Discards from the commercial gillnet fishery for dusky flathead, Platycephalus fuscus, in New South Wales, Australia: spatial variability and initial effects of change in minimum legal length of target species

A scientific observer programme was used to quantify the composition and magnitude of discards in the gillnet fishery for dusky flathead, Platycephalus fuscus (Cuvier), in three barrier estuaries in New South Wales, Australia, during the 2001 fishing season. Regulations only permit the retention of legal‐sized dusky flathead and legal‐sized blue swimmer crab, Portunus pelagicus L., and mud crab, Scylla serrata (Forskål); all other organisms were discarded. Sampling was stratified into two time periods; before and after 1 July 2001 which coincided with the increase in the minimum legal length (MLL) of dusky flathead from 33 to 36 cm total length (TL). Eighty one catches were sampled, yielding 38 finfish species and two portunid crab species. Legal‐sized dusky flathead were the most abundant organism captured, accounting for 23–47% by number and 34–54% by weight of the mean observed catch depending on the estuary and survey period, with a mean catch of 25–59 flathead weighing 13–25 kg per fishing‐night. Species composition and relative abundance of catches differed among estuaries, but not between sampling periods. Predominant bycatch species included legal and undersize blue swimmer crab, sea mullet, Mugil cephalus L., luderick, Girella tricuspidata (Quoy & Gaimard), bream, Acanthopagrus australis (Günther) and yellowfin leatherjacket, Meuschenia trachylepis (Günther). These five species accounted for 82% of total bycatch by number and 71% by weight, pooled across the three estuaries. More crabs were retained than discarded, with retained legal‐size crabs (byproduct) accounting for 16% of total bycatch by number and 13% by weight, with an average of 5–22 crabs weighing 1–6 kg being caught per fishing‐night, depending on the estuary. Overall, 7% of dusky flathead captured (number) were below the MLL of 36 cm and discarded, suggesting the nets as currently configured may be relatively selective in catching legal‐size flathead. However, 41% of dusky flathead were <40 cm TL, indicating that if the MLL for this species is increased to this length as proposed, new nets must be introduced into the fishery. The findings are discussed in terms of making the flathead fishery more sustainable, including alternative management strategies for the fishery.     

Effects of mesh size,fishing depth and season on the catch and discards of short mackerel Rastrelliger brachysoma gillnet fishery at the mouth of Pattani Bay,Thailand

This study evaluates the impacts of mesh size of the net, fishing depth and season on the catches of target, non-target and discarded species for short mackerel Rastrelliger brachysoma gillnet fishery in the vicinity of Pattani Bay, Gulf of Thailand. The catches were examined for species composition, catch efficiency and size of catch. Samples were obtained monthly from February 2019 to February 2020 at three fishing depths (2.0, 4.0 and 6.0 m) using gillnets with three different mesh sizes (3.0, 4.0 and 4.5 cm). Including the target species, 112 species were collected, the majority of which were non-targeted fishes and crustaceans. The target species, Rastrelliger brachysoma, contributed only 6.0% by number and 8.76% by weight to the total catches. The 111 non-target species were classified into five categories based on potential sale prices. A total of 18 species, equivalent to 3.04% by weight of the total catches, were considered to be of negligible value and discarded or sold for the production of fish meal. Temporal variability was observed for number of individuals and biomass of total catches; the compositions of the catches clustered to two distinct seasons from December to March and from April to November, respectively. Spatial variability in this study focused on the depth profile which was found to significantly influence species richness and sizes of some fish species. For 12 species, mesh sizes of the gillnets significantly affected the number of individuals caught, as well as their weight and sizes. The novel findings of this study provide essential information that can be used for the sustainable management of the Rastrelliger brachysoma fishery in the Gulf of Thailand.

     

Bycatch and discarding in the South African demersal trawl fishery

Observers aboard commercial trawlers collected data on the total catch composition of 614 and 479 hauls made by vessels operating off the south and west coasts of South Africa, respectively. On the south coast, four fishing areas were identified on the basis of target species and fishing depth. On the west coast, hauls were separated into those targeting hake Merluccius spp. in four depth ranges (0–300, 301–400, 401–500, and >500 m) and those targeting monkfish Lophius vomerinus. For each area, the catch composition was calculated and the species assemblages were investigated using cluster analysis and multi-dimensional scaling. Finally, for each coast, the weight of fish discarded annually was estimated. On the south coast, although hake dominated, between 21% and 47% of the catch was not hake, depending on the fishing area. In comparison, hake dominated west coast catches, the proportion of hake increasing with depth. For each fishery investigated, approximately 90% of the catch was processed and landed. However, estimates of annual discards indicate that the south and west coast fisheries may annually discard 9000 or 10,000 t and 17,000 or 25,000 t, of undersized and unutilizable fish and offal, respectively, depending on the estimation method used. When developing strategies to limit or enhance utilization of bycatch, cognisance should be taken of the differences in catch composition between the south and west coasts and of the importance of bycatch revenue to south coast fishing companies.     

