appeared to be influenced by depth, temperature and distance to the adjacent estuarine nursery. Size structure varied among locations and sampling periods, and differed inside and outside of closure areas, however in many cases the majority of prawns that were protected within closure areas were consistently smaller than the estimated size at first capture for optimal yield per recruit. The data suggest that the closures are likely to be effective at achieving their objective, but there may be some scope for adaptive management.

Beyond the boundaries: How regulation-centered marine protected area information improves ocean protection assessments

Comprehensive, spatially explicit data that include regulatory information are essential for evaluating the level of protection that marine protected areas (MPAs) and other marine managed areas (MMAs) provide to marine life, and to inform progress towards ocean protection targets. An analysis based on the ProtectedSeas database, which includes information on regulated activities, found that 85% of U.S. waters are in managed areas that restrict living resource extraction at some level above generally applicable regulations, with 52% managed at a low level of protection and 3% managed as highly protected no-take areas. States with the most state waters area in no-take MPAs are Hawaii (~25%), California (~9%), and Oregon (~3%). The majority of highly protected areas in U.S. waters exist in low-populated areas of the Pacific, such as the Papahānaumokuākea and Pacific Remote Islands Marine National Monuments. Under a quarter of U.S. waters are closed to bottom trawling, with the West Coast and Alaska each contributing one-third of trawl closures by area. Bottom trawling is prohibited in nearly 90% of West Coast waters. Focusing on waters off California showed that overlapping management and fishing gear restrictions can increase overall protection. In state waters, no-take MPAs account for roughly 9% of the area, while restricted take MPAs of different types cover 27% of the area. About 40% of California state waters are in some kind of MPA, while 13.4% of state waters have a high level of protection from fishing impacts. In federal waters off California, under one percent are in no-take areas while nearly all waters are subject to some kind of fishery restriction. Capturing regulatory information at the individual MPA and MMA level will improve assessments of current protection, inform planning of new protections, and provide ocean users a more accessible way to increase compliance through awareness.

Impact of Spatial Management on Nontarget Species in an Oceanic Penaeid Trawl Fishery

AbstractTrawling is generally an unselective fishing method that is employed to harvest a number of species. Capture of nontarget species that are subsequently discarded is an important issue for trawl fisheries, especially penaeid trawl fisheries. While gear modifications are a common approach to manage this issue, maintaining areas that are closed to trawling may also have a positive impact on these nontarget species. This study systematically examined the diversity and abundance of nontarget species across a network of areas closed to trawling (trawl closure areas) relative to adjacent areas that were open to trawling. Analysis of nontarget species from 209 trawls and 72,787 animals (across 216 taxa) revealed some impact on both abundance and diversity within trawl closure areas. Latitude was a key variable that was driving differences in the taxonomic assemblage among locations. Within locations, there were inconsistent impacts for different nontarget species in trawl closure areas. Length distributions showed size truncation of abundant nontarget species in fished areas relative to adjacent trawl closure areas. While the impact of trawl closure areas varied among species, it was clear that the spatial management in the fishery provided some refuge for a diversity of nontarget species, observed in patterns of species richness, abundance, and population size structure. Latitudinal breadth appears to be an essential component of the trawl closure network, but localized effects may be important for maintaining reproductive capacity for nontarget species. These data highlight the broader utility of trawl closure networks as a management tool for trawl fisheries.

Evaluation of adaptive spatial management in a multi-jurisdictional trawl fishery

Management of exploited resources that span multiple jurisdictions can be complex, with activities in one area potentially affecting productivity in another. Consequently, management decisions need to consider implications across the entire area in which the resource occurs. The study presents a unique study design that examines the impact of spatial management across two jurisdictions in an Australian penaeid multi-jurisdictional trawl fishery. Specifically, two areas relevant to Eastern King Prawn (Penaeus [Melicertus] plebejus; EKP, an important penaeid species harvested across eastern Australia) that are closed to trawling (on a permanent, and temporary basis) were evaluated using a combination of trawl and tag-recapture surveys. Over 1,250 EKP were tagged and released across the permanent and temporary trawl closure, and ∼15.4% of all tagged prawns were recaptured and reported by fishers in both New South Wales (33% of recaptures) and the adjacent jurisdiction of Queensland (67% of recaptures, up to 730 km from the point of tagging) during 7 months post-tagging. There were significant differences in prawn size and abundance across the permanent and temporary trawl closure areas with both depth and distance to the adjacent estuarine nursery explaining these patterns, but prawns generally exceeded the minimum size-at-first-capture estimated by relevant yield per recruit models before they left areas closed to trawling. While more prawns were captured in Queensland, recapture rates were far greater in New South Wales when standardised by relative effort. Patterns in these data highlight the broader considerations of spatial management in multi-jurisdictional fisheries.

