Antonello Sala

Efficiency of the bottom trawl used for the Mediterranean international trawl survey (MEDITS)

Abstract The aim of the work presented in this paper was to assess the relative efficiency of the GOC 73 sampling trawl used for the Mediterranean international trawl survey programme (MEDITS) compared with that of a typical Italian commercial trawl. The latter was chosen because it is commonly used by fishermen in the central Adriatic, where the experiment was conducted, and therefore appeared as the best possible sampler of the commercial species present in those areas. Moreover, this trawl is similar to the various trawls used for the Italian national survey programme (GRUND). Four fishing trips were conducted between 1996 and 1997 in different areas and seasons to sample different species. Each trip was conducted in the same fishing area. A codend cover mounted on the commercial trawl ensured that the codends of the two nets had the same mesh opening. The two trawls were alternated daily. Net geometry (horizontal and vertical net opening) was measured during all tows. Catch data were converted into abundance per swept area before comparing the trawls. Efficiency comparisons were performed on ten fish species, one crustacean and four molluscs belonging to the MEDITS list of main reference species. The MEDITS trawl was significantly less efficient in terms of both weight and numbers of individuals fished for hake (Merluccius merluccius), common sole (Solea vulgaris) and Norway lobster (Nephrops norvegicus). A highly significant difference in favour of the commercial trawl was found in the weight, but not the numbers, of common pandora (Pagellus erythrinus). Efficiency differences were negligible for red mullet (Mullus barbatus), while the MEDITS trawl was significantly more efficient for the numbers of Atlantic horse mackerel (Trachurus trachurus). For all the other main reference species differences were not significant. The commercial trawl was more efficient for large individuals of some species. The relative efficiency of the MEDITS trawl was especially low for small-size classes of N. norvegicus. The results confirm the lower efficiency of the MEDITS compared with the commercial Italian trawl for benthic species, and its greater efficiency for some others released from the bottom as well as for the pelagic ones. These data allow the results of the MEDITS surveys to be compared with those of the GRUND programme and with commercial-fleet catches in areas where the commercial trawls used are similar to the one studied here.

The footprint of bottom trawling in European waters: distribution, intensity, and seabed integrity

Mapping trawling pressure on the benthic habitats is needed as background to support an ecosystem approach to fisheries management (EAFM). The extent and intensity of bottom trawling on the European continental shelf (0–1000 m) was analyzed from logbook statistics and VMS data for 2010, 2011 and 2012 at a resolution of 1×1 minutes longitude and latitude. Trawling intensity profiles with seabed impact at the surface and subsurface level are presented for 14 management areas in the North-east Atlantic, Baltic Sea and Mediterranean Sea. The footprint (proportion of the seabed trawled 1 or more times every ten years) ranged between 40–90% across EUNIS habitats with largest footprints observed in sandy (A5.2) and muddy (A5.3) habitats. The footprint of the management areas ranged between 52-99% and 5-94% for the depth zone from 0–200 m (Shallow) and from 201–1000 m (Deep), respectively. The footprint was estimated as the total area of all grid cells that were trawled fully or partially. Excluding these untrawled proportions reduced the footprint estimates to 28-85% and 2-77%. Mean trawling intensity ranged between 0.5 and almost 8.5 times per year, but was less in the Deep zone with a maximum intensity of 6.4 times per year. Highest intensities were recorded in the Skagerrak–Kattegat and Adriatic Sea. Largest footprints per unit landings were observed in the Mediterranean Sea. Bottom trawling was highly aggregated. The seabed area where 90% of the effort occurred comprised between 11% and 65% (median 44%) of the total area trawled. Using the longevity distribution of the untrawled infaunal community, the seabed integrity was estimated as the proportion of the biomass of benthic taxa where the trawling interval at the subsurface level exceeds their life span. Seabed integrity was low (<0.1) in large parts of the European continental shelfs, although smaller pockets of seabed with higher integrity values occur. The methods developed here integrate official fishing effort statistics and industry-based gear information to provide high-resolution pressure maps and indicators, which greatly improve the basis for assessing and managing benthic pressure from bottom trawling. Further they provide quantitative estimates of trawling impact on a continuous scale by which managers can steer.

Old Info for a New Fisheries Policy: Discard Ratios and Lengths at Discarding in EU Mediterranean Bottom Trawl Fisheries

