Escape Gaps Research Articles

MODIFIKASI DINDING BUBU LIPAT UNTUK MELOLOSKAN RAJUNGAN YANG BELUM LAYAK TANGKAP

Increasing of fishing pressure poses a serious threat to the sustainability of blue swimminng crab resources. Trap design modifications are needed to improve size selectivity and to release under size crabs. This study aimed to determine the type of wall modification of collapsible trap that is effective in excluding under size blue swimming crab. Laboratory observations were conducted using four escape vents treatments and three different mesh sizes. The escape gap used are rectangular, square, circular and oval respectively. Moreover, the mesh sizes used are 2.0 inches, 2.5 inches and 3.0 inches. Descriptive analysis and scoring were used to determine the most effective type of wall trap modification to be used in the blue swimming crab fishing. The results showed that the rectangular escape gap has better effectiveness than other shapes with the percentage of crabs that pass through at 86.7%. The wall modification using a 3.0-inch mesh size had better performance than the other modification types with a total score of 19. Collapsible trap with a 3.0-inch mesh wall was able to escape 86.7% of the crabs with an escape time of only 11.2 seconds and an average escaped crab carapace width of 78 mm. Keywords: Collapsible trap, escape gap, environmentaly-frendly fisheries, mesh size of trap wall

Selectivity in snow crab (Chionoecetes opilio) pot fishery: Effect of escape gap shape and size for conservation of fishery resources

Conical pots are commonly used fishing gear for capturing snow crab (Chionoecetes opilio). In these fisheries, optimal snow crab size selection is important for reducing unintended mortality of undersized individuals aiming at conserving fisheries resources and reducing sorting time onboard fishing vessels. Size selection in snow crab pot fisheries commonly takes place through pot netting meshes during deployment. The diamond mesh netting has varying opening angles affecting retention of snow crab of different sizes, and often large proportions of catches consist of undersized crab challenging natural resource conservation. Some commercial snow crab fisheries use rigid escape gaps in addition to mesh selection to improve size selectivity. In this study, we predict the size selection potential of escape gaps with different shape and size and investigated whether such additional size selection mechanism can have a potential to improve selectivity compared to mesh selection. Results showed that circular escape gaps have potential to provide sharper size selection compared to netting meshes and thus could be used to limit the capture of undersized snow crab which is relevant for management and conservation of snow crab resources. However, a similar positive effect cannot be obtained to the same extent with elliptical and rectangular escape gaps.

Escape gaps in wire lobster traps reduce bycatch of coral reef fish while maintaining catch of harvestable lobsters in Florida’s Caribbean spiny lobster (Panulirus argus), fishery

Escape gaps are a tool commonly used to reduce the catch of sublegal-size animals and bycatch in crustacean trap fisheries. In Florida’s Caribbean spiny lobster (Panulirus argus) commercial trap fishery, traps are baited with live, sublegal-size lobsters, which precludes the use of escape gaps sized to exclude capture of undersize lobsters. Both wood and wire traps are used in the fishery, but wire traps capture more fish as bycatch than do wood traps. This project was developed and executed cooperatively with commercial fishers to evaluate, for wire lobster traps, the effect of escape gaps on catch rates of bycatch and harvestable lobsters. We tested five wire-trap configurations that included a control trap without escape gaps (i.e., an unmodified commercial trap) and four configurations consisting of a narrow (3.81 cm) or wide (5.40 cm) escape gap, oriented either vertically or horizontally. All traps were fished in the Atlantic Ocean at a deepwater site (ca. 30 m) and a shallow-water (ca. 10 m) site. Control traps and traps with a narrow escape-gap configuration were baited with a live, sublegal-size lobster; traps with a wide escape-gap configuration were baited with a live, legal-size lobster. We compared the number of lobsters caught and coral reef fish bycatch, as well as size frequency distributions of lobster and compressiform fish species, which include fish in the snapper and grouper families, in each trap configuration. Escape-gap traps caught statistically similar numbers of legal-size lobsters in all configurations except the wide horizontal configuration at the deep site. The catch of sublegal-size lobsters was significantly reduced in the wide horizontal and wide vertical escape-gap trap configurations at both sites. Fish bycatch was dominated by compressiform fish of the Haemulidae family and fish bycatch was significantly reduced in all escape-gap trap configurations. Our results suggest that the wide vertical escape-gap configuration maximized both the retention of harvestable lobsters and the escape of sublegal-size lobsters and fish bycatch. Inclusion of any of the escape-gap configurations tested could reduce discard mortality of fish and undersize lobsters, but baiting and trap fishing methods may need to be adjusted to maximize lobster harvest.

