Environmental variations on swordfish (Xiphias gladius) catch rates in the Indian Ocean

2015 ◽  
Vol 166 ◽  
pp. 67-79 ◽  
Author(s):  
Kuo-Wei Lan ◽  
Ming-An Lee ◽  
Sheng-Ping Wang ◽  
Zhao-Yang Chen
2016 ◽  
Vol 4 (2) ◽  
pp. 371 ◽  
Author(s):  
Bram Setyadji ◽  
Irwan Jatmiko ◽  
Arief Wujdi

This paper presents several equations for converting among measures of size (length and weight) for swordfish (Xiphias gladius), black marlin (Makaira indica) and blue marlin (Makaira nigricans) caught by Indonesian longliners in the Indian Ocean. The equations use for transforming non-standard measurement i.e. eye fork length (EFL) and pectoral fork length (PFL) to standard measurement, lower jaw fork length (LJFL). The paper also discussed about the length-weight relationship, including converting from non-standard length (EFL and PFL) to round weight. The result showed that both PFL and EFL were positively related to LJFL but there were no significant differences existed between females and males among length measures for swordfish, blue marlin, and black marlin (ANCOVA, P>0.05). All regression equation models were considered to be valid (P<0.01) with coefficient of determinations (r2) ranged from 0.81-0.99. Allometric growth pattern was statistically observed for all swordfish (b=2.94, r2=0.94), black marlin (b=3.12; r2=0.90) and blue marlin (b=3.30; r2=0.91).


2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Riad Mohammed Sultan

PurposeThis study investigates whether higher catch rates near a marine protected area (MPA), and/or in other fishing areas within a choice set, attract more fishers. A survey conducted in the fishing grounds near an MPA located in south east of Mauritius in the Indian Ocean shows concentration of fishers in regions with lower catch rates. This contrasts with the predictions of the “fishing the line” hypothesis and the ideal free distribution (IFD) that fishers are likely to be attracted near the MPA with higher resource abundance.Design/methodology/approachUsing the random utility model as the framework and the random parameter logit (RPL) model, the study attempts to explain spatial behaviour of fishers. Expected catch and catch variability are modelled using the Just and Pope (JP) production function. The study also estimates effort elasticities with respect to expected catch and catch variability and simulates the relocation of effort from area closure.FindingsThe paper concludes that higher catch does attract fishers but is a partial and very restrictive explanation of fishers' behaviour. The “fishing the line” hypothesis does hold to some extent, but it should not be taken for granted that rising catch rates in adjacent waters will increase fishing pressure. The paper concludes that factors such as catch variability, distance from homeport to fishing ground, potential physical risk and attitudes towards risk of fishers affect spatial behaviour of fishers and should be considered for the placement and size of MPAs. The study also finds that the responsiveness of effort to catch rates is lowest in areas which are already heavily fished and easily accessible.Practical implicationsThe identification of fishing areas as complements (when fishing in one area increases fishing effort in another) and substitutes is valuable information for determining the placement and size of an MPA. A larger reserve is likely to have more displacement effect in this case than a smaller one. Therefore, a small or a network of a small reserve may be appropriate. The premise to select the site and size of the reserve is to avoid overconcentration of fishers in alternative fishing areas, which can be vulnerable to excessive fishing and unintended effects from fishers.Originality/valueThe paper contributes to an understanding of fishing behaviour and its impact on the configuration of marine reserves. It discusses the importance of effort elasticities to determine the placement and size of an MPA. Studies on this topic are very scanty in the Indian Ocean region. It also shows the application of location choice model, the RPL model and the JP production function in the fisheries sector for a small island.


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