The Wing Trawling System (WTS) was tested as an alternative to traditional shrimp capture methods in the Gulf. Compared to an otter trawl, this trawl was conceived to reduce bycatch, retain shrimp catch, and minimize seafloor disturbance. Through seventy-one paired tows, the WTS was assessed against a standard otter trawl. The WTS was found to reduce bycatch by 63-65% and reduce shrimp catch by 30-35%. Additionally, I measured the depth of the scars produced by both trawls and quantified the turbidity of the plumes behind them. The scars left by the WTS and the otter trawl were between 9.9 cm-13.6 cm. The turbidity behind the WTS was 18.6 NTU, while the turbidity behind the otter trawl was 206.8 NTU. In conclusion, the WTS offers an alternative to an otter trawl that reduces bycatch and the impact trawling has on the seafloor but results in a significant amount of shrimp loss.

The present research adopts with the application of the sequential mesh regulations on bottom trawl to study how to protect economic immature fishes. The experimental design includes first the determination of the relationships of fish size and the price per weight (PPW) of the economic demersal fishes sold as the one-hundred Dollars-a-plate manner in Tunkang and Zihguan fish markets in the southwestern coast of Taiwan. The obtained results were used to yield the catch of smaller size fishes and the lower PPW for regulating the economic immature fishes. The three kinds of regulated fish size were defined as the smallest surveyed size, smallest economic size, and smallest matured size. These regulated fish size were used as the body lengths of 50% selection (L50) to calculate the regulating mesh size. This study presents that four steps are needed for the sequential mesh regulations of bottom trawl in the southwestern Taiwan. The first step is to regulate the mesh size between 35 and 45 mm for banning bottom trawler to catch fishes smaller than the smallest surveyed fish size. The objective of first step is to reduce the bycatch without affecting the landings of economic immature fishes sold in the fish market. The second step is to regulate the mesh size between 50 and 60 mm for banning bottom trawler catch fishes smaller than the smallest economic fish size, and to reduce the catch of smaller size fishes and the lower PPW of economic immature fishes. The third step is to regulate the mesh size between 65 and 70 mm for banning bottom trawler to catch fishes smaller than the smallest matured fish size. This is also to reduce the catch of economic immature fishes, and to increase the recruitment. The fourth step is to regulate the mesh size between 70 and 82 mm for banning bottom trawler catching the lower PPW of economic fishes that is not large enough to reach their optimal PPW. The present research provides important data results for regulating the mesh size of bottom trawler operation for the achievement of sustainable coastal fishery in Taiwan.

The Virginia Tech Trawl-Resistant Self-Mooring Autonomous Underwater Vehicle (TRSMAUV) is designed to reside on the seafloor for extended periods of time. The TRSMAUV shape allows for deployment in areas where trawl fisheries are conducted. TRSMAUV is a two stage vehicle. The ingress vehicle is the delivery device, and it is constructed from two symmetric halves. The top half contains the ingress vehicle propulsion system and control surfaces. The bottom half is the trawl-resistant mooring package. A smaller vehicle, the egress vehicle, is housed within the bottom ingress half and provides the guidance, navigation and control algorithms for the TRSMAUV. This report covers the general design elements of the TRSMAUV, the detail design of several prototypes, the results of the field trials, and the next steps that will be taken to build the final vehicle. / Master of Science

L'industrie de la pêche est confrontée à plusieurs contraintes comme l'augmentation du prix du carburant et la diminution des stocks de poisson. Pour améliorer la rentabilité, nous avons fait l'optimisation des chaluts de pêche (pélagique et de fond) afin d'augmenter leurs efficacités énergétiques. Deux facteurs principaux ont été utilisés : la traînée du chalut et sa surface balayée. Notre travail porte sur l'optimisation du plan du chalut par modification du nombre de mailles des pièces du filet et par changement de la longueur des câbles. Nous avons développé une méthode de recherche successive appelée SOT et nous l'avons comparée à une méthode de recherche aléatoire dans le cas d'un chalut pélagique avec un gain net de 54%. La SOT a été utilisée pour optimiser le plan des pièces du filet d'un chalut de fond. Une amélioration du gain énergétique de 38% a été obtenue, ainsi qu'une réduction de 45 jours de pêche. Par souci de risque de baisse de capturabilité, nous avons développé une fonction objectif qui dépend de la distribution de poisson. Trois fonctions de même densité surfacique ont été testées. L'amélioration de l'efficacité énergétique calculée par la méthode SOT sur un chalut de fond est respectivement de 52%, 16% et 32% selon les trois distributions. Avec la méthode SRT (méthode de raffinement séquentiel), nous obtenons des réductions de 56%, 30% et 39% pour les trois distributions. Finalement nous avons adapté la méthode SOT pour optimiser les longueurs des câbles du chalut. Nous obtenons dans un cas une amélioration de l'efficacité énergétique de 49%. L'utilité de ce travail devrait être étendue hors de la pêche comme l'écologie en général. / Nowadays, fishing industry is facing several constraints such as increased fuel prices and declining fish stocks. In this work, we perform optimization of fishing trawls (pelagic and bottom) in order to improve their energy efficiencies. Two main factors were used: the trawl drag and its mouth swept area. Our work focuses on optimizing trawl design by altering mesh numbers and changing cable length. We have developed a method called SOT and compared it to a random search method in the pelagic trawl case with a net energy gain of 54%. The SOT was used in design optimization of bottom trawl panels. Improved energy gain of 38% was obtained and a reduction of 45 total number of fishing days. In order to bypass catchability reduction, we developed an objective function which depends on fish distribution. Three functions with same bottom surface density were tested. Improving energy efficiency calculated by the SOT method on a bottom trawl is respectively 52%, 16% and 32% for the three distributions. With the SRT method (sequential refinement), we obtain reductions of 56%, 30% and 39% for the three aforementioned distributions. Finally we adapted the SOT method to optimize trawl cable lengths. In one case, we obtain energy efficiency improved by 49%. The usefulness of this work should be extended beyond fishery to ecology in general.

