Size Selectivity Curve Research Articles

Size selectivity of a novel non-mesh codend (the Modular Harvesting System) in a New Zealand deepwater fishery

The Modular Harvesting System (MHS) is an inflatable membrane-like fabric tube with escapement holes that replaces the mesh codend of a trawl, and is designed to reduce damage to catch by providing fish a low-flow, low-turbulence environment that allows them to maintain swimming control and avoid compaction during trawling and haulback. The MHS gear is now used within New Zealand’s most valuable finfish fishery, deepwater hoki/blue grenadier (Merlucciidae, Macruronus novaezelandiae). This work presents the novel research used to estimate the size selectivity of the MHS gear, and to compare this to the selectivity of the conventional mesh trawl. Management objectives required estimates of the absolute size-selectivity of both the MHS and conventional gears, and also an estimate of their relative selectivity. An innovative statistical power analysis was developed to specify the required number of twin-trawl tows and number of fish to measure to ensure the desired statistical power to detect a meaningful difference between conventional and MHS gears. A novel twin-trawl experiment was employed whereby the conventional and MHS gears were each paired with a nonselective control, and then the conventional and MHS trawls were paired. All catch data were simultaneously analyzed in a hybrid selectivity model. The MHS and conventional gears had similar estimated size-selectivity curves, and they were not significantly different.

Catch composition and codend selectivity of inshore trawl fishery with the legal minimum mesh size

Fisheries is an important socio-economic contribution to the coastal fishing communities of Vietnam. Unfortunately, inshore natural resources have decreased in recent years. This decline has been largely attributed to overfishing and using a fishing gear with poor size selectivity. This paper estimated size selectivity curves for 8 important economic species using a covered codend attached to the codend of a commercial inshore trawl in Quang Ninh province, Vietnam. Results showed that sublegal-sized individuals accounted for a high proportion of the catch, ranging between 29.22 and 46.69%. The lengths at 50% retention (l50) were below minimum landing sizes (MLS) for all species caught, except conger eel (Muraenesox cinereus). Our study provides important scientific information for the fishery management in the studied area.

Selectivity of Two Commercial Dredges Fished in the Northwest Atlantic Sea Scallop Fishery

Size selectivity curves were estimated for two commercial dredge configurations used in the United States Atlantic sea scallop (Placopecten magellanicus) fishery. Traditionally, the New Bedford Style dredge (New Bedford dredge) has been used by the commercial fleet; however, since 2013, the Coonamessett Farm Turtle Deflector Dredge (turtle dredge) has been required seasonally in the Mid-Atlantic region to minimize the capture of sea turtles. This analysis provides estimates of selectivity and relative efficiency for the turtle dredge and the New Bedford dredge. Selectivity information for the turtle dredge is currently unknown, and selectivity for the New Bedford dredge was originally assessed in 2008. The Share Each Lengths Catch Total method was used to model scallop catch-at-length data for each commercial dredge with data collected during the Virginia Institute of Marine Science fishery-independent surveys in 2015 to 2017, conducted onboard commercial fishing vessels. The surveys were conducted in the Mid-Atlantic and Georges Bank regions of the resource in three distinct areas. A paired study design was used, where a nonselective National Marine Fisheries Service sea scallop survey dredge and either the turtle dredge or New Bedford dredge were towed simultaneously at each survey station. To assess for time-varying changes in selectivity, results were compared with the 2008 New Bedford dredge analysis. Results indicated the 50% retention length was 98.2 mm, with a selection range of 28.2 mm and a relative efficiency of 0.83 for the turtle dredge. New Bedford dredge results estimated a 50% retention length of 107.4 mm, selection range of 50.5 mm and relative efficiency of 0.81. Comparing selectivity profiles for the turtle dredge and New Bedford dredge with the 2008 results indicated a shift toward increased retention probability for smaller size classes of scallops.