Nutrient capture and sustainable yield maximized by a gear modification in artisanal fishing traps

Coral reef artisanal fisheries are an important source of nutrition and economic wellbeing for coastal communities, but their management is subject to conflicts and tradeoffs between short-term food security benefits and long-term ecological function. One potential tradeoff is between nutrient capture and fish yields, where targeting small, nutrient-dense species may be more valuable for food security than maximizing fish yields, which is more closely aligned with supporting biodiversity and ecological function. We explored these potential tradeoffs by comparing two similar gears: traditional African basket traps and traps modified with an escape gap. Traps without escape gaps captured a higher frequency of fish with body sizes below their estimated lengths at maximum sustainable yield than gated traps. Estimates of nutrient yields for six micronutrients among the 208 captured species indicated high hump-shaped relationships for gated traps and low and linear positive relationships for traditional traps. Maximum nutrients in gated traps frequently corresponded to body sizes at maximum sustainable yield. Daily capture rates of nutrients were above daily needs more often in gated than traditional traps, but calcium values were low in both trap designs. Gated traps were more likely to capture species with unique and potentially important functional traits, including browsing herbivores, which could have negative effects on ecological functions and reef recovery. However, gated traps also catch fewer immature fish and fewer predators. Our results indicate that nutrient yields can be maximized while using a gear that captures larger and more sustainable body sizes in coral reef artisanal fisheries. Preferential targeting of nutrient-dense fishes is only one of many metrics for evaluating a nutrition-centered management strategy and may only be a management target in specific contexts.

Fleet‐wide acceptance of escape gaps and their utility for reducing bycatch in south‐eastern Australian Portunus armatus traps

AbstractIn response to widescale, voluntary uptake of escape gaps by commercial trappers using collapsible netted cylindrical (or “round”) traps targeting blue swimmer crabs, Portunus armatus, in south‐eastern Australia, an observer‐based study was used to assess the adoption and effectiveness of the most common escape gaps across two estuaries responsible for >70% of all harvest. Five observers collected data from 5710 deployments of round traps over 116 days. Among 60% of round traps with escape gaps, 73% were rectangular shaped, and the rest were either circular or square. Catches were dominated by P. armatus (93%), but ~60% were undersized (<65‐mm carapace length; CL). Compared with round traps with no escape gaps, traps with a rectangular design consistently retained fewer undersized P. armatus (by up to 54%); similar to earlier, manipulative experiments. However, unlike previous observations, escape‐gap performance did not significantly improve with increasing catches of P. armatus. Eventual 100% adoption of escape gaps should enable large numbers of undersized P. armatus to escape traps and avoid discarding each year in south‐eastern Australia.

Exploring the potential use of escape gaps in the Florida spiny lobster, Panulirus argus, fishery