Στην παρούσα έρευνα αναπτύχθηκε μια γρήγορη μεθοδολογία για την ποσοτικοποίηση των αλιευτικών ιχνών από ηχογραφίες ηχοβολιστή πλευρικής σάρωσης. Πεδίο έρευνας ήταν δυο γειτονικές περιοχές, ενός αλιευτικού πεδίου μηχανοτρατών πυθμένα με υδραετούς («πόρτες») στον Πατραϊκό κόλπο. Οι υψηλής ανάλυσης ηχογραφίες αποκάλυψαν αλιευτικά ίχνη στον πυθμένα από τη σύρση των «πορτών» του αλιευτικού εξοπλισμού και υβώματα βιογενούς προέλευσης (biogenic mounds). Η περιοχή έρευνας ταξινομήθηκε σε επιμέρους περιοχές με βάση τους ακουστικούς τύπους που προέκυψαν από την ερμηνεία των ηχογραφιών. Η στατιστική ανάλυση των αλιευτικών ιχνών περιέλαβε τον υπολογισμό: 1) πυκνοτήτων ανά μονάδα επιφανείας, 2) μέσων διευθύνσεων ανά μονάδα επιφανείας, 3) συνολικής μέσης διεύθυνσης, και 4) συνολικού μήκους. Χρησιμοποιήθηκαν τα λογισμικά ArcMap® και Matlab®. Τα αποτελέσματα αποκαλύπτουν την ύπαρξη έντονης αλιευτικής δραστηριότητας στη περιοχή έρευνας, η οποία φαίνεται να ελέγχεται από την βυθομετρία και την παρουσία των βιογενών υβωμάτων. / This study suggests a promising, reliable and rapid methodology for the quantification of trawl marks from sidescan sonar records. Two adjacent sites were surveyed, from an otter trawl fishing ground in the Gulf of Patras. The high resolution sidescan sonar records revealled trawl marks made by the doors of the otter trawls as well as biogenic mounds. The study area was classified on the basis of the acoustic types resulted from the interpretation of the sidescan records. The statistical analysis of the trawl marks included the calculation of: 1) densities per surface block 2) mean directions per surface block, 3) total mean direction and 4) total length. ArcMap® and Matlab® softwares were used. The results reveal the existence of intensive fishing activity, which seems to be controled by the bathymetry and the presence of biogenic mounds.

The chondrichthyan (shark, batoid and holocephalan) bycatch of the Queensland East Coast Trawl Fishery (ECTF) was examined through a series of fishery-independent trawl surveys, together with fishery-dependent (opportunistic) sampling. Project aims were to document the chondrichthyan bycatch composition in order to test the effectiveness of turtle exclusion devices (TEDs) and bycatch reduction devices (BRDs), to examine biological aspects of bycatch species, and to combine data collected through these parts to assess the conservation status and sustainability of bycatch species. A total of 37 chondrichthyan species (one holocephalan, 19 batoids and 17 sharks) from 18 families were recorded in the bycatch of the fishery. The most speciose families recorded were the stingrays (Dasyatidae; 7 species), the requiem sharks (Carcharhinidae; 5 species), the catsharks (Scyliorhinidae; 4 species) and the stingarees (Urolophidae; 3 species). Chondrichthyan bycatch was highly variable between fishery sectors; catch rates were low in the tiger/Endeavour prawn sector (north Queensland; 0.02–0.12 individuals ha-1 trawled) and in the eastern king prawn (deepwater) sector (southern Queensland; 0.08 individuals ha-1 trawled), intermediate in Hervey Bay (southern Queensland; 0.25 individuals ha-1 trawled) and in the scallop sector (central Queensland coast; 0.31 individuals ha-1 trawled) and highest in the eastern king prawn (shallow water) sector (southern Queensland; 0.96 individuals ha-1 trawled). Chondrichthyan bycatch in the eastern king prawn (shallow water) sector was dominated by the three batoids Aptychotrema rostrata, Trygonoptera testacea and Urolophus kapalensis (~92% of the chondrichthyan bycatch by number), in the eastern king prawn (deepwater) sector by the skate Dipturus polyommata and the two catsharks Asymbolus rubiginosus and Figaro boardmani (~83% of the chondrichthyan bycatch by number), in the scallop sector by the three batoids A. rostrata, Neotrygon kuhlii and Neotrygon picta (~91% of the chondrichthyan bycatch by number), and in the tiger/Endeavour prawn sector by the two batoids Himantura astra and Gymnura australis and the two sharks Chiloscyllium punctatum and Hemigaleus australiensis (~67% of the chondrichthyan bycatch by number). The testing of TEDs and BRDs, which are mandatory throughout the fishery, demonstrated only a limited ability to reduce chondrichthyan bycatch in the ECTF, which is comprised mainly of relatively small species. The shorter trawl durations of the surveys compared with normal commercial activities may have under-represented larger species. No significant reductions in chondrichthyan bycatch were found using a TED and a radial escape section BRD in the eastern king prawn (shallow water) sector, using a TED and a square-mesh codend BRD in the eastern king prawn (deepwater) sector, or using a TED and a fisheye BRD in Hervey Bay. There was however, a significant difference in the probability of capturing the group ‘sharks and guitarfishes’ (comprised largely of A. rostrata) between codend types in the scallop sector, with the lowest probability of capture in nets fitted with both a TED and a square-mesh codend BRD (the difference was largely attributed to the effects of the TED). In the tiger/Endeavour prawn sector, in which three different BRDs were trialed (fisheye, square-mesh codend, square-mesh panel), the probability of capturing chondrichthyans was significantly lower in nets fitted with a fisheye BRD than in the standard (control) net, and the probability of capturing batoids was significantly lower in nets fitted with a fisheye BRD or with a square-mesh codend BRD than in the standard (control) net. The small sample size of chondrichthyan catches in some sectors may have reduced to power to detect bycatch reduction. The biology of several bycatch species from the families Rajidae, Rhinobatidae, Urolophidae and Scyliorhinidae was examined. For D. polyommata, size at birth was estimated at ~100–110 mm total length (LT), size at first feeding at ~105–110mm LT, size at 50% maturity (LT50 and 95% CI) at 321 (305–332) mm LT for females and 300 (285–306) mm LT for males. Diet (described by the index of relative importance as a percentage) was predominantly crustacean based, with carid shrimps (53.6%) and penaeoid prawns (23.3%) being the most significant prey groups. For A. rostrata, size at birth was estimated at <170 mm LT, size at 50% maturity (LT50 and 95% CI) at 640 (618–663) mm LT for females and 597 (551–649) mm LT for males, and litter size was 9–20 (n = 9; mean ± S.E. = 15.1 ± 1.2). For T. testacea, size at birth was estimated at 77–100 mm disc width (WD), size at 50% maturity (WD50 and 95% CI) at 163 (156–169) mm WD for females and 146 (140–150) mm WD for males, and litter size was always one (n = 6). For U. kapalensis, size at birth was estimated at 75–100 mm WD, size at 50% maturity (WD50 and 95% CI) at 154 (145–160) mm WD for females and 155 (149–159) mm WD for males, and litter size was always one (n = 16). The catsharks A. analis, A. rubiginosus and F. boardmani were all confirmed as single oviparous species (carrying only one egg case in each uterus at one time). Ovarian fecundity (the number of vitellogenic follicles) averaged 13.6 (range 13–20) in A. analis, 13.5 (range 5–23) in A. rubiginosus and 10.4 (range 9–13) in F. boardmani. While only limited data were available from southern Queensland, several indicators suggest that Asymbolus catsharks are reproductively active year-round. A general lack of small-sized or immature catsharks captured during the study made assessments of size at maturity difficult for these species. The conservation status of ECTF bycatch species was examined through the application of the IUCN Red List of Threatened SpeciesTM Categories and Criteria, which considers extinction risk at the global level. Of the 24 ECTF chondrichthyan bycatch species evaluated against the IUCN Red List Categories and Criteria, four have been assessed globally as Vulnerable (a threatened category indicating that a species is ‘facing a high risk of extinction in the wild’), seven as Near Threatened, 11 as Least Concern and two as Data Deficient. While the four globally threatened species (A. nichofii, Heteroscyllium colcloughi, Rhynchobatus australiae and Urolophus sufflavus) were only minor components of the ECTF bycatch, their global conservation status warrants that fisheries management and industry should act to ensure minimal impacts on these species. An ecological risk assessment method (Susceptibility-Recovery Analysis) was used to assess the relative sustainability or risk of individual species to the fishing activities of the ECTF. Two separate approaches were taken to the technique, which considers sustainability to be dependent on the susceptibility of a species to the fishery and the recovery potential of a species after depletion by fishing activities. The first approach applied the precautionary principal when data were lacking for the calculation of recovery attributes, while the second used biological data from similar species when species-specific data were lacking. The precautionary approach tended to overestimate risk to poorly known oviparous species. The biological approach suggested that A. nichofii, F. boardmani, Rhizoprionodon acutus, Rhizoprionodon taylori and Rhynchobatus palpebratus face the least risk (i.e. were the most sustainable) while several medium-large batoids and the sharks Loxodon macrorhinus and Heteroscyllium colcloughi were the species most at risk (i.e. least sustainable). Demonstrating ecological sustainability of the ECTF will need to be a continued management objective into the future. To further improve the ecological sustainability of the fishery in relation to sharks, batoids and holocephalans, a number of management recommendations are proposed: (1) give warranted conservation consideration to listed threatened species as well as species identified as being at risk; (2) expand required logbook information on chondrichthyan species to include recording of catches of these species; (3) encourage safe release practices for all chondrichthyans to maximise survivorship of discards; (4) initiate research into the survivorship of discards; (5) ensure long-term observer coverage on commercial vessels to monitor bycatch levels; and, (6) test and quantify reduced TED bar spacings (presently 120 mm) in fishery sectors which show the highest chondrichthyan bycatch levels, that is, the eastern king prawn (shallow water) and scallop sectors.

