Sea turtles are adversely affected by a range of factors, some natural and others caused by human activities, such as fishing operations. As a result, all sea turtle species whose conservation status has been assessed are listed as threatened or endangered in the International Union for the Conservation of Nature’s Red List. While the understanding of the relative risks of the full suite of mortality sources for individual turtle populations is generally poor, there is growing evidence that small-scale artisanal fisheries may be the largest single threat to some sea turtle populations.
Coastal passive net fisheries use gillnets, trammel nets, pound nets, fyke nets and other static gear that catch, and in some cases, drown turtles. Small-scale fisheries have the potential to substantially contribute to sustainable economic development. However, to secure their long-term economic viability and to ensure conformance with international guidelines for the conduct of responsible fisheries, they need to mitigate problematic bycatch of sea turtles and other sensitive species groups. Such mitigation approaches are part of an overall effective fishery management framework that includes measures to prevent the overexploitation of all retained and discarded catch, as well as unobserved fishing mortalities.
Forty-nine participants from 17 countries, representing fishery bodies and other intergovernmental organizations, national fishery management authorities, environmental non- governmental organizations, academic institutions, fishing industries and donor organizations attended the Technical Workshop on Mitigating Sea Turtle Bycatch in Coastal Net Fisheries from 20-22 January 2009 in Honolulu, U.S.A. The five workshop co-hosts were the International Union for the Conservation of Nature, Western Pacific Regional Fishery Management Council, Southeast Asian Fisheries Development Center, Indian Ocean – South-East Asian Marine Turtle MoU and the U.S. National Marine Fisheries Service Southeast Fisheries Science Center.
This workshop represented the first opportunity for experts from multiple disciplines relevant to this issue to meet to share information from 20 coastal net fisheries worldwide to disseminate and transfer best practices for sea turtle bycatch assessment and mitigation. Accomplishments during the three-day workshop included:
- Identifying the status of assessment and mitigation activities of fisheries represented at the workshop;
- Describing the state of knowledge for the effective and commercially viable (economically viable, practical, safe) mitigation of sea turtle capture and mortality in coastal passive net fisheries;
- Identifying characteristics of coastal passive net fishing gear and methods likely to have a significant effect on sea turtle and target species catch and mortality rates;
- Identifying research priorities to advance promising new turtle-friendly fishing gear and methods, based on the understanding and gaps in knowledge of why and how sea turtles interact with passive net gear, and the understanding of gear characteristics that significantly affect turtle capture and mortality rates;
- Exploring the full suite of tools available to assess, mitigate and manage sea turtle bycatch in artisanal fisheries;
- Identifying a list of optimal information to understand the degree of risk a fishery poses to sea turtles and identify mitigation opportunities;
- Sharing lessons learned of effective and ineffective practices and approaches for working with artisanal fishing communities to assess and manage bycatch; and
- Fostering partnerships and catalyzing assessments, commercial demonstrations and mitigation activities identified as priorities during the workshop, in part, by transferring the lessons learned in the few net fisheries where progress has been made to priority fisheries in other regions.
Range of Potential Fishery-Specific Solutions
Several practices were identified as having the potential to effectively avoid, minimize and offset sea turtle capture, and improve the survival prospects following gear interactions in coastal passive net fisheries. Bycatch mitigation practices discussed during the workshop included: modifications to fishing gear and methods; gear restrictions; marine protected areas (temporal and spatial restrictions on fishing); changing to a gear type with lower turtle interactions; and handling and release best practices. However, participants recognized that the efficacy at reducing sea turtle capture rates, economic viability, practicality and safety are fishery-specific and therefore fishery-specific assessment is required before recommending a mitigation approach.
Priority Gaps in Understanding
Participants identified priority gaps in knowledge warranting further investment in order to advance mitigating sea turtle bycatch in coastal net fisheries. There is a need for:
- A generic decision tree or logic framework process tool, which could be used as a starting point to guide artisanal fishery-specific assessment and mitigation activities;
- Improved understanding of why turtles interact with coastal net fishing gear (e.g., are they attracted to the catch and/or floats); how turtles interact with the gear (e.g., what mechanism is responsible for capture [gilling, entangling, entrapping], and in which part of the gear are turtles captured); how the gear behaves under actual fishing conditions; what characteristics of the gear design, materials and fishing methods are significant factors affecting sea turtle capture and mortality rates; and, ultimately, what the opportunities are for mitigating turtle capture, injury and mortality;
- Standardized terminology and a classification scheme for coastal passive net fishing gear, focusing on factors that significantly affect sea turtle capture and mortality rates;
- Standardized units to report sea turtle catch-per-unit-of-effort (e.g., catch per trip, set, unit length of net, unit area of net, unit area per soak time, net weight).