A preliminary appraisal of the contribution of recreational fishing to the fisheries sector in north-west Trinidad

Abstract An assessment of the recreational fishery in north-west Trinidad was made by questioning participants about the principal fishing methods used, location of activities, catches, effort and cost of fishing. Surface handline methods (live baiting [à la vive] and trolling) and rod and line (banking) were the most common methods used and were pursued mainly in the summer months (April to August). Total fish landings from the fishery were estimated at 1000 t year^-1, equivalent to about 10% of commercial catches for Trinidad. The principal species caught were kingfish, Scomberomorus cavalla (Cuv.), carite, Scomberomorus brasiliensis (Cuv.), cavalli, Caranx hippos (L.), snappers, Lutjanus spp., and groupers, Epinephelus spp. Many of the fishermen sold their catch to offset the costs of the fishing trip and thus competed with commercial fishermen. Recommendations for monitoring and possibly regulating the fishery through a licensing scheme are made.     

Effects of 17/0 circle hooks and bait on fish catches in a Southern Atlantic swordfish longline fishery

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Evaluation of separator grates for reduction of bycatch in the silver hake (Merluccius bilinearis) otter trawl fishery off Nova Scotia, Canada

The effectiveness of separator grates in reducing bycatches in the small-mesh otter trawl fishery for silver hake on the Scotian Shelf was examined in three experiments aboard a research and two commercial vessels. Different grate bar orientations, bar spacings, grate insertion angles, and guiding mechanisms were tested. The size selection and escapement levels resulting from these grate configurations are described. A grate with vertical bars spaced 40 mm apart inserted at 45–60°, and with a funnel or panel forward of the grate to direct fish to its base, released 85–98% by weight of pollock and haddock, and 48–70% of other species, while retaining 95% of silver hake. Commercial bycatches contained more small haddock than did experimental catches, and it is projected that commercial use of this grate would release 75–80% by weight of haddock encountered, and only 50% by number. Other grate configurations tested displayed poorer species selection characteristics.     

Wasted fishery resources: discarded by-catch in the USA

Fishery by‐catch, especially discarded by‐catch, is a serious problem in the world's oceans. Not only are the stocks of discarded species affected, but entire trophic webs and habitats may be disrupted at the ecosystem level. This paper reviews discarding in the marine fisheries of the USA; however, the type, diversity and regulatory mechanisms of the fisheries are similar to developed fisheries and management programmes throughout the world. We have compiled current estimates of discarded by‐catch for each major marine fishery in the USA using estimates from existing literature, both published and unpublished. We did not re‐estimate discards or discard rates from raw data, nor did we include data on protected species (turtles, mammals and birds) and so this study covers discarded by‐catch of finfish and fishable invertebrates. For some fisheries, additional calculations were required to transform number data into weight data, and typically length and weight composition data were used. Specific data for each fishery are referenced in Harrington et al. (Wasted Resources: Bycatch and discards in US Fisheries, Oceana, Washington, DC, 2005). Overall, our compiled estimates are that 1.06 million tonnes of fish were discarded and 3.7 million tonnes of fish were landed in USA marine fisheries in 2002. This amounts to a nationwide discard to landings ratio of 0.28, amongst the highest in the world. Regionally, the southeast had the largest discard to landings ratio (0.59), followed closely by the highly migratory species fisheries (0.52) and the northeast fisheries (0.49). The Alaskan and west coast fisheries had the lowest ratios (0.12 and 0.15 respectively). Shrimp fisheries in the southeast were the major contributors to the high discard rate in that region, with discard ratios of 4.56 (Gulf of Mexico) and 2.95 (South Atlantic). By‐catch and discarding is a major component of the impact of fisheries on marine ecosystems. There have been substantial efforts to reduce by‐catch in some fisheries, but broadly based programmes covering all fisheries are needed within the USA and around the world. In response to international agreements to improve fishery management, by‐catch and discard reduction must become a regular part of fishery management planning.     

