Surface habitat modification through industrial tuna fishery practices

Natural floating objects (FOBs) have always been a major component of the habitat of pelagic species. Since the 1990s, the number of FOBs in the open ocean has increased greatly as a result of the introduction of fish aggregating devices (FADs) by the industrial tropical tuna purse seine vessels. These changes, and their potential impacts on the species that associate with FOBs, remain poorly understood. Using fisheries observer data, data from satellite-linked tracking buoys attached to FOBs and Lagrangian simulations, this study quantifies the temporal changes in the density and spatial distribution of FOBs due to the use of FADs in the Indian Ocean (IO) between 2006 and 2018. From 2012 to 2018, the entire western IO is impacted, with FADs representing more than 85% of the overall FOBs, natural FOBs less than 10%, and objects originating from pollution 5%. Results also suggest that both FADs and natural FOBs densities are lower in the eastern IO, but this initial investigation highlights the need for further studies. Our study confirms that FADs have greatly modified the density and spatial distribution of FOBs, which highlights the need to investigate potential consequences on the ecology of associated species.

Detecting anchored fish aggregating devices (AFADs) and estimating use patterns from vessel tracking data in small-scale fisheries

Monitoring the use of anchored fish aggregating devices (AFADs) is essential for effective fisheries management. However, detecting the use of these devices is a significant challenge for fisheries management in Indonesia. These devices are continually deployed at large scales, due to large numbers of users and high failure rates, increasing the difficulty of monitoring AFADs. To address this challenge, tracking devices were attached to 34 handline fishing vessels in Indonesia over a month period each. Given there are an estimated 10,000–50,000 unlicensed AFADs in operation, Indonesian fishing grounds provided an ideal case study location to evaluate whether we could apply spatial modeling approaches to detect AFAD usage and fish catch success. We performed a spatial cluster analysis on tracking data to identify fishing grounds and determine whether AFADs were in use. Interviews with fishers were undertaken to validate these findings. We detected 139 possible AFADs, of which 72 were positively classified as AFADs. Our approach enabled us to estimate AFAD use and sharing by vessels, predict catches, and infer AFAD lifetimes. Key implications from our study include the potential to estimate AFAD densities and deployment rates, and thus compliance with Indonesia regulations, based on vessel tracking data.

Mapping spatial-temporal skipjack tuna habitat as a reference for Fish Aggregating Devices (FADs) settings in Makassar Strait, Indonesia

Hidayat R, Zainuddin M, Mallawa A, Mustapha MA, Putri ARS. 2021. Mapping spatial-temporal skipjack tuna habitat as a reference for Fish Aggregating Devices (FADs) settings in Makassar Strait, Indonesia. Biodiversitas 22: 3637-3647. Skipjack tuna (Katsuwonus pelamis) has a high economic value in the international market. Catching skipjack tuna using fish aggregating devices (FADs) without knowing its habitat characteristics can damage the ecosystem. This study aimed to determine suitable fishing areas for setting skipjack’s FADs. The data used included that on catch, sea surface temperature (SST), and sea surface chlorophyll-a (SSC) in the Makassar Strait obtained for 2017-2019. The generalized additive model (GAM) and empirical cumulative distribution function (ECDF) analyses were used to investigate the skipjack’s tuna habitat. A pelagic habitat index (PHI), with PHI > 75%, was applied to determine suitable FAD positions. The gravity center of the skipjack tuna habitat for ten months (January-October 2020) was calculated to validate the model’s results. The results showed that the optimum SST range was from 28.78°C to 31.25°C, while the SSC from 0.18 to 0.28 mg m-3. The best skipjack habitats in the southern Makassar Strait are criterion 4 (PHI > 90%) and criterion 3 (PHI = 85-90%), having a relatively high consistency of the average PHI values. These results can help determine the optimal positions for setting FADs to benefit the global management and sustainable development of skipjack tuna fisheries.

Utilization of FAD Distribution in South Buton Waters as a Fishing App by Purse Sein Fishermen in Kadatua District, Selatan Buton Regency

Fish Aggregating Devices (FAD's) have long been used by fishermen in South Buton Regency. This study aims to determine the utilization of FAD distribution as a fishing aid by purse sein vessels in the waters of Kadatua District, South Buton Regency. This study aims to determine the utilization of FAD distribution as a fishing tool by purse sein vessels in Kadatua District, South Buton Regency. Data collection methods include FAD point data taken from GPS (Global Position System) fishermen and dominant catch data from purse sein fishermen. The results of the study obtained data on the distribution of FADs in Kadatua District spread between a distance of 0-12 miles, during the study the coordinates of FADs were obtained as many as 79 coordinate points owned by fishermen in Kadatua District. FADs used by purse sein fishermen to carry out fishing operations have 24 FAD points, which are spread over a distance of 0 – 12 miles. In April the distribution of FADs used as fishing aids by purse sein vessels was at a distance of ± 0 – 12 miles, while in May and June FADs used as fishing aids were at a distance of ± 2 – 12 miles. The dominant fish catch data for purse sein fishermen is 690 kg in April, 525 kg in May and 735 kg in June. The dominant catch during the study was dominated by scad fish (Decapterus spp). The level of effectiveness of the dominant catch of purse sein fishermen is highest at a distance of 4-12 miles with a total catch of 1,070 kg of the total catch of 1,950 kg.