The spiny lobster fishery in Florida uses live, sublegal-size lobsters as bait in the approximately 450,000 traps currently permitted in the fishery. Live baits increase the catch of traps, yet confinement in traps compromises lobster health and causes mortality. We conducted a field experiment to test the suitability of traps fitted with escape gaps to address a priority need for reducing catch and mortality of sublegal-size lobsters and other species in Florida’s spiny lobster trap fishery. We then modeled the potential effect of escape gaps on the Florida commercial spiny lobster trap fishery (via a Monte Carlo simulation technique) to identify the effect on fishery harvest. We measured catch rates and mortality of lobsters in traps with or without a 54 mm escape gap and baited with either a live sublegal-size lobster, a live legal-size lobster, or left unbaited. The relationship between catch in traps fitted with escape gaps vs. catch in control traps determined from the field experiment was applied to commercial fishery landings data from 2010 to 2018 and used to model changes in harvest as result of implementing escape gaps and baiting with a legal-size lobster. We found that traps with escape gaps nearly eliminated catch of sublegal-size lobsters in traps, which would lower mortality caused by such confinement and potentially allow hundreds of thousands of lobsters to remain in the population. Alternatively, replacing live bait lobsters every two weeks reduced bait mortality by half in our field experiment; thus, mortality of sublegal-size lobsters used as bait in the fishery could be reduced through frequent release of bait lobsters. Escape gaps also reduced fish bycatch, including some in the snapper-grouper management complex. Traps with escape gaps and baited with legal-size lobsters caught ~27% ± 16% fewer legal-size lobsters than control lobster traps baited with a sublegal-size lobster. However, these traps caught as many legal-size lobsters as control lobster traps baited with sublegal-size lobsters when lobster abundance was high, demonstrating that self-baiting of traps is density dependent. Although traps with escape gaps caught fewer legal-size lobsters per trap, fishery modeling indicated that increased survival of sublegal-size lobsters could increase landings by the second to fourth year after implementation of escape gaps, depending on which model assumptions are used to predict landings.

Effectiveness of Different Mesh Size To Release Small Blue Swimming Crab on Trap Fishing

Blue swimming crab (Portunus pelagicus) is a fishery commodity with important economic value and also become the main commodity for export needs. However, crab production dominantly comes from fishing activities using traps and gillnet. The fisher use traps without escape gaps so that small crabs have no chance of escaping from the traps. One alternative way to improve the crab trap selectivity is the use of larger mesh sizes on the wall of the trap. This study aimed to determine the effective mesh size for escaping small crabs. This study was conducted in Fisheries Laboratory, University of Sultan Ageng Tirtayasa from July to December 2020. We used different mesh sizes on the trap wall including of 2.0; 2.5; and 3 inches. For all experiments, we used 90 crabs with an average carapace width of 72 mm. The results showed that the pattern of crab when escaping through the net at each mesh size was varied. The crab crept up the netting wall before attempting to escape. The fastest time of crab escapes was found on a 3 inch mesh size with an average time of 10 seconds. Moreover, the highest percentage of crabs that can pass was obtained at the 3-inch mesh size with the value 60%. Based on these results, to increase the catch selectivity we recommend a 3-inch mesh to be used in the collapsible trap wall for blue swimming crab fishing.

Disparity among recommended and adopted escape-gap designs and their utility for improving selection in an Australian portunid trap fishery

Over the past decade, most efforts at improving the selectivity of commercial, baited traps targeting the giant mud crab, Scylla serrata in south-eastern Australia have focused on testing rectangular escape gaps (46 mm high × 90–120 mm wide) in spatially and temporally restricted manipulative experiments, followed by some promotion among local fishers. Anecdotal data imply wider adoption of escape gaps throughout unassessed regions of the fishery, but there are no data on escape-gap designs, or if performances correspond to predictions from isolated experiments. This deficit was addressed here via a fishery-wide, observer-based assessment. During two fishing seasons, six observers sampled catches from seven estuaries responsible for 80% of the total S. serrata harvest. Most fishers used collapsible netted cylindrical traps (83% of traps and made from 50–55 mm stretched mesh opening); among which ~10% were fitted with one rectangular escape gap, while 37% had one or two circular escape gaps (85–90 mm diameter). Compared to traps with no escape gaps, those with rectangular escape gaps (46 × 120 mm) reduced the numbers of undersized S. serrata by 92% (similar to observations during previous manipulative experiments); but those with circular escape gaps did not reduce any unwanted catches. Rather, traps with circular escape gaps caught more legal-sized S. serrata, which was attributed to possible species-specific behaviours in the traps and less egress through funnel entrances. This result potentially contributed towards fisher opinions of circular escape-gap success (given they want to maximize desirable catches) and facilitated their wider adoption. The data reiterate ongoing fishery assessments are essential to understand the performances of evolving/devolving gear modifications and ensure intended stakeholder and resource management expectations are realized.

An experimental evaluation of the effect of escape gaps on the quantity, diversity, and size of fish caught in traps in Montserrat.

