Unwanted Catches Research Articles

Estimating purse seine volume during capture: implications for fish densities and survival of released unwanted catches

Abstract High fish densities negatively impact catch welfare and the survival of unwanted catches released from purse seines. To avoid overcrowding fish before being released, regulations have been implemented in the Northeast Atlantic mackerel and herring fisheries that limit the proportion of the seine that can be retrieved before catches are released. However, it is yet unknown how seine volume, and thus fish density, relates to proportion of seine retrieved. In this study, we have estimated the in-water volume of purse seines used in the Norwegian mackerel and herring fisheries as a function of proportion seine hauled and seine size. Purse seine geometry was monitored with multibeam sonar at sea and a log-linear mixed effects model was applied to the estimated seine volumes. The results indicate a 33-fold decrease in contained volume from 10 to 80% seine hauled and a threefold difference in volume between the largest and smallest measured seines. Fish densities in the seine were predicted to vary greatly depending on seine and catch size and under some conditions exceed safe crowding levels before the catch release limit is reached. This study questions the rationale of having the same catch release limit for all seine and catch sizes.

“Crash landing” obligation for Mediterranean mixed fisheries: Evaluation of management strategies using bioeconomic modelling in the Aegean Sea

Minimizing unwanted catches is a major milestone for achieving sustainable fisheries. In the framework of the Common Fisheries Policy, a landing obligation is being established progressively in European waters (Article 15, EU Regulation 1380/2013). Supplementary management measures have been proposed to support and enhance the effectiveness of this new regime. In this context, the effect of the landing obligation on a demersal mixed fishery (coastal and trawl fleet) in the Aegean Sea (NE Mediterranean Sea) was assessed in terms of both biological and economic sustainability. Our results show that the landing obligation alone does not ensure sustainable fisheries. Management action should be directed to the introduction of additional measures. Evidence suggests that improving selectivity and protecting the nursery grounds are possible solutions to decrease discards and ensure sustainable fisheries in the long term. The landing obligation can have a role in incentivizing the adoption of these management measures that ensure lower fishing mortality on juvenile fish.

Use of avoidance behaviours to reduce the economic impacts of the EU Landing Obligation: the case study of a mixed trawl fishery

Abstract The EU Landing Obligation (LO) is designed to reduce bycatch (i.e. unwanted catch) through more selective fishing practices, such as avoidance behaviours which consist in allocating fishing effort to other species, fishing grounds or seasons. Incentives for fishers to change their behaviours depend on their economic performances as well as their ability to avoid bycatch. Changes in economic performances under the LO are evaluated based on cost and revenue equations. The nested grid method is then used to explore the spatial and temporal distribution of landings and discards, and to suggest alternative effort allocation to avoid bycatch. This article is focussed specifically on the French otter trawl fishery in the eastern English Channel and southern North Sea. Results suggest that under the LO the choke species problem will curtail fishing activities earlier in the year, leading to significant economic losses. In the absence of significant quota top-ups (at least 75%), a change in fishing practices consisting in reducing overall bycatch by 30% is insufficient to reduce losses. With a particular attention to choke species, more economically efficient avoidance strategies can be found thanks to the nested grid method.

Discarding in Mediterranean trawl fisheries—a review of potential measures and stakeholder insights

The multi-species/multi-gear nature of the Mediterranean fisheries, the high number and dispersion of landing points, and the varying motivations for discarding make regulation enforcement in the basin challenging. In this study, reasons for explaining discarding are initially explored and then the main focus is on identifying potential incentive mechanisms and other measures that could reduce unwanted catches in Mediterranean trawl fisheries, in the face of the recent landing obligation. Both literature review and stakeholder engagement are employed, while special emphasis is put on the role of socio-economic tools to influence fishers’ behavior. Results show that although discarding is mainly driven by market demand, a number of factors have a synergistic effect which is sometimes difficult to disentangle and capture. Regarding measures, evidence from involved stakeholders (marine scientists and fishers) shows that economic incentives but also “social measures” such as more involvement of the industry and raising awareness are offering common ground. However, specific concerns have been also expressed on measures applicability. Overall, reducing discards is a complex issue and solutions should involve a combination of management measures designed for specific fleets and regions. However, irrespective of the synthesis of the management options, it is important to create a framework of action that takes into account human behavior as a source of variability. In this context, actions that for example encourage, engage, and enable can incentivize behavioral change in order to achieve specific outcomes.