Retained and discarded catches from commercial beach-seining in Botany Bay, Australia

Observer-based estimates of the quantities and size compositions of discarded and retained catches from the commercial beach-seine fishery in Botany Bay, NSW, Australia are presented. A total of 71 finfish and 10 invertebrate taxa were identified in catches sampled between February 1998 and February 1999, with 39 taxa being retained by fishers and 77 taxa discarded. Gerres subfasciatus, Pseudocaranx dentex, Sillago ciliata, Acanthopagrus australis and Rhabdosargus sarba dominated retained catches. Discards included small individuals of many retained species that are also important in other commercial and recreational fisheries, including S. ciliata, A. australis, R. sarba, Pagrus auratus, Meuschenia freycineti and Scobinichthys granulatus, as well as some non-monetary valued species such as Dicotylichthys punctulatus, Anoplocapros inermis and several tetraodontids. The estimated monthly ratio of retained to discarded catch (kg) ranged from 1:0.26 to 1:2.48. An estimated 44% of total individuals and 38% of the total weight of catches were discarded. It was estimated that this fishery annually discarded 93 t of fish and invertebrates, which included hundreds of, thousands of commercially and recreationally important species. The results are discussed in terms of their consequences for interactions with other fisheries.     

Recreational charter fishery attributes and variation in key species catches and discards: Resource management considerations

Strategic long‐term sampling programmes that deliver recreational catch, effort and species demographic data are required for the effective assessment and management of recreational fisheries and harvested organisms. This study used a spatially and temporally stratified observer programme to examine variation in the rates, quantities and lengths of retained and discarded catches of key species in a recreational charter fishery. Geographic region, but not season, significantly influenced catch rates of key demersal species, being driven by temporally persistent latitudinal clines in environmental conditions influencing species distributions. There was considerable trip‐to‐trip variation in catch rates that were attributed to localised differences in fishing operations, locations, environmental conditions and client preferences. Broad trends in retained and discarded catch rates were nevertheless, similar across different fishing effort standardisations (per‐trip, per‐hour, per‐client, per‐client/fished hour), demonstrating that the coarsest unit of effort could be used in fishery assessments. Discard rates of organisms were variable and driven by a combination of mandated legal lengths, individual client and operator preferences for particular species and sizes of organisms, and not due to attainment of catch quotas or high‐grading. This study has identified important fishery attributes that require consideration in assessing charter fisheries and stocks of recreational fish species.     

Discarding practices in a Mediterranean small-scale fishing fleet (Patraikos Gulf, Greece)

Abstract  Discarding practices from 110 fishing operations in a Mediterranean small-scale fishing fleet (Patraikos Gulf, western Greece) from August 2004 to July 2005 were analysed. On average, 1 kg of fish was discarded per fishing operation (10% of the catch). The reasons for discarding were: low commercial value (78% of discards), damage at sea before retrieval of the gear (5%), and bad handling on-board (17%). More than half of discards belonged to Spicara flexuosa (L.), Lepidopus caudatus (Euphrasen), Sardinella aurita Valenciennes and Merluccius merluccius (L.). The bulk of discards of each species were associated with a single fishing method (metier). A Generalized Linear Model (Delta-X – error-model) indicated that, when discards were present, significant differences existed in the discard ratio among different métier groups (groups comprising métiers with similar characteristics). Longlines and trammel nets with small mesh-sizes had the highest discard ratios. Discarding practices for the species Diplodus annularis (L.), S. aurita , Squilla mantis (L.), S. flexuosa and Scorpaena scrofa (L.) did not follow a consistent pattern (these species were either fully discarded or fully retained during a fishing operation). The decision seemed to be dependent on market demands rather than fish size. Significant correlation was found between discarded and catch weight, but the presence of many outliers indicated deviance from a case where discards are high when there is an abundant catch. The findings of the study imply that monitoring and management should be carried out preferably on the métier level. Discards could be reduced by technical measures, controlling effort regulations and by improving working conditions on-board fishing vessels.     

Optimising harvest strategies in a multi‐species bivalve fishery

Abstract Optimising harvests from fishery resources requires appropriate data. In this study, fishery‐independent survey and size‐at‐first maturity (L₅₀) data were used to assess the suitability of current minimum legal sizes (MLS) and total allowable commercial catches (TACC) in the South Australian, mixed‐species, mud‐cockle (Katelysia spp.) fishery. Estimates of L₅₀ suggested the MLS was conservative in one fishing zone (Coffin Bay), but appropriate elsewhere. Harvestable‐biomass estimates (HB) demonstrated that TACCs were excessive in the Port River (41% of HB), suitable in Coffin Bay (10% of HB) and precautionary in the West Coast (1.5% of HB) fishing zones. Consequently, the MLS was decreased by 5 mm shell length in Coffin Bay and the TACCs for the Port River (reduced by 80%) and West Coast (increased by 40%) amended. This study demonstrated that harvest strategies in mixed‐species fisheries can be optimised by explicitly considering data on species composition, abundance and population biology.     