Coral reef fisheries are vital to the livelihoods of millions of people worldwide but are challenging to manage due to the high diversity of fish species that are harvested and the multiple types of fishing gear that are used. Fish traps are a commonly used gear in reef fisheries in the Caribbean and other regions, but they have poor selectivity and frequently capture juvenile fish, impacting the sustainability of the fishery. One option for managing trap fisheries is the addition of escape gaps, which allow small fish to escape. We compared catches of traps with and without two 2.5 cm (1 inch) escape gaps on the Caribbean island of Montserrat. No significant differences were found in the mean fish length, total fish biomass, number of fish, fish species richness, and Shannon diversity index between hauls of the two trap designs, though traps with escape gaps did catch larger proportions of wider-bodied fish and smaller proportions of narrow-bodied fish. Furthermore, traps with gaps caught a smaller proportion of small-sized fish and fewer immature fish (though differences were not statistically significant). Linear mixed effect models predict that soak time (the length of time between trap hauls) increases the mean catch length, total catch biomass and total number of species in the catch. The relatively modest evidence for the effect of the gaps on catch may be explained by the long soak times used, which could have allowed most smaller-sized fish to escape or be consumed by larger individuals before hauling in both traps with and without escape gaps. Despite the small differences detected in this study, escape gaps may still offer one of the best options for improving sustainability of catches from fish traps, but larger escape gaps should be tested with varying soak times to determine optimum escape gap size.

The effect of escape gap on the cube folding trap on fish catches composition and trap rate at the northern coast of Tuban regency

This study aims to determine the effect of escape gap on catch composition, CPUE, and trap rate at the northern coast of Tuban Regency. The research was conducted by ten trips of experimental fishing at different locations in November 2019. A total of 60 units of cube folding traps were installed long line, consisting of cube folding traps without escape gaps, cube folding traps with escape gaps 6x3 cm, cube folding traps escape gaps 7x4 cm, 20 units, respectively. The fish catch composition consists of 18 species of 6 groups, i.e., fish, swimmer crab, shrimp, hermit crab, and snail. Fish were the most dominant group captured by cube folding traps in the northern coast of Tuban Regency (59.7%), followed by swimmer crab, snail, crab, shrimp, and hermit crab. The highest catch per unit effort was found in cube folding traps with escape gaps 7x4 cm as much as 6,94 gr/traps/trip. The highest of the trap rate (18%) was obtained in the cube folding traps without escape gap. There was a significant difference (p=95%) in the weight of fish catches and CPUE between cube folding traps without escape gaps and the cube folding traps with escape gaps 7 x 4 cm.

Key elements in the implementation of escape gaps recommendations for the protection of juvenile vulnerable squaretail coralgroupers (Plectropomus areolatus) in Karimunjawa Island

IUCN classified squaretail coralgroupers into vulnerable status. If this is ignored, there may be a risk of threatening its sustainability and changing its status to endangered. This condition needs proper regulation concerning juvenile protection. Escape gap recommendations are considered to be the proper solution for this particular issue because juveniles were able to release without reducing fishermen's revenues. When implementing an escape gap, various elements support failure and success. Therefore, it is necessary to know what elements will have an effect so that the program could implement successfully. This study aims to identify key elements in escape gap implementation. The key elements are identified through Interpretive Structural Modelling. This method is carried out systematically by ranking several elements that influence the implementation. The result showed that the implementation of the escape gap required prioritizing key elements. These keys are releasing juvenile grouper with high survivability (objectives), trial use of the escape gap on the trap (activities), worries of income reduction (obstacles), Marine and Fisheries Departments of Central Java (institutions involved), and fishermen (affected communities). These key sub-elements will drive other sub-elements to implement the escape gap in trap fisheries successfully.

