Albacore program Print

Project Objectives

The overall objective of the albacore tagging project was to design a tagging study to provide contemporary data for refining our knowledge of albacore movements, exploitation rates and population biology

Background

A significant fishery for south Pacific albacore has operated since the 1950’s, with the majority of the historic catch taken by foreign longline fishing fleets such and Chinese Taipei, Japan and Korea. Since the early 1990’s, albacore have become an increasingly important species for the domestic longline fleets of Pacific Island Countries and Territories (PICT), which now account for nearly half the annual harvest. The overall annual harvest of albacore has increased steadily from around 30,000 t in the 1990’s to between 60,000 and 70,000 t in recent years. The majority of this harvest is caught by longlining, with a small proportion taken by troll fishing.

To date, assessments have indicated that the South Pacific albacore stock is most likely not over-fished and that recent levels of harvest are sustainable. However, there remains considerable uncertainty in these assessments due to our incomplete knowledge on the species ecology and fishing mortality. Given the importance of albacore to the longline fisheries of PICTs, and the uncertainty in stock assessments, there have been increasing demands for more research to be directed at the species. In response, the Secretariat of the Pacific Community (SPC) Oceanic Fisheries Program (OFP) developed a project for south Pacific albacore in consultation with the Forum Fisheries Agency (FFA) Secretariat and member countries, which was funded by the 9th European Development Fund (Overseas Countries and Territories component). The project has a three year time frame and was designed around the need to reduce uncertainty in stock assessments and to provide better management advice both at the regional and national levels.


As part of this project, the OFP designed a tagging study with the overall objective to provide contemporary data for refining our knowledge of albacore movements, exploitation rates and population biology. The objective of the albacore tagging project was to obtain better estimates of exploitation rates, movement patterns, growth rates, and to validate age estimates for albacore. This information will be incorporated into models used to assess the status of albacore stocks and will provide greater certainty in assessment predictions.

Project activities

Two phases of albacore tagging were conducted in 2009 and 2010. The focus was on tagging albacore with conventional dart tags for all tagging cruises, but pop-up archival transmitting tags were trialed on a small number of albacore in 2010. An age validation study, using oxytetracycline (OTC) was also conducted during both years of tagging.

 

Conventional tagging

Albacore were tagged using conventional plastic tip 140 mm PDAT Hallprint™ dart tags. The tag was inserted using a stainless steel applicator just below the second dorsal fin at an oblique angle to anchor the barb between the pterygiophores. Each tag was inscribed with a unique five-digit number, contact details and reward amount for returning tags. Albacore were returned to the water head first as soon as possible after tagging. The tag number, fork length, condition of fish, and tagging quality was recorded.

 

Electronic PSAT Tagging

Wildlife Computers miniPAT tags were chosen as the most suitable tags for albacore, given that they were approximately 30% smaller than the previous satellite tags produced. Each miniPAT was programmed to release after 352 days. A shorter time period would have allowed finer temporal scale data to be recorded and transmitted, but the primary objective was to obtain long-term movement data. A longer time period (maximum allowable 360 days) would have increased the time interval between measurements. An in-built premature release mechanism ensured that each tag would release if the fish exceeded 1800 m or remained at constant depth (+/- 3 m) for more than 2 consecutive days. Each tag recorded the depth (pressure) and water temperature every 75 seconds.

 

The attachment mechanism for each miniPAT consisted of a short 8 cm plastic-coated wire with a 38 x 9 mm stainless steel dart head. A second attachment was also used to reduce excessive movement of the miniPAT once deployed. For the second attachment, a loop was made with the tail of a conventional 140 mm PDAT Hallprint™ tag and secured with a crimp or small piece of shrink wrap. The conventional tag was also fitted with the same stainless steel dart head as the main attachment. The loop in the conventional tag was placed over the narrow part of the main body of the miniPAT.

 

Albacore that were in good condition and > 100 cm FL were initially considered candidates for deployment of miniPSATs. As the tagging cruises progressed, and few large albacore in good condition were landed, the minimum size of an albacore for deployment of a miniPAT was reduced to 90 cm FL.