Biology and fisheries of the spotted flounder (Citharus linguatula) caught by multiple gears with partial spatiotemporal overlaps

Obtaining data to study fish biology can be a challenge if a stock is fished by a variety of gears with different effort units and different selectivity, particularly if these gears only partially overlap in space and time. In this work, we attempted to study the biology of the spotted flounder Citharus linguatula in the Patraikos Gulf and the adjacent central Ionian Sea (eastern Mediterranean) and to evaluate the current fisheries management. We characterized age composition and growth, length-at-maturity, and catch-per-unit-effort (CPUE) of spotted flounder from the catches of bottom trawls, gillnets and trammel nets for the period autumn 2013–2014. Variation of fish total length, gonadosomatic index, hepatosomatic index and condition factor was analyzed using generalized additive models (GAMs) with regard to sex, date, fishing gear and depth. We also modeled CPUE fluctuations of each gear by date, depth, longitude and latitude using GAMs. Fish age ranged from 1 to 5 years. A slightly allometric growth was documented with females attaining larger sizes than males. Length-at-maturity was 163 mm for females and 169 mm for males. The seasonal change of gonad maturity stages and the gonadosomatic index indicated spawning in late summer-autumn. Changes in length frequencies indicated that recruitment to the fisheries occurred in late spring-early winter in shallow depth (<40 m). The catch composition of trawls and the CPUE model results suggested that the selectivity of this gear should be regulated to reduce catching immature individuals of spotted flounder. The results further indicated that the seasonal trawl closure of the Patraikos Gulf contributes to reduce catching juveniles.

Predicted deep-sea coral habitat suitability for the U.S. West coast.

Regional scale habitat suitability models provide finer scale resolution and more focused predictions of where organisms may occur. Previous modelling approaches have focused primarily on local and/or global scales, while regional scale models have been relatively few. In this study, regional scale predictive habitat models are presented for deep-sea corals for the U.S. West Coast (California, Oregon and Washington). Model results are intended to aid in future research or mapping efforts and to assess potential coral habitat suitability both within and outside existing bottom trawl closures (i.e. Essential Fish Habitat (EFH)) and identify suitable habitat within U.S. National Marine Sanctuaries (NMS). Deep-sea coral habitat suitability was modelled at 500 m×500 m spatial resolution using a range of physical, chemical and environmental variables known or thought to influence the distribution of deep-sea corals. Using a spatial partitioning cross-validation approach, maximum entropy models identified slope, temperature, salinity and depth as important predictors for most deep-sea coral taxa. Large areas of highly suitable deep-sea coral habitat were predicted both within and outside of existing bottom trawl closures and NMS boundaries. Predicted habitat suitability over regional scales are not currently able to identify coral areas with pin point accuracy and probably overpredict actual coral distribution due to model limitations and unincorporated variables (i.e. data on distribution of hard substrate) that are known to limit their distribution. Predicted habitat results should be used in conjunction with multibeam bathymetry, geological mapping and other tools to guide future research efforts to areas with the highest probability of harboring deep-sea corals. Field validation of predicted habitat is needed to quantify model accuracy, particularly in areas that have not been sampled.

Evaluation of New Zealand's high-seas bottom trawl closures using predictive habitat models and quantitative risk assessment.