The effect of escape gaps of cylinder folding traps on fish catch at the coastal waters of Tuban Regency

The purpose of this study is to determine the effect of the escape gap of cylinder folding trap on catch per unit effort (CPUE), trap rate, composition, and size of fish caught in the coastal waters of Tuban Regency. The research was conducted in November 2019 by deploying 60 units in ten experimental fishing trips at different locations. The traps were 20 units without escape gap, 20 units with an escape gap of 3 cm x 6 cm, and 20 units with an escape gap of 4 cm x 7 cm. Overall, the experiments resulted in a collection of 22 species of marine organisms, such as swimming crabs (33% of total weight), snails, shrimps, crabs, fishes (55% of total weight), and cuttlefish. The highest CPUE was found for the traps with escape gaps of 4 cm x 7 cm, i.e., 9.18 gr/trap/trip. There was no significant difference in the total catch, the weight of catches, trap rate, and catch per unit effort (CPUE) among the three types of traps.

Length based assessment of spawning potential ratio in data-poor fisheries for blue swimming crab (Portunus spp.) in Sri Lanka and Indonesia: Implications for sustainable management

Quantitative assessment and management of small-scale fisheries is a persistent problem for fisheries. Crustaceans are particularly challenging for conventional techniques because their lack of permanent hard body parts makes ageing difficult. While a growing body of literature is aimed at developing alternative approaches to small-scale fisheries assessment there are concerns about the indiscriminate application of generic methodologies and the need to address the specific circumstances of fisheries. The length-based assessment of spawning potential ratio (LBSPR) is appealing because it has simple data requirements, a well-developed theoretical foundation, and estimates Spawning Potential Ratio (SPR) an internationally recognized indicator of stock status. With the aim of establishing basic standards and providing structured discussion of the issues raised by its application, this study documents its application to the regionally important blue swimming crab (BSC) (Portunus spp.) fisheries, in Sri Lanka and Indonesia. Our study demonstrates the methods technical feasibility and cost-effectiveness for small-scale BSC fisheries and by extension other small-scale fisheries. In Sri Lanka and Indonesia, these LBSPR assessments are successfully informing discussions about sustainability; focusing discussion on managing size selectivity, one of the few management controls available to fisheries managers in many small-scale fisheries. In Indonesia BSC are first caught at around the size of maturity by trawling and with baited traps without escape gaps, reducing SPR to unsustainable levels. Despite similarly high fishing pressure, in Sri Lanka the larger size of first capture with bottom set nets preserves a sustainable level of SPR. Supported by these assessments, in 2018, that fishery attained a provisional sustainability rating from Seafood Watch. We suggest how LBSPR assessment might be used to adaptively manage size selectivity within the harvest strategy being developed in Indonesia. It is hoped this documentation of the methodology will assist other small-scale fisheries to use this technique similarly.

Optimising mesh size with escape gaps in a dual-species portunid-trap fishery

In south-eastern Australia, the same baited, round traps (comprising 50–57-mm mesh netting) are used to target giant mud, Scylla serrata and blue swimmer crabs, Portunus armatus in spatially separated fisheries. Both fisheries are characterised by the common, problematic discarding of undersized portunids (<85 and 65 mm carapace length; CL for S. serrata and P. armatus) and fish (yellowfin bream, Acanthopagrus australis). This poor selectivity was addressed here in two experiments assessing the utility of (1) traps partially or completely covered in larger mesh (91 mm to match the minimum legal size of the smaller P. armatus), and then (2) any cumulative benefits of fitting species-specific escape gaps. In experiment 1, there were no differences among catches of legal-sized portunids associated with either partial, or complete trap coverage with larger mesh. Irrespective of mesh coverage, both designs of 91-mm traps also retained significantly fewer (by up to 42%) undersized P. armatus and A. australis. In experiment 2, replicate traps completely covered in 91-mm mesh were tested against conventional traps comprising 56-mm mesh, and traps with the same mesh sizes, but also three escape gaps configured for either S. serrata (46 × 120 mm) or P. armatus (36 × 120 mm) (i.e. four treatments in total). All modified traps maintained catches of legal-sized S. serrata, and only the 91-mm traps with escape gaps caught fewer legal-sized P. armatus. Fewer undersized S. serrata, P. armatus and A. australis (mean catches reduced by up to 49%) were retained in all larger-meshed than small-meshed traps, and in all of those traps with escape gaps (by up to 95%) than without. While there were no significant cumulative benefits of escape gaps in larger-meshed traps (measured by a statistical interaction), there was a trend of fewer unwanted catches overall. These data support configuring portunid traps with mesh sizes matching the morphology of the smallest legal-sized target species. But, simply retroactively fitting escape gaps in existing, smaller-meshed traps will also realize positive selectivity benefits.

