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Andrews Agyekumhene

Reduction of Sea Turtle By-catch and Mortality in Gill Net Fishery Along the Central Coast of Ghana


Project Update:

The project has successfully started and is making progress.  Interviews and Focal Group Discussions have been conducted with experienced fishers to determine their level of knowledge about sea turtles.  Education programs have been conducted in 20 schools and 5 communities to educate them on sea turtle issues.  Some schools and communities have been visited more than once.  Six radio programs have also been carried out on sea turtle and general environment protection.  Thirty fishermen have been trained in sea turtle rescue and release techniques and are actively working with their skills.  And 20 observers have been trained in by-catch data collection to quantify annual capture of sea turtles in gill net fishery.


Over 90 sea turtles (comprising 3 species- leatherbacks, olive ridleys and greens) have so far been captured by 20 canoes.  Fifteen of the turtles captured were dead but the rest were all released alive back to sea.  The 15 mortality figure is below the usual numbers recorded by the fishermen in the area, indicating that they are applying the rescue and safe release techniques from training.


The next phase of the project is assessing the impact of gear illumination (using LED green lights) on sea turtle capture in the gill net fishing.  Twenty canoes are collecting the data for 12 months; 10 with LED lights and 10 without LED lights.  Captures will be compared between the two sets of canoes for any significance and trends after December 31st, 2016.  The project will continue to educate the fishing communities and work to reduce sea turtle entanglement in fishing gear after the 12 month by-catch assessment period.

Project Description:


Sea turtle populations around the globe are faced with increasing anthropogenic threats that is jeopardizing their survival (IUCN, 2006). Sea turtles face harvesting, egg poaching, disorientation, and degraded habitat on the nesting beaches. But the primary risk to their survival comes from the marine environment where they are routinely challenged with entanglement or capture in commercial and artisanal fisheries (Spotila et al. 2000; Hays et al. 2003; Lewison et al. 2004). In Ghana, a significant number of vulnerable leatherback and olive ridley sea turtles as well as endangered green sea turtles are killed each year from the purse seine and gill net fisheries. Although it is illegal to capture sea turtles in Ghana, the incidental capture of these animals remains a major threat to turtle populations in the region. Recent genetic analyses indicate Ghana’s leatherbacks are part of a wide-ranging population that possibility extends throughout the Atlantic Ocean. Clearly, protecting Ghana’s sea turtles is extremely important for the global recovery of the species. This study will quantify sea turtle capture among different fishing methods in Ghana, and investigate the use of alternative fishing methods and gears to help reduce sea turtle capture while maintaining the current level of fish capture.


Statement of the Problem

By-catch in fisheries has been reported as a major and significant source of sea turtle mortality around the globe. The interaction of small scale coastal gill net fisheries with sea turtles is reported to equal or in some cases exceed sea turtle interactions with industrial scale pelagic fisheries. Over 70% of sea turtle interactions with fishery results in capture (Molony, 2005; FAO, 2009) and this presents significant source of mortality for sea turtles (Nicole et al., 2009). In Ghana for instance, over two hundred and seventy-three mortalities believed to be associated with fishery interaction were recorded during 2013 in the coastal fishing communities (Ghana Wildlife Division, unpublished). This high rate of incidental capture and mortality in coastal fisheries presents a great challenge for sea turtle management and has been the focus of recent conservation work. A few studies revealed that illuminating fishing nets with LED lights significantly reduced sea turtle capture by 40% with no significant impact on targeted fish catch (Dam et al., 2014). Ghana has an estimated fishery of 12,728 boats (Ghana Fisheries Commission, 2014) that fish six days per week for such target species as sardines, tuna, mackerels, barracuda, etc. Since five species of sea turtles utilize the same waters as the fishing vessels (Amiteye, 2002; Agyekumhene, 2009), it is immediately imperative to quantify sea turtle mortality and investigate the use of LED lights on reducing sea turtle captures.

