1/15/14

Tuna in PIPA: FADs (fish aggregating devices)

Guest blogger Jennifer Goldstein has worked in several different departments at the New England Aquarium, including the Edgerton Research Lab and the Conservation Department's Sustainable Seafood Programs. Her career as a researcher and analyst has focused on large pelagics, primarily tuna, including research into the reproductive biology and foraging energetics of bluefin tuna, and more recently, researching aspects of sustainability of various tuna fisheries.

 Jennifer recently left the Aquarium to focus her career on science and environmental writing. Here she presents a series of posts for us on the species of tuna that can be found in the Phoenix Islands Protected Area of Kiribati. Today's post is about fish aggregating devices and bycatch.

It’s difficult to talk about tuna in the western Pacific without talking about the explosion of fish aggregating devices (FADs) used by the purse seine fleet to catch them. There are two types of FADs—natural and man-made. Natural FADs could be logs or tree trunks that have floated into open waters from inshore areas, or palm fronds and beds of seaweed that clump together to form a mass.

Loggerhead turtle swimming around a fish aggregation device (FAD). © Greenpeace

Man-made FADs are constructed by fishermen for the purpose of attracting schools of tuna. They are typically made out of bamboo poles fastened together in a lattice-like formation and covered with netting or dark plastic sheeting. Most have a component that hangs down into the water column that is made up of ropes or netting that helps to slow drift. Man-made FADs have become quite sophisticated and many are radar and sonar equipped, so that fishing vessels can find them easily, and captains can see the mass of fish underneath the to determine whether a trip to the FAD will result in a significant catch.

Skipjack tuna and bycatch caught in the net set on a fish aggregation device (FAD). © Alex Hofford/Greenpeace

For reasons that aren’t completely understood, skipjack tuna, juvenile bigeye, yellowfin tuna and other pelagic fishes tend to aggregate underneath FADs. They may stay associated with a certain FAD for a number of days or weeks. Because the incidence of mixed schools of tuna (including two or more species schooling together) are much higher at FADs, a purse seine vessel that catches a school of skipjack at a FAD is likely to pull up many juvenile bigeye or yellowfin tuna as well. Free-school sets, or sets made on schools of skipjack swimming freely and not associated with a FAD, are generally mono-specific, so a free-school set is likely to net only skipjack.

Due to the ubiquitous use of FADs, and the sheer size and capacity of the purse seine fleet, the incidental catch of juvenile bigeye and yellowfin tuna in FAD sets is causing troubling population declines for these two species.

Posted by Regen Jamieson at 10:09 AM 0 comments
Labels: , ,

1/8/14

Tuna in PIPA: Skipjack

Guest blogger Jennifer Goldstein has worked in several different departments at the New England Aquarium, including the Edgerton Research Lab and the Conservation Department's Sustainable Seafood Programs. Her career as a researcher and analyst has focused on large pelagics, primarily tuna, including research into the reproductive biology and foraging energetics of bluefin tuna, and more recently, researching aspects of sustainability of various tuna fisheries. 

 Jennifer recently left the Aquarium to focus her career on science and environmental writing. Here she presents a series of posts for us on the species of tuna that can be found in the Phoenix Islands Protected Area of Kiribati.

Of the seven commercially important species of tuna, skipjack (Katsuwonus pelamis) are the smallest and most abundant. They are found in the Atlantic, Pacific and Indian Oceans in tropical and warm-temperate regions. Though they are difficult to age, they are thought to live between eight to ten years, and can grow to the length of a meter or more, but are common at smaller sizes. They are opportunistic predators, feeding mainly on small fish, crustaceans and cephalopods (squid). 

Skipjack tuna shoal via 

Skipjack are prolific breeders, and are sequential batch spawners. This means that at any given time, they have oocytes at a variety of different developmental stages in their gonads. This allows them to spawn a “ripe” or mature batch of eggs, and within a day or so, a new batch will have matured and they can spawn again, releasing hundreds of thousands of eggs each time. Though there are seasonal peaks in spawning, they are capable of reproducing throughout the year.