Cumulative selectivity benefits of increasing mesh size and using escape gaps in Australian Portunus armatus traps

AbstractThe individual and cumulative effects of increasing mesh size (from 56‐ to 75‐mm stretched mesh opening) and installing three escape gaps (36 × 120 mm) in collapsible‐netted round traps were assessed to address concerns associated with excessive discarding in an Australian portunid fishery. Compared to conventional traps comprising 56‐mm mesh throughout, those with the same mesh size and escape gaps caught significantly fewer (by 54%) undersized blue swimmer crabs, Portunus armatus Milne‐Edwards and yellowfin bream, Acanthopagrus australis Günther (by 64%). Irrespective of escape gaps, simply increasing the mesh size to 75 mm did not significantly affect catches of undersized P. armatus, although 87% fewer A. australis were retained. Traps with both 75‐mm mesh and escape gaps maintained reductions of A. australis, but had a clear cumulative effect on P. armatus selection, retaining 84% fewer undersized individuals across a larger size at retention. The results support using escape gaps in existing conventional traps, but illustrate the need to configure the minimum legal mesh size to approach the desired target size of P. armatus as a precursor to maximising trap selectivity. Larger‐meshed traps also require less material (i.e. plastic), which benefits their manufacture and, equally importantly, reduces environmental costs when lost.

Relative ghost fishing of portunid traps with and without escape gaps

Owing to concerns about derelict portunid traps perpetually fishing (‘ghost fishing’) in southeastern Australia, the utility of escape gaps for minimising temporal catching efficiencies, and damage and mortality, among key species was investigated. Replicate baited traps with (i) no escape gaps (‘conventional’), (ii) three escape gaps (‘escape-gap’ traps), or (iii) three holes where escape gaps would have been if they were biodegradable (‘open-hole’ traps) were deployed and retrieved after short (one and two weeks), medium (four and six weeks) and long soaks (eight and 10 weeks). No trap had bait remaining after any soak. Total catches comprised 17 species, but 70% was blue swimmer crabs, Portunus armatus—most (78%) of which were smaller than a proposed new legal size (≥65 mm carapace length). Many (62%) P. armatus were injured (typically missing one or two appendages), but had few mortalities (total of 5%). Compared to conventional traps, the escape-gap and open-hole traps retained significantly fewer undersized P. armatus across all soaks (by 93 and 96%) and there were less total injuries (by 86 and 97%) and mortalities trap–1 (by 80 and 85%). Irrespective of the trap, catches of total and undersized P. armatus and injuries trap–1 were greater after short (all by up to 3×) than medium or long soaks. Several traps had broken mesh bars, which was negatively associated with P. armatus catches and injuries. Only three other species had mortalities (n = 7). The data support using escape gaps for minimising ghost fishing among derelict portunid traps.

Configuring escape gaps in recreational rectangular traps to improve size selection for eastern rock lobster, Sagmariasus verreauxi

The utility of escape gaps in rectangular traps for improving the size selection of eastern rock lobster, Sagmariasus verreauxi was assessed during two experiments in an Australian recreational fishery. In experiment one, compared to conventional traps (no escape gaps), those comprising one (57 × 500 mm) or three (each 57 × 200 mm) escape gaps along their sides maintained legal catches of S. verreauxi, but did not significantly affect undersized (<104 mm carapace length; CL) catches; although there were fewer (mean catch reduced by 35%) in the latter traps. In experiment two, three escape gaps all located either on the sides or corners of traps significantly reduced catches of undersized S. verreauxi by up to 82%, with no effect on legal catches, and when catches were pooled between treatments, produced a 50% CL at selection of 102 mm with a selection range of 10 mm. Notwithstanding the inter-experimental differences—which possibly reflected relative catches and density-dependent escape rates—escape gaps should be enforced in recreational traps targeting S. verreauxi as a means for reducing discarding.

