We report data collected between 01 September 2019 and 31 August 2021. Overall, during these years we recorded information about 2751 fishing trips in Penang. The information about these trips was contributed by a total of 53 local fishers and is a combination of tracking and landings.
Up to 31 August 2021, WorldFish installed solar-powered GPS trackers sourced from Pelagic Data Systems Inc. in 24 boats at four key landing sites of Teluk Bahang, Balik Pulau, Kuala Binjai, Kampung Binjai, Kuala Mudah and Sungai Batu. From those boats, 21 transmitted data successfully. Most of the trackers were installed in July or August 2020, but three of them were installed in September or November 2019 which allow us to get a better picture of their activity across 2020. Until 31 August 2021 these units tracked a total of 2671 trips.
In addition to the tracking data, we also collected landings data. Data collection was performed informally through a WhatsApp group set up with participating fishers. In total, we collected landings information for 188 trips by 35 fishers. Landings data is available between 01 September 2019 and 19 September 2020.
Three of the fishers that contributed landings data also had a tracker installed on their boats. Consequently we have both tracking and landing data for 108 trips. Most of the landing data, however, comes from the single most active fisher in the group. This fisher alone contributed landing data for 106 trips which corresponds to about 32% of all their fishing trips over the reporting period.
We are interested in calculating the total catch from artisanal fisheries in Penang and the income it generates. We need four key components to perform these calculations. First, we need to estimate the expected catch weight from each trip. Second, we estimate the expected income that the catch provides to artisanal fishers. Third, we need to obtain an estimate of the vessel activity throughout the year. Fourth, we need an estimate of the number of fishers in Penang.
We use hierarchical Bayesian models as the framework to estimate these figures for four main reasons. First, Bayesian models perform particularly well with relatively small amount of data. Second, a hierarchical model allow us to minimise the biases that a arise from unbalances in the contributed data; both across fishers and across time. Third, using models, instead of simple averages allow us to obtain estimates of the catch even for periods for which we have no comprehensive sampling. Lastly, and most importantly, a Bayesian framework allow us, not only to obtain an estimate of the numbers we are interested on, but also allow us to better understand the uncertainties involved in the calculation.
First, we look at the expected catch weight from a single trip. There was a lot of variability in the catch weight with some trips fishing as little as 0.4kg and some as much as 200kg. Nevertheless, using ten thousand Monte Carlo simulations in our Bayesian models, we found that the average catch was very likely between 10kg and 23kg (90% credible intervals, mean 15.7kg). The average catch showed important differences among fishers, with some consistently landing more catch by weight than the average. More data from a larger number of fishers will allow us to better understand what drives these differences.
Second, we look at the expected income obtained from a fishing trip. We found that each fishing trip was very likely to provide an income between RM170 and RM430 (mean RM283) to artisanal fishers. Similar as the catch weight, average income levels showed a large variation. Some trips provided only RM0 as income for the fishers while some trips provided as much as RM2013.
Third, we investigate the vessel activity coefficient during the study period. We found that this coefficient was very likely to be between 0.28 and 0.44 (mean 0.36). Mathematically, this coefficient can be interpreted in two (equivalent) ways. When applied to a single boat, it can be interpreted as the probability that this boat would to a fishing trip in a given day. When applied to a group of boats, for example the Penang artisanal fishing fleet, it can be interpreted as the proportion of boats that can be expected to be going on a trip in a given day. Although some differences between fishers exist, the largest variations were across time. Vessel activity appeared to be lessened during Fridays and Sundays and in some particular weeks of the year, presumably in response to weahter events.
Lastly, we obtained the information about Penang’s fishing fleet based on the number of active and registered fishers. In 2018 there were 1,658 fishers registered. This number might differ from the number of fishers during the reporting period, but we expect the updated number to be within 50 fishers from the 2018 number. We incorporate this uncertainty in all estimates we present.
Because we only have landings information up until 19 September 2020, we present estimates for only the first year of our reporting period between 01 September 2019 and 31 August 2020.
Using all these pieces of information we estimate that between the period 01 September 2019 and 31 August 2020 artisanal fishers were very likely (90% probability) to catch between 2.3 and 5.7 thousand tonnes in Penang waters, which provided income between RM40 and RM106 million to the local communities.
Although these wide ranges suggest a large uncertainty, it is actually a remarkable achievement considering the limited amount of data used to generate them. During the year we observe that the catch weight and income stayed within the credible intervals of our estimates throughout the years.
A larger sample size, both for landings and tracking (which we use to determine vessel activity) will allow us to detect smaller variations across time and answer other questions to improve the management of the fisheries and improve the livelihoods of artisanal fishers.
We also looked at the catch composition in the trips where we recorded data. Although composition data is, so far, biased and should not be taken as indicative of Penang’s catch, we can already distinguish some interesting patterns. Text to be written once species/grade data is of sufficient quality.
(not to be included in final document)
Between 01
September 2019 and 19 September 2020 we recorded landings for 187 trips
by 35 fishers.
During this time, GPS trackers were installed in 3 boats.