- Accurate data on the relative impact of coastal net fisheries and other anthropogenic hazards on the long-term viability of sea turtle populations, so that limited resources can be allocated to address priority threats, accounting for the likelihood that interventions will successfully mitigate targeted anthropogenic mortality source;
- Characterizations of the degree of risk individual fisheries pose to affected sea turtle populations, based on accurate assessments; and
- Improved understanding of the indirect effects that coastal net fisheries have on sea turtles (e.g., obstacle to critical habitat and migration routes, ghost fishing, repeat captures, altered diet from depredating catch from gear, reduced predators or prey populations), information that is needed to produce precise risk characterizations.
Gear Technology State of Knowledge
Empirical evidence of the fishery-specific efficacy and commercial viability of gear technology approaches (changes in fishing gear designs and materials and fishing methods) at mitigating sea turtle capture in coastal net fisheries is available from only a small number of fisheries and studies. The following are gear technology approaches that have been shown to significantly reduce sea turtle catch rates in individual gillnet fisheries:
- Reducing net profile (vertical height);
- Increasing tiedown length, or eliminating tiedowns;
- Placing shark-shaped silhouettes adjacent to the net; and
- Illuminating portions of the net using lightsticks.
Of these techniques, only net illumination was found to not cause a significant decrease in target species catch rates.
In coastal poundnets, several turtle bycatch mitigation approaches have been explored:
- Replacing mesh with ropes in the upper portion of leaders has been observed to cause a significant reduction in the turtle capture rate with an increase in catch rate of one target species and no significant difference in catch rates of four other target species;
- Incorporating a prototype turtle releasing device into the roof of a cone-shaped pound in the small-scale southern Japan pound net fishery resulted in high escapement of green sea turtles with nominal target species escapement
- Modifying the roof of the pound in the Japanese large-scale pound net fishery to a rectangular-pyramid-shaped pound with the top angled at 20 degrees toward the apex effectively directed turtles towards the roof apex of the pound, where an escapement device could be situated.
- Observations document that pound nets with open versus closed capture chambers (also referred to as pounds or traps) have higher survival rates of captured turtles.
Broad assessments in individual fisheries must precede advocacy for uptake of specific turtle bycatch reduction methods. This is because there are several locally variable factors that significantly affect sea turtle and target species catch rates, and industry acceptability of any reductions in catch rates of commercially important species will depend on the local socioeconomic and regulatory context.
Gear Technology Research Priorities
It is unclear at this incipient stage in investigating this conservation issue whether or not gear technology approaches will be an effective and commercially viable solution to sea turtle interactions in most coastal passive net fisheries. Several promising new approaches warrant additional or new investigation:
- Fishing at sufficiently shallow depths, and increasing net liftability by adjusting the weighting design and/or anchoring system to allow captured turtles to reach the surface and breathe during the gear soak, increasing the proportion of caught turtles that survive the gear interaction;
- Minimizing gear soak time/time between patrolling gear in order to reduce the time incidentally caught turtles remain in the gear;
- Using alternative net materials and illumination to reduce the risk of turtle capture. For instance, making the upper portion of nets more visible, while leaving the lower portion relatively undetectable might be an effective and economically viable method. Using a clear, UV-absorbent plastic material for netting could reduce turtle bycatch without compromising fish catch rates. Using coarse multifilament line in place of monofilament in the upper portion, embedding luminescent materials into netting material and incorporating lightsticks are additional strategies to increase net visibility for turtles but not for target fish species. Continuing research on the effects on turtle and target species catch rates from alternative spectral frequencies and light brightness for net illumination is needed;
- Using buoyless floatlines might reduce turtle attraction to the gear and entanglement in the floatlines. Modifying float characteristics and reducing the number of floats and vertical float lines might reduce turtle attraction and incidence of entanglement in floatlines and the net;
- Conducting research, development and trials of devices to avoid and minimize turtle entrance into pound net and fyke net traps, such as use of a deflector grid;
- Modifying baiting techniques, in cases where baiting is used;
- Setting gear perpendicular to the shore to reduce capture rates with nesting females, and exploring effects of other gear orientations to and distance from the coastline;
- Continuing research on reduced net profile and increased length or elimination of tiedowns. Expanding this to research if increasing the net hanging ratio (ratio of net height to net width) reduces turtle entanglement risk;
- Continuing research on using shark-shaped silhouettes. For example, constructing the silhouette from clear UV-absorbent plastics instead of PVC and plywood could retain the turtle deterrent efficacy but avoid the reduced target species catch rate observed in trials. There is also a need to develop an improved attachment mechanism;
- Developing other sea turtle deterrents, such as chemical olfactory repellents or acoustic repellents;
- Using alternative net materials (appropriate twine diameter and material) to produce a breaking strength that allows turtles to break free of the gear and escape;
- Continuing research, development and testing of prototype turtle escapement devices for use in different types of pound net and fyke net gear;
- Continuing research on shapes of catchment chambers of pound nets with the aim of consistently directing turtles towards a location where an escapement device could be incorporated; and
- Investing in research, development and testing of equipment to disentangle turtles caught in nets (e.g., purpose-made line cutters, selecting a headlamp light color to reduce turtle stress during handling).