Utility of multiple escape gaps in Australian Scylla serrata traps

As part of attempts to promote more selective recreational and commercial portunid trap fisheries in south-eastern Australia, the effects of single and multiple rectangular escape gaps (46 × 120 mm) on catches of the targeted giant mud crab, Scylla serrata and incidental species were investigated. Twenty-five collapsible netted round traps comprising five replicates of those with zero (controls), one, two, three or four escape gaps positioned at the base were simultaneously fished in two estuaries by three commercial fishers. Compared to the control, and irrespective of estuary, all traps with escape gaps similarly maintained catches of legal-sized S. serrata (≥85 mm carapace length–CL) while reducing undersize numbers by 85–93%. At one location, 21% of the portunid catch included the smaller blue swimmer crab, Portunus armatus (legal size of ≥60 mm CL); the numbers of which were also significantly lower by 73–96% (across all sizes) in escape-gap traps than the control and with greater escape from traps with multiple escape gaps. Catches of two abundant teleosts were not affected by either single or multiple escape gaps. The results were attributed to species-specific responses to catch densities and while the data reiterate the utility of escape gaps for improving trap selectivity, configurations might need to be fishery specific and/or spatially regulated according to distributions of the key target and incidental species.

Redistribution of benefits but not detection in a fisheries bycatch-reduction management initiative.

Reducing the capture of small fish, discarded fish, and bycatch is a primary concern of fisheries managers who propose to maintain high yields, species diversity, and ecosystem functions. Modified fishing gear is one of the primary ways to reduce by-catch and capture of small fish. The outcomes of gear modification may depend on competition among fishers using other similar resources and other gears in the same fishing grounds and the subsequent adoption or abandonment of modified gears by fishers. We evaluated adoption of modified gear, catch size, catch per unit effort (CPUE), yield, and fisher incomes in a coral reef fishery in which a 3-cm escape gap was introduced into traditional traps. There were 26.1 (SD 4.9) fishers who used the experimental landing sites and 228(SD 15.7) fishers who used the control landing sites annually over 7 years. The size of fish increased by 10.6% in the modified traps, but the catch of smaller fish increased by 11.2% among the other gears. There was no change in the overall CPUE, yields, or per area incomes; rather, yield benefits were redistributed in favor of the unmodified gears. For example, estimated incomes of fishers who adopted the modified traps remained unchanged but increased for net and spear fishers. Fishers using escape-gap traps had a high proportion of income from larger fish, which may have led to a perception of benefits, high status, and no abandonment of the modified traps. The commensal rather than competitive outcome may explain the continued use of escape-gap traps 3 years after their introduction. Trap fishers showed an interest in negotiating other management improvements, such as increased mesh sizes for nets, which could ultimately catalyze community-level decisions and restrictions that could increase their profits.

In situ video monitoring of by-catch interactions within commercial rock lobster (Jasus edwardsii) fishing traps

ABSTRACTThe incidental capture of non-target and undersized target species during commercial fishing operations has been identified as a major issue and ongoing challenge for fisheries management. In the Northern Zone rock lobster (Jasus edwardsii) fishery (NZRLF) of South Australia, escape gaps have been mandatory in all commercial fishing traps since 2002 to reduce non-target species (by-catch) catch rates and juvenile lobster mortality. This study used in situ video monitoring of by-catch species in traps with and without escape gaps to understand how by-catch species interact within commercial fishing traps. Twenty-two different by-catch species were observed entering commercial rock lobster traps, 20 of which were temperate reef finfish. Overall, on-board by-catch rates were significantly higher in hauled traps without escape gaps and were dominated by reef-dwelling finfish species, particularly Meuschenia hippocrepis and Notolabrus tetricus. However, in situ video monitoring within traps showed no difference in the maximum number of finfish by-catch (MaxN) in traps with or without escape gaps. We suggest that the difference in by-catch rates between hauled traps with and without escape gaps may be driven by species-specific behavioural interactions within traps prior to hauling. Overall, this study shows that the implementation of escape gaps in the NZRLF has considerably reduced fishery by-catch rates. Furthermore, the use of in situ video monitoring has provided a better understanding of by-catch behavioural interactions within traps, not previously identified in on-board sampling research, which may partly explain the mechanisms underpinning escape gap effectiveness.