A randomised controlled trial to test the effects of fish aggregating devices and SBC activities promoting fish consumption in Timor-Leste: A study protocol

Timor-Leste is one of the world's most malnourished nations where micronutrient-deficient diets are a contributing factor to the prevalence of child stunting, currently estimated to be 45.6% of children under five. Fish are an important source of micronutrients and one that may assist the country's predominantly rural population of agriculturalists to exit poverty and malnutrition. However, a small national fishing fleet producing low catch volumes place fish out of reach of most inland and upland populations where it is needed most. Fish consumption is very low in rural areas compared to coastal, regional, and global averages. This trial is a one-year, cluster-randomized, partially masked, controlled trial among families living in rural, inland Timor-Leste. This trial aims to test and compare the effects of two treatments, alone and in combination, on the frequency and volume of household fish consumption in upland areas as a proxy for improved dietary diversity and micronutrient intake. Treatment 1 is the installation of nearshore, moored fish aggregating devices (FADs) to improve catch rates with existing fishing gears. Treatment 2 is social and behaviour change (SBC) activities to promote fish consumption. Villages in inland communities will be randomized to receive treatment 1, treatment 2, both treatments, or neither treatment. Some households with one child under five will be recruited, and data will be collected at baseline (prior to the rollout of the treatments) and endline. Our study will determine the impact of an improved supply of fish, along with nutrition-oriented SBC activities, on the fish purchasing and consumption practices of rural, inland households. Findings from this study are urgently needed by small island developing states in order to make policy and investment decisions on how best to improve households' diets using locally available, nutrient-dense foods such as fish. Investments such as these are needed to break the cycle of malnutrition.

Tuna behaviour at anchored FADs inferred from Local Ecological Knowledge (LEK) of pole-and-line tuna fishers in the Maldives

The Maldives tuna fishery landings in 2018 were 148, 000 t and accounted for nearly a quarter of the global pole-and-line tuna catch. This fishery partially relies on a network of 55 anchored fish aggregating devices (AFADs) deployed around the archipelago. About one-third of the total pole-and-line tuna catch is harvested at AFADs. Although the AFAD fishery has existed for 35 years, knowledge on the behaviour of tuna in the AFAD array is still limited, precluding the development of science-based fishery management. In this study, local ecological knowledge (LEK) of fishers was used to improve our understanding of tuna behaviour, through personal interviews of 54 pole-and-line fishers from different parts of the archipelago. Interview results suggest that during the northeast monsoon tuna are more abundant on the eastern side of the Maldives, while during the southwest monsoon they are more abundant on the western side of the Maldives. Most fishers believed that tuna tend to stay at the AFADs for 3 to 6 days and remain within 2 miles from the AFADs when they are associated. Fishers believe that strong currents is the main factor for tuna departure from AFADs, though high sea surface temperatures and stormy conditions were also thought to contribute to departures. Moderate currents are believed to be a favourable condition to form aggregations at the AFADs while other factors such as suitable temperature, prey and attractants enhance this aggregation. Fishers also believe that there are multiple schools segregated according to size and species at AFADs and that catchability is higher at dawn and in the late afternoon when the tuna occur shallower in the water column. This study is an important step towards engaging the Maldivian tuna fishers into a science-based fishery management.

SEBARAN RUMPON PESISIR PADA DAERAH PENANGKAPAN PURSE SEINE DI PERAIRAN DESA URENG KECAMATAN LEIHITU, KABUPATEN MALUKU TENGAH

The Fish Aggregating Devices (FADs) have been utilized for a long time by the purse seine fishermen in Ureng. This research was aimed at mapping the devices operating by Ureng fishermen and indentifying the dominant captured fish surrounding the set devices. This research was conducted in Lihitu district, Central Maluku Regency. The results showed that there was one large circle that resembled a ball with several groups of five small circles inside. Based on the type, the dominant fish caught around the FADs were mackerel (45 ton), mackerel tuna (25 ton), and skipjack tuna (20 ton). Overall, this study found that the catch using the purse seine in the five FAD groups was dominated by small and medium sized fish. In conclusion, under the potential fishing area for purse saine fishermen in Ureng, if the distance between the FADs is adjusted, fish are not trapped forever in the FADs and can migrate, lay eggs in other areas outside the waters of Ureng.