Refining a simple anterior fish excluder (SAFE) for penaeid trawls

Following recent international efforts to assess anterior modifications to trawls as a means for precluding unwanted catches, a promising device termed the ‘simple anterior fish excluder’ (SAFE) was modified for an Australian penaeid-trawl fishery. We tested a conventional penaeid trawl against those rigged with two SAFEs; each comprising a plastic banner located between the otter boards but orientated as either single- (original design) or double-concave configurations. Compared to the conventional trawl, both SAFEs caught significantly fewer absolute and standardised (ha–1 trawled) numbers of the most abundant non-target species, southern herring (Herklotsichthys castelnaui), although mean reductions were greater in the trawls with the double-concave (by 59 and 50%) than single-concave (44 and 36%) SAFE. Neither absolute nor standardised catches of the targeted school prawns (Metapenaeus macleayi) were affected. The results reiterate the generic utility of anterior modifications for reducing bycatch and maintaining function across different geometries. Configuring the SAFE as a double concave did partially improve its efficiency, but it also complicated fishing operations. Therefore, we conclude that owing to its simplicity, the single-concave design might be a preferable configuration for penaeid-trawl fisheries—pending assessments of other refinements.

Mitigating unwanted catches in the southern Iberian hake stock fisheries: Improving fishing technology vs market control policies

Unwanted catches can be reduced by improving fishing effectiveness in targeting species and sizes and by banning their sale for human consumption. The landing obligation introduced by the European Union can be seen as a combination of these two measures, and the aim of this paper is to analyse its effects on the Southern Iberian Hake Stock fishery. To this end, reference points for a mixed fishery are computed under the two measures as the steady-state solution of a dynamic optimal management problem. Our results show that measures that improve selectivity obtain better results than sales ban strategies in terms of increasing yields and stocks and reducing discards. In particular, we find that reducing the selectivity parameters by 90% for the three early ages leads to an almost six-fold increase in the hake yield and lowers the discard rate by more than 20 percentage points. Banning the sale of the two youngest ages also increases hake yield by 21% and the discard rate by 7 percentage points.

Linking trawl fleet dynamics and the spatial distribution of exploited species can help to avoid unwanted catches: the case of the NW Mediterranean fishing grounds

With the full implementation of the landing obligation on 1 January 2019, In European waters it will become mandatory for the trawling fleet to land at port all catches of certain species because, according to Article 15 of the new European Common Fisheries Policy, the species subject to the minimum conservation reference size (MCRS) cannot be discarded. Additionally, since 2005, trawlers over 15 m in length are required to carry an onboard vessel monitoring system (VMS), which generates information on fleet dynamics. The objective of this work was to provide a tool for avoiding unwanted catches by integrating the catch study of trawlers operating in the port of Blanes together with VMS data. To achieve this objective, the catches of 40 hauls were monitored, sampled and analysed together with VMS data for the years 2012-2014 integrated in a geographical information system. The results show that specimens below the MCRS were often captured in crinoid aggregation habitats, bottoms with maërl and muddy bottoms that were identified as nursery habitats of commercial species, e.g. Merluccius merluccius, Pagellus spp. and Mullus spp. VMS data showed considerable fishing pressure on areas with maërl and muddy habitats during the recruitment periods of these and other commercially relevant species. Implementing spatial or seasonal closures in habitats where species regulated by the MCRS are subject to catches could be a useful tool for preventing unwanted catches.

Reducing unwanted catches of trammel nets: experimental results of the “guarding net” in the caramote prawn, <em>Penaeus kerathurus</em>, small-scale fishery of the Ligurian Sea (western Mediterranean)

This study aimed to test the effectiveness of a “guarding net”, a device placed at the bottom of a trammel net, for reducing unwanted catches in the caramote prawn trammel net fishery of the Ligurian Sea. This specialized and profitable fishery is affected by unwanted catches that generate high discard rates and damage to the nets, with environmental impacts and costs for fishermen. The experimental study consisted in comparing the catches of a standard trammel net (STN) with those of two “experimental” trammel nets, e.g. STNs provided with a guarding net of 19 cm (TGN20) and 24 cm height (TGN25), respectively. The guarding net, a strip of gillnet placed at the bottom of the net, can be considered a by-catch reducer device (BRD). Some fishermen of the investigated fishery have been using this device for several years. The results of the 15 experimental fishing trials performed from June to July 2016 indicate that the guarding nets significantly reduce discards (e.g. crabs and other invertebrates); the biomass of the unwanted species caught was 75% lower than that produced by the STN. The catch rates of the target species obtained with TGN20 and TGN25 were also significantly lower than those of the STN, though of a lesser amount. Nonetheless, this economic loss can be compensated by the decrease in sorting time and material and labour costs that can be achieved using the guarding net.

