Bycatch of non-target species in commercial fisheries is a major source of anthropogenic injury and mortality for marine megafauna, including marine turtles. Their long life histories and large-scale habitat use increase the risk of interaction with multiple fleets and gear types, with consequences for population decline or collapse. However, assessment of bycatch species rarely extends beyond a single-fishery management approach, without considering the impacts of additional bycatch incurred in other fisheries. To demonstrate the need for cross-jurisdictional assessment of turtle bycatch, we evaluate the cumulative patterns of turtle bycatch in Australian commercial fisheries. We sourced logbook bycatch records from multiple fisheries in three separate management jurisdictions over the period 2000–2013. The highest bycatch per unit effort values were reported in pelagic gillnets, otter trawls and pelagic longlines. Spatial analysis revealed a bycatch ‘hotspot’ in the Gulf of Carpentaria, where commercial fisheries impact multiple turtle species and genetic stocks. Our results illustrate the need to set cumulative bycatch quotas for marine turtles, and to evaluate turtle bycatch at the population level instead of separately within individual fisheries. We stress the need for timely collaboration between management agencies in order to implement effective, biologically relevant management strategies for marine turtles and other vulnerable taxa.
Food subsidies have the potential to modify ecosystems and affect the provision of goods and services. Predictable Anthropogenic Food Subsidies (PAFS) modify ecosystems by altering ecological processes and food webs. The global concern over the effects of PAFS in ecosystems has led to development of environmental policies aimed at curbing the production or ultimately banning of PAFS. However, the effects of reducing or banning PAFS are not known. We explore the consequences of PAFS removal in a marine ecosystem under two scenarios: 1) gradual reduction, or 2) an abrupt ban, using a mass balance model to test these hypotheses–The reduction or loss of PAFS will: i) modify trophic levels and food webs through effects on foraging by opportunistic species, ii) increase the resilience of opportunistic species to food shortages, and iii) modify predator–prey interactions through shifts in prey consumption. We found that PAFS lower the trophic levels of opportunistic scavengers and increase their food pathways. Scavengers are able to switch prey when PAFS are reduced gradually but they decline when PAFS are abruptly banned. PAFS reduction to a certain minimal level causes a drop in the ecosystem’s stability. We recommend gradual reduction of PAFS to a minimal level that would maintain the ecosystem’s stability and allow species exploiting PAFS to habituate to the food subsidy reduction.
Discarding of commercially important fish species in the bottom trawl fisheries in the northern Mediterranean Sea was investigated by soliciting the long-term recollections of fishers engaged or formerly engaged in such fisheries. The main aim of our investigation was to describe the prevalence of discarding and its evolution over the past 70 years using information gathered through individual questionnaire-based interviews with fishers from ports in Spain, Italy, and Greece, following a standardized sampling protocol. Although it proved impossible to derive absolute estimates of the volume of discarded catches over the period investigated, we conclude that over the past 70 years, discarding as a practice has gradually increased in the northern Mediterranean trawl fisheries and has been accompanied by a shift in the species composition of the discarded catch. While discarding can occur for a number of reasons, our investigations indicate that discarding in the past was mostly driven by market demand, but recent legal and regulatory constraints have led to changes in fishing strategies and became a significant reason for discards.
Although minke whales in Korean waters have been protected for more than 28 years after a commercial whaling moratorium in 1986, relatively little effort has been focused on assessing their current status of this population in this area after this protection and the efficacy of this protection. Thus, current stock situation and measures for the management and conservation of minke whales in Korean waters was investigated. Although Korea has undertaken significant efforts to archive the biological material of bycaught minke whales, the results remain incomplete. Furthermore, although a number of studies have reported the extent of bycaught minke whales, there has been little effort to reduce this occurrence in Korean waters compared with efforts to report it. Finally, there exists little data for investigating the effect of bycatch on the survival of minke whales in Korean waters. To improve weaknesses in the management of minke whales in Korean waters and to efficiently conserve and manage this population, the following efforts are urgently needed: 1) Conduct research on minke whales including satellite tagging; 2) Establish DNA registers for all minke whale bycatch, market surveys and intensive control of illegal catch; 3) Assess the usefulness of several mitigation measures to reduce bycatch (pingers, fishing gear modifications and time-area closures), and apply these measures; 4) Assess the effect of bycatch on the survival of minke whales in Korean waters; 5) Reduce the incentive for bycaught minke whales and use it as research funds for minke whales and incentives for releasing entrapped or entangled whale in fishing gears; 6) Compare with other studies on the management suggestions to modify the current stock situation. Among these suggestions to modify the current stock situation, the application of bycatch mitigation measures and intensive control of illegal catch are expected to efficiently improve the current stock situation of minke whales in Korean waters by reducing bycatch and illegal catch. Particularly, among bycatch mitigation measures, fishing gear modification and pinger are considered as efficient management suggestions for this stock in this area.