United Nations General Assembly Resolution 61/105 on sustainable fisheries (UNGA 2007) establishes three difficult questions for participants in high-seas bottom fisheries to answer: 1) Where are vulnerable marine systems (VMEs) likely to occur?; 2) What is the likelihood of fisheries interaction with these VMEs?; and 3) What might qualify as adequate conservation and management measures to prevent significant adverse impacts? This paper develops an approach to answering these questions for bottom trawling activities in the Convention Area of the South Pacific Regional Fisheries Management Organisation (SPRFMO) within a quantitative risk assessment and cost : benefit analysis framework. The predicted distribution of deep-sea corals from habitat suitability models is used to answer the first question. Distribution of historical bottom trawl effort is used to answer the second, with estimates of seabed areas swept by bottom trawlers being used to develop discounting factors for reduced biodiversity in previously fished areas. These are used in a quantitative ecological risk assessment approach to guide spatial protection planning to address the third question. The coral VME likelihood (average, discounted, predicted coral habitat suitability) of existing spatial closures implemented by New Zealand within the SPRFMO area is evaluated. Historical catch is used as a measure of cost to industry in a cost : benefit analysis of alternative spatial closure scenarios. Results indicate that current closures within the New Zealand SPRFMO area bottom trawl footprint are suboptimal for protection of VMEs. Examples of alternative trawl closure scenarios are provided to illustrate how the approach could be used to optimise protection of VMEs under chosen management objectives, balancing protection of VMEs against economic loss to commercial fishers from closure of historically fished areas.

Using distribution patterns of small fishes to assess small fish by‐catch in tropical shrimp trawl fisheries

AbstractEcologically sound fisheries management and improving future food security require that small fish by‐catch in tropical shrimp trawl fisheries is maintained at, or reduced to, sustainable levels; restricting trawling in particular places, or at particular times, has been suggested as a means for achieving this goal. The purpose of our research was to compare patterns in occurrence, density and body size across depth, latitude and time for four small fish taxa caught as by‐catch in the southern Gulf of California shrimp trawl fishery: Diplectrum spp., Prionotus stephanophrys, Pseudupeneus grandisquamis and Stellifer illecebrosus. We then used these results to explore the potential for trawler impacts on these taxa, and the possible placement and timing of fishing restrictions to mitigate potential impacts. Our results confirmed, however, the difficulties of regulating such fisheries for multiple by‐catch species, in that their distribution patterns varied in a way that precludes a ‘one size fits all’ solution. The four taxa analysed – only four of the hundreds obtained as by‐catch in this fishery – exhibited distribution patterns at odds with one another. Observed intra‐ and inter‐taxon variations in the relative importance of different spatial and temporal variables in determining occurrence, density and size argues that several permanent trawl closures covering a range of depths and latitudes, and not temporal ones, might be required to mitigate potential trawl impacts on these fishes. Our results also suggested a higher potential for impact on S. illecebrosus than the other taxa: occurrence and density of the former declined, whereas occurrence or density of the others increased across the study area as the fishing season progressed.

A Transactional and Collaborative Approach to Reducing Effects of Bottom Trawling

Private-sector financial and legal transactions have long been used to protect terrestrial habitats and working landscapes, but less commonly to address critical threats in marine environments. Transferrable and marketable fishing privileges, including permits and quotas, make it possible to use private-sector transactions as conservation strategies to address some fishery management issues. Abating the effects of bottom trawling on the seafloor and bycatch and discard associated with the practice has proven challenging. On the Central Coast of California, The Nature Conservancy (TNC), Environmental Defense Fund, local fishers and local, state, and federal authorities worked collaboratively to protect large areas of the seafloor from bottom trawling for groundfish while addressing economic impacts of trawl closures. Contingent on the adoption of trawl-closure areas by a federal regulatory agency, TNC used private funds to purchase federal groundfish trawl permits and vessels from willing sellers. Trawl-closure areas were designed collaboratively by combining regional biological diversity and fisheries data with local fishers' knowledge. The private transactional strategy was designed to remedy some deficiencies in previous federal buyouts, to mitigate economic impacts from trawl closures, and to carefully align with a public regulatory process to protect "essential fish habitat" under the Magnuson-Stevens Fishery Conservation and Management Act. This collaborative effort protected 1.5 million ha (3.8 million acres) of seafloor, reduced trawl effort in the area by 50%, and set a precedent for collaborative partnerships between conservation and fishing interests. This is the first time a large conservation organization has taken an ownership position in a fishery and demonstrates how nongovernmental organizations can invest in fisheries to improve environmental and economic performance.

