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Sharks caught by Malagasy longline in 2012

Year of publication 2013

Product type Meeting

Edition 1

Synopsis (short abstract) Madagascar started exploring longline fishery in 2007 by shifting from trawl gear to small longliners. The number of vessels, targeting tu and tu-like species in the IOTC area of competence, has been increasing. In 2012, Malagasy flag deployed 8 longliners less than 24 m off the east coast (Annexe1). Note that some of them are multigear, wherebery fishing vessels may target demersal resources and at othertimes they may target tu and tu-like species. The following results were obtained from the M alagasy observer program database and from pelagic species companies’ declarations. The trend of total declared catches decreased throughout recent years and ranged from 497 tons to 388 tons in 2010 and 2012, respectively. The decline of catches is due to the reduction of number of big vessels. Indeed, a significant declining trend in percentage of shark landings (from 17% to 13%) was observed over the period. This paper figured out that monthly effort ranged from 14,000 hooks deployed in April to 49,447 hooks deployed in October. Total catch was 388,361 tons which was composed of 44.66% tu, 25.38% billfishes, 13.24% sharks and 16.72% of others species. Sharks landed were composed mainly of mako shark (92.42%) and blue shark (6.84%) and their CPUEs’ were 143.5 Kg/1,000 hooks and 13.6 Kg/1,000 hooks, respectively. Two specimens of shortfin mako ranged from 212 to 258 cm FL were identified by observers on board. In the same way, 37 specimens of Blue shark ranged from 164 cm to 352 cm FL. This study showed some biological information of all observed species such as length, weight, sex, GSI maturity. Observers reported that Malagasy longliners still caught IOTC prohibited species such as bigeye thresher and thresher.

Statutory body / Meeting title Indian Ocean Tuna Commission (IOTC)

Meeting symbol IOTC-2013-WPEB09-14 Rev_1

Meeting Session Number 9

Language English

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    The longline fishing is one of a recent fishery practiced by Malagasy fishing fleets. Partial alyzes were made on their activities during the year 2012. VMS Positions, logbooks and observer data sampling were used for these alyzes. Mapping of VMS positions shows that tiol longliners fishing zones focus in the North East of the EEZ. For the year 2012, a slight decrease of the total catch was observed compared to the previous two years (From 490 tons in 2010 to 388 in 2013 tons). The description o f the species composition of catches show the predomince of tropical tu catch rate (45%) compared to other pelagic species such as billfishes, sharks ... In the Tropical tus, the catch rate in Bigeye predomites (44%) followed by albacore (29%) and Yellowfin tu (26%). The catch rate in Skipjack is very low (less than 1%). The samples made by observers on board were used to calculate the average size of individual catches. Bigeye, Yellowfin, Albacore and Skipjack have respectively an average size of 116.51, 127.55, 105.82 and 63.08cm.
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    Standardized CPUE series for blue and shortfin mako sharks caught by the Portuguese pelagic longline fishery in the Indian Ocean, between 1999 and 2012 2013
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    Portuguese longliners targeting swordfish and operating in the Indian Ocean regularly capture elasmobranch fishes as bycatch. Of those, the blue shark (Prioce glauca) and the shortfin mako (Isurus oxyrinchus) constitute the two main shark species captured. A recent effort by IPMA (Portuguese Sea and Atmospheric Institute) has been made to recover historical catch data on elasmobranchs captured since the late 1990’s to the present date in that fishery. Nomil CPUEs for these two major sharks were calculated as kg/1000 hooks and standardized with Generalized Linear Models (GLM). Several different modeling techniques were tested and compared, chosen depending on the specific proportion of zeros in the catch data for each species. The models tested included the delta method, tweedie, gamma and lognormal models. Model validation was carried out with residual alysis, and relative indexes of abundance for the two species were calculated. The results presented in this paper update a previous al ysis on the trends of elasmobranch catch rates available from the Portuguese longline fishery operating in the Indian Ocean.
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