Estimation of at-sea discards is an issue that has received considerable attention worldwide. With this increasing focus, there is a need for greater precision of weight estimates for less common and fishery-limiting species. While one solution is to mandate full (100%) observer coverage to reduce uncertainty in estimation at the trip level, variance from on-deck sampling methods (e.g. within-haul) should also be properly addressed. Commercial fishing vessels are not perfect sampling platforms and all sampling methods suffer from implementation issues that potentially impact the quality of the data collected and the resulting estimates. We conducted a cooperative study with industry to evaluate two observer sampling methods on trawl vessels delivering their catch to shoreside processors. The alternative observer sampling method that targets the portion of the haul that would be discarded directly at-sea, relying on shoreside reports of retained catch to generate total catch estimates, was tested against the standard methods currently used by the NMFS North Pacific Groundfish and Halibut Observer Program that sample the entire catch, both retained and discarded portions (combined). Methods were tested simultaneously by deploying two observers to sample each haul on study trips within three Gulf of Alaska trawl fisheries that varied widely in amount and species composition of discards: Rockfish Program, arrowtooth flounder, and shallow water flatfish. Although the alternative method was successfully implemented in two of the three fisheries, logistical constraints decreased sampling effectiveness in the third. In some situations, observers were unable to collect multiple samples under both methods, preventing variance estimation. This occurred more often for the observer using standard methods. Detection of less common and rare species was higher using the alternative sampling method. Discard estimates from the two methods were found to be significantly different in two of the fisheries examined (Rockfish Program and arrowtooth flounder). Discard estimates under the alternative method tended to have smaller variances than for the standard method, although this was not universally the case. These results provide an important comparison of the relative performance of different on-deck sampling methods under varying catch conditions and fisheries.
A combination of fisheries dependent and independent data was used to assess the vulnerability of the oceanic whitetip shark to pelagic longline fisheries. The Brazilian tuna longline fleet, operating in the equatorial and southwestern Atlantic, is used as a case study. Fisheries dependent data include information from logbooks (from 1999 to 2011) and on-board observers (2004 to 2010), totaling 65,277 pelagic longline sets. Fisheries independent data were obtained from 8 oceanic whitetip sharks tagged with pop-up satellite archival tags in the area where longline fleet operated. Deployment periods varied from 60 to 178 days between 2010 and 2012. Tagging and pop-up sites were relatively close to each other, although individuals tended to travel long distances before returning to the tagging area. Some degree of site fidelity was observed. High utilization hotspots of tagged sharks fell inside the area under strongest fishing pressure. Despite the small sample size, a positive correlation between tag recorded information and catch data was detected. All sharks exhibited a strong preference for the warm and shallow waters of the mixed layer, spending on average more than 70% of the time above the thermocline and 95% above 120 m. Results indicate that the removal of shallow hooks on longline gear might be an efficient mitigation measure to reduce the bycatch of this pelagic shark species. The work also highlights the potential of tagging experiments to provide essential information for the development of spatio-temporal management measures.
We present the outcomes of a collaborative research programme tasked with reducing bycatch, and thus discards in a temperate Australian prawn trawl fishery. Sea trials in the Gulf of St Vincent, South Australia, assessed the performance of a modified trawlnet that incorporated a rigid polyethylene grid and a T90-mesh codend. Compared with conventional designs, the modified net yielded marked reductions in bycatch (cumulatively >81% by weight), with pronounced decreases in sponge (92%), elasmobranchs (80%), teleost fish (71%), molluscs (61%), and crustaceans (78%). Using commercial logbook data, we estimate that the use of modified nets could reduce discards by ∼240 tons per year. This outcome was achieved with moderate declines in the catch rate (kg h−1) of the target species, Western King Prawn (mean ∼15%), of which almost all were small adults of low commercial value. Adoption of the modified net by industry was realized in March 2012, because it met environmental objectives (i.e. reducing bycatch and improving public perceptions of sustainability), reduced prawn damage, demonstrated commensurate financial returns, and engaged stakeholders throughout the development process. Overall, the project provides a useful example of bycatch research with demonstrable outcomes of improving the ecological and economic sustainability of prawn harvests.