Temperature‐based targeting in a multispecies fishery under climate change

Temperature controls important physiological processes in fish and determines aspects of their niches. In an effort to inform selective fishing and spatiotemporal management in the U.S. Northeast Multispecies fishery, we used 16 years of data from the Northeast Fisheries Science Center Spring and Fall Scientific Trawl Surveys to determine if bottom temperature can be used to differentiate the distribution of Atlantic cod (Gadus morhua) from other species within the fishery management plan (FMP). We identified two separate regimes in spring temperatures and used empirical cumulative distribution functions to calculate biomass availability by temperature for each species. We applied a bagged approach to find optimum thermal threshold values that maximize the difference in cod biomass from each of the other species. For our study area, 38% to 54% of the species considered were well separated from cod by temperature in spring, whereas only 17% were separable in the fall. This study suggests that temperature targeting can be used seasonally to separate cod from many other species in the FMP including top catches and no‐retention species. The use of temperature targeting may allow fishermen to better meet multiple quotas while avoiding choke species. Our results also suggested increasing thermal overlap between cod and species inhabiting higher median temperatures (e.g., spiny dogfish, Squalus acanthias) under the current warming temperature regime. These results indicate that the ability to selectively fish in the US Northeast Multispecies fishery will become more difficult under a warming ocean.     

Non-commercial invertebrate discards in an experimental trammel net fishery

Abstract  Non-commercial invertebrate discards in an experimental trammel net fishery were studied in relation to selectivity of the gear, depth, soak time and season. Forty experimental fishing trials were carried out over a 1-year period with six combinations of small mesh (100, 120 and 140 mm) inner and large mesh (600 and 800 mm) outer panels. On average, 43.8 ± 12.2 (SD) (individuals 1000 m⁻¹ of net) of non-commercial invertebrates were discarded, accounting for 48% and 65% of the total catch and total discards by numbers, respectively. Within non-commercial invertebrates discards, the six most abundant species by number were Phallusia mammillata (Cuvier) (27.5%), Cymbium olla (L.) (13.0%), Sphaerechinus granularis (Lamarck) (11.3%), Paracentrotus lividus (Lamarck) (10.9%), Astropartus mediterraneus (Risso) (8.2%) and Astropecten aranciacus (L.) (8.1%); Echinoderms (43.1%) particularly important. The highest and lowest discard ratios were found in autumn and winter, respectively. Discards generally decreased with depth, varied considerably in relation to soak time and were not related to mesh size combinations. Trammel nets seem to be the most important gear in terms of ecological impacts on benthic invertebrates compared with other coastal fishing gears and at the depths studied (15–60 m).     

Fishing strategy choices of purse seines in the Mediterranean: implications for management

ABSTRACT:   An observer's sampling scheme, that employed fisheries scientists onboard fleet vessels was used to examine temporal fishing tactics and strategies affecting catches of the purse seine fishery in the Mediterranean. The month, water depth and the fishers' behavior were found to have an effect on total and Trachurus spp. retained catches, with fishers' behavior explaining the largest percentage of the data variation. The distance of the fishing ground from port and the market price modulated both the retained catches and the fishing location choice. Results confirmed that fishers while in a specific fishing ground developed strategies that would allow them to retain, and thus land, the best possible combination of landings × market value. The current findings also revealed that, when constrained by physical and economic conditions, fishers preferred to minimise risk rather than maximize landings. The observed major switches in fishing strategy were attributed to fishers' risk attitude response towards higher profitability. As the Mediterranean fishery system is mainly based on control effort and technical measures regimes, the current findings are discussed in the light of the need to consider additional information to management plans and decisions.     

Evaluation of observer‐ and industry‐based catch data in a recreational charter fishery

There is international recognition for greater inclusion of recreational fisheries catch data in species, fisheries and ecosystem assessments. Recreational charter fisheries provide important social services and contribute to total species catches. This study compares and validates industry logbook catch and effort data (1,357 trips) against observer data (154 trips) across six ports in a recreational charter fishery in eastern Australia. The mean numbers of clients and fishing effort (hours) per trip varied inconsistently between data sources and among ports. Logbooks did not adequately report released catches, and the mean number of species retained per trip was consistently underestimated in logbooks compared to observer data. For both data sources, catch rates of total individuals and key species displayed similar trends across different units of effort; catch per hour, client, client/hour and trip. The mean catch rates of total individuals and most key species, except those retained for bait, were similar across data sources, as were estimates of total fleet harvests. The length compositions of retained catches of some key species displayed truncation of larger organisms in the observer data whereas other species did not. Despite the shortcomings of the logbook data, future fishery and species monitoring strategies could include industry and observer data sources.     

