How lift-net fisheries influence cetacean ecology in Kaimana, Indonesia

Cetaceans—marine mammals that come with dolphins, porpoises, and whales—are an important to coastal ecology. Their presence fosters carbon sequestration, nutrient biking and redistribution, and keep watch over of sure prey species. Additionally, they function bioindicators of general ocean well being.

The sea waters surrounding Indonesia are house to greater than 30 species of cetaceans. 3 of those species—Bryde’s whales (Balaenoptera edeni), Australian humpback dolphins (Sousa sahulensis) and Pacific bottlenose dolphins (Tursiops aduncus)—are identified to take care of an ordinary presence within the house of Kaimana, West Papua, Indonesia.

On the 2018 North East Indian Ocean and South East Asian Seas Workshop, spearheaded by way of the Marine Mammal Secure Spaces Job Pressure, this location used to be designated as an Necessary Marine Mammal Space (IMMA), however till lately, main points at the area’s cetacean populations were scarce.

Now a group together with unbiased researchers, at the side of investigators from a number of conservation and analysis techniques in Indonesia and New Zealand, has carried out surveys in Kaimana and known a complete of 5 cetacean species, at the side of information on their inhabitants sizes and feeding behaviors.

The group’s findings seem in Frontiers in Marine Science.

IMMAs and their conservation function

The Marine Mammal Secure Spaces Job Pressure—which companions with the IUCN Global Fee on Secure Spaces, the IUCN Species Survival Fee, and the International Ocean Biodiversity Initiative, amongst others—has established definitions for IMMAs and standards for qualifying and supporting species and geographical spaces of passion.

Those come with specs on species/inhabitants vulnerability; resident species distribution and abundance; key lifestyles cycle actions together with feeding, migration, and replica; and resident species particular attributes together with area of expertise and variety.

The brand new paper notes, “On the time of its proposal, Kaimana IMMA used to be handiest identified as vital habitat for aggregation websites and feeding spaces of ‘Prone’ Australian humpback dolphins (Sousa sahulensis), ‘Close to Threatened’ Indo-Pacific bottlenose dolphins (Tursiops aduncus), and ‘Least Fear’ Bryde’s whales (Balaenoptera edeni). Additionally, the Kaimana IMMA could also be house for ‘Prone’ dugongs (Dugong dugon), even though it stays unclear referring to how this species makes use of the realm for its key life-cycle actions.”

Prior to the present analysis, the newest cetacean survey—carried out in Kaimana in 2015—had recorded 64 pods of Australian humpback dolphins and 40 pods of bottlenose dolphins (Tursiops sp.).

Carry-net fisheries and cetaceans

For the brand new research, the group noticed cetaceans round quite a lot of lift-net fisheries—coastal operations occupied with gathering bait fish for fishers equivalent to anchovies, sergestid shrimp, and different species—inside the Kaimana IMMA on 111 days between Would possibly 2021 and March 2023. The 5 cetacean species the group documented, and their present IUCN statuses, have been:

• Bryde’s whale (Balaenoptera edeni, Least Fear, 48 people)
• Killer whale (Orcinus orca, Information Poor, 1 particular person)
• Australian humpback dolphin (Sousa sahulensis, Prone, 441 people)
• Spinner dolphin (Stenella longirostris, Least Fear, 478 people)
• Indo-Pacific bottlenose dolphin (Tursiops aduncus, Close to Threatened, 2,612 people)

Of those species, Indo-Pacific bottlenose dolphins, essentially the most a large number of, represented 72.96% of all particular person sightings. Feeding habits noticed amongst this species used to be upper than non-feeding habits, whilst spinner dolphins essentially displayed non-feeding habits. The opposite 3 species didn’t show vital prevalences of both form of habits.

Significantly, the group carried out the surveys at the same time as with tracking of whale sharks (Rhincodon typus), and located dolphins and whale sharks steadily feeding in combination on anchovies interested in the nets ahead of they may well be accrued and hauled up.

The paper explains, “…the focal point of every survey used to be to file occurrences of whale sharks and cetaceans across the lift-net fishery. Cetacean observations came about between 5:00 AM and six:30 PM. The lift-net fishery normally wrapped up operations round 5–6 AM. Alternatively, when the catch used to be plentiful, now not all of the fish-filled nets have been hauled up and saved in cool bins, with some nets left submerged and nonetheless preserving fish, which might steadily draw in whale sharks and dolphins. Observations came about all over the day.”

Across the Kaimana IMMA’s lift-net fisheries, the abundance of particular person sightings throughout all species used to be easiest throughout the northwest monsoon season (December–February), the Transition 1 intermonsoon duration (March–Would possibly), and the Transition 2 intermonsoon duration (September–November), with considerably decrease abundance throughout the southeast monsoon duration from June–August.

Learn about boundaries and long run analysis

Whilst this analysis highlights the function of this area’s coastal lift-net fisheries in its cetacean ecology, the researchers recognize that unique use of this option to survey cetaceans may exclude oceanic species. As well as, lift-net fishery operations will also be weather-dependent, and occurrences of unhealthy climate can have offered temporal bias to those effects.

“Subsequently, those patterns must be interpreted as particular to cetacean interactions with lift-net fisheries. Additional unbiased cetacean commentary research are vital to higher perceive their prevalence inside the Kaimana IMMA,” the researchers write.

They counsel that long run exams happen in each coastal and ocean spaces.

Kaimana’s larger conservation image

In regards to broader conservation issues, the paintings notes that the majority cetacean–lift-net fishery interactions came about outdoor the Kaimana Marine Secure Space (MPA), and that it can be crucial for fisheries to make use of steps outdoor the MPA to take care of anchovy sustainability.

Additionally, Kaimana’s in depth mangrove ecosystem is important to maintaining the area’s anchovies and banana prawns (Penaeus merguiensis), a species believed to be crucial meals supply for the area’s Bryde’s whales. Mangroves supply necessary meals and safe haven for younger anchovies and prawns.

Alternatively, in line with an research showing in Faraway Sensing in 2022, roughly 5 hectares in line with 12 months of mangrove deforestation passed off within the house from 1996–2020.

Whilst it is a “fairly small” loss charge, the paper concludes, “…this presentations that rising human task is nevertheless inflicting vital detrimental affects. It is a caution indicator that mitigating movements will have to be carried out to forestall ongoing and important harm to the mangrove ecosystems of Kaimana.”

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