The chondrichthyan (shark, batoid and holocephalan) bycatch of the Queensland East Coast Trawl Fishery (ECTF) was examined through a series of fishery-independent trawl surveys, together with fishery-dependent (opportunistic) sampling. Project aims were to document the chondrichthyan bycatch composition in order to test the effectiveness of turtle exclusion devices (TEDs) and bycatch reduction devices (BRDs), to examine biological aspects of bycatch species, and to combine data collected through these parts to assess the conservation status and sustainability of bycatch species. A total of 37 chondrichthyan species (one holocephalan, 19 batoids and 17 sharks) from 18 families were recorded in the bycatch of the fishery. The most speciose families recorded were the stingrays (Dasyatidae; 7 species), the requiem sharks (Carcharhinidae; 5 species), the catsharks (Scyliorhinidae; 4 species) and the stingarees (Urolophidae; 3 species). Chondrichthyan bycatch was highly variable between fishery sectors; catch rates were low in the tiger/Endeavour prawn sector (north Queensland; 0.02–0.12 individuals ha-1 trawled) and in the eastern king prawn (deepwater) sector (southern Queensland; 0.08 individuals ha-1 trawled), intermediate in Hervey Bay (southern Queensland; 0.25 individuals ha-1 trawled) and in the scallop sector (central Queensland coast; 0.31 individuals ha-1 trawled) and highest in the eastern king prawn (shallow water) sector (southern Queensland; 0.96 individuals ha-1 trawled). Chondrichthyan bycatch in the eastern king prawn (shallow water) sector was dominated by the three batoids Aptychotrema rostrata, Trygonoptera testacea and Urolophus kapalensis (~92% of the chondrichthyan bycatch by number), in the eastern king prawn (deepwater) sector by the skate Dipturus polyommata and the two catsharks Asymbolus rubiginosus and Figaro boardmani (~83% of the chondrichthyan bycatch by number), in the scallop sector by the three batoids A. rostrata, Neotrygon kuhlii and Neotrygon picta (~91% of the chondrichthyan bycatch by number), and in the tiger/Endeavour prawn sector by the two batoids Himantura astra and Gymnura australis and the two sharks Chiloscyllium punctatum and Hemigaleus australiensis (~67% of the chondrichthyan bycatch by number). The testing of TEDs and BRDs, which are mandatory throughout the fishery, demonstrated only a limited ability to reduce chondrichthyan bycatch in the ECTF, which is comprised mainly of relatively small species. The shorter trawl durations of the surveys compared with normal commercial activities may have under-represented larger species. No significant reductions in chondrichthyan bycatch were found using a TED and a radial escape section BRD in the eastern king prawn (shallow water) sector, using a TED and a square-mesh codend BRD in the eastern king prawn (deepwater) sector, or using a TED and a fisheye BRD in Hervey Bay. There was however, a significant difference in the probability of capturing the group ‘sharks and guitarfishes’ (comprised largely of A. rostrata) between codend types in the scallop sector, with the lowest probability of capture in nets fitted with both a TED and a square-mesh codend BRD (the difference was largely attributed to the effects of the TED). In the tiger/Endeavour prawn sector, in which three different BRDs were trialed (fisheye, square-mesh codend, square-mesh panel), the probability of capturing chondrichthyans was significantly lower in nets fitted with a fisheye BRD than in the standard (control) net, and the probability of capturing batoids was significantly lower in nets fitted with a fisheye BRD or with a square-mesh codend BRD than in the standard (control) net. The small sample size of chondrichthyan catches in some sectors may have reduced to power to detect bycatch reduction. The biology of several bycatch species from the families Rajidae, Rhinobatidae, Urolophidae and Scyliorhinidae was examined. For D. polyommata, size at birth was estimated at ~100–110 mm total length (LT), size at first feeding at ~105–110mm LT, size at 50% maturity (LT50 and 95% CI) at 321 (305–332) mm LT for females and 300 (285–306) mm LT for males. Diet (described by the index of relative importance as a percentage) was predominantly crustacean based, with carid