For proper management and conservation goals to be achieved, a better understanding of the ecology and threats both on land and in the water is needed. These form the underlying justification of this study which is the first of its kind in West Africa. When completed, the study will contribute experimental data for the development of a fishery management plan that will reduce sea turtle by catch in a fishery type (gill net fishery) where data are extremely limited.


Goal and Objectives of the Study

The goal of this study is to identify alternative fishing methods/techniques that reduce sea turtle by-catch without reducing target catch rates. To accomplish this goal, I propose two objectives: (1) quantify current sea turtle capture rate in the gill net fisheries, and (2) compare sea turtle captures in gill net fisheries with unmodified and modified (gear illumination with LED lights) fishing gear (3) Compare market values of target fish from unmodified and modified (gear illumination with LED lights) fishing gear. I hypothesize that sea turtle capture will vary with time (season), weather, and fishing effort; and that adding LED lights will decrease sea turtle capture in fishing gears, and not impact capture rate and value of target fish.


Proposed Research Design, Methods and Procedures

There will be an initial sensitization of fishing communities about the project and about sea turtle conservation issues. Sea turtle education program (employing talks, documentaries, video shows and radio programs) will be conducted in schools and fishing communities to improve knowledge of fisher folks about the importance of sea turtles and the need to conserve the species. The Split-Block sampling Design (Fisher, 1925; Box et al., 2005) will be used in data collection which will be carried out for two years. Data will consist of sea turtle nesting activity and trends data which include population, species composition, nesting rates, rate of turtle by-catch and fate of by-catch in the study area. Information will also be collected on current fishing methods and gear types, gear design and operation, gear success in reducing by-catch, and fish catch assessment.

A total of 20 canoes with trained observers will be involved in the sampling design. The fishing boats will be divided into two groups (A and B) of ten boats each. Group A, will fish with their own fishing gear with no modification to the fishing nets. Group B will have their nets fitted with LEDs (gear modification/illumination). Each group will then be asked to fish in the same area for the same amount of time that they normally fish and each will report all by-catch information (species, description/scute counts, number of captures, and biometric data) and target catches (species, quantity caught, length-weight measurements, market value). Flipper tags will be installed on all sea turtles captured in fishing gears to determine re-capture rates. Trained observers will be used in data collection. Support items will be provided for fishing boats used in the research and observers will be given monthly allowances to sustain interest in research.


Data Analysis

A standard, mixed-model, ANOVA-based approach to analysis (Kutner et al., 2005; Montgomer, 2008) will be employed in data analysis. With this approach, all experimental factor effects are assumed to be fixed. Excel will be used to present data in graphs and tables.

Catch-per-unit-effort (CPUE) for sea turtles and total target fish species will be calculated for each net using the equation below. The mean CPUEs will be compared between boats with LED and boast without LEDs. Also mean Value Per Unit Effort (VPUE) of fish catch will be compared.


Catch-Per-Unit-Effort (CPUE) = Number of sea turtles captured

([Length of net/120 m]) x ([net submersion time/12h])


Catch-Per-Unit-Effort (CPUE) = Number of individual target species

([Length of net/120 m]) x ([net submersion time/12h])


Expected Outcome

This work is the first in-water study to be conducted on sea turtles in Ghana. The study is expected to reveal the rate at which sea turtles are captured in fishing operations. The study will also show the efficiency of LEDs as a By-catch Reduction Device (BRD). The study is expected to initiate attitudinal change in the behavior of fishermen towards sea turtle conservation and increase community participation in wildlife management activities. The project is aimed at gaining trust of fishermen to help protect sea turtles while maintaining their livelihood. A fishery management plan that includes LED lights to reduce sea turtle by-catch in gill net fishery will be developed by the project. Capacity of fishermen is expected to be built to reduce sea turtle mortality at sea due to poor handling and release of entangled turtles. It is expected that local fishermen will actively participate in sea turtle conservation through improved knowledge about the species and its contribution to livelihood of fishermen (improving fish stock). The project is expected to encourage other coastal nations in the region to utilize LED light.


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