Gillnet catchability of Walleye (Sander vitreus): comparison of North American and provincial standards

Multi-mesh index gillnet surveys are widely employed for the assessment of fish populations, including Walleye (Sander vitreus), an important commercial and recreational species in North America. In this paper, we estimate gillnet catchability of Walleye for two standard sampling protocols: the North American (NA) and the Fall Walleye Index Netting (FWIN), allowing the conversion of Catch Per Unit Effort (CPUE) into absolute estimates of fish density or abundance. We combined mark-recapture studies from 14 lakes in Ontario and Quebec, 11 of which were concurrently sampled using NA and FWIN methods, totalling 53 recapture surveys from 1996 to 2012. To account for lake-specific influences on catchability, we analyzed the data with Generalized Linear Mixed Models (GLMMs) using lake as a random factor and a model-averaging approach to calculate mean estimates and variances. Catchability for Walleye ≥ 350mm total length was 1.04 ha/gang for the FWIN, meaning each fish caught in a FWIN net gang (1.8 x 61 m) represents roughly one fish per hectare. Catchability for one gang of NA net (1.8 x 24.8 m) was 0.52 ha/gang, which is 20% higher than FWIN catchability after accounting for net area. Two important sources of variation in catchability were: (i) lake-specific differences and (ii) seasonal changes within the NA protocol. The mechanisms underlying such variation are still not clear and will require additional studies covering a broader geographic range to reveal potential environment-catchability relationships. We provide recommendations for estimating Walleye density and confidence intervals, and for how to combine our catchability estimates with size-selectivity curves to predict density at any specific size interval.

Effect of ultrasonic cavitation treatment on liberation and hydrocyclone separation of bituminous coal

Testing was conducted to evaluate the effects of hydroacoustic cavitation (HAC) treatment on two bituminous coal slurries and the subsequent separation of each slurry in a classifying hydrocvclone. HAC treatment was performed using a pilot-scale circuit fabricated by Fumess-Newb urge Inc. The circuit was designed to induce cavitation by means of flow through an ultrasonic resonator chamber or enhanced cavitation by initial flow through a cavitation chamber followed by flow through the ultrasonic chamber. The test materials were nominal −1,500-micron and −150-micron lllinois-basin bituminous coal slurries, which were obtained from an operating coal preparation facility. After 5 sec of HAC treatment, the median size of the −1,500-micron material was reduced, with ash values for certain size fractions decreasing more than 5 percent compared with untreated samples. Extending treatment time led to greater degradation of the +1,180-micron material and an increase in the −25-micron material, with ash reductions occurring for material in the −850+150-micron size range. Size degradation was less for the −150-micron material. Subsequent separation of the treated slurries was carried out in a hydrocvclone with diameter of 102 mm. HAC treatment led to a decrease in the ash value and an increase in the heating value of the underflow stream compared with the feed material. For example, the ash value was reduced by about 16 percent for the −1,500-micron material and 25 percent for the −150-micron material with heating value increases of 7 and 33 percent, respectively, after HAC treatment. Overall, HAC treatment appeared to have a slight effect on the size selectivity curves.

망목형 탈출장치의 선택성과 정치망에 적용 가능성

This thesis is the fundamental study on the adaptation of escape device for reducing small fishes in set-net. The escape devices for experiments were made the mesh-type devices with three different mesh sizes (60.6, 75.8 and 120.0mm). The experiments of size selectivity on escape devices were conducted by using two kinds of species as black rockfish (Sebastes schlegeli) and sea perch (Lateolabrax maculatusi) in the experimental tank. The size selectivity curve was fitted by using a logistic function and the parameters of selectivity curve were estimated by a maximum likelihood method. In the results; 50% selection ranges for the mesh-type escape devices with three different mesh sizes were; a black rockfish was 18.99 in mesh size 60.6mm and 21.96 in mesh size 75.8mm (120mm could not estimate). A sea perch was 22.02 in mesh 60.6mm and 24.46 in mesh size 75.8mm (120mm could not estimate). The 50% selection range of a black rockfish was wilder than a sea perch about 1.1~.2 time. Therefore, the small fishes are able to reduce by using the mesh type escape device. However, the optimum mesh size should be decided to consider the size of target species and economics of catches.