Seabird interactions and by‐catch in the anchovy pelagic trawl fishery operating in northern Argentina

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Remotely sensed spatial dynamics of the Illex argentinus fishery, Southwest Atlantic

Illex argentinus, the Argentine short-finned squid, is an important species within the Patagonian shelf ecosystem, where it supports a major multi-national fishery. The fishing fleet operating in this region is comprised of jigging vessels which attract squid using powerful incandescent lights. These fishing lights are detectable in remotely sensed satellite imagery which makes the fishery unusually amenable to a large-scale analysis of its spatial dynamics. In this paper, long-term inter-annual variability in fleet distribution and extent is examined using imagery from the Defence Meteorological Satellite Program-Operational Linescan System (DMSP-OLS) for the period 1993–2005. The fishery was found to occupy a wide area across the shelf and slope, with regions of consistent fishing activity observed on the high seas (45–47°S) and to the north of the Falkland Islands (Malvinas). Distribution of the fishery over the 13-year study period was variable, with 28% of the fished area occupied in 1–2 years, and 7% of the area occupied in 12–13 years. Annual catch levels were positively associated with the extent of the area occupied by the fleet. Higher catches corresponded to the fishery occupying a wide latitudinal range, whereas lower catches were observed during 2004 and 2005 corresponding to a contraction of the fishery away from the south of its range. In years of very high catches, fishing took place along almost the entire latitudinal range of the species. Due to the intensity of fishing, changes in the distribution of the fleet can reflect shifts in the distribution of I. argentinus; this has potential for the long-term monitoring of this highly variable squid fishery.     

The development of fisheries at Bornholm,Denmark (Baltic Sea) during 1880s–1914

For centuries the abundance of fish in the Baltic Sea has had an important role in the economy of Bornholm, Denmark. This study examines the development of Bornholm fisheries between approximately 1880s and 1914 on the basis of the first officially recorded Danish fisheries data. Several species were caught, but prior to 1914 especially herring, salmon and cod were economically most important. In the late 19th and early 20th century, the catch composition changed fundamentally due to complex interactions between biological, technological and economical factors. During the late 19th century the catches of herring increased, while the catches of salmon and cod decreased. This development coincided with the introduction of new technologies and fishing practices, including motorization of fishing vessels and the exploitation of herring in previously unexploited areas (i.e., expansion of fishing areas). In addition, the salmon fishery diminished after the introduction of driftnets, which caught large numbers of small salmon. The high catches of small salmon, in combination with other factors, probably contributed to the decline in catches of larger salmon. Each of the fisheries for the three species required different types of vessels and gear, and when catches began to drop in the salmon fishery, Bornholm fishermen were faced with two options. They could either specialise in the growing herring fishery, thereby hoping to maintain their income level, or they could pursue a strategy of risk minimization, by acquiring an income outside the fishing industry, while continuing to work part-time in the salmon and cod fisheries. This dual tendency was intensified further as marine engines and new types of vessels were introduced, raising the costs of fishing.     

The sea cucumber fishery in Australia's Great Barrier Reef Marine Park follows global patterns of serial exploitation

Tropical sea cucumber fisheries follow a predictable pattern of serial depletion. Overfishing is exacerbated in developing countries where management systems lack capacity to control large numbers of fishers influenced by poverty. In contrast, the tropical sea cucumber fishery in Australia's World Heritage listed Great Barrier Reef Marine Park (GBRMP) is operating in a developed high‐income country with relatively few licensed fishers to manage. The development of this fishery is reviewed here in a meta‐analysis of catches from 1991 to 2011. The fishery expanded to replace high‐value teatfish species (Holothuria whitmaei and H. fuscogilva), fished heavily in initial stages of the fishery, with newly commercialized medium‐value species such as burying blackfish (Actinopyga spinea) and curryfish (Stichopus herrmanni). These two species now constitute 80% of total catch. The annual average catch of burying blackfish was 208 tonnes years 2004–11 and curryfish catches increased rapidly at an average annual pace of 200% from 2007–11. This serial harvest pattern occurred in the absence of baseline studies and without independent resource assessments, information required to inform relevant harvest predictions and to determine fishery impacts. This situation does not support ecologically relevant and adaptive decision‐making in management and the unfolding catch patterns in the GBRMP follow those in low‐income developing countries. The missing knowledge and lack of data serve as arguments to support precautionary reductions in harvests and extending fallow periods in fishing zones.