Discarding is considered globally among the most important issues for fisheries management. The recent reform of the Common Fisheries Policy establishes a landing obligation for the species which are subject to catch limits and, in the Mediterranean, for species which are subject to Minimum Conservation Reference Size (MCRS) as defined in Annex III to Regulation (EC) No 1967/2006. Additionally, several other initiatives aim to reduce unwanted catches of target and bycatch species, including species of conservation concern. This raises the need to study discarding patterns of (mainly) these species. In this work we collated a considerable amount of historical published information on discard ratios and lengths at discarding for species caught in EU Mediterranean bottom trawl fisheries. The main aim was to summarize the available historical records and make them more accessible for scientific and managerial needs, as well as to try identifying patterns in discarding. We show discard ratios and lengths at which 50% of the individuals were discarded (L50) for 15 species (nine bony fishes, three crustacean decapods and three elasmobranchs). Discard ratios were usually low for target species such as hake, red mullets and highly commercial shrimps and exemptions from the landing obligation under the de minimis rules could be sought in several cases. Discard ratios were usually higher for commercial bycatch species. Discarding is affected by a combination of factors and for a given species, especially for non-target ones, discards are likely to fluctuate within a fishery, across seasons, years and regions. For most species considered, L50s were lower than the MCRS (when in place) and length at first maturity. L50s of target species, such as hake, were very small due to the existence of market demands for small sized individuals. However, for species of low demand, like horse mackerels, a higher retention size was observed, often exceeding MCRS. Lengths at discarding are affected by legal provisions, market demands but also by biological, population and ecological traits. Understanding the factors that affect discarding constitutes the starting point for designing mitigation measures and management plans to reduce discards and improve the sustainability of the stocks.

Assessment of the Relative Catch Performance of a Surrounding Net without the Purse Line as an Alternative to a Traditional Boat Seine in Small-Scale Fisheries

Abstract The catch performance of a traditional Ligurian boat seine, which is not in line with the European Union regulation, was compared with an experimental surrounding net without the purse line as a potential legal alternative. The relative catch performance between the two gear types was assessed using a new catch comparison method requiring neither paired data collection nor equal number of hauls with the two gears. The comparison was based on the catches of the three species that comprise the bulk of the catch in traditional Ligurian boat seine fisheries: Bogue Boops boops, Saddle Bream Oblada melanura, and Blotched Picarel Spicara maena. The experimental gear exhibited poor catch efficiency for all three species, since it was estimated that the catches would only be 2, 64, and 6%, respectively, of those with the boat seine. For both Bogue and Blotched Picarel these reductions in catch performance were found to be highly significant proving that the experimental surrounding net is not a viable solution to replace the traditional boat seine.

Effect of Codend Circumference on the Size Selection of Square-Mesh Codends in Trawl Fisheries

It is well established that increasing mesh number in the circumference of a diamond-mesh trawl codend can reduce size selection for round fish, whereas selection for flat fish species is unaffected. This effect has also been documented in Mediterranean trawl fisheries. In contrast, no information is available with regard to the effect of increasing mesh number in the circumference of square-mesh codends on the size selection of round fish and flat fish species. A field study was devised to bridge this gap and formulate proposals aimed at improving trawl fishery management. Size selection data were collected for a round fish species, red mullet (Mullus barbatus), and two flat fish species, Mediterranean scaldfish (Arnoglossus laterna) and solenette (Buglossidium luteum). Fishing trials were conducted in the Adriatic Sea (Central Mediterranean) using three square-mesh codends that differed only in mesh number around the circumference. Results demonstrated that increasing the number of meshes from 107 to 213 reduced the 50% retention length (L50) for red mullet by 2.5 cm but did not affect size selection for the two flat fish species. In some fisheries, regulatory provisions regarding the number of meshes in the circumference should therefore be carefully considered both for diamond- and square-mesh codends.

A Bond Graph Approach to Improve the Energy Efficiency of Ships

High fuel consumption coupled with increasing fuel prices, emission regulations and increasing concern about the environment, act as incentives to reduce the energy consumption of ships. However, different barriers hinder the adoption of cost-effective energy saving measures by ship owners and operators. These barriers are the reason for the existence of an ‘energy efficiency gap’ between the current level of energy efficiency and the potential for development of higher order efficiency. Imperfect information regarding the current level of energy consumption of vessels, availability and application of energy saving measures, and the impact of adopting these measures, form a group of so called ‘information barriers’.The main objective of this article is to reduce those information barriers, as faced in shipping and more specifically in the fishing sector. The bond graph methodology is presented as a potential solution to these issues. It is utilized as a modeling and simulation method by which to visualize energy flow in a fishing vessel. The bond graph method is employed to estimate the fuel consumption of the vessel under different operational conditions: steaming, trawling and hauling of the fishing gear. It is also applied in pinpointing the major energy consuming apparatuses onboard the vessel. In this way knowledge regarding the current levels of energy consumption can be increased. The main energy consumers can then be studied to further improve energy efficiency knowledge and subsequently reduce the energy efficiency gap of the fishing vessel. Finally, the effectiveness of implementing a slow steaming strategy as a possible energy saving mechanism is studied.Copyright

How many fish need to be measured to effectively evaluate trawl selectivity

The aim of this study was to provide practitioners working with trawl selectivity with general and easily understandable guidelines regarding the fish sampling effort necessary during sea trials. In particular, we focused on how many fish would need to be caught and length measured in a trawl haul in order to assess the selectivity parameters of the trawl at a designated uncertainty level. We also investigated the dependency of this uncertainty level on the experimental method used to collect data and on the potential effects of factors such as the size structure in the catch relative to the size selection of the gear. We based this study on simulated data created from two different fisheries: the Barents Sea cod (Gadus morhua) trawl fishery and the Mediterranean Sea multispecies trawl fishery represented by red mullet (Mullus barbatus). We used these two completely different fisheries to obtain results that can be used as general guidelines for other fisheries. We found that the uncertainty in the selection parameters decreased with increasing number of fish measured and that this relationship could be described by a power model. The sampling effort needed to achieve a specific uncertainty level for the selection parameters was always lower for the covered codend method compared to the paired-gear method. In many cases, the number of fish that would need to be measured to maintain a specific uncertainty level was around 10 times higher for the paired-gear method than for the covered codend method. The trends observed for the effect of sampling effort in the two fishery cases investigated were similar; therefore the guidelines presented herein should be applicable to other fisheries.