정치망의 치어혼획저감을 위한 그리드형 탈출장치의 선택성에 관한 연구

This thesis is the fundamental study on the adaptation of escape device for reducing small size of fish in set-net. The escape devices for experiments were made the grid-type devices with three different slit sizes (15, 20 and 25mm). The experiments of size selectivity on escape devices were conducted by using two kinds of species as black rockfish (Sebastes schlegeli) and sea perch (Lateolabrax maculatusi) in the experimental tank. The size selectivity curve was fitted by using a logistic function and the parameters of selectivity curve were estimated by a maximum likelihood method. In the results; 50% selection ranges for the grid-type escape devices with three different slit sizes were; a black rockfish was 13.30, 19.22 and 22.06cm and a sea perch was 17.64, 20.91 and 22.78cm, respectively. The 50% selection range of a black rockfish was wilder than a sea perch about 1.1~1.3 time. Therefore, the small size of fish are able to reduce by using the grid type escape device. However, the optimum slit size of grid should be decided to consider the size of target species and economics of catches.

Tentacle-breakage mechanism for the neon flying squid Ommastrephes bartramii during the jigging capture process

In squid jigging operations for neon flying squid (Ommastrephes bartramii), 30–40% of hooked squid are estimated to fall off (i.e., become detached) from the jigs during the drum-hauling process, caused by breakage/severance of the hooked tentacle(s). Reducing fall-off events can lead to higher productivity and more efficient use of the squid resource. In the present study, there were 950 fall-off events either directly observed or assessed from the residue of tentacle(s) left on the jigs compared with the 1720 total captures, which comprises 35.6% of 2670 total hooked squids. The fall-off ratio according to the mantle length (ML) was examined using logistic curve analysis and a higher fall-off ratio for smaller squid was confirmed through size selectivity curve analysis. F50, the 50% probability of fall off from the jig, was estimated to be 37.4cm ML. The breaking strength of a single tentacle was determined to be similar to the body weight (BW) of squid smaller than 41.4cm ML, indicating a high possibility of tentacle breakage in the case of 1 tentacle grabbing the jig for smaller-sized squid.

Estimation of basket trap selectivity for changeable nassa ( Nassarius mutabilis) in the Adriatic Sea

Size selectivity of basket traps for changeable nassa ( Nassarius mutabilis) was estimated through comparative fishing trials with traps varying in mesh size and net colour. Selectivity curves of two commercial (19 mm white twine and 19 mm black twine) and three experimental (23, 26 and 28 mm white twine) traps were estimated using SELECT method. In addition, theoretical size-selectivity curves were calculated from morphometric data using a simplified version of Sechin method. Differing from the opinion of fishermen, N. mutabilis did not show any preference for dark coloured twine. Retention curves estimated with SELECT method had a very sharp selectivity and well fitted catch data in all cases. Theoretical size-selectivity curves were very close to size-selectivity curves obtained from experimental data. The two types of curve were very similar in shape, although the theoretical ones were shifted towards larger size classes and showed a slightly steeper slope than SELECT curves. The mesh size commonly used by fishermen is not adequate for rationally exploiting the resource, as catches mainly included undersized specimens, whilst the 23 and 26 mm mesh sizes would represent a good compromise between reduced occurrence of undersized individuals and satisfactory yields of commercial product.

Size-Selectivity of the Northwest Atlantic Sea Scallop (Placopecten magellanicus) Dredge

A size-selectivity curve was constructed to characterize the performance of the New Bedford style Atlantic sea scallop (Placopecten magellanicus, Gmelin 1791) dredge when it is configured to meet the requirements of Amendment #10 to the Sea Scallop Fishery Management Plan. The curve was generated using the SELECT model on catch-at-length data, obtained by simultaneously towing a New Bedford style dredge and a nonselective National Marine Fisheries Service sea scallop survey dredge from commercial scallop vessels. Data were collected during three cruises in the Northwest Atlantic between 2005 and 2006. The resultant selectivity curve yielded a 50% retention length of 100.1 mm, a selection range of 23.6 mm, and a value of 0.77 for the efficiency of the commercial dredge relative to the survey dredge. A length of 100.1 mm corresponds to a meat weight of 17.2 g in Georges Bank and 16.8 g in the mid-Atlantic. These results can assist fisheries managers with stock assessments, fishing mortality estimates, and the interpretation of catch data from resource surveys. Additionally, the curve can be used as a baseline to evaluate the effect of future changes to sea scallop dredge configuration.