shrimps (53.6%) and penaeoid prawns (23.3%) being the most significant prey groups. For A. rostrata, size at birth was estimated at <170 mm LT, size at 50% maturity (LT50 and 95% CI) at 640 (618–663) mm LT for females and 597 (551–649) mm LT for males, and litter size was 9–20 (n = 9; mean ± S.E. = 15.1 ± 1.2). For T. testacea, size at birth was estimated at 77–100 mm disc width (WD), size at 50% maturity (WD50 and 95% CI) at 163 (156–169) mm WD for females and 146 (140–150) mm WD for males, and litter size was always one (n = 6). For U. kapalensis, size at birth was estimated at 75–100 mm WD, size at 50% maturity (WD50 and 95% CI) at 154 (145–160) mm WD for females and 155 (149–159) mm WD for males, and litter size was always one (n = 16). The catsharks A. analis, A. rubiginosus and F. boardmani were all confirmed as single oviparous species (carrying only one egg case in each uterus at one time). Ovarian fecundity (the number of vitellogenic follicles) averaged 13.6 (range 13–20) in A. analis, 13.5 (range 5–23) in A. rubiginosus and 10.4 (range 9–13) in F. boardmani. While only limited data were available from southern Queensland, several indicators suggest that Asymbolus catsharks are reproductively active year-round. A general lack of small-sized or immature catsharks captured during the study made assessments of size at maturity difficult for these species. The conservation status of ECTF bycatch species was examined through the application of the IUCN Red List of Threatened SpeciesTM Categories and Criteria, which considers extinction risk at the global level. Of the 24 ECTF chondrichthyan bycatch species evaluated against the IUCN Red List Categories and Criteria, four have been assessed globally as Vulnerable (a threatened category indicating that a species is ‘facing a high risk of extinction in the wild’), seven as Near Threatened, 11 as Least Concern and two as Data Deficient. While the four globally threatened species (A. nichofii, Heteroscyllium colcloughi, Rhynchobatus australiae and Urolophus sufflavus) were only minor components of the ECTF bycatch, their global conservation status warrants that fisheries management and industry should act to ensure minimal impacts on these species. An ecological risk assessment method (Susceptibility-Recovery Analysis) was used to assess the relative sustainability or risk of individual species to the fishing activities of the ECTF. Two separate approaches were taken to the technique, which considers sustainability to be dependent on the susceptibility of a species to the fishery and the recovery potential of a species after depletion by fishing activities. The first approach applied the precautionary principal when data were lacking for the calculation of recovery attributes, while the second used biological data from similar species when species-specific data were lacking. The precautionary approach tended to overestimate risk to poorly known oviparous species. The biological approach suggested that A. nichofii, F. boardmani, Rhizoprionodon acutus, Rhizoprionodon taylori and Rhynchobatus palpebratus face the least risk (i.e. were the most sustainable) while several medium-large batoids and the sharks Loxodon macrorhinus and Heteroscyllium colcloughi were the species most at risk (i.e. least sustainable). Demonstrating ecological sustainability of the ECTF will need to be a continued management objective into the future. To further improve the ecological sustainability of the fishery in relation to sharks, batoids and holocephalans, a number of management recommendations are proposed: (1) give warranted conservation consideration to listed threatened species as well as species identified as being at risk; (2) expand required logbook information on chondrichthyan species to include recording of catches of these species; (3) encourage safe release practices for all chondrichthyans to maximise survivorship of discards; (4) initiate research into the survivorship of discards; (5) ensure long-term observer coverage on commercial vessels to monitor bycatch levels; and, (6) test and quantify reduced TED bar spacings (presently 120 mm) in fishery sectors which show the highest chondrichthyan bycatch levels, that is, the eastern king prawn (shallow water) and scallop sectors.