 

All albacore brought to the side of the vessel that appeared to be in good condition were lifted on board with a purpose-built sling to reduce additional injuries to the fish. When landed, each albacore to be tagged with a miniPAT remained in the sling and was placed on the deck to be measured. A deck hose with a light flow of seawater was placed in the mouth to oxygenate the gills and a moist chamois was placed of the eye to calm the fish. Two small incisions were made with a small knife immediately below the first dorsal fin to assist with the insertion of the main and second miniPAT attachments. Both attachments were bathed in a solution of iodine and inserted between the pterygiophores with a small tag applicator at an oblique angle. The fish was then picked up with the sling and released. The condition of the fish, time on deck and the time, latitude and longitude of release was recorded for each tagged fish.

 

Age Validation Study

The most reliable method for estimating the age of fish is by counting the number of increments in hard parts (otoliths, spines or vertebrae). However, this method is only reliable when the periodicity (e.g. daily, annual) in which the increments are deposited is known. For south Pacific albacore, this periodicity has not been validated, but is critically important to ensure accurate age estimates for parameter estimation and stock assessments. The most effective method to validate the periodicity of increment formation in hard parts is by an experiment involving the mark-recapture of chemically-tagged fish.

 

Oxytetracycline (OTC) is a natural antibiotic that also leaves a mark in the bones and otoliths (ear bones) of the fish at the time of injection. Otoliths have growth rings similar to trees, which are counted to estimate the age of the fish. When otoliths are removed from recaptured fish that were injected with OTC, they can be viewed under a microscope to locate the position of the OTC mark relative to the growth rings. The amount of otolith growth since the fish was injected then allows scientists to determine how frequent (e.g daily, annually) the growth rings are deposited in the otolith.


During the albacore tagging project, a large proportion of tagged albacore also received an injection of oxytetracycline (OTC). These albacore received an approximate dosage of 25-50 mg/kg body weight of Oxytetra LA (200 mg/ml). The dosages varied due to the difficulties in administering precise doses to different sized albacore within a short time period. The OTC was administered using a 40 mm 18-gauge needle in an automatic syringe connected via UV-resistant tubing to a 100ml bottle of Oxytetra which was kept in an insulated holder. OTC was injected deeply within the muscle tissue under the first dorsal fin. Fish injected with OTC received a white conventional tag with “keep whole fish” inscribed.

Phase 1 - 2009

New Zealand

The specific aims of Phase 1 were to tag approximately 3000 albacore with conventional dart tags, and inject approximately 1000 of these tagged albacore with oxytetracycline (OTC) as part of an age validation experiment. OTC is a natural antibiotic that also leaves a mark in the bones and otoliths (ear bones) of the fish at the time of injection. Otoliths have growth rings similar to trees, which are counted to estimate the age of the fish. When otoliths are removed from recaptured fish that were injected with OTC, they can be viewed under a microscope to locate the position of the OTC mark relative to the growth rings. The amount of otolith growth since the fish was injected then allows scientists to determine how frequent (e.g daily, annually) the growth rings are deposited in the otolith.

 

The first albacore tagging cruise commenced in January 2009 off the west coast of New Zealand. A local commercial fishing vessel was chartered for the cruise, and juvenile (5-6kg) albacore were targeted using surface troll lines. This meant that fish were caught near the surface and were in relatively good health to be tagged and released.


A total of 2766 albacore were tagged with conventional dart tags and released, with 1457 of these fish also receiving an injection of OTC. To date, only 1 recapture has been reported from these tagged fish. This fish was recaptured in New Zealand waters, relatively close to the release site, approximately 11 months after release. It is unclear whether the low number of reported recaptures is due to low reporting rates, low recapture rates, low survival of tagged fish, or a combination of these factors.

Phase 2 - 2010

The objective for 2010 tagging activities was to focus on tagging larger albacore than were tagged in 2009 in an attempt to increase tag recapture rates. Larger albacore (>70 cm FL) are more available to longline fisheries and, consequently, a greater proportion of the tagged population will be available to longline fisheries if larger, rather than smaller, albacore are tagged because smaller fish would be subject to a number of years of mortality prior to becoming vulnerable to longlining.

The capture of larger albacore also allowed the deployment of miniPATs, which were small enough to deploy on fish as small as 20kg. These tags provide detailed information on the vertical and horizontal movement of fish, and are particularly suited for albacore which typically suffer from low recapture rates, such that standard archival tags are not a viable option.

 

The specific aims of the second year of tagging were to tag 30 albacore with Wildlife Computers miniPATs with releases spread across New Caledonia, New Zealand and Tonga and tag all other albacore landed in good condition with conventional dart tags, and inject all of these tagged albacore with OTC.