Towards more selective Mediterranean trawl fisheries: are juveniles and trash excluder devices effective tools for reducing undersized catches?

Mediterranean trawl fisheries are characterized by a critical combination of high fishing effort and low size at first capture for most commercial species. In this study we tested the use of sorting grids installed on bottom trawl nets to minimize the catch of undersized deep-water rose shrimp (Parapenaeus longirostris, DPS) and European hake (Merluccius merluccius, HKE). The catch of a traditional trawl net was compared with that obtained with the same net equipped with ad hoc designed juveniles and trash excluder devices (JTEDs) during an experimental survey. Three different JTEDs were tested: the first (G1-SM40) was built with a net of 40-mm square mesh; the second (G2-ST20) and third (G3-ST25) with vertical steel bars spaced 20 and 25 mm, respectively. The probability of retaining DPS and HKE by length class in trawl nets with and without JTED was analysed using generalized additive mixed models. With G1-SM40, the reduction of undersized individuals in the cod-end was about 60% and 44% for DPS and HKE, respectively. With G2-ST20, a 34% catch decrease of HKE individuals smaller than 20 cm total length was observed. A loss of marketable fractions of DPS was recorded with G1-SM40 (–25%) and G2-ST20 (30%). Finally, JTD G3-ST25 was efficient at reducing the catch of undersized specimens of DPS and HKE, but showed a higher loss of marketable fractions than the other JTEDs. Although further fishing trials would be required to maximize the sorting efficiency of the grids, the results obtained clearly indicated that grids can substantially reduce unwanted catches of undersized DPS and HKE in Mediterranean bottom trawl fisheries.

Assessment of the relative catch performance of hake, red mullet and striped red mullet in a modified trawl extension with T90 netting

We studied the relative catch performance of a modified trawl fitted with an extension piece using a 90º turned mesh (T90) in comparison with a standard trawl net used in NW Mediterranean bottom trawl fisheries employing a diamond mesh net. The comparison was made by means of paired experimental hauls using the same fishing vessel with alternate deployments of the standard net (control) and the experimental net. We used the catch comparison approach for three target species of the fishery: European hake, red mullet and striped red mullet. Our results show that the experimental net significantly reduces the catches of small-size hake and red mullet (though there was no discernible difference for striped red mullet), reducing unwanted catches of regulated species under the Landings Obligation. The overall catch rates of hake, pooled over all sizes, also increased by an estimated 50%, while the catch rates of red mullet and striped red mullet were significantly lower. However, considering all commercial species, the experimental net produced losses of commercial catch and income estimated at 17% and 18%, respectively, which may pose a barrier to the adoption of this relatively simple, inexpensive solution.

Bioeconomic analysis of the effects of modifying the trawl extension piece with T90 netting

We assessed the effect of the European discards ban on the profitability of bottom trawlers in a case study fishery (GSA06, NW Mediterranean) in the transition period 2017-2018, when the species that characterize the fishery, viz. hake and red mullet, fall under the discards ban. We used the results of Sola and Maynou (2018) to simulate the adoption of a modified bottom trawl design using a T90 extension net to reduce the catches of undersize hake and red mullet. Our results show that the economic impact of the former discards brought to land on the fisheries operators is expected to be low, regardless of the possible commercial use of these unwanted catches. Furthermore, the adoption of a more selective bottom trawl design would increase the escape of undersize individuals and likely reduce fishing mortality of the target species, contributing to stock rebuilding and providing higher income to the fisheries operators in the medium to long term.

Quota exhaustion and discarding: how Ireland’s monthly quota system has a limited relationship with discarding patterns in the commercial fishing fleet

Abstract The Irish fishing fleet is subject to monthly quotas which are designed to ensure an equal share between vessels and to spread uptake throughout the year. This monthly quota system also allows us to study the links between discarding and quota exhaustion once a month rather than once a year, as would be the case in most other countries. The hypothesis that discards of cod, haddock, and whiting would increase through the month, as quotas were used up, was tested using observer data collected from commercial fishing vessels. Other than for whiting the results showed no relationship between discarding and day of the month. Instead gear type and target fishery were bigger drivers of discarding with restrictive quotas for cod and haddock resulting in consistent discarding of these species throughout the month. Improvements in gear selectivity may aid in reducing discards but due to the mixed nature of the fishery there is limited ability for vessels to reduce catches of these quota restricted species. Understanding how such a quota management system may influence fishing and discarding behaviour is important when developing management tools to assist in avoiding unwanted catch. This is especially important with the introduction of the Landing Obligation in EU fisheries.