The chondrichthyan (shark, batoid and holocephalan) bycatch of the Queensland East Coast Trawl Fishery (ECTF) was examined through a series of fishery-independent trawl surveys, together with fishery-dependent (opportunistic) sampling. Project aims were to document the chondrichthyan bycatch composition in order to test the effectiveness of turtle exclusion devices (TEDs) and bycatch reduction devices (BRDs), to examine biological aspects of bycatch species, and to combine data collected through these parts to assess the conservation status and sustainability of bycatch species. A total of 37 chondrichthyan species (one holocephalan, 19 batoids and 17 sharks) from 18 families were recorded in the bycatch of the fishery. The most speciose families recorded were the stingrays (Dasyatidae; 7 species), the requiem sharks (Carcharhinidae; 5 species), the catsharks (Scyliorhinidae; 4 species) and the stingarees (Urolophidae; 3 species). Chondrichthyan bycatch was highly variable between fishery sectors; catch rates were low in the tiger/Endeavour prawn sector (north Queensland; 0.02–0.12 individuals ha-1 trawled) and in the eastern king prawn (deepwater) sector (southern Queensland; 0.08 individuals ha-1 trawled), intermediate in Hervey Bay (southern Queensland; 0.25 individuals ha-1 trawled) and in the scallop sector (central Queensland coast; 0.31 individuals ha-1 trawled) and highest in the eastern king prawn (shallow water) sector (southern Queensland; 0.96 individuals ha-1 trawled). Chondrichthyan bycatch in the eastern king prawn (shallow water) sector was dominated by the three batoids Aptychotrema rostrata, Trygonoptera testacea and Urolophus kapalensis (~92% of the chondrichthyan bycatch by number), in the eastern king prawn (deepwater) sector by the skate Dipturus polyommata and the two catsharks Asymbolus rubiginosus and Figaro boardmani (~83% of the chondrichthyan bycatch by number), in the scallop sector by the three batoids A. rostrata, Neotrygon kuhlii and Neotrygon picta (~91% of the chondrichthyan bycatch by number), and in the tiger/Endeavour prawn sector by the two batoids Himantura astra and Gymnura australis and the two sharks Chiloscyllium punctatum and Hemigaleus australiensis (~67% of the chondrichthyan bycatch by number). The testing of TEDs and BRDs, which are mandatory throughout the fishery, demonstrated only a limited ability to reduce chondrichthyan bycatch in the ECTF, which is comprised mainly of relatively small species. The shorter trawl durations of the surveys compared with normal commercial activities may have under-represented larger species. No significant reductions in chondrichthyan bycatch were found using a TED and a radial escape section BRD in the eastern king prawn (shallow water) sector, using a TED and a square-mesh codend BRD in the eastern king prawn (deepwater) sector, or using a TED and a fisheye BRD in Hervey Bay. There was however, a significant difference in the probability of capturing the group ‘sharks and guitarfishes’ (comprised largely of A. rostrata) between codend types in the scallop sector, with the lowest probability of capture in nets fitted with both a TED and a square-mesh codend BRD (the difference was largely attributed to the effects of the TED). In the tiger/Endeavour prawn sector, in which three different BRDs were trialed (fisheye, square-mesh codend, square-mesh panel), the probability of capturing chondrichthyans was significantly lower in nets fitted with a fisheye BRD than in the standard (control) net, and the probability of capturing batoids was significantly lower in nets fitted with a fisheye BRD or with a square-mesh codend BRD than in the standard (control) net. The small sample size of chondrichthyan catches in some sectors may have reduced to power to detect bycatch reduction. The biology of several bycatch species from the families Rajidae, Rhinobatidae, Urolophidae and Scyliorhinidae was examined. For D. polyommata, size at birth was estimated at ~100–110 mm total length (LT), size at first feeding at ~105–110mm LT, size at 50% maturity (LT50 and 95% CI) at 321 (305–332) mm LT for females and 300 (285–306) mm LT for males. Diet (described by the index of relative importance as a percentage) was predominantly crustacean based, with carid shrimps (53.6%) and penaeoid prawns (23.3%) being the most significant prey groups. For A. rostrata, size at birth was estimated at <170 mm LT, size at 50% maturity (LT50 and 95% CI) at 640 (618–663) mm LT for females and 597 (551–649) mm LT for males, and litter size was 9–20 (n = 9; mean ± S.E. = 15.1 ± 1.2). For T. testacea, size at birth was estimated at 77–100 mm disc width (WD), size at 50% maturity (WD50 and 95% CI) at 163 (156–169) mm WD for females and 146 (140–150) mm WD for males, and litter size was always one (n = 6). For U. kapalensis, size at birth was estimated at 75–100 mm WD, size at 50% maturity (WD50 and 95% CI) at 154 (145–160) mm WD for females and 155 (149–159) mm WD for males, and litter size was always one (n = 16). The catsharks A. analis, A. rubiginosus and F. boardmani were all confirmed as single oviparous species (carrying only one egg case in each uterus at one time). Ovarian fecundity (the number of vitellogenic follicles) averaged 13.6 (range 13–20) in A. analis, 13.5 (range 5–23) in A. rubiginosus and 10.4 (range 9–13) in F. boardmani. While only limited data were available from southern Queensland, several indicators suggest that Asymbolus catsharks are reproductively active year-round. A general lack of small-sized or immature catsharks captured during the study made assessments of size at maturity difficult for these species. The conservation status of