Consideration for Successful Artisanal Fishery Assessments
Participants identified optimal information to collect through fishery assessments in order to understand the degree of risk a fishery poses to sea turtles and to identify mitigation opportunities. Participants identified four broad categories of information to be collected during fishery assessments:
- Magnitude of the problem both in terms of effect on sea turtle populations (conservation status of affected turtle populations, age classes affected, status and trends in levels of turtle mortality from fishery interactions, and ultimately are population-level effects occurring) and effect on the fishery (gear damage and loss from interactions, time to remove turtles from the gear and repair or replace gear, lost catch, effects of any relevant regulatory measures);
- Fishery characterization, including gear types used, characteristics of each gear type, fishing operations, and catch characteristics;
- Management framework (self-management, co-management, or no management), including monitoring, control and surveillance; and
- The socioeconomic context.
Considering potential socioeconomic effects of alternative sea turtle bycatch mitigation practices was seen as a fundamental requirement to achieve successful sea turtle bycatch management. This includes considering all potential effects on a fisheries’ commercial viability, including economic viability, practicality, and crew safety. Long-term data series may be needed to account for high inter-annual variability in gear used, gear designs, fishing grounds, turtle interaction rates and other fishery characteristics.
Pros and cons were discussed for alternative assessment practices, including: social surveys; onboard and dockside observers; logbooks; satellite imagery (to observe number of participating vessels); and electronic vessel monitoring systems in combination with data on spatial distribution of turtle abundance (to provide an indirect index of turtle interactions). At-sea data were seen as optimal for understanding catch characteristics and rates, noting that limited observer coverage can provide an index of the fleet as a cost-effective preliminary assessment.
Fisher surveys were seen as useful in providing a first order qualitative understanding of whether or not problematic sea turtle capture levels are occurring and an initial understanding of the magnitude of the problem. Techniques to optimize the quality of results from social surveys were discussed.
Practices and Approaches to Work with Artisanal Fishing Communities
Participants discussed reasons why direct participation of artisanal fishers is critical for successful fishery assessment and bycatch mitigation activities. Fishers have a large repository of knowledge, which can be tapped to contribute to finding effective and commercially viable solutions to problematic bycatch that will ultimately be acceptable to the artisanal fishing community. To optimize the likelihood of fishers adopting measures identified as effective at reducing unwanted turtle bycatch, fishers must first be convinced that catching turtles is a problem and then must buy into the use of the mitigation practices.
Considerations and lessons learned for maximizing the direct participation of artisanal fishers and effectively working with artisanal fishing communities were identified and discussed. For instance, identifying progressive individuals in a fishery who are open to consider changes and lead by example, the need for a sufficiently long-term investment to develop the credibility needed to gain the trust and access of stakeholders, and expertise needed on teams working with artisanal fisheries to mitigate bycatch were highlighted.
Participants committed to pursue development of a decision tree process tool to guide future interventions with artisanal fishing communities, to further explore sea turtle sensory physiology and behavior with an aim to identify differences with target species, to expand collaborative research on gear technology approaches to mitigate sea turtle bycatch in coastal passive net fisheries, and to contribute to finalizing an in-progress IUCN technical report Mitigating Sea Turtle Bycatch in Coastal Passive Net Fisheries. On-the-ground assessment, commercial demonstration and mitigation activities will hopefully folllow as a result of the workshop, leading to direct sea turtle conservation benefits, and improved environmental sustainability and long- term economic and social viability of passive coastal net fisheries.