 

New Caledonia

Tagging in New Zealand occurred off the west coast of the mainland in May/June 2010. A local commercial longline vessel was chartered and targeted larger albacore using standard longline gear. No conventional tagging was done during this cruise, with the focus solely on deploying PSATs. Catch rates of albacore were very good with around 600 fish landed. However, most of these were in poor condition and unsuitable for tagging. The small number of albacore landed in good condition allowed all 10 PSATs to be deployed on albacore (97-107 cm FL) during this cruise.

Since their deployment, 8 of the 10 miniPATs deployed in New Caledonia have released prematurely after between 4 and 24 days. There remain two PSATs that have yet to transmit, and it is hoped they are still attached to the albacore. The data from the released tags have been received from the satellites and are currently being analysed.

 

New Zealand

Tagging in New Zealand occurred off the east coast of the north island in April/May 2010. A local longline vessel was chartered and targeted larger albacore using surface (<50m) longline gear. Catch rates were low with only around 190 fish landed. The condition of albacore was poor during initial sets but increased substantially with the use of smaller hooks. A total of 92 albacore (52-97 cm FL) were tagged with conventional tags and injected with OTC. Five albacore (93-102 cm FL) were released with miniPATs.

Since their deployment, all miniPATs deployed in New Zealand have released prematurely after between 10 and 50 days. The data from these tags have been received from the satellites and are currently being analysed.

 

Tonga

Tagging in Tonga occurred in June/July 2010 and was focussed around the main island of Tongatapu, the Capricorn Seamount to the north-east and briefly around the FADs in Niue. A local longline vessel was chartered and targeted larger albacore using standard longline gear. Catch rates of albacore were very poor with only about 170 fish landed. Most of these were in very poor condition and unsuitable for tagging. No fish were tagged with conventional tags, but 4 albacore (89-105 cm FL) were tagged with miniPSATs.

Since their deployment, all miniPATs deployed in Tonga have released prematurely after between 7 and 13 days. The data from these tags have been received from the satellites and are currently being analysed.

History

Tagging programs for albacore using conventional dart tags have been conducted throughout the South Pacific since the 1960’s by a range of fisheries agencies with the aim to obtain information on movement patterns, exploitation rates and growth of albacore. More than 20,000 albacore have been tagged and released by these various programs to date. Prior to 1986, tagging of albacore was limited to a few small-scale projects off the coast of Australia and New Zealand. The large majority of albacore (>17,000) have been tagged during dedicated tagging programs between 1986 and 1992 in the Subtropical Convergence Zone and off the east and west coasts of New Zealand (Table 1). These tagging programs have provided the most useful information to date on the potential movement patterns (Fig. 1), growth rates and exploitation rates of South Pacific albacore and provide the only tagging data currently used in albacore stock assessments.

 

The reported recapture rates of conventionally tagged south Pacific albacore have been remarkably low compared to other tuna species.  For example, 138 recaptures were reported from 9,691 tagged and released albacore in 1990-1991, giving a recapture rate of 1.4%. The low number of recaptured albacore has limited the usefulness of tagging data for stock assessments to date. Recapture rates for North Pacific albacore tagging programs have been slightly higher (~5%) than that experienced in the South Pacific. One possible reason for the higher recapture rates in the North Pacific is that the albacore fishing fleet is much larger in the North Pacific and exploitation rates are likely to be higher.



Season

Agency

Region

Season Total

STCZ

NZ

1985-86

NMFS

724

-

724

1986-87

NMFS

993

386

1379

1987-88

NMFS

762

644

1406

1988-89

NMFS

1498

914

2412

1989-90

NMFS

490

235

1305

MAF

580

-

 

1990-91

SPC

2826

500

3476

NMFS

150

-

 

1991-92

SPC

6454

64

6518

Region Total

 

14477

2743

17220

Summary of tagged and released albacore from 1985 to 1992 in the Sub Tropical Convergence Zone (STCZ) and New Zealand (NZ) waters. NMFS = US National Marine Fisheries Service, MAF = NZ Ministry of Agriculture and Fisheries, SPC = South Pacific Commission. (source: Laurs and Nishimoto 1989, Labelle and Sharples 1991, Labelle 1993):



Movements of conventionally tagged South Pacific albacore

 

South Pacific Albacore tagging pamphlet:

 

South Pacific Albacore Tagging

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2012-09-14
2012-09-13
1.15 MB

 

Map of Albacore tagging cruises

 

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