ECTF bycatch species was examined through the application of the IUCN Red List of Threatened SpeciesTM Categories and Criteria, which considers extinction risk at the global level. Of the 24 ECTF chondrichthyan bycatch species evaluated against the IUCN Red List Categories and Criteria, four have been assessed globally as Vulnerable (a threatened category indicating that a species is ‘facing a high risk of extinction in the wild’), seven as Near Threatened, 11 as Least Concern and two as Data Deficient. While the four globally threatened species (A. nichofii, Heteroscyllium colcloughi, Rhynchobatus australiae and Urolophus sufflavus) were only minor components of the ECTF bycatch, their global conservation status warrants that fisheries management and industry should act to ensure minimal impacts on these species. An ecological risk assessment method (Susceptibility-Recovery Analysis) was used to assess the relative sustainability or risk of individual species to the fishing activities of the ECTF. Two separate approaches were taken to the technique, which considers sustainability to be dependent on the susceptibility of a species to the fishery and the recovery potential of a species after depletion by fishing activities. The first approach applied the precautionary principal when data were lacking for the calculation of recovery attributes, while the second used biological data from similar species when species-specific data were lacking. The precautionary approach tended to overestimate risk to poorly known oviparous species. The biological approach suggested that A. nichofii, F. boardmani, Rhizoprionodon acutus, Rhizoprionodon taylori and Rhynchobatus palpebratus face the least risk (i.e. were the most sustainable) while several medium-large batoids and the sharks Loxodon macrorhinus and Heteroscyllium colcloughi were the species most at risk (i.e. least sustainable). Demonstrating ecological sustainability of the ECTF will need to be a continued management objective into the future. To further improve the ecological sustainability of the fishery in relation to sharks, batoids and holocephalans, a number of management recommendations are proposed: (1) give warranted conservation consideration to listed threatened species as well as species identified as being at risk; (2) expand required logbook information on chondrichthyan species to include recording of catches of these species; (3) encourage safe release practices for all chondrichthyans to maximise survivorship of discards; (4) initiate research into the survivorship of discards; (5) ensure long-term observer coverage on commercial vessels to monitor bycatch levels; and, (6) test and quantify reduced TED bar spacings (presently 120 mm) in fishery sectors which show the highest chondrichthyan bycatch levels, that is, the eastern king prawn (shallow water) and scallop sectors.

Thesis (Ph.D.) - James Cook University, 2002. / Bibliography: leaves 222-244.

Made available in DSpace on 2015-04-17T14:55:16Z (GMT). No. of bitstreams: 1 parte1.pdf: 2329943 bytes, checksum: 1cc93d9438f7097161f07a019201fb74 (MD5) Previous issue date: 2009-09-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The Corumbau marine extractive reserve (MER) was the first MER specifically designed to protect coral reefs. Fishers and their families were directly dependent on extractive activities in the area. The objective of this research, was to study the biology of the sea bob shrimp Xiphopenaeus kroyeri (Heller, 1862), its fisheries aspects and evaluate the effectiveness of a bycatch reduce devices (BRD). Fish landings were daily monitored between Aug/04 and Dec/06. Shrimp samples landed (Jul/04 to Jan/07) were weekly analyzed. Monitored fisheries, in the ten main fishing grounds around the region (Jan/07 to Jan/09), were seasonally carried out. The BRD was tested (Feb/06 and Aug/06) in an experimental net, with a conded composed of a standard net (30mm mesh) and a squaremesh (50mm) front top panel (50x50cm) and compared with a net control. A total of 55.409 individuals were sampled. The CL50 found was 12.55 mm. Females reach larger sizes (CL = 38.59 mm), a higher longevity (tmax = 26 months) and had lower growth rate (kmonth = 0.17) than males (CL = 32.35 mm; tmax = 16 months and kmonth = 0.28). The sex ratio did not differ between females and males, suggesting that trawl fisheries in Corumbau MER act mainly in growth and mating areas, not in spawning locations. There was a higher female frequency in reproductive activity in the first semester, mainly related to a higher transparency, salinity and water temperature. Rare events of Tropical Water mass probably led to favorable spawning conditions, even in places near to the coast. Recruitment period was continuous with the main peak occurring in July/August. The highest juvenile abundance was associated with higher water turbidity and pH values. Trawl fishery in Corumbau MER is handmade, not going over an isobaths average of 15m. The departures are daily held, mainly focused in the morning, minimizing the need for fish cooling and reducing the operations cost. Fishing effort varied among the communities, being greatest in Corumbau, followed by Cumuruxatiba and then Caraíva. The fishing grounds use varied seasonally, often related to climatic conditions and water visibility. X. kroyeri was the most abundant penaeid (96.4%) in all communities landings, with high fishing performance in Corumbau. The higest X. kroyeri CPUEs occurred during the autumn and winter, showing a negative correlation with water visibility and temperatures, coinciding with species recruitment. Around 50% of the fisheries act on less than 15mm CL