Reducing unwanted catches of trammel nets: experimental results of the "guarding net" in the caramote prawn, Penaeus kerathurus, small-scale fishery of the Ligurian Sea (western Mediterranean)

Reducing unwanted catches of trammel nets: experimental results of the "guarding net" in the caramote prawn, Penaeus kerathurus, small-scale fishery of the Ligurian Sea (western Mediterranean)

Assessing ecological and fisheries implications of the EU landing obligation in Eastern Mediterranean

Discards are of primary target for the European Union policy and concerns have been expressed on the consequances that the landing obligation may have on the fisheries resources and other ecosystem components. In this context, we used an ecosystem modelling approach based on a previously constructed food web model for the Greek Ionian Sea to explore changes in food web components and fisheries due to the application of the landing obligation. Time series were also used to tune the trophic relationships during a hindcast period (1998–2014) and six scenarios were explored after 2015 simulating the current policy; a partial and a total discard ban (implemented after 2017) under both constant and decreasing fishing effort. Results indicated that, under constant fishing effort, changes in the management of unwanted catches (from discarding to landing them) had a significant consequences on certain functional groups, especially on marine birds which were even more adverse in the scenario tuned for the total discard ban. However, the new management practices seem pointless for the sustainability for most of the stocks, because there were no changes in the main commercial fish species apart from few exceptions (e.g. flatfish, deep water shrimps, continental shrimps) in which biomass changes were generally low. In contrast, simulations of declining fishing effort affected to higher extent more groups, whereas additionally representing changes in discarding policies had little effect. The model presented here is intended to shed light in the importance of discards in the food-web structure and subsequently to incentivize the practices to avoid producing discards in the first place.

Barotrauma and Successful Release of Fish Caught in Deep Water

If you catch a fish you are not going to keep, help it survive and get back to the deep! Throwing back your unwanted catch is good practice because healthy released fish can live to grow and reproduce, which benefits the fish population and the future of fisheries. But deepwater fish can have trouble getting back where they came from without a little assist from the angler. This 4-page fact sheet written by Betty Staugler, Holly Abeels, Angela Collins, Shelly Krueger, and Kai Lorenzen and published by the UF/IFAS Florida Sea Grant College Program describes barotrauma, a problem that, if left untreated, will kill otherwise perfectly healthy fish, and explains a few quick and simple methods to relieve fish suffering from barotrauma and help them get back home healthy and strong.https://edis.ifas.ufl.edu/sg160

The use of demersal trawling discards as a food source for two scavenging seabird species: a case study of an eastern Mediterranean oligotrophic marine ecosystem

BackgroundThe banning of fisheries discards by imposing an obligation to land unwanted catch constitutes a key point of the Common Fishery Policy reform proposed by the European Commission. The effect of such a ban on discards on top marine predators such as seabirds is largely unknown, especially in oligotrophic systems of the Mediterranean. The current study investigates the presence of scavenging seabirds around fishing trawlers as well as the exploitation of discards produced by bottom trawlers in the eastern Ionian Sea.MethodsOn-board observations were randomly conducted in May and December 2014, in order to record the presence and use of fishery discards by two common seabird species, namely, Scopoli’s Shearwater (Calonectris diomedea) and the Yellow-legged Gull (Larus michahellis).ResultsA total of 3400 seabirds were counted during May of which 2190 individuals were Scopoli’s Shearwaters and 1210 were Yellow-legged Gulls. The latter species was the only scavenger observed during winter and in total, 768 individuals were counted. Differences in species abundance in the study area are related to breeding phenology and migratory movements. The number of seabirds attending bottom trawler operations during morning and afternoon hours showed no significant differences for both seabird species. Both scavenging seabirds extensively exploited fishery discards, which were mainly demersal fish, and consumed 70–80% of the total fishery discards biomass; however, they appeared to avoid poisonous species and/or large-sized fish. Yellow-legged Gulls displayed kleptoparasitic behaviour on Scopoli’s Shearwater during feeding experiments. The number of such incidents depended on the number of gulls around the fishing vessel, with more than 90% success rates.ConclusionsConsidering the average annual biomass of discards estimations and the consumption rate found in this work, 106.1–117.9 t may be offered as a food subsidy to scavenging seabirds in the study area and should support a substantial part of local populations. Our results constitute baseline information on the annual amount of fishery discards and their exploitation rate by seabirds in the Ionian Sea, and suggest further work for a complete understanding of the potential impacts of the discards reform bill on seabirds.