Trawl fisheries, catch shares and the protection of benthic marine ecosystems: Has ownership generated incentives for seafloor stewardship?

Abstract Proponents of catch share-based fisheries have claimed ecological stewardship can result from the assignment of individual catch quotas. This claim is examined by analyzing the distribution of benthic habitat protection measures adopted by quota-owning industry sectors within the exclusive economic zones (EEZs) of the U.S. (Alaska), New Zealand, and high seas seamounts within the Southern Indian Ocean Deepsea Fishers Association (SIODFA) competence area. Results suggest the protection of both benthic ecosystems and essential fish habitat (EFH) are marginal at best when quota owners have primacy in determining the boundaries of bottom trawl closures. The majority of the areas in these three regions that are closed to trawling are too deep to fish, may not contain vulnerable marine ecosystems, and do not have high abundances of commercially important species. “Freezing the footprint” of bottom trawling is not the best method for benthic habitat protection in areas where the fishing industry is actively fishing vulnerable habitats. Analytical methods should be applied to help determine boundaries of future bottom trawl closures rather than allowing the fishing industry to place benthic protection areas (BPAs) in areas where they are not interested in fishing.

Impact of Depth and Season on the Demersal Trawl Discard

Given that the discard has crucial impact on the coastal ecosystems, various countries around the world adopted various regulations to reduce the discard of non-commercial and undersized commercial species in the trawl catch, such as trawl exclusion depths and closed season. In this work discarded part of the catch of a trawl has been assessed to evaluate impact of depth and season. Monthly trawl-survey data, collected by the same research vessel operating all year round over the entire depth ranges of the same fishing ground, were used in order to minimize the sources of variation. By this mean, potential rather than absolute composition and quantity discarded by a trawl boat were estimated regardless of fishing regulations applied to the fleet. A generalized additive model was used to model the quantity of discarded catch as a function of depth and time. The model outputs were then used to quantify the impact of fishing regulations on the reduction in discard. The results suggested that the quantity of the catch returned to the sea is reduced 49% by trawl closure and 57% by trawling depth limitations. Overall, season and depth regulations reduce the discard by 77% at the expense of a 73% reduction in marketable catch. Finally, past trawl-survey data collected in the 1980s at the same site with the same research vessel and with the same net were used to evaluate possible impacts of regulations on the modification of fish composition

Advice in spite of great uncertainty: assessing and addressing bycatch of small fishes with limited data using Stellifer illecebrosus as a case study

ABSTRACT Tropical shrimp trawlers mostly catch small fish species as bycatch, and commitments to ecosystem‐based management and food supply demand adjustment of such bycatch to sustainable levels. Pragmatic ways to assess and address the impact of nonselective fishing practices on small fishes need to be found, especially given the limited knowledge of their life histories, population dynamics, and ecology. The use of matrix models for understanding and mitigating such impacts is explored using a small fish, Stellifer illecebrosus (silver stardrum) in the southern Gulf of California, Mexico, as a case study. A deterministic matrix model, populated with vital rates generated through six months of fisheries‐dependent sampling, was used to estimate the rate of population growth for the species, conduct elasticity analyses to see which vital rates have greatest relative effects on population growth, test the sensitivity of model outcomes to uncertainties in life history parameters, mortality rates and the number of age classes modelled, and explore potential mitigation tools. Despite great uncertainty regarding the impact of industrial shrimp trawling on S. illecebrosus, principally due to uncertainty in mortality rates but also in other life history parameters, the matrix model was still useful in indicating that any precautionary management should focus on increasing the survival of younger age classes. This could be achieved with trawl closures where smaller fish live. The study demonstrates the importance of understanding age‐based changes in vital rates to the predictions of matrix models; estimated population growth rates were most uncertain when all mature individuals were assumed to contribute equally to recruitment. But nevertheless, the study supports claims that deterministic matrix models may be useful for conservation and management where life history parameters can only be estimated crudely. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Ecological Meltdown in the Firth of Clyde, Scotland: Two Centuries of Change in a Coastal Marine Ecosystem