Herring supports Northeast Pacific predators and fisheries: Insights from ecosystem modelling and management strategy evaluation

This paper analyzes the trophic role of Pacific herring, the potential consequences of its depletion, and the impacts of alternative herring fishing strategies on a Northeast Pacific food web in relation to precautionary, ecosystem-based management. We used an Ecopath with Ecosim ecosystem model parameterized for northern British Columbia (Canada), employing Ecosim to simulate ecosystem effects of herring stock collapse. The ecological impacts of various herring fishing strategies were investigated with a Management Strategy Evaluation algorithm within Ecosim, accounting for variability in climatic drivers and stock assessment errors. Ecosim results suggest that herring stock collapse would have cascading impacts on much of the pelagic food web. Management Strategy Evaluation results indicate that herring and their predators suffer moderate impacts from the existing British Columbia harvest control rule, although more precautionary management strategies could substantially reduce these impacts. The non-capture spawn-on-kelp fishery, traditionally practiced by many British Columbia and Alaska indigenous peoples, apparently has extremely limited ecological impacts. Our simulations also suggest that adopting a maximum sustainable yield management strategy in Northeast Pacific herring fisheries could generate strong, cascading food web effects. Furthermore, climate shifts, especially when combined with herring stock assessment errors, could strongly reduce the biomasses and resilience of herring and its predators. By clarifying the trophic role of Pacific herring, this study aims to facilitate precautionary fisheries management via evaluation of alternative fishing strategies, and thereby to inform policy tradeoffs among multiple ecological and socioeconomic factors.

Preliminary design of the hybrid propulsion architecture for the research vessel “G. Dallaporta”

This paper presents energy and power evaluations on propulsion and generation systems related to a research vessel, named G. DALLAPORTA. This vessel is used by the National Research Council of Italy for oceanographic campaigns, which are generally carried out in the Mediterranean Sea. The analysis is based on measurements of the main electrical and mechanical parameters, related to on board propulsion, oleodynamic and electric auxiliary systems, with reference to the original thermal configuration of the ship. These preliminary results, obtained through theoretical methodology, make possible the identification of a designing procedure for the hybridization of this vessel, in order to respect the international marine standards, in terms of emissions and safety procedures.

Bottom trawl fishing footprints on the world’s continental shelves

Significance We conducted a systematic, high-resolution analysis of bottom trawl fishing footprints for 24 regions on continental shelves and slopes of five continents and New Zealand. The proportion of seabed trawled varied >200-fold among regions (from 0.4 to 80.7% of area to a depth of 1,000 m). Within 18 regions, more than two-thirds of seabed area remained untrawled during study periods of 2–6 years. Relationships between metrics of total trawling activity and footprint were strong and positive, providing a method to estimate trawling footprints for regions where high-resolution data are not available. Trawling footprints were generally smaller in regions where fisheries met targets for exploitation rates, implying collateral environmental benefits of effective fisheries management. Bottom trawlers land around 19 million tons of fish and invertebrates annually, almost one-quarter of wild marine landings. The extent of bottom trawling footprint (seabed area trawled at least once in a specified region and time period) is often contested but poorly described. We quantify footprints using high-resolution satellite vessel monitoring system (VMS) and logbook data on 24 continental shelves and slopes to 1,000-m depth over at least 2 years. Trawling footprint varied markedly among regions: from <10% of seabed area in Australian and New Zealand waters, the Aleutian Islands, East Bering Sea, South Chile, and Gulf of Alaska to >50% in some European seas. Overall, 14% of the 7.8 million-km2 study area was trawled, and 86% was not trawled. Trawling activity was aggregated; the most intensively trawled areas accounting for 90% of activity comprised 77% of footprint on average. Regional swept area ratio (SAR; ratio of total swept area trawled annually to total area of region, a metric of trawling intensity) and footprint area were related, providing an approach to estimate regional trawling footprints when high-resolution spatial data are unavailable. If SAR was ≤0.1, as in 8 of 24 regions, there was >95% probability that >90% of seabed was not trawled. If SAR was 7.9, equal to the highest SAR recorded, there was >95% probability that >70% of seabed was trawled. Footprints were smaller and SAR was ≤0.25 in regions where fishing rates consistently met international sustainability benchmarks for fish stocks, implying collateral environmental benefits from sustainable fishing.