Ecological and economic effects of the landing obligation evaluated using a quantitative ecosystem approach: a Mediterranean case study

Abstract The reformed Common Fisheries Policy [Regulation (EU) 1380/2013] introduces the obligation to land unwanted catches gradually from 2015 to 2019 with the aim to reduce discards. The ecological and economic consequences of this controversial regulation are evaluated here using an ecosystem model for the North-Eastern Adriatic Sea to quantify the long-term stocks’ biomass, landings, and fisheries revenues under future scenarios with and without landing obligation. Results indicate that landings will increase by +13%, causing an increase in fishermen workload, reduction of biomasses at sea (∼−0.20%) for species of both commercial and non-commercial interest, thus a small decrease in fisheries revenue (∼−0.50%). Selling landed unwanted catches for fishmeal production will not compensate the economic losses. Additional adaptation scenarios were tested: (i) introduction of quotas for small pelagics, (ii) reduction of effort for bottom trawlers, (iii) improvement of gear selectivity, and (iv) a combination of (i) and (iii). Improving selectivity and introducing quotas resulted the best alternative but none of the adaptation scenarios compensated the adverse effects of the landing obligation, suggesting that this management measure has ecological and economic negative effects in systems where fisheries are not regulated by quota such as the Mediterranean Sea.

A Review of the European Union Landing Obligation Focusing on Its Implications for Fisheries and the Environment

Discarding is a common practice in fisheries. Total discards are estimated to be about 30 million tons, representing around 23% of worldwide catches. Discarding is an undesirable practice, not only because of the waste of resources, but also because of its contribution to the overexploitation of fish stocks. Several countries have already established discard bans, to different extents (e.g., Norway, Iceland, Chile, New Zealand). The EU’s landing obligation (discard ban) is a major measure of the latest reform of the Common Fisheries Policy for EU fisheries. It aims to reduce unwanted catches in EU fisheries, by incentivizing improved selectivity and restoring fish stocks to levels that can sustain the maximum production over time without harming the biodiversity and the capacity of future generations to obtain fish. However, banning discards will inevitably induce diverse short- and long-term ecological, economic, and social impacts, which may determine whether the landing obligation’s objectives will be achieved.

Impact assessment of EMFF measures on Good Environmental Status (GES) as defined by Italy

Fisheries involve an intensive use of European maritime regions according to the Common Fisheries Policy (CFP). The recent CFP reform has adopted an ecosystem-based approach to fisheries management that is characterised by enhanced regionalisation and multi-annual management plans. It aims to avoid the adverse environmental impacts of fishing activities, which are to be mitigated as far as possible, while the wasteful practice of discarding unwanted catches is to be phased out by 2019, at least for species with minimum landing size. The paper investigates the ability of selected measures, envisaged by the CFP reform through the European Maritime and Fisheries Fund (EMFF), to sustain and attain the objectives of the European Marine Strategy Framework Directive, which aims at achieving Good Environmental Status (GES) in marine waters according to an ecosystem-based approach. The analysis uses an expert judgment-based approach and a specially devised questionnaire, where fisheries science and management experts were asked to assess the impact and interaction of selected EMFF measures on GES achievement as defined for the Italian seas. Their responses are discussed and compared with information coming from an extensive literature review. The results of the analysis highlight a general agreement between EMFF actions and GES objectives but also identify some potential conflicts.

Cold fins, murky waters and the moon: what affects shark catches in the bather-protection program of KwaZulu–Natal, South Africa?

The influence of environmental variables on shark catch in the bather-protection program along the eastern coast of South African was investigated for 11 commonly caught species (Carcharhinus limbatus, C. obscurus, C. brachyurus, C. plumbeus, C. brevipinna, C. leucas, Carcharodon carcharias, Carcharias taurus, Sphyrna lewini, S. zygaena, Galeocerdo cuvier). Data for the period 1986–1994 were analysed using generalised additive models and generalised additive mixed models. The influence of temporal and spatial factors was respectively considered and removed within a standardisation procedure to investigate and predict the influence of lunar cycle, sea-surface temperature (SST) and water visibility on daily catch. The catches of C. taurus and C. brevipinna were significantly affected by all three factors. Catches of all other species were affected by at least one of the three factors, e.g. six were affected by lunar phase, six by SST and seven by water visibility. The results suggested that measurable, predictable relationships exist between environmental conditions and presence and, consequently, catch of shark species in this program. Understanding these relationships could be useful to mitigate against unwanted catch and to further reduce risk for bathers.