We apply an integrated and interdisciplinary conceptual framework to assess the potential for uptake of bycatch reduction measures by small-scale fisheries along the Andaman coast and eastern Gulf of Thailand, and in Sabah, Malaysia. Specifically, we characterize the current governance, socio-economic, ecological, and scientific context for marine megafauna bycatch, and identify the enabling and limiting factors to bycatch reduction at each location. Enabling factors are those that motivate or facilitate conservation actions among resource users, managers, and other stakeholders, while limiting factors are those that act as barriers to conservation. We conduct a comparative analysis of the strength of enabling and limiting factors at the two study locations by using a qualitative scoring system. Overall, conditions in Thailand appear to be relatively more supportive of bycatch reduction than Sabah. Many enabling factors, such as community based marine management and positive attitudes towards conservation, occur at the local scale, suggesting potential marine megafauna bycatch reduction approaches can be implemented successfully from the bottom-up. We show that intervention points for reducing marine megafauna bycatch lie within a much broader realm than conventionally considered in bycatch reduction schemes. Effective policies for reducing marine megafauna bycatch thus have to address multifaceted drivers of small-scale fishing behaviour in addition to ecological considerations.
Biological limit reference points (LRPs) for fisheries catch represent upper bounds that avoid undesirable population states. LRPs can support consistent management evaluation among species and regions, and can advance ecosystem-based fisheries management. For transboundary species, LRPs prorated by local abundance can inform local management decisions when international coordination is lacking. We estimated LRPs for western Pacific leatherbacks in the U.S. West Coast Exclusive Economic Zone (WCEEZ) using three approaches with different types of information on local abundance. For the current application, the best-informed LRP used a local abundance estimate derived from nest counts, vital rate information, satellite tag data, and fishery observer data, and was calculated with a Potential Biological Removal estimator. Management strategy evaluation was used to set tuning parameters of the LRP estimators to satisfy risk tolerances for falling below population thresholds, and to evaluate sensitivity of population outcomes to bias in key inputs. We estimated local LRPs consistent with three hypothetical management objectives: allowing the population to rebuild to its maximum net productivity level (4.7 turtles per five years), limiting delay of population rebuilding (0.8 turtles per five years), or only preventing further decline (7.7 turtles per five years). These LRPs pertain to all human-caused removals and represent the WCEEZ contribution to meeting population management objectives within a broader international cooperative framework. We present multi-year estimates, because at low LRP values, annual assessments are prone to substantial error that can lead to volatile and costly management without providing further conservation benefit. The novel approach and the performance criteria used here are not a direct expression of the “jeopardy” standard of the U.S. Endangered Species Act, but they provide useful assessment information and could help guide international management frameworks. Given the range of abundance data scenarios addressed, LRPs should be estimable for many other areas, populations, and taxa.
Sea turtles in Indian waters are impacted by incidental catch in fisheries, coastal development, habitat loss and depreda-ion of eggs1. Incidental catch in fishing gear is considered to be one of the major factors responsible for declining population of sea turtles and other marine megafauna2,3. Turtles are particularly vulnerable to entanglement and drowning in gillnets and associated gears, as the rough skin on their head and flippers catches easily on the meshes of these nets4,5. Incidental bycatch of sea turtles at a hooking rate of 0.108 for every 1000 hooks during the exploratory tuna longlining was carried out by the Fishery Survey of India in the Indian Exclusive Economic Zone (EEZ) during 2005– 2008. Maximum hooking rate of 0.302% of 1000 hooks was reported from the Bay of Bengal6. It is observed that the biological and physical oceanographic processes are closely coupled at some locations of oceans, indicating an enhanced production where fishery resources accumulate for foraging. Remotely sensed data on chlorophyll-a concentration (CC) and sea-surface temperature (SST) has been used in India for identifying meso-scales features like eddies, fronts, rings for potential fishing zones (PFZs) forecast7,8. In this study, we used CC, SST and sea-surface height anomaly (SSHa) derived from space- borne data to correlate the reported instances of sea turtle interactions in the tuna longline fishery for identification of areas with high risk of sea turtle bycatch.