Size selectivity of a trammel net for oval squid Sepioteuthis lessoniana

The size selectivity of a trammel net for herded oval squid Sepioteuthis lessoniana in Tateyama Bay, Chiba Prefecture, was estimated by comparison between the mantle length frequency distributions of oval squid caught by a trammel net and by a set net. The measured mesh sizes of the inner net of the trammel net and of the final section of the set net were 85.3 and 11.3 mm, respectively. In the trammel net fishery where oval squid are herded into the net, most of the oval squid are caught in the bag-shaped inner net. Hence, the logistic function was employed for the size selectivity curve of the trammel net. The ‘share each length's catch total’ (SELECT) model was implemented for the estimation of the selectivity curve. The size selectivity r(l) of the trammel net for the oval squid was expressed as a logistic function of the mantle length l: r(l)=exp (-18.57+0.88 l)/[1+exp (-18.57+0.88 l)]. From these logistic parameter estimates, the 50% selection mantle length and selection range (L75-L25) were calculated as 21.07 and 2.49 cm, respectively. The selection probability of oval squid whose mantle girth was equivalent to the mesh perimeter of the inner net was 0.09. Accordingly, oval squid of a girth smaller than the mesh perimeter were likely to pass through the mesh to escape from the net.

Evaluation of a solid-bowl centrifuge for ultrafine size separations

Solid-bowl (decanter) centrifuges are used extensively to dewater slurries in a wide range of industries. However, the application of decanters as classification devices is not as common. In this study, the performance of a continuous, pilot-scale, solid-bowl centrifuge was evaluated when classifying an ultrafine coal slurry containing nearly 60% material less than 10 μm. The test conditions included centrifuge bowl and scroll speeds, volumetric feed rate, solids concentration and pond depth. Centrifuge performance was evaluated using size selectivity curves and the corresponding performance parameters, along with product yields and solids concentrations.

Size-selectivity of lobster pots with escape-gaps: application of the SELECT method to the southern rock lobster ( Jasus edwardsii) fishery in Victoria, Australia

We have utilised a relatively new modelling method, SELECT, to calculate size-selectivity curves for data from two escape-gap field experiments on southern rock lobster ( Jasus edwardsii) in Victoria, Australia. Size-selectivity curves based on an asymmetric Richards model fitted the data better than the commonly used logistic model, possibly because of higher than expected retention of small lobsters. Theoretical size-selectivity curves, calculated from morphometric data, were remarkably close to size-selectivity curves obtained from one experiment. In a second experiment, we showed that retention probabilities for lobsters close to the legal minimum length were lower than that predicted by the theoretical size-selectivity curves. Size-selectivity curves confirm that the current escape-gap size of 60 mm is close to optimum for the legal minimum lengths used in the Victorian southern rock lobster fishery. Our analyses failed to support the common assertion that escape-gaps increase the fishing power of lobster pots.

ヒメエゾボラかごの漁獲選択性について

Fishing of whelks Neptunea arthritica in Shiriuchi, Hokkaido is carried out using three types of trap. However, the size selectivity of these traps is not known. Size selectivity significantly depends on the mesh size and hanging ratio of the bottom net of the trap. In this study the size selectivity curve of traps for whelks was estimated by calculating the probability of retention (Pn) that en-trapped whelks can not pass through the bottom net of a trap. Pn is expressed as a function of mesh bar length l, hanging ratio α and shell length L'. The results of an examination of 48 individuals with α values of either 0.50 or 0.29 indicate that Pn can be expressed as a partial sigmoid curve. The regression curve can be expressed approximately as: where L' is the measured shell length. The slope of the latter is greater than that of the former and the values of the selection span (the difference of L'/2l between 25% and 75%) are 0.22 when α=0.50 and 0.19 when α=0.29. The resultant selection factors are 0.60 for the former and 0.65 for the latter.

Performance Evaluation of an Entrained Solids-Fed Pneumatic Centrifugal Classifier

An evaluation of the operating performance of a recently designed pneumatic centrifugal classifier is presented. This classifier has been modified from a separate air and feed input design to an entrained solids in air feed input. The evaluation first required determining the size distributions for the three streams (feed, fine, and coarse). Using size distribution data and mass flow rates, a size selectivity curve was calculated for each operating condition tested. This curve, in turn, was characterized by appropriate selectivity parameters (i.e., the equiprobable or cut size, the sharpness index, and the apparent bypass values). The variation of these parameters with classifier operating conditions was examined. From these evaluations, the “best” operating conditions for the classifier were then determined.