Cetaceans and western Indian Ocean tuna fisheries

Tropical tuna fisheries have expanded enormously in recent decades. Increased interactions with cetaceans are inevitable, and those in the western and central Indian Ocean are no exception. A new report from the region finds that there has been a widespread failure to monitor and manage cetacean interactions and bycatch in Indian Ocean tuna fisheries, and to develop and implement mitigation measures. The enormous, and still growing, gillnet capacity in the region should be of particular concern. The major gillnet fishing fleets are from the countries bordering the Arabian Sea: Sri Lanka, India, Pakistan, Iran, Oman and Yemen. It is estimated that at least 60,000 small cetaceans are taken annually by tuna gillnetters in this region. Illegal high-seas gillnetting is common. Purse seiners (mainly from France and Spain) regularly set on baleen whales (probably Bryde’s whale, Balaenoptera brydei); mortality rates are not known, but are probably in the 10s per year. Purse seiners report that tuna do not associate with dolphins in this region, but that is not true. Large yellowfin tuna do regularly associate with both pantropical spotted dolphins (Stenella attenuata) and spinner dolphins (Stenella longirostris) as well as with long-beaked common dolphins (Delphinus capensis). This discrepancy does not necessarily mean that purse seiners set on dolphins, but it does open it to question. There are also issues with the longline fisheries, where depredation (by both sharks and cetaceans) is a serious problem for some fishermen. There is a suggestion that some longline fishermen may be shooting cetaceans, especially false killer whales (Pseudorca crassidens).

The full report is available at: http://www.ipnlf.org/

Irrawaddy dolphins (Pesut) in Indonesia’s Mahakam River

At the chairman’s request, CSG member Danielle Kreb provided the following summary.

A Critically Endangered pesut surfaces in the Mahakam River, East Kalimantan, Indonesia. Photo Credit: Danielle Kreb

One of the three Critically Endangered freshwater populations of Irrawaddy dolphins, Orcaella brevirostris, inhabits the Mahakam River, East Kalimantan, Indonesia. Analysis of tissues samples from 8 individuals indicated that this population has two unique genetic haplotypes compared to the coastal Irrawaddy dolphins in Northeast Kalimantan (Malinau), Thailand and Philippines. All sightings of pesut (as the dolphins are called locally) in the main Mahakam River during surveys between 1997-2012 were in the area between Muara Kaman (about 180 km from the river mouth) and the village of Tering (about 420 km from the mouth). Based on interviews, the distribution area could extend outside this area at some times of the year, both downstream (up to 90 km from the mouth) and upstream, where however it would be limited by the rapids upstream of Long Bagun (600 km from the mouth).  Pesut have also been found in the tributaries in the middle Mahakam, i.e. Kedang Rantau, Kedang Kepala, Belayan, Kedang Pahu, Pela, Semayang and Melintang Lakes, and in-between fast-flowing streams at about 20 and 100 km upstream of the Ratah River, which empties into the Mahakam at least 500km from the sea.

Based on Petersen mark–recapture analysis, the total population of pesut was estimated at 89 in 2005 (Cl 70-128; CV=0,18), 90 (Cl 68-145; CV= 0,19) in 2007, 91 (Cl 76-116; CV=0,13) in 2010 and 92 (CL 73-131; CV=0,15) in 2012, indicating no marked increase or decrease over this period. A survey to obtain a new abundance estimate is planned for later this year.

Large coal barges ply the water of the Mahakam threatening the Irrawaddy dolphins. Photo Credit: Danielle Kreb

The mean number of detected dead dolphins per year between 1995-2013 is 4 (ca 4% of total population); total recorded deaths in 19 years: 79. Most deaths have been caused by gillnet entanglement (66% of 71 deaths with known cause) followed by vessel strike (10%).

Other threats include noise from high-speed boats and oceanic coal-carrier ships passing through core habitat, chemical pollution from coal-mining waste cleaning and large-scale mono-culture plantations (especially oil palm) and prey depletion as a result of unsustainable fishing (e.g. electro-fishing, poison and trawl). Displacement of dolphins from core areas has been caused by container barges moving through narrow tributaries, sedimentation of lake habitat and conversion of fish spawning areas into palm oil plantations. One example is the ‘Muara Pahu – Penyinggahan sub-districts area’ which had the highest density of dolphins before 2007 and was designated as a dolphin reserve in 2009. Dolphins have been observed less and less often by local residents and during four extensive surveys in 2010 and 2012, no dolphins were

Human habitation along the Mahakam River. Photo Credit: Danielle Kreb

encountered there or in areas upstream of Muara Pahu, except for one isolated group that has resided in the Ratah River for the last 14 years.

Currently, conservation activities focus on gaining local governmental and community support to protect important dolphin habitat through multi-stakeholder workshops and preparing a management plan with tasks allocated to relevant organizations in each area. A major goal is to mitigate (or preferably eliminate) unsustainable fishing techniques, e.g. by introducing more sustainable fishing techniques, law enforcement, restoring and maintaining fish spawning areas and reducing pollution (chemical waste and boat noise). On a positive note, the government in the one district where dolphins still occur in good numbers (Pela/ Semayang –Muara Kaman area) is seriously considering a proposal to protect a50,000 ha area. All potentially affected villages participated in design of the proposed protected area and a final decision by the government is expected in early December.

Vaquita conservation update

As promised in the news item posted 2 August regarding availability of the vaquita recovery team’s (CIRVA) report, this is an update following the most recent (5th) meeting of the Advisory Commission to the Presidency of Mexico for Recovery of the Vaquita (‘presidential commission’) in Mexico City, 31 July – 1 August 2014. At this meeting, the alarming findings from the acoustic monitoring program intended to track trends in the vaquita population (18.5% annual decline) and a new estimate of current abundance (97 individuals) were presented by Barbara Taylor on behalf of CIRVA. Presentations by Mexican authorities indicated that illegal fishing has continued in the northern Gulf of California and that the transition from gillnets to ‘vaquita-safe’ light trawls in the shrimp fishery has gone much slower than required under Mexican law. Most importantly, the illegal fishery for totoaba, a giant croaker whose swim bladder is highly valued in China as a ‘health food’, has resurged over the last few years, driving the dramatic decline in vaquita numbers because of mortality in the large-mesh gillnets used to catch totoaba.

Scientists from Mexico’s National Institute of Fisheries are currently reviewing CIRVA’s analyses of vaquita abundance and trend. The presidential commission will recommend a course of action to President Nieto when it meets again at the end of August. The shrimp fishery is scheduled to open in September, and it is urgent that the Mexican Government acts decisively and favourably on CIRVA’s recommendation to immediately eliminate and exclude gillnets from the full range of the vaquita. Other nations that consume fishery products from the northern Gulf of California also need to step up and help Mexico shut down the black market trade in totoaba swim bladders. Only by bold, swift actions can we expect to avert another extinction of a cetacean species following that of China’s freshwater dolphin, the baiji, less than a decade ago.

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