individuals size. Thus, fishing in that region, may be running in an inappropriate way to sustainable resource management. The white shrimp (L. schmitti) production was very low compared to other species, although it was present all year round, in the three communities. The pink shrimp (F. brasiliensis and F. paulensis) production was higher in Cumuruxatiba, where a clear seasonal pattern is observed. A low CPUE was registered during winter and gradually increasing over the years, with harvest peak occurring in fall. Shrimp captures were probably limited to species recruitment period. During the experiment for bycatch reduce us identified 93 fish taxa, 89 belonging to Actinopterygii Class and 3 to Chondrichthyes Class. The square mesh nets are effective in excluding bycatch without affecting the catch of sea bob shrimp. The behavior, body shape and swimming ability were crucial for fish escape success from the panel, favoring especially the larger ones. A difference in fish assemblage could be established between sampling periods, not changing the device efficiency. Besides, depth regardless, a positive effect of square mesh panel was observed. Thus, this device use is very promising tool due to its structural features, as well as having low cost, been easy to purchase and to install. / A RESEX Corumbau é uma Unidade de Conservação de uso direto, que abriga uma porção representativa do Banco dos Abrolhos, sendo que a maior parte dos extrativistas dedica-se à pesca. O objetivo deste trabalho foi estudar a biologia do camarão Xiphopenaeus kroyeri (Heller, 1862), os aspectos da sua pesca e testar a eficiência de um dispositivo de redução de captura da fauna acompanhante. Os desembarques pesqueiros foram monitorados diariamente entre ago/04 e dez/06. Amostras dos camarões desembarcados (jul/04 a jan/07) foram analisadas semanalmente. Arrastos monitorados nos dez principais pesqueiros da região (jan/07 a jan/09) foram realizados sazonalmente. O dispositivo de redução foi testado (fev/06 e ago/06) em uma rede experimental, com o ensacador de malha 30mm e com um painel (50x50cm) localizado na parte anterior superior, confeccionado com malha quadrada (50mm) e comparados com uma rede controle. O total de 55.409 indivíduos foi amostrado. O CC50 encontrado foi de 12,55mm. As fêmeas atingem tamanhos maiores (CC=38,59mm), uma longevidade mais alta (tmax=26 meses) e apresentam índice de crescimento menor (kmês=0,17) que os machos (CC=32,35mm; tmax=16 meses e kmês=0,28). A razão sexual não diferiu, sugerindo que as pescarias de arrastos na RESEX Corumbau atuam principalmente em áreas de crescimento e acasalamento e não de desova. Verificou-se uma maior freqüência de fêmeas em atividade reprodutiva no primeiro semestre, relacionada principalmente com uma maior transparência, salinidade e temperatura da água. Eventos raros de entrada da massa de Água Tropical provavelmente propiciaram condições favoráveis à desova, mesmo em locais próximos a costa. O período de recrutamento foi contínuo, com o pico principal ocorrendo em julho/agosto. A maior abundância de jovens ocorreu associada a maiores valores de turbidez e pH da água. A pesca de arrasto na RESEX Corumbau é artesanal, não ultrapassando a isóbata média de 15m. As saídas são realizadas diariamente, concentrando-se principalmente pela manhã, minimizando a necessidade de resfriamento do pescado e diminuindo o custo das operações. O esforço de pesca variou entre as comunidades, sendo maior em Corumbau seguido por Cumuruxatiba e depois Caraíva. A utilização dos pesqueiros variou sazonalmente, sendo freqüentemente relacionada com as condições climáticas e com a visibilidade da água. X. kroyeri foi o peneídeo mais abundante (96,4%) nos desembarques de todas as comunidades, com o rendimento pesqueiro médio mais elevado em Corumbau. As maiores CPUEs de X. kroyeri ocorreram no durante o outono e o inverno, e apresentando uma relação negativa com a visibilidade e a temperatura da água e coincidindo com o período de recrutamento da espécie. Cerca de 50% das pescarias atuam sobre indivíduos com tamanho inferior à 15mm de CC. Assim, a pesca na região pode estar sendo executada de maneira inadequada ao manejo sustentável deste recurso. A produção do camarão VG (L. schmitti) foi muito baixa em relação às outras espécies, embora o mesmo esteja presente em todas as estações do ano, nas três comunidades. A produção de camarão rosa (F. brasiliensis e F. paulensis) foi maior em Cumuruxatiba, onde se pode observar uma nítida variação sazonal, com a CPUE baixa durante o inverno e aumentando gradativamente ao longo do ano, com o pico da safra ocorrendo no outono. As capturas do camarão rosa, provavelmente, foram limitadas ao período de recrutamento da espécie. Durante o experimento de redução de fauna acompanhante foram identificadas 93 espécies de peixes, sendo 89 pertencentes a Classe Actinopterygii e 3 a Classe Chondrichthyes. Foi possível verificar que as redes com o painel de malha quadrada são eficientes na exclusão da ictiofauna acompanhante, sem alterar as capturas de camarões sete-barbas. O comportamento, o formato do corpo e a capacidade de natação influenciaram a capacidade dos peixes para escaparem pelo painel, favorecendo, principalmente, os indivíduos de maior porte. Foi possível identificar diferenças nas assembléias de peixes entre os dois períodos analisados, sem alterações na eficiência do dispositivo. Além disso, independente da profundidade, o efeito positivo do painel de malha quadrada foi observado. Desta forma, a utilização desse dispositivo é bastante promissora devido à suas características estruturais, além de possuir baixo custo e ser de fácil aquisição e instalação.