Biologists would say that the skipjack tuna’s suite of life history characteristics make them an “R-selected” species, meaning that they have a relatively short life span, start reproducing at an early age and have high reproductive output during their lifetime. At the other end of the spectrum are “K-selected” species, which have long lifespans, start reproducing later in life, and have a relatively low lifetime reproductive output, for example, whales or humans.

Migratory patterns for skipjack are complex, and vary among individuals and regions. Though they are not the most highly migratory of the tuna species (that claim belongs to the bluefin tuna), it’s likely that they will move between the territorial waters of several Pacific Island countries during their lifetime, meaning that no one country can adequately manage the resource. Kiribati and the seven other Pacific Island countries known collectively as the Parties to the Nauru Agreement (PNA) are doing just that: they negotiate for conservation and management measures as a block to ensure sustainable management of skipjack in the greater Western and Central Pacific Ocean (WCPO) management area, and to increase the economic return for their citizenry.

Global geographic distribution of skipjack tuna. Source: Fishbase

The importance of the sustainable management of this stock for Kiribati cannot be understated, as the purse seine fishery for skipjack tuna in and around Kiribati is one of the biggest fisheries in the world. Skipjack landed in this fishery account for 69 percent of all tuna landed in the WCPO and 36 percent of worldwide tuna landings[1]. For Kiribati, revenues from fishing licenses make up about 40 percent of the country’s gross domestic income.  

Another behavioral quirk that has had wide-ranging effects on the nature of the skipjack fishery is their propensity to associate with other larger fish or marine mammals, or under floating objects like logs, or man-made fish aggregating devices (FADs) used to attract fish and make them easier to catch. In the next installment on the tuna of the Phoenix Islands, I’ll discuss the growing use of FADs in the purse seine fishery for skipjack, and how it has affected the population of another important PIPA resident, bigeye tuna.


[1] ISSF Stock Status Ratings – 2013. Available from: http://iss-foundation.org/status-of-the-stocks/report/ 
Posted by Regen Jamieson at 2:22 PM 0 comments
Labels: , , , , , ,

1/7/14

Tuna in PIPA: Introduction

Guest blogger Jennifer Goldstein has worked in several different departments at the New England Aquarium, including the Edgerton Research Lab and the Conservation Department's Sustainable Seafood Programs. Her career as a researcher and analyst has focused on large pelagics, primarily tuna, including research into the reproductive biology and foraging energetics of bluefin tuna. More recently, she's been researching aspects of sustainability of various tuna fisheries. 

 Jennifer recently left the Aquarium to focus her career on science and environmental writing. Here she presents a series of posts for us on the species of tuna that can be found in the Phoenix Islands Protected Area of Kiribati.

Of all the pelagic creatures that live within or migrate through PIPA, tuna are likely the most important, at least from a monetary perspective. Historical fishing data and tuna tagging studies clearly demonstrate that Skipjack tuna (Katsuwonus pelamis), bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacores) are all resident in or common visitors to PIPA. One of the largest fisheries in the world, the purse seine fishery for skipjack tuna, takes place here and in the territorial waters of the other Pacific Island nations.

Image copyright Brian Skerry

Kiribati presently has limited capacity to fish for or process tuna caught within its territorial waters, but it is able to benefit from its tuna resources in another way: Revenues brought in from the sale of fishing licenses to foreign tuna-fishing vessels are a primary source of income for Kiribati. Determining the proper balance between conservation of tuna habitat within PIPA and continued prosperity from tuna fishing elsewhere in the Kiribati EEZ is a major goal of the PIPA Conservation Trust Fund.

This is the first entry in a series of guest blog posts to share details about the tuna that inhabit PIPA, and how the biology and behavior of highly migratory species can create challenges for the sustainable management of their populations.

Posted by Regen Jamieson at 2:56 PM 0 comments
Labels: , ,
Subscribe to: Posts (Atom)