BackgroundThe Firth of Clyde is a large inlet of the sea that extends over 100 km into Scotland's west coast.MethodsWe compiled detailed fisheries landings data for this area and combined them with historical accounts to build a picture of change due to fishing activity over the last 200 years.FindingsIn the early 19th century, prior to the onset of industrial fishing, the Firth of Clyde supported diverse and productive fisheries for species such as herring (Clupea harengus, Clupeidae), cod (Gadus morhua, Gadidae), haddock (Melanogrammus aeglefinus, Gadidae), turbot (Psetta maxima, Scophthalmidae) and flounder (Platichthys flesus, Pleuronectidae). The 19th century saw increased demand for fish, which encouraged more indiscriminate methods of fishing such as bottom trawling. During the 1880s, fish landings began to decline, and upon the recommendation of local fishers and scientists, the Firth of Clyde was closed to large trawling vessels in 1889. This closure remained in place until 1962 when bottom trawling for Norway lobster (Nephrops norvegicus, Nephropidae) was approved in areas more than three nautical miles from the coast. During the 1960s and 1970s, landings of bottomfish increased as trawling intensified. The trawl closure within three nautical miles of the coast was repealed in 1984 under pressure from the industry. Thereafter, bottomfish landings went into terminal decline, with all species collapsing to zero or near zero landings by the early 21st century. Herring fisheries collapsed in the 1970s as more efficient mid-water trawls and fish finders were introduced, while a fishery for mid-water saithe (Pollachius virens, Gadidae) underwent a boom and bust shortly after discovery in the late 1960s. The only commercial fisheries that remain today are for Nephrops and scallops (Pecten maximus, Pectinidae).SignificanceThe Firth of Clyde is a marine ecosystem nearing the endpoint of overfishing, a time when no species remain that are capable of sustaining commercial catches. The evidence suggests that trawl closures helped maintain productive fisheries through the mid-20th century, and their reopening precipitated collapse of bottomfish stocks. We argue that continued intensive bottom trawling for Nephrops with fine mesh nets will prevent the recovery of other species. This once diverse and highly productive environment will only be restored if trawl closures or other protected areas are re-introduced. The Firth of Clyde represents at a small scale a process that is occurring ocean-wide today, and its experience serves as a warning to others.

Modeling the effects of fishery management and marine protected areas on the Beibu Gulf using spatial ecosystem simulation

The Gulf of Beibu, recognized as one of the traditional fishing grounds, is a center of rich biodiversity in the northern South China Sea. Based on the Beibu Gulf ecosystem constructed by the Ecopath and Ecosim model (in the late 1990s), we used Ecospace to evaluate the existing fishery management system and assess the potential of marine protected areas (MPAs) in the Beibu Gulf over a short (5-year), medium (10-year), and long-term (20-year) scenario. The results suggest that the current trawl closure and the midsummer moratorium system used in the Gulf fishery management approach appear to offer minimal benefits for stock recovery because of the high implementation and administrative costs; also, the biomass of valuable groups would decrease drastically with simulation time, and the large predator groups, such as the large demersal and pelagic fishes, would even be reduced to depletion in the long-term (20-year) simulation. Simulations of MPAs indicate that outcomes beneficial to all are possible but not guaranteed. Both ‘no-take’ MPAs, inshore closures (<30-m isobath) and offshore closures (common fishing zone) can drastically reduce fishing effort (between 20% and 30% reduction from 1999 levels), achieving much to avert the collapse of the fishery sector, especially for large-sized, high-value species. The magnitude of the biomass and the catches would obviously increase with simulation time. In a 20-year simulation, the total catches of all fishing gears would be doubled in the inshore closure simulation compared with that of offshore closure simulation with biomass recovery. The results suggest that, for purposes of fishery management in the Gulf, the inshore area within the 30-m isobath should be considered as ‘no-take’ MPAs; this may be an effective management tactic to conserve the ecosystem and to stop the decline in fisheries resources. Considering the complexity of ecosystem-based fishery management, an extension of the current work will incorporate the costs associated with restoration and monitoring efforts as well.